Piling Handbook

Contents - Corus Piling Handbook

CORUS PILING HANDBOOK Piling Handbook Internet Edition (2001) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Product information Durability Earth and water pressure Retaining walls Axially loaded sheet piling Cofferdams Installation Bearing piles Sample specification Formulae and tables References

Contents

Cofferdams

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Product Information - Corus Piling Handbook

PRODUCT INFORMATION Click on one of the brochures below for technical information about the illustrated range of products

For further information, visit the Corus Construction Centre website Copyright ©2001 Corus plc. All rights reserved. Legal disclaimer Web design by

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PRODUCT INFORMATION Corner and junctions

Interlocking options

BS Omega Rotation

BS20 BS7 BS22

180° 170° 160° 150° 140° 130° 120° 110° 100° 90° 80° 70° LX8 LX12 LX16 LX20 LX25 LX32 LX38 L6-42 L6(131) L6(138) GSP2 GSP3 GSP4

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= possible = contact Corus Construction Centre to discuss or blank = not possible

BS Omega

BS 20

BS 7

BS 22

Mass = 17.3 kg/m

Mass = 15.4 kg/m

Mass = 6.3 kg/m

Mass = 10.3 kg/m

Examples of other types of LX and Larssen junction piles

Examples of other types of LX and Larssen corner piles (bent or welded)

Examples of other types of Frodingham junction piles

Examples of other types of Frodingham corner piles



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Corus Construction Centre

CORUS PILING HANDBOOK Corus Construction Centre The Corus Construction Centre is a centre of excellence created to encourage faster, more precise construction and develop an integrated approach to construction design. Our team of experts' knowledge covers the use of carbon steel, stainless steel and aluminium in construction, and includes professional civil and structural engineers, architects and construction economists. By providing a one-stop shop for designers, together we can help facilitate innovation and speed up the design process. Most of the advice that we offer you is free and can cover all aspects of steel and aluminium in construction, from budgeting, design guidance and environmental advice to product information and applications. If you need advice, please contact us on our Technical Hotline +44 (0)1724 405060 or you can visit our website at www.corusconstruction.com. We will be pleased to help you.

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Corus Piling Handbook

CORUS PILING HANDBOOK Landmarks in strength - steel piling products from Corus Construction and Industrial

Piling Handbook Internet Edition (2001)

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Disclaimer - Corus Piling Handbook

CORUS PILING HANDBOOK Disclaimer Your use of this website is subject to this Disclaimer and Copyright Statement. By using this website you agree to the Disclaimer and Copyright Statement. If you do not agree with them please do not use this website. The information contained in this website is provided in good faith but no warranty, representation, statement or undertaking is given either regarding such information or regarding any information in (or any software at) any other website connected with this website through any hypertext or other links (including any warranty, representation, statement or undertaking that any information or the use of any such information either in this website or any other website complies with any local or national laws or the requirements of any regulatory or statutory bodies) and any warranty, representation, statement or undertaking whatsoever that may be expressed or implied by statute, custom or otherwise is hereby expressly excluded. The use of this website and any information on this website or any other website (or of any software at any other site) is entirely at the risk of the user. Under no circumstances shall Corus Group plc or any of its subsidiaries be liable for any costs, losses, expenses or damages (whether direct or indirect, consequential, special, economic or financial including any losses of profits) whatsoever that may be incurred through the use of any information contained in the Corus Group plc website or in any other website. Nothing contained in the Corus Group plc website shall be deemed to be either any advice of a financial nature to act or not to act in any way whatsoever or any invitation to invest or deal in any form of investment including shares, bonds, ADSs or securities. This website may contain inaccurate information. Corus Group plc is under no responsibility to update or correct any such information or to even maintain this website. Corus Group plc reserves its right to change any information or any part of this website without notice. Copyright Statement Copyright on all of the images on this web site are owned by Corus Group plc, or by others and used under licence, in accordance with the terms of the Copyright Designs and Patents Act 1988.

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PRODUCT INFORMATION LX and Larssen Sections ● ● ● ● ●

●

Contents

LX and Larssen piles Box piles High modulus piles Steel qualities Tolerances for LX and Larssen sections Interlocking options

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PRODUCT INFORMATION LX and Larssen sections LX and Larssen piles

section dimensions per

mm LX8

m of wall

sectional mass combined elastic plastic coating area moment section section area* of inertia modulus modulus cm2

kg/ m

cm4

cm3

cm3

m2/m

116

91.0

12863

830

1017

2.54

54.6

2746

263

single 70 pile

1.52

Download AutoCAD drawing Instructions

LX12

m of wall

136

single 81 pile

106.5 18727

1208

63.9

272

3239

1381

2.72 1.63


LX12d

m of wall

139

single 83 pile

108.8 19217

1240

65.3

276

3302

1417

2.72 1.63

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LX12d10

m of wall

155

single 93 pile

121.5 19866

1282

72.9

342

3943

1493

2.74 1.64


LX16

m of wall

157

single 94 pile

123.5 31184

1641

74.1

404

5620

1899

2.91 1.75


LX20

m of wall

177

single 106 pile

138.7 43484

2023

83.2

531

8154

2357

3.00 1.80




LX20d

m of wall

179

single 107 pile

140.5 45197

2009

84.3

601

9183

2380

3.07 1.84


LX25

m of wall

202

single 121 pile

158.3 57656

2507

95.0

635

10485

2914

3.15 1.89


LX25d

m of wall

212

166.7 57246

2544

single 127 pile

100.0 10241

636

2984

3.05 1.83




LX32

m of wall

243

190.7 73802

3209

single 146 pile

114.4 11614

668

3703

3.11 1.86


LX32d

m of wall

269

210.8 75325

3348

single 161 pile

126.5 12164

727

3920

3.03 1.82


LX38

m of wall

298

234.0 87511

3805

single 179 pile

140.4 14075

814

4460

3.11 1.87




6W

m of wall

109

single 57 pile

85.3

6508

614

44.8

1253

153

711

2.54 1.34


20Wd

m of wall

196

single 103 pile

153.7 40574

2029

80.7

499

7060

2375

3.26 1.71


GSP2

m of wall

157

single 63 pile

123.5 8756

876

49.4

140

1135

1020

2.85 1.14


GSP3

m of wall

191

single 77 pile

150.3 16316

1305

60.1

226

2253

1520

3.08 1.23


GSP4

m of wall

242

single 97 pile

190.3 38742

2279

76.1

355

4585

2652

3.53 1.41




L6-42

m of wall

339

266.0 94755

4211

single 169 pile

133.0 13407

789

4933

3.64 1.82


6 (122)

m of wall

371

291.7 92115

4187

single 156 pile

122.5 12545

781

4996

3.92 1.65


6 (131)

m of wall

396

single 166 pile

311.2 101598

4618

130.7 12971

787

5481

3.90 1.64




m of wall

6 (138)

419

single 176 pile

329.3 110109

5005

138.3 13285

791

5924

3.89 1.63


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CORUS PILING HANDBOOK LX8

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CORUS PILING HANDBOOK Sheet pile section downloads The following AutoCAD R14 files are available for download from this website. The files can be used in AutoCAD R14 and AutoCAD LT R14 and subsequent releases. For further information about AutoCAD, visit the AutoDesk website. Frodingham Sections

Larssen Sections

LX Sections

Junctions

1BXN.dwg (25 kB)

20Wd.dwg (23 kB)

LX8.dwg (36 kB)

7.dwg (7 kB)

LX12.dwg (36 kB)

bs20.dwg (6 kB)

1N.dwg (24 kB)

6-122.dwg (35 kB)

2N.dwg (24 kB) 3NA.dwg (37 kB) 4N.dwg (37 kB) 5.dwg (24 kB)

6-131.dwg (33 kB) 6-138.dwg (34 kB) 6-42.dwg (34 kB) 6W.dwg (35 kB) GSP2.dwg (44 kB) GSP3.dwg (39 kB) GSP4.dwg (34 kB)

bs22.dwg (6 kB) LX12d.dwg (36 kB)

bsomega.dwg (7 kB)

LX12d10.dwg (36 kB) LX16.dwg (38 kB) LX20.dwg (36 kB) LX20d.dwg (36 kB) LX25.dwg (36 kB) LX25d.dwg (36 kB) LX32.dwg (36 kB)

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CORUS PILING HANDBOOK LX12d

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CORUS PILING HANDBOOK LX12d10

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CORUS PILING HANDBOOK 6W

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CORUS PILING HANDBOOK 20Wd

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CORUS PILING HANDBOOK GSP2

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CORUS PILING HANDBOOK L6-42

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CORUS PILING HANDBOOK 6(122)

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PRODUCT INFORMATION LX and Larssen sections Box piles

section B H d mass sectional approx least nominal nominal nominal per perimeter area radius metre steel whole of gyration only pile

moment of inertia

section modulus

about X-X

about Y-Y

about about X-X Y-Y

mm

mm

mm

kg/m cm2

cm2/ m

cm

mm

cm4

cm4

cm3

cm3

LX8

600

350

8.2

109.2 139

1595

12.19

1881

20680

58849

1182

1851

LX12

600

350

9.7

127.8 163

1800

13.47

1993

29555

69745

1689

2193

LX12d

600

351

10.0

130.6 166

1803

13.53

1993

30442

70840

1735

2228

LX12d10 600

355

10.0

145.8 186

1833

13.24

2107

32523

84305

1832

2651

LX16

600

423

10.5

148.2 189

2140

15.91

2128

47791

82792

2260

2595

LX20

600

477

12.5

166.4 212

2326

17.68

2215

66233

89280

2777

2790

LX20d

600

497

11.2

168.6 215

2421

17.86

2252

68536

95805

2758

2996

LX25

600

508

13.5

190.0 242

2533

18.96

2383

86971

104396 3424

3257

LX25d

600

497

15.0

200.0 255

2423

18.44

2251

86582

104978 3484

3281

LX32

600

508

19.0

228.8 291

2520

19.53

2374

111184 113590 4377

3544

LX32d

600

498

21.5

253.0 322

2415

18.86

2239

114578 121564 4602

3793

LX38

600

513

22.5

280.8 358

2550

19.44

2298

135207 140173 5271

4374

6W

525

252

7.8

89.6

114

1132

9.40

1685

10090

39318

801

1402

20Wd

525

447

11.3

161.4 206

2013

16.37

2120

55090

74390

2465

2633

GSP2

400

239

10.5

98.8

848

9.13

1580

10492

25263

878

1159

GSP3

400

299

120.2 153

1041

11.3

1659

19556

30178

1308

1365

GSP4

400

386

15.5

152.2 194

1346

14.12

1912

41397

38664

2145

1761

6-42

500

506

20.5

266.0 339

2219

17.71

2426

124487 106305 4920

3902

6 (122)

420

502

22.0

245.0 312

1802

14.79

2114

105409 68240

4200

2935

6 (131)

420

502

25.4

261.4 333

1802

14.49

2114

116104 69880

4626

3005

6 (138)

420

502

28.6

276.6 352

1802

14.23

2114

125746 71366

5010

3069

Contents

13.5

126

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PRODUCT INFORMATION LX and Larssen sections High modulus piles

universal beam

serial size

mass

mass of

combined moment of inertia of primary unit about XX

primary complete per unit unit wall

section modulus of primary unit about XX

per metre

per unit

per metre

mm x mm kg/m

kg/m

kg/m2

cm4

cm4/m

cm3

cm3/m

686 x 254

125

208.4

243.0

240511

200426

4734

3945

762 X 267

147

230.1

261.1

321006

267505

5901

4918

838 X 292

176

259.1

285.3

435702

363085

7528

6273

914 X 305

201

284.1

306.1

549007

457506

9021

7518

914 X 305

253

336.6

349.8

669898

558248

11343

9453

914 X 305

289

372.3

379.6

748470

623725

12838

10698

1016 X 305

222

305.2

323.7

666589

555491

10407

8673

1016 X 305

349

432.2

429.5

1028148 856790

16341

13618

1016 X 305

487

570.2

544.5

1358548 1132123

20325

16938

LX20 High Modulus Piles are shown above. Other sections may be used - contact Corus Construction Centre for details.

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PRODUCT INFORMATION Steel qualities designation EN 10027

classification EN 10020

minimum yield strength**

minimum tensile strength**

minimum elongation on a gauge length of Lo = 5.65 √So

N/mm2

N/mm2

A%

steel name

steel number

EN 10248 S270GP

1.0023

Base Steel

270

410

24

EN 10248 S355GP

1.0083

Base Steel

355

480

22

S390 or S430 equivalent steel grades can be ordered upon request **The values in the table apply to longitudinal test pieces for the tensile test Contents

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PRODUCT INFORMATION LX and Larssen sections Tolerances for LX and Larssen sections

width

thickness of section

squareness of cut

single interlocked ≤8.5mm >8.5mm weight length X-X pile piles axis ±2%

±3% (2b)

Contents

(s or t) ±0.5 mm

±6%

±5%

±200 mm

≤2% b

depth of section (h)

Y-Y straightness h≤200 h>200 axis ≤2% b

≤0.2% of length

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±4 mm

±5 mm


PRODUCT INFORMATION LX and Larssen sections Interlocking options

LX8 LX12 LX16 LX20 LX25 LX32 LX38 6W 20Wd GSP2 GSP3 GSP4 LX8

•

•

•

•

•

LX12†

•

•

•

•

•

LX16

•

•

•

•

•

•

•

LX20†

•

•

•

•

•

LX25†

•

•

•

•

LX32†

•

•

•

LX38

•

•

•

6W

•

•

20Wd GSP2

• •

•

•

•

•

•

•

• •

•

•

•

•

• •

•

•

•

•

•

• •

•

•

•

•

•

• •

•

•

•

• •

•

•

•

•

•

66 42

• •

• •

•

•

•

•

•

•

•

•

•

•

•

•

• •

•

• •

GSP3

•

•

•

•

•

GSP4

•

•

•

•

•

6-42

•

•

•

•

•

•

• •

6

•

•

•

•

•

•

• •

•

†Interlocking capability also applies to d versions of these sections

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PRODUCT INFORMATION Frodingham Sections ● ● ● ●

Frodingham piles Straight web SW1A Steel qualities Tolerances for Frodingham sections (including straight web)

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PRODUCT INFORMATION Frodingham Sections Frodingham Piles

section dimensions sectional mass mass combined elastic plastic coating coating area moment section section area* area* of inertia modulus modulus per pile per m wall

1BXN

mm

cm2/m

kg/ m

kg/ m2

see below

170

63.4

133.2 4947

cm4/m

cm3/m

cm3/m

m2/m

m2/m2

692

859

1.16

2.44

Download AutoCAD R14 file (25 kB) Instructions

1N

see below

126

48.0

99.4

6072

714

831

1.22

2.53


2N

see below

145

54.8

113.5 13641

1161

1333

1.34

2.78


3NA

see below

166

62.7

129.8 25710

1687

1937

1.48

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3.06



4N

see below

218

82.7

171.2 39869

2415

2787

1.52

3.16


5

see below

302

101.0 237.1 49329

3171

3683

1.51

3.56


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CORUS PILING HANDBOOK 1BXN

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CORUS PILING HANDBOOK 1N

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CORUS PILING HANDBOOK 3NA

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CORUS PILING HANDBOOK 5

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PRODUCT INFORMATION Frodingham Piles Straight Web SW1A

section B t nominal

SW1A

area mass mass single per per pile m of m2 pile of pile

mm

mm cm2

kg/m kg/ m2

414

12.7 81

63.5

ultimate mass interlock per m strength of junction S270GP S355GP

coating area per single pile

coating max deviation area angle per m wall

kg/m

153.4 95.2

t/m

t/m

m2/m

m2/m2

degrees

285

384

1.00

2.41

6

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CORUS PILING HANDBOOK SW1A

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PRODUCT INFORMATION Steel qualities designation EN 10027

classification EN 10020

minimum yield strength**

minimum tensile strength**

minimum elongation on a gauge length of Lo = 5.65 √So

N/mm2

N/mm2

A%

steel name

steel number

EN 10248 S270GP

1.0023

Base Steel

270

410

24

EN 10248 S355GP

1.0083

Base Steel

355

480

22

S390 or S430 equivalent steel grades can be ordered upon request **The values in the table apply to longitudinal test pieces for the tens

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PRODUCT INFORMATION Frodingham Sections Tolerances for Frodingham Sections (including Straight Web)

width

thickness of section

squareness of cut

single interlocked ≤8.5mm >8.5mm weight length X-X pile piles axis ±2%

±3% (2b)

(s or t) ±0.5 mm

Contents

±6%

±5%

±200 mm

≤2% b

depth of section (h)

Y-Y straightness h≤200 200
≤0.2% of length

±5 mm

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±6 mm

±7 mm

Durability - Corus Piling Handbook

DURABILITY Contents 1. Introduction 2. Corrosion of Steel Piling in Various Environments 1. Underground Condition 2. Atmospheric Condition 3. Fresh Water Environments 4. Marine Environments 5. Other Environments 3. Effective Life of Steel Sheet Piles 1. Mean Corrosion Rates and Calculations 2. Example Durability Calculations 1. Section Modulus against Loss of Thickness - LX Piles 2. Section Modulus against Loss of Thickness - U Piles 3. Section Modulus against Loss of Thickness - ZPiles 4. Example Calculation to Determine the Effective Life of a Sheet Pile Structure 4. Methods of Increasing Effective Life 1. Use of a Heavier Section 2. Use of a High Yield Steel 3. Coatings 1. Tar Vinyl (PC1) 2. High Build Epoxy Pitch (PC2) 4. Coatings for Sheet Piling in Contact with Potable Water or Raw Sewage 5. Concrete Encasement 6. Cathodic Protection 7. Resistance to Abrasion and Erosion 5. Recommendations for Various Environments 1. Underground Exposures 2. Sea Water Immersion Exposures 3. Fresh Water Immersion Exposures 4. Fresh Water Exposures at or Above the Water Level 5. Marine Low Water Zone 6. Marine Tidal Exposures 7. Marine Splash Zone Exposures 8. Atmospheric Exposure

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DURABILITY Introduction Steel piling is widely used in permanent earth retaining and structural foundation works, and in the majority of cases it can be used in an unprotected condition. The degree of corrosion and whether protection is required depends upon the working environment which can be variable, even within a single installation. Characteristic corrosion rates have been established for most environments and the following pages outline the performance of steel piling in various conditions and reviews the measures that can be taken to increase effective life in aggressive situations.

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DURABILITY Corrosion of Steel Piling in Various Environments In determining the effective life of unprotected piles, the selection of pile section and the need for protection, it is necessary to consider the corrosion performance of bare steel in different environments. The corrosion rates given for the following environments indicate the loss of steel where only one face is exposed to that environment. In practice, opposite sides of a pile may be exposed to different conditions. For example, one side of a harbour wall could be exposed to a marine environment whilst the other side could be in contact with soil. Mean corrosion rates for combinations of environments are given here. ● ● ● ● ●

Underground Condition Atmospheric Condition Fresh Water Environments Marine Environments Other Environments

Underground Condition

A review of published data and evaluations by Corus have concluded that the corrosion of steel piles driven into undisturbed soils is negligible irrespective of soil type and characteristics. This is attributed to the very low levels of oxygen present in undisturbed soils. For the purposes of calculations, a maximum corrosion rate of 0.015 mm/side/year may be used. In the special case of recent fill or industrial waste soils, where corrosion rates may be higher, protective systems may be required, but these should be considered on an individual basis. Further assistance with this condition can be obtained from the Corus Construction Centre. Atmospheric Condition

Corus research indicates that the atmospheric corrosion of steel in the UK averages approximately 0.035mm/side/year. This value can be used for most atmospheric conditions, although specialist advice should be sought where localised conditions and pollution produce very aggressive microclimates. Fresh Water Environments

Corrosion losses in fresh water, the term fresh being used to distinguish it from sea or estuarine brackish water, are generally lower than for sea water and, therefore, the effective life of steel piles is proportionately longer. However, due to the variability of fresh water no general advice can be given to quantify this increase in life.

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Marine Environments

Marine environments normally en-compass several different exposure zones, and each one requires individual consideration. ●

●

●

●

●

Below Bed Level Where piles are below the bed level, very little corrosion occurs and the corrosion rate given for the underground condition is applicable, ie 0.015mm/ side/year. Sea Water Immersion Zone Where piles are continually under water the corrosion rate is normally low, and a mean value of 0.035mm/side/year can be taken. Low Water Zone This is the zone between mean low water neap and mean low water spring tides. In this zone a mean corrosion rate of 0.075mm/side/year can be allowed for most structures. Occasionally, accelerated corrosion has been encountered on the outpans of piles in this zone. In these cases reductions in steel thickness of between 0.3mm and 0.8mm per year have been experienced. Corus recommends the regular inspection of piles in this zone, and suggest that all piles in marine environments are coated with a protective system. There is considerable evidence indicating that accelerated corrosion is microbially induced, and research is currently being carried out on a pan-European basis to gain an under-standing of and a solution to the problem. This topic is dealt with in more detail in a separate brochure. (Accelerated Low Water Corrosion of Steel Sheet Piling) Tidal Zone In this zone the pile is immersed and exposed on a regular basis with each tide. However marine growths give appreciable protection to the piles by sheltering the steel from wave action and by limiting the oxygen supply to the steel surface. Therefore the corrosion rate is similar to the immersion zone with a mean value of 0.035mm/side/year. Splash and Atmospheric Zones This area above the normal tidal range is often wet as a result of splashing by wave action and has a plentiful supply of oxygen. These two factors combine to produce a relatively aggressive environment with a mean corrosion rate of 0.075mm/side/year. In this zone, thick stratified rust layers can develop and at thicknesses above about 10mm these tend to spall from the steel especially on curved parts such as the shoulders and the clutches. However, since rust has a much greater volume than the parent metal, steel corrosion losses may amount to no more than 10% to 20% of the rust thickness. The boundary between splash andatmospheric zones is not well defined but corrosion rates reduce rapidly with distance above wave height, and then the mean atmospheric rate of 0.035mm/side/year can be applied.



Other Environments

There is very little corrosion data available for industrial waste tips, land reclamation schemes, or sites affected by man made pollution. Therefore, each location of this type will require a separate assessment. The Corus Construction Centre can provide assistance with this if required.

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CORUS PILING HANDBOOK Mean Corrosion Rates for Various Environments

Notes to Table

1. The corrosion rates quoted are based upon investigations carried out by Corus and others on steel exposed in temperate climates. For most environments mean values are quoted since they are considered to be most relevant to the design and performance of most sheet piling structures. However, in some circumstances the designer may wish to take account of higher values. It is suggested that in these circumstances a reasonable practical upper corrosion rate limit would be that corresponding to a 95% probability value. (Values given in parentheses) 2. All corrosion rates quoted in the table are measured as total loss of section thickness from both sides, taking into account both environments. 3. For combinations of environments where low water corrosion is involved, in a small number of locations, higher rates than those quoted have been observed at or just below the low water level mark and Corus recommends that periodic inspection is undertaken. In the case of uncertainty, please contact the Corus Construction Centre for advice. 4. A maximum value is quoted for soil corrosion and this applies to natural undisturbed soil or well compacted and weathered fill ground where corrosion rates are very low. Recent fill ground or waste tips will require special consideration. 5. Corrosion losses due to fresh water immersion are generally lower than for seawater, however, fresh waters are very variable and no general advice can be given to quantify the increase in life.

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DURABILITY Effective Life of Steel Sheet Piles The effective life of unprotected steel piling depends upon the combined effects of imposed stresses and corrosion rates. BS8002 and BS6349 consider the end of the effective life of steel sheet piles to occur when any part of the pile reaches the maximum permissible working stress as a result of the loss of section due to corrosion. The opposite faces of a sheet pile may be exposed to different combinations of environments. These are illustrated in the figures below and mean corrosion rates for these environments in temperate climates are given below. Guidance on determination of the effective life of a pile section is given below. Atmospheric/Soil

● ●

Marine/Soil

Marine/Marine

Mean Corrosion Rates for Various Environments Example Durability Calculations

Mean Corrosion Rates for Various Environments

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Example Durability Calculations

To establish the effective life of a pile section in a specific environment it is necessary to follow the procedure below:1. Establish the corrosion zones that exist for the piles using Graph 1, Graph 2, and Graph 3, and the mean corrosion rate for each zone using the table above. 2. Using the bending moment diagram establish the maximum bending moment in each corrosion zone. 3. Calculate the minimum required section modulus for each corrosion zone. 4. Select a pile section which will provide the largest calculated minimum section modulus value. 5. Using Graph 1 or Graph 2 for Larssen sections or Graph 3 for Frodingham sections, establish the thickness of sacrificial steel that is available within each corrosion zone for the pile section selected in Step 4. 6. Using the mean corrosion rates established in Step 1, and the sacrificial steel thicknesses established in Step 5, calculate the effective life for each corrosion zone. 7. The effective life of the pile is equal to the lowest value calculated in Step 5. Example calculation to determine the effective life of a sheet pile structure

This figure below illustrates a typical marine wall constructed in steel sheet piling.



Step 1 » Step 2 » Step 3 » Step 4 » Step 5 » Step 6 » Step 7



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CORUS PILING HANDBOOK Figure 3.2.1 Atmospheric/Soil

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CORUS PILING HANDBOOK Figure 3.2.2 Marine/Soil

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CORUS PILING HANDBOOK Figure 3.2.3 Marine/Marine

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CORUS PILING HANDBOOK Graph 1 - Section modulus against loss of thickness - LX piles

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CORUS PILING HANDBOOK Graph 2 - Section modulus against loss of thickness - U piles

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CORUS PILING HANDBOOK Graph 3 - Section modulus against loss of thickness - Z piles

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CORUS PILING HANDBOOK Typical marine wall constructed in steel sheet piling

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CORUS PILING HANDBOOK Step 1

Depth (m)

Face 1

Face 2

Zone

Total mean corrosion rate (mm/year)

0-1

Soil

Splash

A

0.09

1-5

Soil

Tidal

B

0.05

5-6

Soil

Low Water

C

0.09

6-12

Soil

Immersion

D

0.05

12-18

Soil

Soil

E

0.03

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Zone

Maximum Bending Moment kNm/m

A

10

B

440

C

520

D

660

E

370

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Zone

Minimum Section Modulus cm³/m

A

10x10³/180 = 56

B

440x10³/180 = 2445

C

520x10³/180 = 2889

D

660x10³/180 = 3667

E

370x10³/180 = 2056

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CORUS PILING HANDBOOK Step 4 From the minimum section modulus requirements calculate in Step 3 (Zmin = 3667cm³/m), an appropriate pile section can be selected; in this case, Larssen 6 (122kg/m) in grade S270GP steel is to be adopted

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Zone

Scrificial Steel Thickness mm

A

7

B

7

C

6.4

D

2.5

E

7

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Zone

Effective Life years

A

7/0.09 = 77

B

7/0.05 = 120+

C

6.4/0/09 = 71

D

2.5/0/05 = 50

E

7/0.03 = 120+

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CORUS PILING HANDBOOK Step 7 Effective life of Larssen 6 (122kg/m) piles in this location is 50 years. NOTE: with application of PC2 coating (recommended for marine exposure conditions), an additional 20+ years life can be anticipated.

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DURABILITY Methods of Increasing Effective Life In many circumstances steel corrosion rates are low and the use of protective systems unnecessary. Where methods of increasing the effective life need to be considered the measures that can be taken include the following: Use of a Heavier Section

Effective life can be easily increased by the provision of an additional thickness of steel. In many situations the most corrosive zones will not coincide with the most highly stressed zone. Consequently the use of a sacrificial thickness is a cost effective method of increasing effective life. Use of a High Yield Steel

An alternative approach to using mild steel in a heavier section is to use a higher yield steel and retain the same section. Although both types of steel have similar corrosion rates, the use of grade S355GP (EN10248:1995) rather than grade S270GP (EN10248:1995) will allow a 30% additional loss of section modulus without exceeding the maximum allowable working stress. This method effectively builds in a corrosion allowance and gives approximately a 30% increase in effective life for an increase in steel cost of about 7%. Coatings

Corus has developed two coatings specifically designed for application to steel piling under workshop conditions. The characteristics of the coatings are summarised as follows. ●

●

Tar Vinyl (PC1) This coating is based on an aromatic pitch modified with suitable vinyl resins. It can be applied to both manually cleaned and blast cleaned steel surfaces, at up to 150 microns in a single coat, and is rapid drying. The durability of the coating is dependent on the chosen method of surface preparation and the coating thickness. High Build, Epoxy Pitch (PC2) This coating is based upon special coal-tar pitches modified with epoxy resins and cured with isocyanate adducts. It can be applied to blast cleaned surfaces, at up to 400 microns in a single coat. It has very rapid drying properties and produces a thick, hard, durable coating with low water permeability.

The protective coatings recommended for steel piling are given here. The cost and file:///C|/Documents%20and%20Settings/bantinone/My%20Do...0Webs/myweb19/Durability/Increasing_effective_life.html (1 of 3)5/26/2005 3:59:55 AM


durability of the recommended systems depend upon steel surface preparation and coating type and thickness. For Coating Areas see 'Coating Areas'. Coatings for Sheet Piling in Contact with Potable Water or Raw Sewage

Coatings for use in potable water in the UK must meet the requirements of the Water Supply Bylaws and are approved by the Water Research Centre. Most are based on either bitumen or on two pack epoxy resin systems. Coal-tar based coatings are not suitable for potable water. Coal-tar epoxy coatings are normally used for sheet piling in contact with raw sewage and can be applied on a blast cleaned surface either on site or in the shops. The Corus PC2 coating is suitable and should be used where shop application is required. Concrete Encasement

Concrete encasement can be used to protect steel piles in marine environments. Often the use of concrete is restricted to the splash zone by extending the concrete capping beam to below the mean high water level. However, both splash and tidal zones can be protected by extending the capping beam to below the lowest water level. Concrete for protecting steel in sea water must be of good quality, provide adequate cover and be properly placed and cured. Cathodic Protection

Coatings for use in potable water in the UK must meet the requirements of the Water Supply Bylaws and are approved by the Water Research Centre. Most are based on either bitumen or on two pack epoxy resin systems. Coal-tar based coatings are not suitable for potable water. Coal-tar epoxy coatings are normally used for sheet piling in contact with raw sewage and can be applied on a blast cleaned surface either on site or in the shops. The Corus PC2 coating is suitable and should be used where shop application is required. Resistance to Abrasion and Erosion

Abrasion or erosion can reduce piling life significantly and consideration should be given at the design stage to structures which are likely to be subject to significant levels of wear.

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CORUS PILING HANDBOOK Protective coatings recommended for steel piling

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*Minimum film thickness

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DURABILITY Recommendations for Various Environments The recommendations outlined below are based on the corrosion data given here for the various environments and on Corus experience. It is not practical to apply a variable thickness of coating to the face of a pile where more than one type of exposure occurs along its length. Where local conditions are likely to impair life, for example where the piling is subject to abrasion, erosion or localised pollution, these circumstances should be considered separately. ● ● ● ● ● ● ● ●

Underground Exposures Sea Water Immersion Exposures Fresh Water Immersion Exposures Fresh Water Exposures at or Above the Water Level Marine Low Water Zone Marine Tidal Exposures Marine Splash Zone Exposures Atmospheric Exposure

Underground exposures

Steel piles driven into undisturbed ground seldom require protection irrespective of the soil type due to the very low corrosion rates. This also applies to piles driven in below the bed level of harbours, rivers and the sea. When piles are driven into recent fill soils and especially industrial fill materials some protection may be required, though each case should be judged on its merits. Where protection is required it is recommended that PC2 is applied to a minimum dry film thickness of 400 microns. Sea Water Immersion Exposures

The corrosion rate of steel immersed in sea water is low enough to give acceptable steel losses over the design life of a piling structure. Therefore, bare steel is recommended for use in immersion conditions. Protective coatings can be used to increase effective life but once degraded, maintenance is difficult. Special coatings that can be maintained under water are available but are very expensive. Where the costs can be justified, cathodic protection can also be effective. Fresh Water Immersion Exposures

For practical purposes, the situation is the same as for sea water immersion and corrosion is low enough to permit the use of bare steel. In fresh water immersion conditions, protective coatings would be expected to last longer but again, once file:///C|/Documents%20and%20Settings/bantinone/My%2...ts/My%20Webs/myweb19/Durability/Recommendations.html (1 of 3)5/26/2005 3:59:56 AM


applied, they are difficult to maintain. Fresh Water Exposures at or Above the Water Level

In non-tidal situations, corrosion can occur at the water line of piled river embankments and, more usually, canals where these support roughly a constant water level. In such circumstances, it is recommended that PC2 protective coating is applied to a depth of 1m above and below the water level to a dry film thickness of 250 microns on the water side. Where the water level is variable and at areas other than the water line, protection is unnecessary. Marine Low Water Zone

For ports and structures where mean low water corrosion rates are about 0.075 mm/side/year, it is considered that the most effective method is to use bare steel with a corrosion allowance where appropriate. Protective coatings can be used to increase effective life but these will be difficult to maintain once degraded. If a steel structure is to be repaired or constructed at a site where accelerated low water corrosion has occurred, appropriate measures should be considered to obtain the desired effective life. These measures are given in detail in a separate brochure (Accelerated Low Water Corrosion of Steel Sheet Piles) and include the use of high yield steels, use of increased steel thickness, including attachment of plates locally at the low water level, use of protective coatings and application of cathodic protection. Marine Tidal Exposures

Tidal zones tend to accumulate marine fouling which affords considerable protection to the underlying steel and acceptable corrosion rates occur over this zone. Coatings can be used but maintenance is difficult. Therefore, it is considered that the most cost effective method is to use bare steel with a corrosion allowance where appropriate. Marine Splash Zone Exposures

This zone presents relatively aggressive corrosive conditions for steel and several options exist. In many circumstances, bare steel can be used with a corrosion allowance where appropriate. Alter-natively, protection can be provided in the form of coatings or concrete encasement. With the former it is recommended that PC2 be applied to a dry film thickness of 400 microns and that the coating should extend to at least 1 metre below mean high water level. It should be borne in mind that, in the absence of good borehole data, it is often impossible to estimate beforehand the driven depth of piling. In such cases more of the pile length may have to be coated to ensure that the piles in situ are protected file:///C|/Documents%20and%20Settings/bantinone/My%2...ts/My%20Webs/myweb19/Durability/Recommendations.html (2 of 3)5/26/2005 3:59:56 AM


in the splash zone. The ease and effectiveness of maintenance will depend upon local conditions, for instance the degree of shelter from wave action. Where the tidal range is small, concrete encasement can also be used. With this method the capping beam should be extended to a minimum of 1 metre below mean high water level and the highest quality concrete used. Good coverage of the encased steel should be ensured. Atmospheric Exposures

Piling exposed to rural, urban or industrial atmospheres is usually painted for aesthetic reasons. PC1 or PC2 can be used depending on requirements. Where sheet piled bridge abutments or other piled land-sited structures are subject to road salt spray, it is recommended that PC2 be used. This system is also recommended for inaccessible structures, for example piled walls or bridge abutments that are hidden by stand-off brick or stone facias. For driven piling, the paint should be applied to about 0.5m below final ground level, below which protection is not usually required. The atmospheric zone of a marine piling structure is normally considered on the same basis as the splash zone and if protection is used on the splash zone then it is normally extended to protect the atmospheric zone.

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Earth and Water Pressures - Corus Piling Handbook

EARTH & WATER PRESSURES Contents 1. Notation 2. Determination of Soil Properties 3. Types of Borehole Samples and Methods of Testing 1. Cohesionless Soils (Gravel, Sand etc) 2. Cohesive Soils (Clays and Silts) 3. Mixed Soils (Sand with Clay, Sand with Silt) 4. Rock 5. Geophysical Methods of Site Investigation 6. Chemical Analysis 7. Seepage Water 4. Information Required for the Design of Retaining Walls and Cofferdams 5. Typical Soil Properties 6. Earth Pressure Calculation 7. Cohesionless Soils 8. Cohesive Soils 1. Permanent Structures 2. Temporary Structures 9. Cohesive and Mixed Soils 10. Wall Adhesion 11. Tension Crack 12. Superimposed Loading 13. Battered Walls 14. Pressure Calculations 15. Concentrated and Linear Surcharge 16. Sloping Ground Surface 17. Earth Pressure Calculation Example

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EARTH & WATER PRESSURES Notation Units γ

Bulk weight density of soil

kN/m³

γ'

Submerged weight density of soil

kN/m³

Weight density of water

kN/m³

γw

Angle of internal friction of soil (total stress)

degrees

φ'

Angle of internal friction of soil (effective stress parameter)

degrees

δ

Angle of friction between soil and piles

degrees

c

Cohesion of soil (total stress)

kN/m²

c'

Cohesion of soil (effective stress parameter)

kN/m²

ca

Adhesion between soil and piles

kN/m²

h

Height of soil above any level under consideration

m

Ka

Coefficient of active pressure for cohesionless soils

-

Kac

Coefficient of active pressure for cohesive soils

-

pa

Intensity of active pressure

Pa

Total load per metre run of wall due to active pressure

φ

kN/m² kN

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Kp

Coefficient of passive pressure for cohesionless soils

-

Kpc

Coefficient of passive pressure for cohesive soils

-

Pp

Total load per metre run of wall due to passive pressure

pw

Intensity of water pressure

kN/m²

pp

Intensity of passive pressure

kN/m²

kN

"Weight Density" in kN/m³ can be readily converted to "Mass Density" in kg/m³ by multiplying by 102. Types of Soil

1. Cohesionless soils: granular materials such as sand, gravel, hardcore, rock filling etc. 2. Cohesive soils: clays and silts. Under certain conditions chalk and other similar materials can be treated as cohesive soils. 3. Mixed soils: combinations of groups 1 and 2 such as sand with clay, or sand with silt. 4. Rock. Note: There are certain qualifications to the information contained in this chapter which are dependent upon the type of structure under consideration, ie a temporary cofferdam, permanent retaining wall, etc. These are given in the appropriate place.

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EARTH & WATER PRESSURES Determination of Soil Properties Site Investigation, Boreholes, Soil Sampling and Testing

The precise and adequate determination of site conditions prior to the commencement of any form of civil engineering con-struction work is necessarily regarded as standard practice. Work of this nature should be carried out in accordance with BS 5930:1981 – Code of Practice for Site Investigations. Where piled foundations, cofferdams, retaining walls etc are to be driven it is essential that as much information as possible be obtained regarding strata, ground water, tidal water, embankments, existing foundations, buried services and the like in order to design the most suitable piling in terms of strength, stability and economy. Full use should therefore be made of all available information, no matter how old, in regard to previous investigation of the proposed site and its surroundings. Such information should be supplemented with data obtainable from borehole sampling and testing, the number of boreholes depending upon the size and nature of the site For piling work, it is customary to sink boreholes at intervals of 30 to 60m centres and to carry them well below the anticipated depth of the proposed piling. Cofferdam boreholes should be sunk within the proposed enclosure area. To assess the precise nature of the ground, samples should be taken at regular intervals of a depth or whenever the change in stratum occurs. Samples obtained by the borehole method must be correctly labelled to avoid possible error. Duplicate records of all boreholes giving depth and location, should also be maintained. Field Identification of Soils

Very Soft

Exudes between fingers when squeezed in fist.

Soft

Can be readily excavated with a spade and can be easily moulded with the fingers.

Firm

Can be excavated with a spade and can be moulded by substantial pressure in the fingers.

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Stiff

Requires a pick or pneumatic spade for its removal and cannot be moulded with the fingers.

Very Stiff

Requires a pick or pneumatic spade for its removal and will be hard and brittle or very tough.

Many stiff clays exist in their natural state with a network of joints or fissures. A large piece of such clay, when dropped, will break into polyhedral fragments. If possible, it should be determined whether the clay is fissured or intact, as this could be a criterion in the design of steel sheet structures.

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EARTH & WATER PRESSURES Types of Borehole Samples and Methods of Testing Cohesionless Soils (Gravel, Sand etc)

Air tight jar or bag samples (disturbed). Normally forwarded to the laboratory for scientific analysis. When examined on site, this should be carried out by a qualified engineer or geologist. Relationship of In-situ Tests to Relative Density of Cohesionless Soils

Relative Density

Standard Penetration Test 'N' Value

Cone Penetration Test qs (MN/m²)

φ' (Degrees)

0-4

2.5

25

4-10

2.5-7.5

28

Med Dense

10-30

7.5-15.0

30

Dense

30-50

15.0-25.0

36

Over 50

Over 25.0

41

Very Loose Loose

Very Dense

(see M J Tomlinson - Foundation Design and Construction and TESPA - Installation of Steel Sheet Piles) Standard Penetration Test (in-situ density)

The resistance offered by a cohesionless soil to a 50mm external diameter thickwalled sample tube when driven into the bottom of a borehole can be approximated to the relative density of the soil encountered. It is usual to neglect the disturbance. The force applied is equated to a free-falling load of 64kg travelling 760mm before impact, the number of blows (N) per 300mm of penetration being recorded. See table above for interpretation of results. Shear Box Test

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relatively free draining, any excess pore water pressures developed, even under rapid loading, will dissipate readily. Hence the results of this test will always give effective stress values (φ’). Mechanical Analysis

This comprises two stages involving the separation of coarser particles by means of BS sieves and determination of the size of finer particles by a special sedimentation process known as wet analysis. The subject of mechanical analysis exceeds the scope of this type of handbook. Reference should be made to appropriate literature for methods of procedure. Cohesive Soils (Clays & Silts) Shear strength

Two distinct methods of testing are given as the correct procedure, ie “direct” shear tests and “indirect” shear tests. Direct shear testing involves the use of the Vane Test in which a metal vane is pushedinto the soil in the borehole and torque applied. Measurement of the resultant angle-of- twist in the transmitting rod or spring indicates the magnitude of the torque, hence, the strength of the sample material. Indirect shear tests are carried out on undisturbed samples in two forms: 1. Triaxial Compression Test wherein a cylindrical specimen (undrained) is subjected to a constant lateral hydrostatic pressure whilst the axial pressure is steadily increased to the yield point of the material. This test will give the “total” stress parameters of φ and c for all types of clay. When “effective” stress parameters are required (φ’ and c’), a drained triaxial test should be performed, with the strain rate sufficiently low to ensure the dissipation of pore water pressures. If no effective stress parameters are available from drained triaxial tests, the following table may be used for initial design studies and would tend to give conservative results. Relationship of moisture content and plasticity index to the strength of cohesive soils (see BS8002)

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Description

Plasticity Index (%)

Undrained Cohesion c (kN/m²)

Drained Cohesion c' (kN/m²)

φ' Degrees

Very Soft

>80

<20

0

15

Soft

80

20-40

0

15

Firm

50

50-75

0

20

Stiff

30

100-150

0

25

Very Stiff

15

>150

0

30

2. Unconfined Compression Test which measures the shear strength of undrained cohesive soils under zero lateral pressure by means of a special test apparatus, normally portable. Natural Moisture Content. Determination of the natural or in-situ moisture content of a soil sample by weighing before and after drying the sample in a ventilated oven at 105°C. The loss of weight is expressed as a percentage of the final or “dry weight”. Bulk Density, Liquid and Plastics Limits. Moisture content is similarly involved in these tests which are best described in BS 1377, to which the reader should refer. Mixed Soils (Sand with Clay, Sand with Silt)

The method referred to in “Cohesive Soils” may be applied to the testing of mixed or combined soils. Rock

The resistance to drilling is a good indication of strata material strength. Where possible, especially during the exploration of virgin territory, samples of rock should be obtained for analysis. Geophysical Methods of Site Investigation

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of site investigation. Chemical Analysis

The destructive influence of natural deposits and buried waste of industrial effluent should be fully investigated during soil sampling and testing. Examination will reveal the suitability of the anti-corrosion measures referred to in Chapter 3, or the need for special precautionary measures. Seepage Water

The effect which water has on the engineering properties of a soil must be clearly understood and carefully considered during the site investigation period. In addition to the tests on individual soil samples, the direction of seepage, upwards and downwards, should be determined before any decision is reached on the design of a piling system.

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EARTH & WATER PRESSURES Cohesive Soils The strength parameters of cohesive soils may change significantly over a period of time due to the pore water pressure changes induced following construction of a retaining structure. The change of strength is caused by equalisation of negative pore water pressure in the soil and results in reduced values of cohesion (c’) but increased values of angle of internal friction (φ). The initial parameters are referred to as “total” stress values (which are derived from undrained triaxial tests) and the modified condition is referred to as “effective stress values” (which are derived from drained triaxial tests 4/3). Whilst all cohesive soils are subject to these changes, the effective stress condition is not usually critical when fine silts and naturally consolidated and slightly overconsolidated clays, ie those with undrained cohesion values of less than 40kN/m2 , are involved, since the change from total to effective parameters gives an overall increase in soil strength. However, the reverse is true for over-consolidated clays, ie those with undrained cohesion values in excess of 40 kN/m2 . The overall strength will, in most cases, be reduced as the stress condition changes from total to effective because the loss of substantial cohesive strength is not compensated adequately by the increasing angle of internal friction. Permanent Structures

The critical design condition for permanent structures in fine silts, normally and slightly over consolidated clays, will usually be that using total stress parameters, although a check with the alternative effective values may be advisable. The critical design condition for permanent structures in over consolidated clays will usually be with effective stress parameters, but a check using total values may be advisable. Temporary Structures

When the anticipated life of the structure is less than three months and subject to the degree of permeability of the strata and protection it receives from weathering, the design need only be executed with total stress parameters. In these cases it is wise to assume that where cohesive soils are exposed at the passive soil surface, there will be a total loss of cohesion at the passive surface with a progressive recovery to full cohesion at a depth of one metre below the surface. This is to make an allowance for the effects of softening due to the relief of overburden pressures during excavation and the resulting heave, and the remoulding induced by the passage of excavating equipment.

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Temporary structures of greater than three months anticipated life should be treated as permanent structures.

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EARTH & WATER PRESSURES Information Required for the Design of Retaining Walls and Cofferdams Having determined the precise nature of the ground within the site and ascertained the individual soil properties, it is desirable to release certain basic information to the piling designer to ensure the best possible arrangement in terms of strength and economy. The minimum details should include the following: ●

●

● ● ●

Copies of relevant site drawings showing the projected retaining wall/ cofferdam areas and the proximity of the roads, rail or crane tracks, buildings, embankments, viaducts and waterways. Information regarding any under-ground workings, surface traffic loadings, capital plant or heavy machinery which could be affected by piling operations or in turn, affect ground stability by vibration. Copies of actual borehole logs, soil analyses and test reports. Details of any faults or fissures encountered during drilling. Details of seasonal rainfalls, standing water levels, tidal waters and the depths of off-shore reaches. Stream and river velocities, currents etc, should be given where possible.

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EARTH & WATER PRESSURES Typical Soil Properties

Note: Soil properties should normally be obtained from ground investigation.

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EARTH & WATER PRESSURES Earth Pressure Calculation Calculation of Earth Pressures for Limit State Design

The method of calculation of design earth and water pressures will be subject to some change in the future as designers adopt the ‘limit-state’ approach given in Eurocodes 1 - ‘Basis of Design and Actions and Structures’, 3 – ‘Design of Steel Structures’ and 7 – ‘Geotechnical Design Rules’. Using this approach, the value of earth pressures (which are classed as actions on the wall) due to both permanent and transient actions eg weights of soil, water pressure and traffic loads and the characteristic strength parameters of the soils, will be modified by the application of partial factors. The value of these factors will depend on the limit state and design case under consideration and whether the action is permanent or variable, favourable or unfavourable. Until these new codes are widely adopted by designers this chapter will focus on the ‘traditional’ methods of earth and water pressure calculation. Throughout this chapter formulae and tables are shown in terms of φ and c wherever appropriate (see Cohesionless Soils and Cohesive Soils). The pressures applied to a vertical wall when the ground surfaces are horizontal are calculated as follows: Active pressure = pa = γ.h.tan² (45 - φ/2) - 2.c.tan (45 - φ/2) Passive Pressure = pp = γ.h.tan² (45 + φ/2) + 2.c.tan(45 + φ/2) The terms tan² (45 - φ/2) and tan² (45 + φ/2) can be more conveniently referred to as Ka coefficient of active pressure and Kp coefficient of passive pressure respectively. Hence pa = γ.h.Ka - 2.c. √ Ka and pp = γ.h.Kp + 2.c. √ Kp The above expressions do not allow for the effects of friction and adhesion between the earth and the wall. They are based on the extensions to the Rankine Equation (by the addition of cohesion), from ‘Earth Pressures’ - A.L. Bell: Proceedings of the Institution of Civil Engineers, Vol. 199 -1915.

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P = (wh² / 2) (1 - sin φ) / (1 + sin φ) - 2c (1 - sin φ) / (1 + sin φ)

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EARTH & WATER PRESSURES Cohesionless Soils Cohesionless soils are free draining, therefore excess pore water pressures, created during construction, will dissipate so rapidly that “effective” stress condition exists in both the short and long term. Hence φ is used throughout. The effect of wall friction on active pressures is small and usually ignored. Values of Ka are given in the table below. Values of Ka

25º

30º

Values of φ 35º

40º

45º

0

0.41

0.33

0.27

0.22

0.17

10º

0.37

0.31

0.25

0.20

0.16

20º

0.34

0.28

0.23

0.19

0.15

30º

-

0.26

0.21

0.17

0.15

Values of δ

The value of the coefficient of wall friction, tan δ, for passive pressures is usually assumed to be 2/3rds of tan φ, but it is sufficiently accurate to take the angle as 2/3rds of φ. The effect of wall friction on passive pressures is taken into account by using modified values as Kp as given in the table below. Values of Kp

Values of δ(º) Values of φ(º) 0

1/2φ

2/3φ

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15

1.7

2.0

2.0

20

2.1

2.5

2.7

22

2.2

2.7

3.0

24

2.4

3.0

3.3

26

2.5

3.4

3.8

28

2.8

3.8

4.3

30

3.0

4.4

5.0

32

3.3

5.0

5.8

34

3.6

5.8

6.8

36

3.9

6.6

7.8

38

4.2

7.8

9.0

40

4.6

9.0

45

5.8

Note: For the design of maritime structures using sheet piling, clause 50 BS.6349 : Part 1 : 1984 gives guidance on the maximum angle of passive wall friction that may be used. In cohesionless soils, the soil below ground water level should be taken at submerged density when calculating the earth pressures. To these pressures, the full water pressure is added.



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EARTH & WATER PRESSURES Cohesive and Mixed Soils The effects of wall friction and adhesion on active pressures are taken into account by using modified values of Ka and substituting Kac for the terms 2√ Ka. The expression for active pressure thus becomes: pa = γ.h.Ka - Kac.c Values Ka and Kac are given in the table below. Values of Ka and Kac

Values of δ

Values of ca/c

0

Values of φ 0º

5º

10º

15º

20º

25º

All values

1.00

0.85

0.70

0.59

0.48

0.40

φ

All values

1.00

0.78

0.64

0.50

0.40

0.32

0

0

2.00

1.83

1.68

1.54

1.4

1.29

0

1

2.83

2.6

2.38

2.16

1.96

1.76

φ

0.5

2.45

2.1

1.82

1.55

1.32

1.15

φ

1

2.83

2.47

2.13

1.85

1.59

1.41

Ka

Kac

The effects of wall friction and adhesion on passive pressure are taken into account by using modified values of Kp and substituting Kpc for the term 2√ Kp. The expression for passive pressure thus becomes: pp =γ.h.Kp + Kpc.c Values of Kp and Kpc are given in table below. Values of Kp and Kpc

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Values of δ

Values of ca/c

0

Values of φ 0º

5º

10º

15º

20º

25º

All values

1.00

1.2

1.4

1.7

2.1

2.5

φ

All values

1.00

1.3

1.6

2.2

2.9

3.9

0

0

2.00

2.2

2.4

2.6

2.8

3.1

0

0.5

2.4

2.6

2.9

3.2

3.5

3.8

0

1

2.6

2.9

3.2

3.6

4.0

4.4

φ

0.5

2.4

2.8

3.3

3.8

4.5

5.5

φ

1

2.6

2.9

3.4

3.9

4.7

5.7

Kp

Kpc

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EARTH & WATER PRESSURES Wall Adhesion Wall adhesion ca should be taken as being equal to c, up to a maximum of 50kN/ m² for active pressures, and equal to 1/2c up to a maximum of 25kN/m² for passive pressures. The effect of wall friction and wall adhesion on active pressures should only be taken into account when the wall is prevented from moving downwards by adequate penetration. Similarly, the effects of wall friction and wall adhesion on passive pressures should only be taken into account when the wall is adequately restrained against upward movement. Such restraint is usually provided by friction between the retained earth and the back of the wall. Where the wall tends to move downwards due to the application of external permanent vertical loading the value of ca for passive pressures may be taken as equal to c but should not exceed 50kN/m² . Under these conditions the effects of wall adhesion on active pressures should be ignored.

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EARTH & WATER PRESSURES Tension Crack When soils with a high cohesion are involved, it may be found that the calculated active pressure has a negative value, which in fact represents zero pressure. However, when this occurs, allowance should be made for the intrusion of water between the piles and the soil which will produce an active pressure equivalent to full hydrostatic head up to ground water level. If ground water is not likely to be present, an alternative substitution for zero active pressure in cohesive soils is that of the pressure due to an equivalent fluid of 5 kN/m³ weight density.

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EARTH & WATER PRESSURES Superimposed Loading This is taken into account by adding the intensity of the load to the value of γ.h.

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EARTH & WATER PRESSURES Battered Walls The effect of batters up to 5º may be neglected.

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EARTH & WATER PRESSURES Pressure Calculations A convenient system for the calculation of earth pressures is as follows: 1. Calculate the value of γ.h at the ground surface and each subsequent change in stratum down to a point well below the excavation level. This is done commencing at existing ground level for active pressures and at excavation level for passive pressures. 2. The earth pressure at any level is then obtained by substituting the appropriate value of γ.h in the expressions for the active or passive pressure, using the coefficients and properties applicable to the stratum under consideration.

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EARTH & WATER PRESSURES Concentrated and Linear Surcharge

! These are treated in a similar manner to superimposed loads except that allowance should be made for dissipation of the load at increasing depth. There are various methods of allowing for this dissipation and the following is suggested by Krey when designing for cohesionless soils. The maximum increase in horizontal total stress (∆σh) is given by: (∆σh max) = 4q.tan² (45º - φ'/2) / (2 + (1 + tan² (45º - φ'/2)) x/z) where

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q = magnitude of surcharge (kN/m² ) a = x.tan φ' c = x / tan (45º - φ'/2) d = z / tan (45º - φ'/2)

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EARTH & WATER PRESSURES Sloping Ground Surface

Approximate pressures can be obtained by assuming a horizontal surface and increasing the pressures thus obtained by 5% for each 5º inclination above the horizontal. Alternatively an arbitrary horizontal ground surface, at some level above that at which the sloping surface intersects the wall, may be assumed. When dealing with cohesionless soils the following method may be adopted pa at A= 0.Ka pa at B= γ.h1 Ka pa at C= γ.h2 Ka

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EARTH & WATER PRESSURES Earth Pressure Calculation Example The coefficients of earth pressure for each type of soil are obtained from tables in sections Cohesionless Soils and Cohesive and Mixed Soils Values of Ka, Kac, Kp, Kpc

Ka

Kac

Kp

Kpc

Loose Fine Sand

0.33

-

4.90

-

Soft Clay

1.00

2.83

1.00

2.40

Sand and Gravel

0.27

-

6.00

-

Firm Clay

1.00

2.00

1.00

2.30

Calculation of Overburden The mass densities of the materials must be converted to weight densities before calculation of overburden, ie the mass density in kg/ m³ divided by 101.97 will give the weight density in kN/m³ . For simplicity the figure of 100 has been used in the following calculations. As cohesive strata are impervious to the passage of water, the bulk weight density should be used. This in turn means that the uplift thus created on the underside of such strata must be deducted when calculating the over-burden in subsequent non-cohesive strata. The method of calculating the overburden is shown below: Soil Overburden: Active Side Overburden at...

In soil...

Calculation

Value (kN/m²)

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Ground level

10.0

-1.2m

Loose fine sand

(17.5 x 1.2) + 10

31.0

-2.4m

Loose fine sand

(10 x 1.2) + 31

43.0

-2.4m

Soft clay

-6.1m

Soft clay

-6.1m

Compact gravel

-7.9m

Compact gravel

(11 x 1.8) + 113.3

133.1

-11.0m

Compact gravel

(11 x 3.1) + 133. 1

167.2

-11.0m

Firm clay

-13.0m

Firm clay

43.0 (19 x 3.7) + 43

113.3 113.3

167.2 (20 x 2) + 167.2

207.2

Calculation

Value (kN/m²)

Soil Overburden: Passive Side Overburden at...

In soil...

-7.9m

Compact gravel

-11.0m

Compact gravel

-11.0m

Firm clay

-13.0m

Firm clay

0.0 (11 x 3.1)

34.1 34.1

(20 x 2) + 34.1

74.1



Revised Overburden with effects of water pressure and buoyancy added: Active Side Overburden at...

In soil...

Calculation

Ground level

Value (kN/m²) 10.0

-1.2m

Loose fine sand

31.0

-2.4m

Loose fine sand

43.0

-2.4m

Soft clay

43 + 12

55.0

-6.1m

Soft clay

113.3 + 12

125.3

-6.1m

Compact gravel

125.3 - 49

76.3

-7.9m

Compact gravel

(11 x 1.8) + 76.3

96.1

-11.0m

Compact gravel

(11 x 3.1) + 96.1

130.2

-11.0m

Firm clay

130.2 + 98

228.2

-13.0m

Firm clay

(20 x 2) + 228.2

268.2

Revised Overburden with effects of water pressure and buoyancy added: Passive Side Overburden at...

In soil...

Calculation

Value (kN/m²)

-7.9m

Compact gravel

0.0

-11.0m

Compact gravel

34.1



-11.0m

Firm clay

34.1 + 31

65.1

-13.0m

Firm clay

(20 x 2) + 65.1

105.1

Calculation

Value (kN/m²)

10 x 0.33

3.3

Earth Pressures: Active Side Pressure at...

In soil...

Ground level -1.2m

Loose fine sand

31 x 0.33

10.2

-2.4m

Loose fine sand

(43 x 0.33) + 12

26.2

-2.4m

Soft clay

55 - (2.83 x 20)

-1.6 or 12 pw

-6.1m

Soft clay

125.3 - (2.83 x 20)

68.7

-6.1m

Compact gravel

(76.3 x 0.27) + 49

69.6

-7.9m

Compact gravel

(96.1 x 0.27) + 67

93.0

-11.0m

Compact gravel

(130.2 x 0.27) + 98

133.2

-11.0m

Firm clay

228.2 - (2 x 65)

98.2

-13.0m

Firm clay

268.2 - (2 x 65)

138.2

Calculation

Value (kN/m²)

Earth Pressures: Passive Side Pressure at...

In soil...



-7.9m

Compact gravel

0x6

0.0

-11.0m

Compact gravel

(34.1 x 6) + 31

235.6

-11.0m

Firm clay

65.1 + (2 x 65)

214.6

-13.0m

Firm clay

105.1 + (2.3 x 65)

254.6

Pressure at...

In soil...

Calculation

Value (kN/m²)

-7.9m

Compact gravel

93 - 0

93.0 Active

-11.0m

Compact gravel

235 - 133.2

102.4 Passive

-11.0m

Firm clay

214.6 - 98.2

116.4 Passive

-13.0m

Firm clay

254.6 - 138.2

116.4 Passive

Net Pressures

The limit of water pressure in the soft clay stratum is the point at which the water pressure = the active pressure. -1.6 + 19X = 12 + 10X 9X = 13.6 X = 1.51m Water pressure = 10(1.2 + 1.51) = 27.1 kN/m² Overburden = (19 x 1.51) + 43 + 12 = 83.7 kN/m² file:///C|/Documents%20and%20Settings/bantinone/My%20Documents/My%20Webs/myweb19/Earth_pressures/Calculation_example.html (5 of 7)5/26/2005 4:00:03 AM


Active pressure = 83.7 - (2.83 x 20) = 27.1 kN/m²



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Retaining Walls - Corus Piling Handbook

RETAINING WALLS Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

Introduction Types of Wall Design (General) Dealing with Water Design Situations Factor of Safety Softened Zone Analysis of Pressure Diagrams Design for Bending Moments Bending Moment Reduction Support Location Calculating Support Forces Walls Supported by More Than One Level of Struts or Ties Selection of Pile Section Development of Section Strength Design Bending Stresses Low Propped Walls Anchorages Walings Design of Walings in Continuous Anchor Walls Tie Rods Relieving Platforms Miscellaneous Details Design of Cantilever Retaining Walls Design of Walls with Free Earth Support Design of Walls with Fixed Earth Support Analysis by Graphical Method Design of Sheet Pile Deadman Anchorage Design Example

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RETAINING WALLS Introduction A sheet pile retaining wall has a significant portion of its structure embedded in the soil and a very complex soil/structure interaction exists as the soil not only loads the upper parts of the wall but also provides support to the embedded portion. Current design methods for retaining walls do not provide a rigorous theoretical analysis due to the complexity of the problem. The methods which have been developed to overcome this, with the exception of finite element modelling techniques, introduce empirical or empirically based factors which enable an acceptable solution to the problem to be found. As a result, no theoretically correct solution can be achieved and a large number of different approaches to this problem have been devised. The design of a retaining structure using currently available techniques requires the performance of two sets of calculations, one to determine the geometry of the structure to achieve equilibrium under the design conditions, the other to determine the structural requirements of the wall to resist bending moments and shear forces determined from the equilibrium calculations. The selected design conditions occur during the life of the structure are taken into account. Designers should not overlook the possibility of global failure resulting from deep seated slip failure of the soil and ensure that the proposed

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RETAINING WALLS Types of Wall Retaining walls can be classified into cantilever or supported types. Cantilever walls are dependent solely upon penetration into the soil for their support and clearly, fixity of the toe is required to achieve equilibrium of the forces acting on the structure. As fixity of the wall toe requires longer and, in many cases, heavier piles to achieve the necessary penetration into the soil, this type of wall can only be economic for relatively small retained heights. Variations in soil properties, retained height and water conditions along a wall can have significant effects on the alignment of a cantilever wall and care must be taken when designing them for permanent structures, although provision of a capping beam will often alleviate alignment problems.

Supported walls, which can be strutted or tied, achieve stability by sharing the support to be provided between the soil and the supporting member or members. In this situation the soil conditions at the toe of the wall are not as critical to the overall stability of the structure as in the case of a cantilever wall. The provision of longitudinal walings to transfer the tie or strut force uniformly along the wall also caters for variations in displacement along the structure.

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RETAINING WALLS Design (General) A retaining wall structure must be designed to perform adequately under two particular sets of conditions, those that can be regarded as the worst possible to occur during the life of the structure and those that can be expected under normal service conditions. These design cases represent the ultimate and serviceability limit states for the structure. Ultimate limit states to be taken into account in design include instability of the structure as a whole including the soil mass, failure of the structure by bending or shear and excessive deformation of the wall or soil to the extent that adjacent structures or services are affected. Where the mode of failure of the structure involves translation or rotation, as would be expected in the case of a retaining wall, the stable equilibrium of the wall relies on the mobilisation of shear stresses within the soil. Full mobilisation of soil shear strength results in limiting active and passive conditions and these only act together on the structure at the point of collapse, the ultimate limit state. Design for serviceability involves a consideration of the deformation of the structure and movement of the ground to ensure that acceptable limits are not exceeded. The deformations of the ground which accompany full shear strength mobilisation are large in comparison to those which occur in normal service and as the forces on the structure and the forces from the retained soil are inversely proportional to movement, the serviceability limit state of displacement will often be the governing criterion for equilibrium. Although it is impossible, or impractical, to directly calculate displacements, serviceability requirements can generally be achieved by limiting the magnitude of the mobilised soil strength. The designer of a retaining wall must assess the design situations to which the wall could be subjected during its lifetime and apply these to the structure to analyse their effect. The design situations should include the following where appropriate: Applied Loads and any Combinations

Surcharges and externally applied loads on each side of the wall: a minimum surcharge of 10kPa on the retained side of the wall should be used in design. Where very high levels of surcharge or concentrated loads occur, eg ports and harbours, it is often more economical to carry the loads on bearing piles which transfer them to a lower stratum where no lateral pressure is exerted on the retaining structure. Geometry of the Problem

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A minimum unplanned depth of excavation in front of the wall of 0.5m or 10% of the retained height of a cantilever or 10% of the distance below the lowest support in a supported wall should be included. In the case of a retaining structure with services buried in the passive zone, allowance should be made for future excavation to replace or maintain the cables or pipes. Material Characteristics

In permanent structures, the long term performance of steel must be considered. Environmental Effects

Variations in ground water level, due to dewatering, flooding or failure of drainage systems. Consider the effects of providing weep holes to prevent the accumulation of ground water behind the wall; however these must be designed to prevent clogging by any fines transported in the flowing water. Scour, erosion and tree removal will all affect the structure. Weathering, freezing and other effects of time and environment on the material properties. Mining Subsidence

Consider the tolerance of the structure to deformation. Construction

Driving of sheet piles into dense soils may necessitate the provision of a section larger than that needed to satisfy the structural requirements. Drivability should be considered at an early stage in the design process as the need to provide a minimum section for driving may lead to a more efficient support system.

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RETAINING WALLS Dealing with Water The water pressure conditions adopted in retaining wall design should be the most onerous that can be possibly imagined as the effect of water pressures on design calculations is very significant. When an analysis is being carried out assuming that drained conditions exist, the effect of flow beneath the toes of the sheet pile wall is to increase the active pressures on the wall and decrease the passive pressures. The minimum design pressure acting on a retaining wall should be the pressure due to retention of a fluid with an effective density of 5kN/m³. However, if the designer considers that water could be present behind the wall to the ground surface, in a tension crack for example, then the design should incorporate full hydrostatic pressures behind the wall. In order to reduce the effect of large water pressures resulting from differences in water level on each side of a retaining structure, the designer may provide weep holes through the wall preventing an accumulation of ground water. These will generally be located at the bottom of the exposed section of wall to maximise their effect as a means of reducing water levels. It should be noted, however, that weep holes are only fully effective when free drainage is possible and they should be designed in such a way that any fine material transported by the flow of ground water will not cause them to become clogged. In cohesive soils, weep holes are ineffective in the relief of water pressure behind the wall.

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RETAINING WALLS Design Situations When designing a retaining wall, the designer may choose between the adoption of free and fixed earth conditions at the toe of the wall. The difference between these two conditions lies in the influence which the depth of embedment has on the deflected shape of the wall. This is illustrated in the figures below and in the examples section. A wall designed on free earth support principles can be considered as a simply supported vertical beam, one support being provided by the soil pressures acting in the embedded zone, the other support being provided by a prop or tie near the top of the wall. In this situation, the wall is embedded into the soil a sufficient distance to prevent translation, but is able to rotate at the toe. For a given set of conditions, the length of pile required is minimised, but the bending moments are at a maximum. A wall designed on fixed earth principles is a propped vertical cantilever, fixity at the foot of the wall being provided by the soil pressures resulting from increased embedment, the upper support reaction being provided by either a tie or a prop. In this case the pile length is such that the toe of the wall is sufficiently embedded to prevent both translation and rotation. The effect of this toe fixity is to reduce the bending moments for a given set of conditions but at the expense of increased pile length. When a retaining wall is designed using the assumption of fixed earth support, provided that the wall is adequately propped and capable of resisting the applied bending moments and shear forces, no failure mechanism relevant to an overall stability check exists. However, empirical methods have been developed to enable design calculations to be carried out, an example of which is given later in this chapter. Designers must be careful when selecting the design approach to adopt. For example, walls installed in soft cohesive soils may not generate sufficient pressure to achieve fixity and in these soils it is recommended that free earth conditions are assumed. Similarly, where driving to the required depth may be problematic, assumption of free earth support conditions will minimise the driven length and ensure that the bending moment is not reduced by the fixity assumed.

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The design methods used to determine the pile length required for both free and fixed earth support conditions do not apply if the support is provided below the mid point of the retained height as the assumptions made in the analysis models will not be valid.

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RETAINING WALLS Design of Walls with Free Earth Support In this condition the penetration of the piles is such that the passive pressure in front of the piles is sufficient to resist the forward movement of the toes but not sufficient to prevent rotation. Thus the piles are supported by ties at the top of the wall and the soil at its base in a manner similar to a beam on simple supports.

The figure above indicates the loads acting on the wall. Area A.O.B1 = total net active pressure Area O.C.C1 = total net passive pressure (Factor of safety = 1) Area O.D.D1 = total net passive pressure (Factor of safety = 2) T = Force applied at waling level The depth of cut off should be sufficient to give a factor of safety of 2 against rotation of the wall about the waling. For stability the moments of areas A.O.B1 and O.C.C1 about the waling level should be in equilibrium. file:///C|/Documents%20and%20Settings/bantinone/My%20...0Webs/myweb19/Retaining_walls/Free_earth_support.html (1 of 5)5/26/2005 4:00:05 AM


The bending moment on the piles is derived by calculating the level XY at which zero shear occurs (ie where area X.Y.B1.O = Area O.C.C1) and obtaining the net moment of these areas about this level. The force T at waling level = Area A.O.B1. - Area O.C.C1. The depth of cut off should be such that the moment of area O.D.D1 is twice the moment of area A.O.B1 about tie rod level.

Free Earth Support - Example Active pressure Passive pressure

pa = γ.h.Ka - 2c√Ka + pw kN/m² pp = γ.h.Kp + 2c√Kp + pw kN/m²

The coefficients of earth pressure used in the calculations are: Loose fine sand: Ka = 0.33, Kp = 4.9 Kp = 6.0 Dense fine sand: Ka = 0.27,

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pa at : ground level

= 10 x 0.33

= 3.3 kN/m²

4m below ground level in loose fine sand

= 78.6 x 0.33

= 26 kN/m²

4m below ground level in dense fine sand

= 78.6 x 0.27

= 21.3 kN/m²


= 89.6 x 0.27 + 9.8

= 34 kN/m²


= 111.2 x 0.27 + 29.4

=59.4 kN/m²


= 154.4 x 0.27 + 68.6

=110.3 kN/m²

pw at 7m below ground level

= 19.6 kN/m²

pp at 11m below ground level in dense fine sand

= 43.1 x 6.0 + 58.8

= 317.4 kN/m²

Net pp at 7m below ground level in dense fine sand

= 59.4 - 19.6

= 39.8 kN/m²


= 317.4 - 110.2

= 207.2 kN/m²

Moments of active pressures about waling level: Active Pressure 3.3 x 4.0 x 0.5 =

Moment of Active Pressure about 'O' 6.6

6.6 x 0.333 =

2.2

26 x 4.0 x 0.5 =

52.0

52.0 x 1.667 =

86.7

21.2 x 1.0 x 0.5 =

10.6

10.6 x 3.333 =

35.3

34 x 1.0 x 0.5 =

17.0

17.0 x 3.667 =

62.3



34 x 2.0 x 0.5 =

34.0

34.0 x 4.667 =

158.7

39.8 x 2.0 x 0.5 =

39.8

5.9 x 5.333 =

212.3

39.8 x 0.645 x 0.5 =

12.8

12.8 x 6.215 =

= 172.7 kN

79.8 = 637.3 kNm

For stability the moment of passive pressure about the waling level must be at least equal to the moment of active active pressure about the waling. The rate of increase of the passive pressure with depth: = (39.8 + 207.2) / 4 = 61.75 kN/m² per metre. Hence 61.75 / 2 * x² (6.645 + 2x/3) = 673.3 and therefore x » 1.63m The total net passive pressure is 61.75 x 1.63² x 0.5 = 82.0 kN/m. Moment of passive pressure about waling level = 82 x (6.645 + 2 x 1.63 / 3) = 634 kNm Total net active pressure = 172.7 kN Therefore the force in the aling ans supports = 172.7 - 82.0 = 90.7 kN/m run of wall. Zero shear (where area of active pressure diagram = waling force) is at 5.12m below pile top. Moments about and below level of zero shear: 82.0 x 3.612 =

296.2

-34.3 x 1.880 x 0.5 x 0.627 =

-20.2

-39.8 x 1.880 x 0.5 x 1.25 =

-46.8

-39.8 x 0.645 x 0.5 x 2.095 =

-26.9 = 202.3 kNm

The maximum bending moment on the piles = 202.3 kNm per metre run of all. Section modulus required = (202.3 x 1000 x 100) / (180 x 100) = 1124 cm³/m In this example it has been assumed that the wall is to be used for permanent works for which a working stress of 180 N/mm² is adopted. Penetration required to give a factor of safety of 2 against rotation of the wall about the waling level = y + 0.645 + 7.00 To find y, 61.75y²/2 * (6.645 + 2/3y) = 2 x 636.4 and therefore y » 2.24m.



Moments of net passive pressure with 2.24 + 0.645 = 2.885m penetration. 2.24 x 61.75 x 2.24 x 0.5 x (6.645 + 2 x 2.24 / 3) = 1260.7 kNm (c.f. 2 x 637.3 = 1275 kNm) Therefore actual Factor of Safety against rotational failure = 1260.7 / 637.3 = 1.98 Total pile length required = 7.00 + 0.645 + 2.24 = 9.885 say 10m. Use LX12 or Frodingham 2N piles in EN10248: S270GP steel, 10m long. Note: Although these sheet pile sections will be adequate for structural purposes the designer must check that they will be drivable to the required depth and will provide the required effective life.

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RETAINING WALLS Factor of Safety Many different methods of analysis have been developed to calculate the embedment depth required to ensure stability in a retaining structure. In the main, these methods are empirical and start with the concept that the soil will attain active and passive pressure conditions at the point of failure. The pressure diagrams resulting from this ultimate condition are then used to determine the length of the pile required to achieve moment equilibrium. However, as this represents imminent failure of the wall, a factor of safety is applied, to ensure that the soil stresses are limited to an appropriate value and that the failure condition is not realised in practice. The factor of safety can be applied in a number of different ways: ●

● ●

Application of a multiplying factor to increase the calculated depth of embedment required for limiting equilibrium. Reduction of the soil strengths by application of an appropriate factor. Increasing the net or gross pressures acting on the structure by application of an appropriate factor.

The magnitude of the factor or factors to be applied is dependent upon the method of analysis to be used and should reflect the confidence the designer places in his choice of soil parameters for design and the deformation limits to be applied to the structure. Methods by which factors of safety can be introduced to design calculations based on active and passive limit pressures include the gross pressure method, the net pressure method, the revised method and the factor on strength method. These are discussed in general terms below. Gross Pressure Method (Fp)

Commonly referred to as the CP2 method, the factor of safety is applied to the gross passive pressure diagram only. This approach can lead to an anomaly in undrained conditions where Ka = Kp =1 as, beyond a certain depth of embedment, the calculated factor of safety decreases with increasing length of wall. This situation results from the fact that the bulk weight of the soil on the passive side, used to calculate the earth pressures acting on the wall, is effectively reduced by the factor of safety.

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Net Pressure Method (Fnp)

The method has been used by designers for many years and is often referred to as the British Steel Piling Handbook method. The factor of safety is applied to the net passive pressure diagram which is derived by subtracting the active earth pressure and water pressure at a given level from the passive earth pressure and water pressure. The method tends to give higher factors of safety for a given geometry when compared to other methods, but careful selection of conservative design parameters will give acceptable analysis results.



Revised Method (Fr)

Often referred to as the Burland and Potts method, the factor of safety is applied to the moment of the net available passive components of the active pressure which result from the weight of soil below dredge level. In effect the factor of safety is applied to the dead weight of soil below dredge level on both sides of the wall. This method partially overcomes the anomaly in the gross pressure method.

Factor on Strength Method (Fs)

In this approach, the strength parameters of the soil are reduced by an appropriate factor in a method analogous to the calculation of embankment stability. The effect is to increase Ka and decrease Kp, modifying the pressure distribution relative to that used as a base in the other described methods. This distortion of the pressure diagram affects the bending moment calculation and it is recommended that this method is only used to determine the wall length. The advantage of this method is that the parameters which introduce the greatest uncertainty to a design are factored. With each method of analysis, for the same input parameters, the limiting equilibrium condition (factor of safety = 1), will result in the same depth of penetration. The application of the factor of safety to different areas of the moment equation as required by the various methods of analysis will result in different penetration lengths for the same factor of safety value. Note: The factor on strength approach to design is favoured by BS 8002:1994 and Eurocode 7, the standards which govern the design of earth retaining structures in file:///C|/Documents%20and%20Settings/bantinone/My%20...%20Webs/myweb19/Retaining_walls/Factor_of_safety.html (3 of 4)5/26/2005 4:00:06 AM


the UK. In both documents, partial factors are applied to the various parameters affecting the wall design (ie soil density, surcharges, loads etc) to enhance unfavourable (disturbing) loads and pressures and downrate favourable ones. The ‘adjusted’ input data are then analysed to determine the equilibrium condition as the partial factors provide the appropriate factor of safety. Different factors are applied dependent upon the nature of the analysis being carried out, ie serviceability or ultimate limit state.

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RETAINING WALLS Softened Zone Where soft cohesive soils are exposed at dredge or excavation level it is advisable when calculating passive pressures to assume that the cohesion increases linearly from zero to the design cohesion value over the top metre of passive soil.

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RETAINING WALLS Analysis of Pressure Diagrams When creating a pressure diagram to work with, it is essential that the pressure conditions are calculated at every change of state of the problem, ie strata boundaries, water tables, excavation depth etc. However, when designs involve a support, it is often convenient to include a pressure calculation at this level. When taking moments of pressures about a given position, the diagram can be broken down in different ways to produce a series of sensible units. It should be noted that in the situation where the pressure diagram is divided into rectangles and triangles, care must be taken to introduce the 1/2 factor for areas of triangles and either 1/3, 2/3 or 1/2 when assessing moments of areas about a point. When divided only into triangles, the 1/2 factor in the area calculation appears everywhere and the moment factor will be 1/3 or 2/3.

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RETAINING WALLS Design for Bending Moments There are two methods by which bending moments in retaining structures can be calculated from limit equilibrium pressures, one for the equilibrium condition where the earth pressure diagram is truncated at the wall length where the rotational factor of safety is 1 and the other for the in-service condition where the earth pressure diagram over the specified wall length is adopted. These are often referred to as ultimate and working bending moments respectively (to the confusion of some structural engineers). For the equilibrium condition, bending moments and shear forces in the wall are computed at limiting equilibrium with unfactored soil parameters, ie factor of safety = 1. The actual design depth of embedment is deeper than required to achieve stability against rotational failure, but this additional length, which will in effect cause a partial fixity of the wall and therefore a reduction in maximum bending moment, is not taken into account in calculations. For the in-service condition, bending moments and shear forces in the wall are computed from the earth pressures acting on the wall in its specified state. The service pressures are obtained from the limiting equilibrium pressures by dividing the relevant pressure component by the current factor of safety. The result of the calculation is therefore dependent upon the method used to determine the factor of safety. In the case of a cantilever, the difference in bending moments calculated by each method is very small. In the new partial factor design methods, a service condition for the bending moments results as the earth pressures are already factored and the calculated pressure diagram is used to compute structural forces and moments in the wall.

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RETAINING WALLS Bending Moment Reduction The simplifying assumptions made in design calculations concerning the linear increase in active and passive pressures in a material does not take into account the interaction between the soil and the structure. Studies have shown that this can have a significant effect on the distribution of earth pressures and consequent bending moments and shear forces on a structure. The reduction in calculated bending moments is a function of the soil type and the flexibility of the wall in comparison to the supported soil. When a supported, flexible wall deflects, a movement away from the soil occurs between the support position and the embedded portion of the wall. This effect often leads to a form of arching within the supported soil mass which allows the soil to maximise its own internal support capabilities effectively reducing the pressures applied to the wall. For a relatively flexible structure, such as an anchored sheet pile wall, the effect of wall deformation will increase the pressures acting above the anchor level, as the wall is moving back into the soil using the support as a pivot, and reduce the pressures on the wall below this level where the biggest deflections occur. The result of a redistribution of pressures is therefore a reduction in the maximum bending moment on a wall, but an increase in support reaction. Redistribution should not be considered for cantilever walls or where the structure is likely to be subjected to vibrational or large impact forces which could destroy the soil ‘arch’. Similarly, if the support system is likely to yield or movement of the wall toe is expected, moment reduction should not be applied. Where stratified soils exist, moment reduction should be viewed with caution since soil arching is less likely to occur in soils of varying strength.

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RETAINING WALLS Support Location The location of supports to a retaining structure has a critical bearing on the structural requirements of the wall itself. As has been illustrated in the preceding sections, consideration of the wall as either fixed or free in terms of its mode of operation directly affects the bending moments and shear forces to be resisted by the wall. Similarly, the position at which supports are assumed to act will affect the magnitude of bending moments and shear forces and consequently the support reaction required for stability. Conventional design methods assume a particular form of failure for the structure. For example, in the case of a wall designed for free earth support, forward rotation of the toe of the wall occurs and to achieve this, the support system must act above the mid-point of the retained height. The factor of safety methods discussed previously all assume that this form of failure occurs and are all based on the provision of a single support location. When multiple supports are provided, the conventional methods of analysis do not apply and consideration must be given to the mode or modes of failure which will occur.

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RETAINING WALLS Calculating Support Forces For a wall with a single support, the support reaction can be calculated using either of the two methods indicated for the calculation of bending moments; ie under equilibrium conditions when the factor of safety equals 1 or under in-service conditions when the particular factor of safety calculated for the prescribed pile length is used to factor the applied earth pressures. It is recommended that the calculated reaction force is increased by 25% to allow for arching and stress redistribution behind the wall. However, experience with similar structures in the particular soil types may enable the designer to reduce that figure. The design of the support system for a retaining structure should incorporate a factor of safety of at least 2 and it is prudent to be conservative when assessing the support loads and member sizes as the effects of under design can be catastrophic. As with bending moment calculations, adoption of a partial factor design philosophy will result in the calculation of support reactions for the service condition.

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RETAINING WALLS Walls Supported by Multi-Level Struts or Ties As discussed above, the conventional design methods based on a factor of safety against rotational failure assume that the wall will fail in a particular manner. When more than one level of support is provided to a wall the potential failure mode changes provided that the supports are not close enough together to act as a single support. With multiple levels of support, the wall will not fail by rotation and failure will be as a result of collapse of the support system or excessive bending of the piles. Consequently, provided that the wall and supports are sufficiently strong to resist the worst credible loading conditions, failure of the structure cannot occur. To assess the bending moments and reaction forces in a multipropped wall, a number of analysis methods have been developed. Unfortunately, the structure is statically indeterminate and a number of assumptions need to be made to enable the structure to be analysed. Hinge Method

This method allows the structure to be analysed at successive stages of construction, modelling the retaining wall at a number of construction stages when additional supports are introduced. The method assumes that a hinge occurs at each support position except the first, the spans between the frames being considered as simply supported beams loaded with earth and water pressures; the span between the lowest support and excavation level is designed as a single propped wall with the appropriate earth and water pressures applied. Prop loads calculated using this method include the respective load from adjacent spans. The analysis of structures using this method is carried out on a stage by stage basis with excavation being carried out to sufficient depth to enable the next level of support to be installed. It is therefore possible that the support loads and bending moments calculated for a given stage of excavation are exceeded by those from a previous stage and it is important that the highest values of calculated support force and bending moments are used for design purposes. Using this method, it is possible to calculate a depth of penetration to give a factor of safety against rotational failure as the lowest span is treated as a singly supported wall and can therefore be analysed as such. This can be a comfort to designers as the calculations show that a given FoS has been achieved. However, this should only be considered as an indicative value as the remainder of the piled wall has been ignored and failure will not be in the form assumed.

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Pressure Envelopes

This method of analysis is empirical and based upon loads measured in struts which were then used to construct envelope diagrams of the horizontal earth pressures acting on a wall. The envelopes, which take into account the variations in strut load that occur in practice, are trapezoidal in form, the magnitude of the loading diagram being a function of the ground type. The total load represented by the area of the trapezoid exceeds the load predicted using the Rankine pressure distribution by a factor between 1.3 and 1.75 depending on soil types. The most frequently used diagrams are those developed by Terzaghi and Peck, which were subsequently modified by Peck. For granular and mixed soils, the water and surcharge pressures should be added to the diagram to enable the prop forces to be calculated. No allowance should be made for continuity of the wall when using this method, each support load being calculated from a summation of the appropriate parts of the pressure envelope. This method of analysis is not recommended for the calculation of bending moments.



Continuous Beam Method

The wall is assumed to act as a vertical beam subjected to a pressure distribution with reactions at support points. The bottom of the beam is also assumed to be supported below excavation level by a soil reaction at the point at which the net active pressure on the wall falls below zero. Mobilised earth pressures are assumed to act on the wall, the magnitude of these pressures are dependent upon a factor governed by the permissible movements of the wall being designed. The minimum recommended mobilised earth pressure is however 1.3 times that resulting from the use of ka to determine soil pressures on the wall. Each support is modelled either as rigid or as a spring, depending on its compressibility. The displacement at a rigid support is zero, whereas in a spring it is propor-tional to the force carried by the spring. The hypothetical soil support is modelled in one of three ways. If the net pressure does not fall to zero anywhere along the wall, the hypothetical soil support is ignored and the embedded portion of the wall is treated as if it were a cantilever. This situation is likely to occur if there is only a short depth of embedment or the active pressures are particularly large. The applied load in this case is carried entirely by the props. If the net pressure does fall to zero along the length of the wall, the hypothetical soil support is considered as a rigid prop. This situation is likely to occur if there is a large depth of embedment or the active pressures are particularly small. The applied load in this case is shared by the props and the soil. The force carried by the soil is equal to the jump in shear force that occurs at file:///C|/Documents%20and%20Settings/bantinone/My%20.../myweb19/Retaining_walls/Walls_supported_by_more.html (3 of 4)5/26/2005 4:00:08 AM


the hypothetical soil support. Under this assumption it is essential to check that the force assumed to be provided by the hypothetical soil support is not greater than the available soil resistance below that support. If it is greater, the following method should be applied. If the net pressure falls to zero, but the available soil resistance below the point at which that occurs is less than that required by the rigid soil prop, a finite soil reaction equal in magnitude to the available soil resistance should be adopted in subsequent calculations. This situation is likely to occur if there is a moderate depth of embedment. The applied load in this case is shared by the props and the soil. The force carried by the soil is equal to the change in shear force that occurs at the hypothetical soil support.

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RETAINING WALLS Selection of Pile Section The section required for installation should be considered at an early stage in the design process as it may be necessary to provide a heavy section and/or a high quality of steel where it is anticipated that piles will need to be driven to deep penetration or where driving will be hard. Provision of piles for driving will influence the support requirements. Information regarding the selection of piles on the basis of installation conditions is given in Installation. The absolute minimum sheet pile section required for the retaining wall is obtained from the bending moments which have been derived by calculation for the particular case in question. The requirements with respect to the effective life of the retaining wall should then be applied to the minimum section required for bending. The effect of corrosion on the steel piles is to reduce the section strength and the design must ensure that the section selected will be able to resist the applied bending moments at the end of the specified life span without exceeding design stresses. In many instances the need for a heavy section for driving automatically introduces the additional strength needed for durability. This is covered in more detail in Installation.

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Installation - Corus Piling Handbook

INSTALLATION Contents 1. Introduction 2. Plant and Equipment 1. Plant Type Selection for Granular Soils 2. Plant Type Selection for Cohesive Soils 3. Plant Type Selection for Mixed Soils 3. External Considerations 4. Pile Section for Drivability 1. Cohesionless Soils 2. Cohesive Soils 5. Impact Hammer Energy for Pile Section 6. Vibratory Hammer Energy for Pile Section 7. Driving Method 1. Pitch and Drive Method 2. Panel Driving Method 8. Ancillary Equipment 1. Pile Threading Devices 2. Ground Release Lifting Shackles 3. Pile Extractors 4. Pumping Equipment 9. Driving Sheet Piling 1. Alignment of Driving Hammer 2. Submerged Piling 3. Driving in Limited Headroom 4. Control of the Wall Length 10. Hard Driving Conditions 1. Rock 2. Hard Ground 3. Toe Pinning 11. Obstructions 1. Correction of Leaning 12. Drawing Down 13. Jetting Steel Sheet Pilling and Bearing Piles 14. Ground Pre-Treatment

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INSTALLATION Introduction The success of any piling scheme requires satisfactory completion of the following stages.

1. Competent site investigation, sampling and relevant testing to build up an informed picture of the task. 2. Adequate design of all the stages of the construction. 3. Setting out and installation of the piles.

The first two stages are dealt with elsewhere in this handbook and can be referred to as required. The last one can be divided into two equally important parts, namely the selection of plant to give optimum performance and pile selection to enable this performance in terms of drivability. The following details are intended as a guide to efficient and economical pile installation.

As with all site operations the relevant legislation and guidance on matters pertaining to safety must be strictly adhered to

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INSTALLATION Plant and Equipment A wide variety of plant is available to facilitate the economical installation (and extraction for temporary works) of all types of conventional piling. The choice of piling plant must be considered well in advance of actual driving operations to ensure the best results from the outset. The following tables do not list every piece of plant available for economical pile installation but gives an indication as to the categories of plant which are available, which ground characteristics they are suited to, and other consider-ations relevant to their use. Plant Type Selection For Granular Soils

Plant Type Selection For Cohesive Soils

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Plant Type Selection for Mixed Soils

Sites where the soils can be classified as wholly granular or wholly cohesive over the entire depth of penetration for the pile are very rare and hence the selection of plant must be a compromise, choosing the plant suited to the dominant soil type, but then checking that the chosen plant has a reasonable capability to penetrate the other soils.

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INSTALLATION External Considerations The choice of plant will often be influenced by noise and vibration limitations. The table below gives guidance on the noise emissions associated with different plant types and the type of vibration caused. It is very important to note that noise and vibration waves attenuate quickly with distance from source, so although a particular hammer may exceed given limits at source, by the time these waves have propogated to the nearest affected structure etc they may be well within the stipulated levels deemed acceptable. This table relates to levels of noise and vibration at source and not at distance from source.

Key: V Low

acceptable in all circumstances

Low

acceptable in all but extreme cases

Medium

borderline when occupied facade is close

High

not acceptable close to occupied or susceptible facades

Cont

continuous vibration during drive

Int

intermittent vibration from each hammer blow

Note: Further guidance is available from the Corus Construction Centre.

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INSTALLATION Pile Section for Drivability It is important to check that the pile section is capable of withstanding the rigours of driving and will reach the desired penetration in a condition suited to the application for which it is intended. The strength of the pile in driving is a function of its width (interlock spacing), the thickness of the pan and web and its moment of inertia. In order to consider all these factors in terms of one descriptor, the section modulus (cm3/m) is used. Generally, sheet piles increase in driving capacity as the section modulus increases. Drivability of a particular section may be increased by specification of a higher grade of steel. The following tables are intended to be used as a guide to pile sizing for drivablilty using percussive methods. Cohesionless Soils

NOTE: The ‘N’ value is the Standard Penetration Test Value. “Dominant” means the high average for the soils to be penetrated. Where piles are to be driven to a toe hold in rock, the ‘N’ value shall be divided by a factor of 4 for that stratum only. It should be stressed that these figures are for guidance purposes only for the less experienced designer and cannot be seen as a substitute for previous job experience.

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Cohesive Soils

It is difficult to provide precise guidance for drivability in cohesive soils due to variations in pile adhesion, moisture content of the soil, etc which will affect the driving resistance. However the following table may be used as a guide:

It will be noted that this table does not take into account the overall length of the pile and hence does not allow for cumulative skin friction/adhesion effects in the selection of the required pile section for drivability. When considering the length of the pile to be driven it is recommended that the following maximum driving lengths are not exceeded:



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INSTALLATION Impact Hammer Energy for Pile Section

When the most suitable hammer type has been chosen, after consideration of the site conditions and external limitations, the actual size of hammer must be selected to give the input energy required to drive the pile or piles to the required depth. The table above gives guidance as to the actual energy which must be imparted to the pile (ie after allowance for any efficiency losses), to drive it to the required depth. However this is not intended as a substitute for engineering experience or local knowledge and should be treated as the preliminary process in hammer sizing.

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INSTALLATION Vibratory Hammer Energy for Pile Section These types of hammers temporarily disturb the soil local to the pile, reducing friction and allowing the pile to penetrate under self weight and the weight of the hammer and, in the correct ground conditions, offer the best production rates. Thus they are suited only to granular soil (less than very dense) and only the softest cohesive materials, since these respond to particle excitement. Hence it is a matter of experience to determine which size and frequency of vibratory hammer will achieve best results in given soil conditions. As preliminary guidance the following formula may be applied:

F = 15 (t + 2G) / 100 kN

where F

is centrifugal force in kN

t

is driving depth in m

G

is mass of the pile/piles in kg

A penetration rate of 500mm/ minute is usually applied, below which close monitoring is required to avoid excessive heat production in the interlocks.

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INSTALLATION Driving Method After initial plant type considerations, thought must also be given to the type of driving method to be adopted. The methods of driving can be broken into two distinct groups : Pitch and Drive Method

As the name suggests this method entails the pitching of each pile or pair of piles and driving to finished level before repeating the operation. The plant required for this usually comprises a crane or specialist lifting machine with a leader attachment. The pile/s are winched into the leader and guided by restraints at the pile head and at a second position usually near to the base of the leader, ensuring that verticality is maintained throughout the installation. The advantage of this method is that speed of installation is maximised. However it would not be considered a suitable technique where long piles are to be installed, where the ground conditions may give rise to hard driving or where obstructions are likely to be encountered during the drive. As each driving operation is carried out, with the trailing clutch interlocked with the previously driven pile but the leading lock free, there can be a tendency for the piles to lean in the direction of wall progress. Only with care and frequent monitoring and correction can this problem be avoided. This method is suited to the installation of bearing piles and King Pile systems. Panel Driving Method

Once guide frames (on at least two levels) have been correctly positioned, the first pair of piles should be carefully pitched, plumbed and partly driven to form a guide for adjacent piles. The remaining panel of piles (usually 10-20m run of wall per panel) is then pitched and interlocked. The last pair of piles pitched into the panel are then partially driven, followed by the partial driving of the rest of the panel, working back towards the first pair in the panel. Care must be taken not to allow any departure from the vertical. The top guide walings can then be removed and all but the last pair of piles in the panel are driven to level. The last pair of piles are left partially upstanding to form the guide pair for the commencement of the next panel. This process is repeated panel by panel. Where long piles are to be driven, it is common to use a lighter hammer for the initial driving and a heavier hammer for the deeper driving stages. Where obstructions are encountered, the remainder of the panel can be completed

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and the piles which are obstructed will then have support from neighbouring piles during any attempt to drive through the obstruction. If this is not successful, panel driving can continue whilst the obstruction is removed, minimising delays to construction. Adoption of this method allows difficult driving conditions to be more capably dealt with and will generally result in better vertical alignment.

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CORUS PILING HANDBOOK Panel driving

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INSTALLATION Ancillary Equipment Pile Threading Devices

Pile threaders are mechanical devices for interlocking sheet piles into panels. They are attached to the piles to be interlocked at ground level and eliminate the need for a top man to manually guide the piles into interlock, which has always been a dangerous occupation. In addition to improving safety on site, pile threaders can also be operated in fairly severe weather conditions when pile pitching with a top man would not normally be considered. Ground Release Lifting Shackles

These devices were developed for lifting piles into position and for the quick release of the shackle from a safe location at ground level. Used in conjunction with a pile threading device, the need for a man at the top of the piles is eliminated.

Pile Extractors

Where piling is intended to serve only as temporary works it can be extracted for re-use by means of a suitable extractor. Extraction can be carried out by means of a purpose built impact extractor or by use of a conventional vibro driver. In either case, care must be taken to ensure that the crane has an appropriately sized jib to prevent damage when the extraction force is applied.

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Pumping Equipment

In cases where flooding or water seepage could occur within the area, sufficient pumping capacity should be made available to ensure the continuity of work.

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INSTALLATION Driving Sheet Piling Alignment of Driving Hammer

It is essential that pile driving hammers be correctly positioned so that the hammer will deliver its blow in line with the axis of the pile. Driving with the hammer ‘offcentre’ or ‘out of line’ merely contributes to leaning and can damage the pile heads. Submerged Piling

When it is required to drive piling below water level, a dolly pile should be inserted between the hammer and the pile head, the dolly pile being of such a length that the hammer is always above water. Some types of hammer operate under water, in which case the dolly pile is not required. Driving in Limited Headroom

The great difficulties imposed when pitching and driving with restricted headroom warrant the consideration of the practical and economic possibilities of removing the overhead obstruction. If this is not possible, headroom may be increased by the excavation of a trench along the proposed line of the piling. In situations where headroom is limited the piles should be pitched and driven in panels, but this leads to difficulties due to lack of pitching height. These can be overcome by assembling a panel of piles horizontally on the ground, the length of the piles being less than the headroom. The panels should be bolted to temporary walings and moved into position by means of an overhead runway. Alternatively, where convenient, the panel may be floated into position on the side of a barge. It may be necessary to have a shorter pile in the end of the panel to facilitate interlocking with the previously driven piles. A supplementary making-up piece is required to be inserted over the short pile after partial driving of the panel, the two shorter lengths being fishplated or welded together. When the length of the pile exceeds the available headroom, the piles must be driven in short lengths which are welded or fishplated together as driving proceeds, the joints being to the full strength of the section. Driving is commenced using a double-acting hammer mounted in a cradle suspended at the side of the pile. As soon as sufficient headroom is available the hammer should be moved to the normal driving position. Alternatively the initial penetration may be achieved by jacking the piles down from the overhead obstruction.

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Control of the Wall Length

Some control over the running length of the wall can be established during pitching by adjusting the overall depth of the pile section and consequently adjusting the theoretical distance between lock centres. Larssen Sections:

If the wall is found to be gaining in length, this gain may be corrected by reducing the depth of the section with timber blocks placed between the outside faces of the piles and the guide walings. Conversely a loss in length may be corrected by increasing the depth of the section with timber blocks between the inside faces and the guide walings. (See Figure below) Frodingham Sections:

If the wall is found to be gaining in length, this gain may be corrected by increasing the depth of section with timber blocks placed between the inside faces of the piles and the guide walings. Conversely a loss in length can be corrected by decreasing the depth of the section, however this will decrease marginally the effective strength of a wall. (See Figure below)



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INSTALLATION Hard Driving Conditions Each pile, or pair of piles, should be marked off in 25mm intervals to enable the engineer to record the penetration during the later stages of driving; the number of hammer blows taken to drive a pile over a given number of these intervals will indicate the measure of progress being made. Rock

Where penetration into rock is required, the selection of pile section, steel quality, and type and size of hammer is most important. In this case, driving conditions may require a heavier pile than that derived from design considerations. It may also be necessary to use high yield quality steel (S355GP) to reduce the distortion of the piles. Where very hard driving occurs it is possible that the pile heads will be distorted before full penetration has been achieved. Immediately damage to the pile head becomes apparent, driving should be stopped and the damaged portion burnt off in order to avoid further damage and reduction of hammer energy. In extreme cases it may be an advantage to use a shaped cast steel driving cap. Hard Ground

Similar qualifications to those given for rock regarding the size of piling and quality of steel are applicable. A considerable choice of hammer is available, the main consideration being that the hammer should be of ample size. Toe Pinning

It is possible to secure pile toes into rock by use of steel pins. This may be required where it is not feasible to drive piles to the required penetration or where there is concern that the pile may slide down a sloping rock stratum. The pins can be welded to the pile before driving or may be installed via tubes which are attached to and driven with the piles. In the latter case, a hole is drilled into the rock and the pin is then grouted into position.

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INSTALLATION Obstructions Increased resistance to driving at an early stage could be considered attributable to boulders, rubble, roots, etc. Under these conditions it is essential to drive the piling in panels. If a pile encounters an obstruction during driving, the hammer should be transferred to subsequent piles in the panel until piles clear of the obstruction are located. These piles should then be driven and the hammer returned to the difficult section of the panel where there will be a greater possibility of displacing or breaking through the obstruction without damage to the piles as the obstructed piles would be guided by the adjacent driven piles. Piles which for any reason become badly distorted should be withdrawn and replaced if possible. Where regular obstructions are expected pile toe strengthening, by cast shoes, may be worth consideration to give better strength on the toe during impact on the obstruction and to minimise driving resistance due to wall adhesion/friction from upper strata. However the effects of this must be allowed for in design calculations, especially if wall adhesion/friction has been included in the design analysis. Correction of Leaning

In order to avoid the tendency of sheet piling to lean, the hammer should be placed over the centre of gravity of the piles being driven and should be

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INSTALLATION Drawing Down When piles are being driven in soft ground, particularly when they are allowed to lean, the pile being driven may draw down the adjacent pile below its intended final level. If this occurs the affected pile should be extended by welding on a short length. In order to prevent the drawing down of already driven piles, several may be bolted together with a waling, or alternatively the interlocks may be tack welded. As a further precaution against drawing down when using Larssen sections, a rivet or bolt may be inserted in the leading interlock of the pile prior to driving, thus preventing soil entering the interlocks, and reducing friction in the driving of the next pile. cross-sectional area. It is not necessary to attach the jetting pipe to the pile, it often helps to surge it into the ground slightly ahead of the pile.

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INSTALLATION Jetting Steel Sheet Pilling and Bearing Piles Driving in sand, silty sand, fine sandy gravel, and similar non-cohesive soils can usually be assisted by jets of water at high pressure directed into the ground alongside and below the pile. In some cases jetting is so effective that ordinary driving can almost be dispensed with, but at least the last metre of driving should be carried out without jetting, so that the lower part of the pile is in undisturbed soil. With steel sheet piling jetting is not essential but may be very effective in improving the progress of the work. In fine waterlogged sand jetting with compressed air sometimes gives good results. It is best to have a pipe on either side of the pile as a single jet pipe tends to make the pile go off line. Occasionally a single pipe is positioned on the centre of each pile with a special nozzle opening at the same level as the pile toe. The water from the jetting pump is led through a flexible hose into pipes of 40mm to 50mm diameter, terminating in a nozzle or fishtail of slightly smaller cross-sectional area. It is not necessary to attach the jetting pipe to the pile, it often helps to surge it into the ground slightly ahead of the pile. When jetting steel piling the pump should be able to deliver up to about 450 to 600 litres per min at a pressure of 0.5 to 0.8 N/sq mm or more, but for box piles, 1500 litres per min or even more may be required. Jetting must be discontinued at 1 metre minimum from final level of piles. A possible serious disadvantage of jetting is that it may cause disturbance either to nearby piles which have already been installed or to adjacent existing structures.

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INSTALLATION Ground Pre-Treatment Where the section choice is dominated by driving considerations rather than the moment capacity it may be cost effective to consider pre-treatment of the ground to allow a lighter section choice for drivability. This can take many forms depending on the ground conditions:

1. Pre auguring to weaken or replace hard ground, can be adopted either in advance of piling or alongside part driven piles. 2. Driving of heavier section or similar drivable unit along the proposed piling line, extract the heavy unit and drive the working piles in the prepared ground 3. Use of controlled explosions to reduce very dense soil or obstructions to a fine granular material without displace-ment rather than to blast a cavity.

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Canary Wharf Jubilee Line Extension Photograph by kind courtesy of London Underground Limited Contractor: Christiani O’Rourke JV

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RETAINING WALLS Development of Section Strength The development of full section modulus in a sheet pile wall is based upon the assumption that any two adjacent flanges are able to work together when subjected to bending. Bending induces tension in one face of the wall and compression in the other and the parts of the pile connecting the two flanges together must maintain this stress state for the wall to develop full inertia and hence section modulus. The flange sections of Z profile piles are connected by continuous webs and full section modulus will always be developed in this type of sheet pile wall. In the case of U profile piles, the connecting section incorporates an interlock which is located on the centre line or neutral axis of the wall. This is the position where the stress induced in the wall due to bending is theoretically zero with one pile in the interlocked pair in tension and the other in compression. If the two piles are able to displace relative to one another along the interlock then the full modulus of the combined sections will not be realised, but if that movement is prevented they will act as a combined unit and full modulus will result. The movement can be resisted or eliminated by physically connecting the individual sections together. This can be practically achieved by welding or crimping the interlocks or by embedding the pile in a capping beam or in soil. In most situations, the longitudinal movement will be resisted by the development of friction in the common interlock; the greater the frictional resistance generated in the interlocks, the higher the proportion of the combined section modulus which can be developed. If it is assumed that there is no interaction at all, which is a very extreme situation, the section modulus of single piles must be used in calculations as the piles will be able to bend independently and combined action will not occur. In practice, friction will always be present in one form or another, and the following are some of the factors which will affect the development of friction in interlocked piles. ●

●

●

●

The variation of interlock geometry along the length of a pile as a result of production tolerances will result in a degree of interference when adjacent sections are interlocked. Driving the piles into the ground will cause soil particles to be forced into the interlocks enhancing any frictional resistance. The application of strut or tie forces through walings will force the interlocks together preventing relative movement. The fact that the piles are driven substantial distances into the soil to generate the required passive resistance will prevent relative longitudinal movement.

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Retaining Walls - Corus Piling Handbook ●

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●

● ●

Any deflection will cause adjacent piles to bind up due to the relatively close fitting nature of the interlocks. The situations which may require consideration regarding the development of full section modulus when designing U profile pile walls are as follows: Piles acting in cantilever when no head restraint in the form of a capping beam is to be provided. Piles cantilevering for significant distances above or below a support. Piles supporting water or very soft materials when the piles are not driven to the design penetration depth, ie as a result of obstructions.

The introduction of lubricants into the interlocks of Larssen piles as an aid to driving will effectively reduce the frictional resistance developed in the interlocks and it should not be overlooked that this action may reduce the section modulus of the wall. Larssen or U profile piles have been in use for over 60 years in the construction of embedded retaining walls and only in a limited number of very specific cases has reduced modulus action been observed, for example where piles were not embedded or very soft clays were present. However, should the designer wish to guarantee the wall modulus, the main options are to specify Z piles or alternatively weld/crimp piles together into pairs. (see here for further details.)

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RETAINING WALLS Design Bending Stresses The allowable bending stresses which may be used for the design of sheet piled retaining walls are given below. When designing the wall as a temporary structure, a higher stress can be allowed to develop in the steel than in the case of a permanent structure as a temporary wall will not require any allowance for corrosion and increased deflections may be acceptable. The design stress in the steel may be slightly increased over the allowable temporary stress for design cases which occur during intermediate stages in the construction of a temporary wall at the descretion of the engineer. However this condition must be of short duration for an increase in allowable stress to be adopted. The following table indicates the design stresses to be used in calculations:

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RETAINING WALLS Low Propped Walls Research at Imperial College, London has shown that the earth pressures acting on retaining walls that are restrained with a single level of support at or near excavation level, are different to those assumed in conventional limit equilibrium calculations. Conventional calculations assume that the mode of failure for a retaining structure supported at or near the top will be in the form of a forward rotation of the pile toe and the pressure distribution at failure is based on this assumption. The failure mode assumed for a low propped wall is that the pile will move away from the soil in a similar manner to a cantilever and the pile will move back into the soil below the support level. This will result in the generation of passive pressures on the back of the wall and active pressures on the front. To design a wall incorporating a low prop, there are two fundamental requirements which must be satisfied for the calculation method to be correct. Firstly, the prop must be sufficiently rigid to act as a pivot and prevent any forward movement of the wall and secondly, the sheet piles forming the wall must be capable of resisting the bending moments induced at the prop level to ensure that rotation of the pile occurs rather than buckling.

The design rules resulting from the Imperial College work suggest that the earth pressures below the support should be calculated assuming that active pressures apply at and above the prop position with full passive pressure at the toe of the pile; the change from one to the other being linear. The support may be considered to be at low level if the depth to the support exceeds two thirds of the retained height of the excavation.

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RETAINING WALLS Anchorages General

An anchorage for an earth retaining structure is a system installed into the retained soil to provide a tensile support to the main wall. Consideration must be given to the ground conditions, the effect of the installation method on the soil properties and the effect of the anchor system on adjacent buildings and the land under which the anchorage is to be installed. Anchorages can be divided into three general categories, rock or soil anchors, tension pile anchors and deadman anchorages. The design of soil or rock anchors is dealt with in BS 8081 but should be undertaken by a specialist with appropriate experience and knowledge of both the soils and the techniques to be employed. It is normal for anchors of this type to be inclined in order that the anchorage can be formed in the more competent ground found at depth. The depth achieved by inclination of the anchors also results in increased overburden pressures acting on the anchor. Tension piles used as an anchor for retaining walls are usually found either beneath relieving platforms, as part of an A frame with compression piles or as a raked tension anchorage attached directly to the wall. The capacity of a driven pile can be assessed from the soil properties, but the effective anchorage length should not include any part of the tension member which is within the active failure zone behind the wall to be supported. It is recommended that any calculations based on soil properties to assess the resistance of the section to tensile loading are verified by means of a pull-out test. This will not only supply data relevant to the capacity of the pile under tension but will also yield valuable information on the likely movement of the pile under working load conditions. The effect of cyclic loading and creep must be considered when designing tension anchorages in cohesive soils and weak rocks as the resistance can fall to a residual value under these conditions. Deadman anchorages generally comprise a second row of sheet piles or concrete blocks installed at an appropriate distance behind the main wall and attached to the wall by tendons or tie rods. In each instance the anchorage can be a continuous wall or discrete units depending upon the anchorage capacity required and any physical limitations on position dictated by the structure being built. Sheet pile anchorages can be either of the balanced or cantilever type. Whilst the concrete deadman anchorage does not require walings for the distribution of load from the tie rod, it is necessary to excavate to the full depth of the anchorage during construction which may cause difficulties when the water table is close to the ground surface. The deadman anchorage is designed to mobilise the passive resistance of the soil in front of the anchorage plus any shear resistance resulting from the movement of the anchorage and passive soil wedge through the soil.

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RETAINING WALLS Walings Walings usually comprise two rolled steelchannel sections placed back to back and spaced to allow the tie rods to pass between the channels. This spacing must allow for the diameter of the tie rod and thickness of any protective material applied to the rod and take into account any additional space required for inclined tie rods which will pass between the walings at an angle. It is generally convenient to use 102mm or 127mm channel section diaphragms at approximately 1.5m centres. The walings may be fixed either at the back or front of the retaining wall. The first arrangement is usually adopted for the sake of appearances and, in the case of a wall in tidal or fluctuating water level conditions, to prevent damage to the waling by floating craft or vice versa.

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When the waling is placed behind the wall it is necessary to use short anchor bolts and plates at every alternate pile to connect the waling and the wall together. Placing the waling in front of the wall eliminates the need for connection bolts and this arrangement is therefore more economical. For ease of handling, walings are generally supplied in 10m lengths. Splices should be located at a distance of 1/5 of the tie rod spacing from the tie rod as this will be close to the position of minimum bending moment in the waling. The walings should be supplied 75mm longer than the theoretical dimensions to allow for any creep which may develop in the wall as the piles are driven, one end only of each length being drilled for splicing (if the splice is achieved by bolting). The other end should be plain for cutting and drilling on site, after the actual length required has been determined by measurement of the driven piles. In order to facilitate drainage, holes should be provided at 3m centres in the webs of the walings. Where sheet pile anchorages are used, similar walings to those at the retaining wall are required. These are always placed behind the anchor piles and consequently no anchor bolts are required. Where walings form part of the permanent structure they can be supplied with a protective coating applied before despatch, a further coat being applied at site after completion of the works.

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RETAINING WALLS Design of Walings in Continuous Anchor Walls For design purposes, the waling may be considered to be simply supported between the tie rods (which will result in a conservative bending moment) with point loads applied by the anchor bolts. The magnitude of the tie bolt load is a function of the bolt spacing and the design support load per metre run of wall. Alternatively, the waling can be considered as continuous with allowance being made for end spans. Although the waling is then statically indeterminate it is usual to adopt a simplified approach where the bending moment is assumed to be wL²/10 where w is the calculated support load acting as a uniformly distributed load and L is the span between tie rods. Where inclined ties are used, the vertical component of the anchor load must not be overlooked and provision must be made to support the waling, usually in the form of brackets or welded connections. The walings should be designed to accommodate the possibility of the failure of a tie rod. The wall and waling should be designed to be capable of distributing the load from a failed tie rod or anchor. Under these conditions, it is permissible to increase the allowable steel stress to the yield value.

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RETAINING WALLS Tie Rods When designing tie rods, it must be remembered that the load cannot be determined with any great degree of accuracy due to factors such as arching of the retained soil and variability of the material retained. It is possible that the actual load on a tie rod may exceed the theoretical value by as much as 15%. It is, therefore, usual to adopt a working stress lower than the value which would be used in most structural applications. The required diameter of tie rods is calculated from the permissible stress acting on the stress area of the thread as defined in BS3580. Permissible stresses in tie rods specified in most European codes of practice are governed by the nature of the load conditions, and are greater in the parent bar than in the threaded section. The table below sets out the value to be used as a proportion of the yield stress, fy.

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2. 0.1% proof stress Suggested permanent working loads for steel sheet piling tie rods are given in the table below, based on rolled threads. The suggested working loads for high strength alloy tie rods are based on a factor of safety of three on the failure load.

The elongation of the tie rods under the design load should be checked. For steels of higher tensile strength used at a working stress greater than the mild steel value, the strain at working load may be more than the structure can accommodate. Move-ment under superimposed loads may be reduced in many cases by pre-loading the tie rods at the time of installation to develop the passive resistance of the ground. Details of this technique are given in Site Assembly. The effect of sag of the tie rods and forced deflection due to settlement of fill should also be considered. Bending stresses induced at a fixed anchorage may significantly increase the tensile stress in the tie rod locally. Shear stresses may also be induced if a tie rod is displaced when the fill settles causing compound stresses which must be allowed for in the detailed design. This can often be overcome by provision of articulated joints or settlement ducts. Fittings

For normal use, tie rod assemblies are provided with a nut at each end, a plate to suit the bearing

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conditions at each end, and usually a turnbuckle with right and left hand threads to give length adjustments and take out sag. If the length of the complete rod is such that more than two elements of bar are required, couplers with two right hand threads are also included. For very large diameter ties, a coupler with left hand and right hand threads can be provided to eliminate the need to turn the whole bar, which could weigh up to 1 tonne, when making the connection. Taper washers or spherical seating washers are used when the axis of a tie rod is not perpendicular to its seating. In some instances it is desirable to allow for rotation of the axis of a tie rod relative to the bearing face, and “articulated” anchorages are available for this purpose. Plates are needed to transmit the load imposed on sheet piling to the tie rods and from the tie rods to the anchorages. Washer plates are used when the tie rods are anchored within the pans of sheet piles and bearing plates when the load is transmitted through walings. When the load is taken to a concrete wall or block, anchorage plates distribute the load to the concrete. The waling loads are transmitted to the anchorages by means of anchor bolts which also require bearing plates and washers of such size as to provide adequate bearing to the sheet piling, walings, etc. Tie rods are generally available in lengths of up to 12m and it is advisable to provide them with turnbuckles. Lengths over 12m can be made up by using additional turnbuckles and couplers. Tie rods are normally supplied in weldable structural steel complying with BS EN10025 grades S275 and S355. For very high loadings steels with higher tensile strengths are available, as shown in this Table. Threads may be produced by cold rolling or machining. ISO metric threads to BS3643 are usually offered on tie rods. However, Macalloy high strength alloy steel bars are supplied with a rolled thread of a specially designed profile. Tie Bar Corrosion Protection

Steel sheet piles are used in many aggressive environments and conse-quently corrosion protection or factors influencing effective life must be considered. Several options are available to the designer. Effective Life With No Corrosion Protection In this situation, consideration should be given to the probable corrosion rates in a particular environment. If the design calculations are completed using stress levels appropriate to BS EN10025 S355JR (BS 4360 Gr 50B) and a higher grade of steel is provided, it is permissible to allow sacrificial corrosion to take place because of the superior mechanical properties of the steel. Protective Coatings Several options are available, such as painting using the Corus paint systems, galvanising or wrapping. It is however usual to wrap tie bars to give an appropriate level of corrosion protection. The vulnerable anchor head should be protected, and the figure below shows a recommended detail.





Plates

Dimensions suggested for each type of plate with each diameter and type of steel tie rod are set out in the tables below. Their use is illustrated in the Figure below. Dimensions of washer plates are governed by the type of sheet piling used. Details are given for Larssen and Frodingham sections. Washer plate dimensions have been increased from those previously used, bringing them more in line with those used elsewhere in Europe. As a general rule the plate length is approximately 80% of the pan flat and its thickness is approximately 40 to 50% of the thread diameter. Plates for high strength alloy steel tie rods are designed to suit each specific application. Taper washers are required when the axis of the tie rods are not perpendicular to their anchorage seatings. The thickness is varied to enable the nut to seat square with the axis of the tie rod



Special Fittings

Any bending in a tie rod, especially in the thread length increases the stress locally with the possibility of yield or even failure if the bending is severe. In order to eliminate the risk of bending, several options are available which allow rotation of the axis of a tie rod while maintaining its tensile capacity. Some of these methods are illustrated in the Figure below. These include fork ends and spades or a fork end pinned to a bracket onto the sheet pile. Other options are nuts and washers with spherical seatings or pairs of taper washers which can be rotated to give any angle between zero and a predetermined maximum. The last two methods will cater for initial angularity but will not move to accommodate rotation in service.

Site Assembly

Tie rods are normally assembled with component bars supported to the correct level. Any slack is then taken out by tightening either a turnbuckle or the nut at one end. It is not possible to apply more than a nominal tension by tightening the end nut. Installation

Tie bars perform best in pure tension, so it is good practice to ensure that this is achieved. The following is a recommended sequence of events to ensure that tie rods are installed and tensioned correctly. 1. Backfill to approximately 150mm below the finished level for the ties. 2. Lay out tie bars on sand bags placed every 6m and on either side of a coupler/turnbuckle or articulated joint. 3. Fit settlement ducts over the ties. 4. Assemble with turnbuckles set such that there is a 100mm gap showing between the ends of the bars. Couplers should be fully engaged. 5. Tension from the anchorage outside of the wall to take up the slack. 6. Tension turnbuckles. 7. Place sand fill over the settlement ducts.



8. Backfill to required level. This procedure applies to a simple situation and additional activities may be considered, for example applying pretensioning to pull the piles in before final backfilling, stressing after backfilling to prevent future movement due to subsequent loading. Further information on stressing details is available on request from tie rod manufacturers. Examples of plates in use

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RETAINING WALLS Relieving Platforms When the depth of soil to be retained and/or the applied surcharge loading (eg from heavy wharf cranes) is excessive, soil pressures may be reduced by the use of a relieving platform. The relieving platform is constructed such that it will support the surcharge loads and the upper portion of the retained soil, these loads being transferred to lower strata where there will be no effect on the pressures acting on the wall. Bearing piles, which support the platform and transfer the loads into the soil at depth, may also be designed to provide an anchorage to the wall. The platform can be supported in part by the main sheet pile wall (see Axially Loaded Sheet Piling) and if the vertical loading becomes excessive, box or high modulus piles may be introduced into the wall at appropriate intervals to carry this load. Alternatively, bearing piles may be provided immediately behind the wall. The relieving platform must be designed such that it will intersect the plane of rupture from the soil above and behind the platform preventing any load from that soil acting on the wall. The main sheet piles may extend up to ground level or be curtailed at platform level with a concrete retaining wall being provided above that level; the concrete wall must be designed to derive its stability from the platform.

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Axially loaded sheet piling - Corus Piling Handbook

AXIALLY LOADED SHEET PILING Contents 1. 2. 3. 4.

Introduction Steel Sheet Pile Types Application of Steel Sheet Piling in Bridge Construction Design 1. General 2. Vertical Load Capacity 1. Skin Friction 2. End Bearing 5. Propped Embedded Abutments 1. Example 1 2. Example 2 6. Integral Abutments 7. The Advantages of Using Steel Sheet Piling

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AXIALLY LOADED SHEET PILING Introduction All the applications of steel sheet piling that have been covered in the handbook so far have focused on its ability to resist horizontal earth and water pressures, typically in a retaining wall or cofferdam structure. In such structures there is no requirement for the sheet piles to resist vertical loads, however, the ability of steel sheet piling in this respect has long been proven in maritime applications; quay walls often being designed to resist the vertical load applied via crane rails, etc in addition to the horizontal loads from backfill and/or in-situ soil. This dual ability of steel sheet piling is of particular relevance to land-sited structures such as bridge abutments and this chapter aims to briefly cover the use of steel sheet piling to carry axial loads, with particular emphasis on bridge abutment construction and the relevant design issues.

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AXIALLY LOADED SHEET PILING Steel Sheet Pile Types The choice of the most suitable pile section for the abutment or pier will depend on a number of factors including the configuration of the bridge, the loads involved and the ground conditions at the site. With these factors in mind, the designer may choose from the LX, Larssen and Frodingham ranges, giving a range of section moduli from 610cm³/m to 5066cm³/m. Should a larger section be required, high modulus piles (Larssen, Frodingham) may be used, with a range of section moduli from 4832cm³/m to 24687cm³/m. Usually ‘Hi-Mod’ sections are fabricated with the beam extending 50mm beyond the sheet piles at the top and at least 500mm beyond the sheet piles at the bottom. The projection at the bottom can be increased if large vertical loads are to be carried, and require a pile length considerably greater than that necessary to resist horizontal load.

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AXIALLY LOADED SHEET PILING Application of Steel Sheet Piling in Bridge Construction There is continual pressure on engineers to produce even more economical and faster solutions to construction problems and here steel sheet piling can help. Steel pile installation is fast - the abutments to Shrivenham Bridge, a British Rail structure, were completed in only 40 hours of line possession. If necessary, the piles can be loaded immediately after they have been propped or anchored back. When thinking about bridge construction, the structural elements which are most readily built in steel sheet piling are: ● ● ●

Bridge Abutments Intermediate Pairs Wing Walls

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AXIALLY LOADED SHEET PILING Design General

Steel sheet piling is a flexible form of construction and has advantages over materials such as reinforced concrete. Two of these are: ●

●

The flexibility of the piles allows them to move away from horizontal earth and water pressures, creating ‘active earth’ conditions behind the wall and therefore reducing the load on them. Rigid walls must be designed for the more onerous ‘earth at rest‘ conditions, since their lack of flexibility results in them attracting greater loads. The flexibility of the piles allows the bending moments in the wall to be re-distributed, further reducing the size of pile section that will be required.

Since the wall is flexible, there is a need to restrain the heads of the piles against movement due to vehicle braking loads etc and this can be achieved by using one of the following methods: ● ● ●

●

Tying back the piles as in a conventional retaining wall using tie rods and ‘deadman anchors’. Using grouted ground anchors, post-tensioned after installation. On short span bridges, it may be economical to use a stiffened para-pet edge beam as a strut between abutments. The deck slab can be cast integral with the heads of the piles.

Vertical Load Capacity

As with any other form of bearing pile, steel sheet piles resist vertical load by a combination of endbearing and skin friction and the contribution of each is calculated as follows: Skin Friction

The ultimate skin friction (Qs) on the pile may be calculated using one of the following equations, depending on the soil type. Granular Soils:

Qs = 2Ns.As Ns = average SPT ‘N’ value over embedded length (for submerged soils the ‘Ns’ value should be factored down by 0.67) As = embedded area of pile Cohesive Soils:

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Qs = α.Cs.As Cs = average undrained shear strength over embedded length As = embedded area of pile α = an adhesion factor which is dependent on Cs and the soil profile and varies between around 0.2 and 1.0 Where plug formation at the toe of the pile does not occur during driving, the developed surface area used to calculate Qs can be taken from the table below. Where a soil plug forms during driving, the surface area available for frictional resistance is limited to the interface between the remoulded soil in the plug and the in-situ soil and is usually taken as twice the elevation area of the piling.

End Bearing

The ultimate base resistance of the piles is calculated by using one of the following equations,



depending on the soil type. Granular Soils:

Qs = 400Nb.Ab Nb = SPT ‘N’ value at pile toe level (for submerged soils the ‘Nb’ value should be factored down by 0.67) Ab = area of pile base Cohesive Soils:

Qs = 9.Cb.Ab Cb = undrained shear strength at toe of pile Ab = area of pile base Clearly the end-bearing capacity is directly proportional to the base area Ab, which is itself a function of plug formation. In cohesive strata, plug formation may be expected to occur and 50% of the gross pile area is commonly used for Ab. In cohesionless strata, plug formation is usually neglected. In any event, vertical load carrying capacity must be confirmed on site by an appropriate test loading programme.

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AXIALLY LOADED SHEET PILING Propped Embedded Abutments If the bridge being designed is a Department of Transport Structure, then the provisions of BD42/94 (Design Manual for Roads and Bridges) apply, but in any case the initial stage in the design process is to design the abutment as a retaining structure resisting earth and water pressure, a ‘free earth support’ or a ‘fixed earth support’ being adopted at the discretion of the designer. Once the length of pile required for rotational stability of the abutment is determined using this method, to this must be added a length of pile which will be adequate to resist the vertical load, through a combination of skin friction and end-bearing. This extra length may be calculated using the formulae appropriate to the ground conditions over the section of pile involved and the procedure is dealt with in detail in the Steel Construction Institute publication ‘Steel Bearing Piles Guide: 1997’. ● ●

Example 1 Example 2

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AXIALLY LOADED SHEET PILING Propped Embedded Abutments Example 1

Steel sheet piles are to be used to construct a 7.0m high abutment, anchored back at a level 1.0m down from the pile head. The piles are to be clad with masonary. Soil: natural, undisturbed, uniform medium dense gravel with φ = 35° and an SPT ‘N’ value of 37 (submerged ‘N’ = 0.67 x 37 = 25). Ground water is 2.5m below ground level in front of the wall. Wall friction on the active side of the piles is ignored, whilst that on the passive side is taken as 2/3φ° Assume a 350kN/m vertical load is applied to the piles and that an LX25 section in grade S270GP steel is required for drivability. The design life required is 120 years. The pile length required for Fnp = 2.0 (using free earth support) against rotational failure is 8.9m, the design anchor load is 100.4kN/m and the design bending moment is 172kNm/m. Consider Durability of Pile Section

From BD42/94, Clauses 5.3 and 5.8 and given the protection against corrosion that the cladding will offer, it would seem reasonable to design for a total sacrificial loss of 4mm. From Graph 1 in Chapter 3, the section modulus of the corroded section = 1809 cm³/m Consider Bending Resistance of Pile Section

Bending stress (fb) = M/Z fb = 172 x 10³ / 1809 fb = 95N/mm² (< 180 \ OK for bending) Consider Combined Bending and Axial Resistance of Pile Section

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le = 0.7L (Assume L = the pile length for Fnp = 1 (8.4m), less the depth of the anchorage below the top of the pile) → le = 0.7 x (8.4 - 1) → le = 5.2m → le/r = 520/16.9 = 31 → from Table 17a, B.S. 449 gives pc = 154N/mm² → fc = (350 x 10³) / (200 x 10 ²) =18N/mm² Now, from B.S. 449: fc / pc + fb / pb < 1 → 18/154 + 106/180 = 0.12+ 0.59 = 0.71 (< 1 \ OK for bending and axial load) Consider Axial Load Capacity For the strata described, it will be assumed that no soil plug forms at the toe of the piles and therefore base resistance will be neglected. Using the Meyerhof equations: Ultimate shaft resistance Qs = 2Ns.As Ns = average SPT ‘N’ value, below 8.9m depth As = embedded area of pile shaft For the LX25 section the effective perimeter = 1.80m Load/pile = 350 x 0.6 = 210kN

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For a factor of safety of 2, the penetration ‘x’ in metres required is given by: x = (2 x 210) / (2 x 25 x 1.18) = 4.7m Therefore the overall pile length required becomes 8.9 + 4.7 = 13.6m NB - The calculated load capacity of the piles should always be proved by a maintained load test.

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AXIALLY LOADED SHEET PILING Propped Embedded Abutments Example 2

The structure in Example 1 is to be designed in accordance with Chapter 3 BD42/94 and B.S. 5400: Part 3 as follows: Consider Ultimate Limit State of Overall Stability For this limit state, the designer is required by BD42/94 to use the ‘worst credible design approach’ and to simulate this the soil strength has been reduced from 35º to 32º and the water table level behind the abutment has been raised by 2m. The recommended factors of safety for use in this limit state are given in Table 5 of CIRIA Report 104. The Net Pressure (Piling Handbook) method may be used (see Clause 3.1 (iv) BD42/94), so long as it is checked by one of the recommended methods and Fr is used in this case. The length of pile required for Overall Stability is 9.6m (for Fnp = 2.0 and 9.5m for Fr = 1.5), an increase of 0.7m over that from Example 1. The maximum bending moment has increased to 197kNm/m and the anchor load to 111kN/m. As noted in Clause 3.2. of BD42/94, the Serviceability Limit State of Deformation will normally be satisfied by the adoption of recommended safety factors as above. Consider Ultimate Limit State of Structural Elements Structural Design of Abutment Piles The design load effects, ie moments and shear forces, for use in this limit state are obtained by multiplying those obtained using the ‘worst credible design approach’ above, by a partial load factor (yfL) of 1.0 and a partial safety factor (yf3) of 1.1 from B.S. 5400: Part 3. Therefore the design ultimate bending moment in the abutment piles is: 197 x 1.0 x 1.1 = 217kNm/m Now that the design load effects have been calculated for this limit state, reference can be made to B.S. 5400: Part 3 for the procedure to be followed for the structural design of the sheet piling. B.S. 5400:Part 3 (and BD13/90 which clarifies and replaces several clauses in B.S. 5400) is geared towards the design of the structural steel elements that make up bridge decks and is therefore mainly file:///C|/Documents%20and%20Settings/bantinone/My%2...uments/My%20Webs/myweb19/Axial_loading/Example2.html (1 of 4)5/26/2005 4:00:20 AM


concerned with beams. Therefore, in order to use the standard to design steel piled bridge abutments, it is necessary to view the bridge abutment as a bending member which is also taking some axial load - from the bridge deck. This is not as unreasonable as it may first sound since the compressive stress in the piles is usually very small when compared with that due to bending. Therefore, the section of B.S. 5400: Part 3 that is applicable to the structural design of steel sheet piled structures is Clause 9 -Design of Beams. Consider Bending Resistance of Piles (Clauses in this section are taken from BS 5400:Part 3) Clause 9.9.1.3. gives the bending resistance (M D ) of a member which is not of compact section as: MD = Zxc. σlc / γm.γf3 from Clause 9.8.3, σlc = σyc = 270N/mm² from Table 2, page 9 γm = 1.2 from Clause 4.3.3, page 9 γf3 = 1.1 therefore MD = (1809 x 270) / (1.2 x 1.1 x 10³) therefore MD = 370kNm/m (> 217 \ OK) Consider Combined Bending and Axial Resistance of Piles Clause 9.9.4.1 - Check yielding of piles: P / Ae + Mx / Zx + My / Zy ≤ σy / γm.γf3 = 270 / (1.2 x 1.1) = 205N/mm² P = 1.5 x 350 = 525kN/m (where 1.5 is the partial load factor (γfl) for Load Combination 1 - Table 1, B.S. 5400: Part 2) → (525 x 10³) / (200 x 10²) + (217 x 10³) / 1809 = 26 + 120 = 146N/mm²



(≤ 205 therefore Piles OK for yielding) Clause 9.9.4.2 - Check buckling of piles: Pmax / PD + Mxmax / MDx + Mymax / MDy ≤1 PD is the axial resistance of the piles derived in accordance with Clause 10.6.1 From Table 10, page 73, le = 0.7L (assume L=the pile length for Fnp = 1, less the depth of the anchorage below the top of the pile) → le = 0.7 x (8.9 - 1) → le = 5.5m From Clause 10.6.1: PD = Ae.σc / γm.γf3 r = √(I/A) = √(56824/200) = 16.9cm therefore r/y = 16.9 / 22.5 = 0.75 → (le / r) x √(σy / 355) = (5500 / 169) x √(270 / 355) = 28.3 From figure 37, using curve A, σc / σy = 0.96 therefore σc = 0.96 x 270 = 259N/mm² → PD = (200 x 10² x 259 x 10-³) / (1.05 x 1.1) → PD = 4484kN/m → 525 / 4484 + 217 / 370 = 0.12 + 0.59 = 0.71 (≤ 1 \ Piles OK for buckling) Consider Shear Resistance of Piles



By inspection, the maximum shear force will be at the location of the anchorage waling. Anchor load = 111kN/m Sectional area of piles = 200cm²/m therefore Max shear stress = (111 x 10³) / (200 x 10²) = 5.5N/mm² (by inspection, this is negligible) Consider Length of Pile Required to Resist Axial Load From Example 1, the additional pile length = 5.1m, therefore the overall pile length required becomes 9.6 + 4.7 = 14.3m Structural Design of Anchorage/Propping System At this limit state, the design load for the ground anchorage system is obtained from the ‘worst credible design approach’ and the design of the anchorage itself shall be in accordance with the recommendations of BS 8081:1989 -Ground Anchorages, as modified by Clause 6.5 of BD42/94. If instead of a ground anchorage system, the bridge deck, parapet beams or some other form of prop is used, the design axial force in the member(s) for this limit state is obtained by multiplying the figure from above, by a partial load factor (yfl) of 2.0 and a partial safety factor (yf3), for concrete or steel construction from BS 5400: Parts 3 or 4.

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AXIALLY LOADED SHEET PILING Integral Abutments Movement or expansion joints in bridge decks present highway authorities with a continual maintenance requirement which is both costly and involves significant disruption to traffic. It is, of course, possible to design bridge decks without movement joints, provided that the abutments are flexible enough to tolerate the movements and imposed loads that result from thermal expansion and contraction of a deck which is continuous with the abutments. In fact, jointless bridges have been constructed in the USA since the early 1950’s, where bridges up to 180m in length have been built. Steel piled abutments, in the form of sheet piles or high modulus piles are the ideal way of providing the required flexibility and for further information on the subject, reference should be made to the Steel Construction Institute publication ‘Integral Steel Bridges - Design Guidance’.

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AXIALLY LOADED SHEET PILING The Advantages of Using Steel Sheet Piling The use of a ready made, driven system, such as steel sheet piling to form bridge abutments, allows work on the permanent structure to start as soon as possible, without involving deep excavations and the temporary works associated with conventional techniques. So where the construction of bridge abutments is on the critical path of an overall programme or where space for a structure is limited, steel sheet piling can be used to the advantage of all parties involved by cutting construction time and therefore site establishment costs. The completed structure can then be test loaded immediately if required and put into service without delay. These qualities make the use of steel sheet piling ideal where construction is taking place close to existing roads, railways and other services where the use of conventional techniques would mean costly disruptions in the form of extended lane rental or possession time.

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RETAINING WALLS Miscellaneous Details

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The following pages contain sample calculations employing the net pressure approach for the design cases detailed below:

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RETAINING WALLS Design of Cantilever Retaining Walls

The earth pressures are calculated as in here - one metre of wall being considered. The figure above indicates the theoretical forces acting on the wall F1 (Representing area A.O.B1) = total net active pressure F2 (Representing area O.C.C1) = total net passive pressure F3 (Representing area C.D.D1) = total net passive pressure required to fix the toe of the wall Forces F1, F2 and F3 act through the centres of gravity of their respective areas. Calculations may be simplified by considering the line C1.C.D1. to be horizontal and to pass through point C. The area C. D. D1. is replaced by force F3 acting at C as shown in the figure below.

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The depth O.C. should be such that the moments of forces F1 and F2 about F3 are in equilibrium. The value of force F3 is such that the algebraic sum of forces F1, F2 and F3 is zero. The ‘Piling Handbook’ method of design for cantilever piles has been successfully used over many years but as can be seen from these sample calculations, a finite factor of safety has not been incorporated. The factor of safety is introduced by the adoption of reasonably conservative soil strength parameters. Should designers wish to include a specific factor of safety against rotational failure, the depth O.C. is determined such that restoring moments about point C equate to the disturbing moments multiplied by the desired factor of safety. In uniform cohesionless soils, when the depth O.C. has been derived, it should be increased by 0.2 x O.C. in order to correct the error produced by the simplified method. Hence, depth of cut off = B.O. + 1.2 x O.C. The maximum bending moment on the piles is derived by calculating the level X.Y. at which zero shear occurs (ie where area O.X.Y. = area A. B1.O.) and obtaining the net moment of these areas about this level.



A wall is to be builtto retain a height of 3.5m of sandy soils. The effective wall height =3.5m + 0.5m = 4m (Minimum over excavation allowance = 0.5m or 10% of retained height) Minimum surcharge load = 10 kN/m². Pressure on active side pa = γ .h.Ka - 2c√Ka + pw Pressure on passive side pp = γ .h.Kp + 2c√Kp + pw The coefficients of earth pressure are obtained from the tables in Chapter 4 on Earth and Water Pressures. Loose fine sand Compact fine sand

Ka=0.33 Kp=3.0 Kp=3.7 Ka=0.27

Note: Wall friction has been ignored in this example, however, its benefitial effect can be included at the discretion of the designer. pa at : ground level

= 10 x 0.33

= 3.3 kN/m²

4m below ground level in loose sand

= 78.6 x 0.33

= 25.9 kN/m²




= 95.8 x 0.33

= 31.6 kN/m²

5m below ground level in compact sand

= 95.8 x 0.27

= 25.9 kN/m²


= 114.4 x 0.27

= 30.9 kN/m²


= 146.8 x 0.27 + 29.4

= 69 kN/m²

pp at : 4m below ground level in loose sand

= 0 kN/m²


= 17.2 x 3

= 51.6 kN/m²


= 17.2 x 3.7

= 63.6 kN/m²


= 35.8 x 3.7

= 132.5 kN/m²


= 68.1 x 3.7 + 29.4

= 281.4 kN/m²


= 51.6 - 31.6

= 20 kN/m²


= 63.6 - 25.9

= 37.7 kN/m²


= 132.5 - 30.9

= 101.6 kN/m²


= 281.4 - 69.0

= 212.4 kN/m²

Net pp at :

Try Oc = 3.0m Moments about above point C: file:///C|/Documents%20and%20Settings/bantinone/My%20D...yweb19/Retaining_walls/Cantilever_retaining_walls.html (4 of 6)5/26/2005 4:00:22 AM


3.3 x 4.0 x 5.56 = 22.6 x 4.0 x 0.5 x 4.893 =

73.4 221.2

25.9 x 0.56 x 0.5 x 3.373 =

24.5

-20 x 0.44 x 0.5 x 2.707 =

-11.9

-37.7 x 1.0 x 2.06 =

-77.7

-63.9 x 1.0 x 0.5 x 1.893 =

-60.5

-101.6 x 1.56 x 0.78 = -57.6 x 1.56 x 0.5 x 0.52 =

-123.6 -23.4 = +22.0 kNm

As the sum of the moments is slightly positive, the correct value of OC is marginally greater than 3.0m. Depth of cut-off required = 0.56 + 1.2 x 3.0 = 4.2m (rounded to nearest 0.1m) Total active pressure = (3.3 + 25.9) x 0.5 x 4.0 = + 25.9 x 0.56 x 0.5 =

58.4 7.25 = 65.65 kN/ m

The level of which zero shear occurs (where the area of the net passive diagram equals the active force calculated above) is 5.9m below the top of the pile. Moments about and above the level of zero shear: 3.3 x 4.0 x 3.9 = (25.9 - 3.3) x 4.0 x 0.5 x 3.233 =

51.5 146.1

25.9 x 0.56 x 0.5 x 1.713 =

12.4

-20.0 x 0.44 x 0.5 x 1.047 =

-4.6

-37.7 x 0.9 x 0.45 = -(95.2 - 37.7) x 0.9 x 0.5 x 0.3 =

-15.2 -7.8 = 182.4 kNm/m

The calculated bending moment on the piles is 182.4 kNm/m. Section modulus required = (182.4 x 1000 x 100) / (180 x 100) = 1013 cm³/m Provide LX 12 or Frodingham 2N sheet piles in EN 10248:S270GP steel, 8.2m in length. file:///C|/Documents%20and%20Settings/bantinone/My%20D...yweb19/Retaining_walls/Cantilever_retaining_walls.html (5 of 6)5/26/2005 4:00:22 AM


Note: Although this sheet pile section will be adequate for structural purposes the designer must check that it will be drivable to the required depth and for permanent construction ensure that the pile will provide the required life expectancy (as outlined in Chapter 13).

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RETAINING WALLS Design of Walls with Fixed Earth Support

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In this condition the penetration of the piles is such that the passive pressure generated is sufficient to prevent both forward movement and rotation at the toes. Thus the piles have a simple support due to the ties or struts at the top of the wall and fixed support due to soil at the wall base in a manner similar to a propped cantilever. Figure 5.25.1 indicates the forces acting on the wall. F1 (Representing area A.O.B1) = total net active pressure. F2 (Representing area O.C.C1) = total net passive pressure. F3 (Representing area C.D.D1) = total net passive pressure required to fix the toe of the wall. T = Support force applied at waling level. Forces F1, F2 and F3 act through the centres of gravity of their respective areas. As in the case of a cantilever wall, calculations may be simplified by considering the line C1.C. file:///C|/Documents%20and%20Settings/bantinone/My%20...Webs/myweb19/Retaining_walls/Fixed_earth_support.html (2 of 6)5/26/2005 4:00:23 AM


D1 to be horizontal and to pass through the point C. The area C.D.D1 is replaced by force F3 acting at C, as shown in Fig 5.25.2. The force T at waling level is obtained by taking moments of area A.O.B1 about O. The depth OC should be such that the moments of forces T, F1 and F2 about F3 are in equilibrium. The value of the force F3 is such that the algebraic sum of forces T, F1, F2 and F3 is zero. When depth OC has been derived, it should be increased by 0.2 x OC in order to correct the error produced by the simplified method. In uniform cohesionless soils, the penetration is obtainable directly from the formula. Depth of cut-off below excavation level = Y + 1.2√{6R/g.(kp - ka)} where Y is the depth below excavation level of the point O (zero net pressure) and R is the reaction at point O when the pile is considered as a beam simply supported at the waling level and point O and loaded with active pressure A.O.B1. The maximum bending moment is obtained again by considering the pile as a beam simply supported at the waling level and point O loaded with active pressure A.O.B1.



Active pressure Passive pressure

pa = g.h.Ka - 2c√Ka + pw kN/m² pp = g.h.Kp + 2c√Kp + pw kN/m²

The coefficients of earth pressure used in the calculations are: Loose fine sand: Ka = 0.33, Kp = 4.9 Dense fine sand: Ka = 0.27, Kp = 6.0

pa at : ground level

= 10 x 0.33

4m below ground level in loose fine sand

= 78.8 x 0.33

= 3.3 kN/m² = 26 kN/m²




= 78.8 x 0.27


= 89.6 x 0.27 + 9.8


= 111.2 x 0.27 + 29.4

=59.4 kN/m²


= 154.4 x 0.27 + 68.6

=110.3 kN/m²

pw at 7m below ground level

= 21.3 kN/m² = 34 kN/m²

= 19.6 kN/m²

pp at 11m below ground level in dense fine sand

= 43.1 x 6.0 + 58.8


= 59.4 - 19.6


= 317.4 - 110.2

Active Pressure

= 317.4 kN/m²

= 39.8 kN/m² = 207.2 kN/m²

Moment of Active Pressure about 'O'

3.3 x 4.0 =

13.2

13.2 x 5.645 =

74.5

(26 - 3.3) x 4.0 x 0.5 =

45.4

45.4 x 4.978 =

226.0

21.2 x 1.0 =

21.2

21.2 x 3.145 =

66.7

6.2 x 2.978 =

18.5

(34 - 21.7) x 1.0 x 0.5 = 34 x 2.0 = (39.8 - 33.9) x 2.0 x 0.5 = 39.8 x 0.645 x 0.5 =

6.2 68.0 5.9 12.8

68.0 x 1.645 =

111.9

5.9 x 1.312 =

7.7

12.8 x 0.430 =

5.5

= 172.7 kN

= 510.8 kNm

Force in walings and supports = 510.8 / 6.645 = 76.9 kN/m of wall. Total active force = 172.7 kN/m and is applied 510.8 / 172.7 = 2.957 above 'O'. file:///C|/Documents%20and%20Settings/bantinone/My%20...Webs/myweb19/Retaining_walls/Fixed_earth_support.html (5 of 6)5/26/2005 4:00:23 AM


Net passive pressure at any depth below point 'O'

= g'.(kp-ka).d

= 10.8 x (6.0 - 0.27) x d = 61.9d Moments of the total active force, net passive pressure and support force t about the pivot point at the toe of the pile must be in equilibrium. Hence 172.7 x (2.957 + d) = 76.9 x (6.645 + d) + (d x 61.9d x 0.5 x 0.33d) d = 3.1 m Depth of cut-off required for fixity = 0.645 + 1.2 x 3.1 = 4.365 say 4.5m Zero shear occurs 4.7m below ground level. Moments about and above level of zero shear: 79.6 x 3.70 =

284.5

-3.3 x 4.0 x 2.70 =

-35.6

-22.7 x 4.0 x 0.5 x 2.033 =

-92.3

-21.2 x 0.7 x 0.35 =

-5.2

-8.9 x 0.70 x 0.5 x 0.233 =

-0.7 = 150.7 kNm/m (say 151 kNm/m)

Section modulus required = (151 x 1000 x 100) / (200 x 100) = 755 cm³/m (assuming teporary works stress) Length of pile required = 4.5m + 7m = 11.5m Use LX8 or Frodingham 2N piles in EN10248: S270GP steel, 11.5m long. Note: Although these sheet pile sections will be adequate for structural purposes the designer must check that they will be drivable to the required depth and will provide the required effective life.

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RETAINING WALLS Analysis by Graphical Method

As an alternative to the analytical method, the bending moment, embedment and the anchor force can be obtained by means of graphical construction. Explanation of the Method

The pressure diagram is constructed in the normal way and subdivided into a number of sections which need not be equal but must be of sufficient number to form a reasonably smooth curve when the bending moment diagram is plotted. From the centre of gravity of these sections, horizontal lines are drawn and numbered to represent the forces acting on the wall. A vector diagram is then constructed by marking out horizontally the forces acting in each section. Choosing polar distances ‘O’ and ‘O 1 ’, lines are drawn from each point on the horizontal vector lines to their respective points ‘O’ and ‘O 1 ’. A funicular polygon or bending moment diagram is then constructed by drawing lines parallel with those of the vector diagram to the horizontal lines drawn from the centre of gravity of each section of the pressure diagram. The first upper line of the funicular polygon is produced to cut the horizontal line of the tie bar force at X. From the point X a base line is drawn so that the area A multiplied by the distance from its centre of gravity to X equals the areas B multiplied by the distance from its centre of gravity to X. The force T is obtained by drawing line OZ parallel to the base line XY. The depth of cut off is shown where the base line cuts the bending moment curve at Y. It is necessary to increase this distance by 20% to allow for satisfactory cut off and full fixity at the toe.

Results of Analysis Maximum bending moment Required section modulus Embedment depth

= 140 kNm x 1.07m

= 150 kNm

= {150 x 1000}/200 x 100/100 = 0.6 + 1.2 x 3.12

= 750 cm 3 /m

= 4.344m

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Length of pile required

= 4.4m + 7m

= 11.4m



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RETAINING WALLS Design of Sheet Pile Deadman Anchorage The following example illustrates the method which has been widely used for the design of balanced anchorages.

Tie rod load (calculated from limit equilibrium condition) = 77kN/m Assume LX anchor piles are selected:Assume tie rods will be at 8 pile centres. Tie rod spacing = 4.8m Load per tie rod = 77 x 4.8 = 369.6 kN Therefore from Table 5.20.3 of permissible tie rod loads select 70mm diameter rods in S275 grade steel or 60mm diameter rods in S355 grade steel A factor of safety of 2 is applied to the tie rod load to calculate the ultimate anchorage load required. (The factor of safety against failure will therefore be 2) Ultimate anchorage load = 2 x 369.6 = 739.4 kN file:///C|/Documents%20and%20Settings/bantinone/My%20D...web19/Retaining_walls/Sheetpile_deadman_anchorage.html (1 of 4)5/26/2005 4:00:24 AM


The net passive pressure at any depth ‘d’ in front of the anchorage = g x d x (kp - ka) Assume that the depth to the centre of the anchorage is 2m. Therefore, for a balanced anchorage, the depth to the toe = 3m Average net pressure in front of the anchorage = 17.2 x 1.5 x (3 - 0.33) = 68.9 kN/m² (g = 17.2 kN/m 3 , depth to mid point of anchorage = 1.5m, k p = 3 and k a = 0.33 ) Total soil shear resistance at the ends of the anchorage: = 1/3 x g x d 3 x ka x tan(45 + f/2) x tanf = 0.33 x 17.2 x 3 3 x 0.33 x tan(45 + 30/2) x tan 30 = 51 kN Therefore, the anchorage width required = (739.4 - 51)/(68.9 x 3) = 3.33m Therefore, adopt a 5 pile anchorage giving a width of 3.00m (When designing an anchorage using Larrsen piles an odd number of piles should be used) The depth of anchorage must therefore be increased to allow for this reduction in nominal width but can be approximated to (739.4 - 51) / (68.9 x 3) = 3.33m (A more accurate calculation will result in a smaller anchorage depth as the ‘d’ variable used to calculate both the average pressure in front of the anchorage and shear resistance at the sides should be increased, but it is normally sufficiently accurate to use previously calculated values at this stage) Area of anchorage

= 3.0 x 2.22

Average pressure on the anchorage

= 6.66m²

= 739.4 / 6.66

= 111kN/m²

Consider 1m width of anchorage. Bending moment on the piles

= w x L²/8 = 111 x 2.22²/8

= 68.4kNm

(L = actual length of anchor piles ie 2 x 3.33 / 3) Therefore minimum section modulus required = 68.4 x 1000 / 270 = 254 cm³/m (Note that the yield stress of the steel anchor piles is used in this calculation as the loading applied to the anchorage has already been factored by 2 to calculate the ultimate achorage load) Therefore, adopt Larssen LX8 steel sheet piles in EN 10248: S270GP steel, 2.2m in length.

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Load on the anchorage waling = 111 x 2.22 = 246.4 kN/m Bending moment on the waling = 246.4 x 3² / 8 = 277.2 kNm Therefore, minimum section modulus required = 277.2 x 1000 / 275 = 1008cm³/m Adopt 2 / 305 x 102 x 46.18 kg/m R.S.C in grade S275 steel as the waling. If Z piles are to be used, an even number of piles should be chosen. For this example, the overall width of piling to be provided should be approximately 3.33m Therefore, consider 6 Nr Frodingham piles. Overall width = 6 x 0.483 = 2.898m Depth of anchorage required = (739.4 - 51) / (68.9 x 2.898) = 3.45m Area of anchorage = 3.45 x 2/3 x 2.898 = 6.665m² Average pressure on anchor piles = 739.4 / 6.665 = 111kN/m² Consider 1m width of anchorage. B.M. on anchor piles = 111 x 2.3²/8 = 73.4kNm/m Section modulus required = 73.4 x 1000 / 270 = 272 cm³/m Use 6 Nr. Frodinghan 1N profile piles in EN 10248: S270GP steel, 2.3m long Load on anchorage waling = 111 x 2.3 = 255.3 kN/m Bending moment on the waling = 255.3 x 2.898² / 8 = 268 kNm Section modulus required = 268 x 1000 / 275 = 975 cm³ Use 2 / 305 x 102 x 46.18 kg/m R.S.C in grade S275 steel as the waling.



River Retaining Wall, Swansea Client: West Glamorgan County Council Main Contractor: Edmund Nuttall Limited Sub-Consultant: Ove Arup & Partners

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RETAINING WALLS Design Example Consider a cantilever sheet pile wall in good granular material to retain 4.0m of water. The work is temporary and the intention is to use grade S270GP grade steel piles. Select the appropriate table, in this case Table 'Cantilever Walls Cohesionless Soils'. On the horizontal scale select 4.0m. 1. Read up the chart to the line for S270GP steel (temporary). Read the required minimum section modulus from the left hand vertical scale. In this case 1300cm 3 / m. Therefore use either LX16 or Frodingham 3N or 3NA sheet piles. 2. Read up the chart to the maximum pile length line. Read the required minimum pile length from the right hand vertical scale. In this case 9.0m long. Suggested piles for this example LX16 or Frodingham 3N or 3NA in grade S270GP steel Typical Retaining Walls

The following charts indicate the requirements for a retaining wall for the conditions specified. The user should select the conditions which represent the case in question and then scale off from the charts the bending moment, support force and minimum pile length. The figures thus obtained are unfactored. The sheet pile section required may then be ascertained by dividing the theoretical bending moment by the permissible design stress to obtain the minimum section modulus. The charts are based on the assumption that weep holes are provided where necessary and the retained soil is capable of allowing the design water regime to be realised. In the case of cohesive soils, the charts allow for the accumulation of ground water in any tension cracks which may develop. The soil conditions adopted in the production of the charts assume a softened zone to a depth of 1m below excavation level when cohesive soils exist at excavation level. The length of pile below excavation level has not been checked to ensure that there is sufficient penetration to prevent piping or heave and provide a water cutoff where appropriate. This must be considered separately.

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The selected section must be checked for drivability. Note: Cantilever walls in excess of 4.5m high are not generally recommended as the section required to resist bending moments and the length required for stability mean that uneconomic designs may result. In circumstances where the retained height exceeds 4.5m, a cantilever wall may be considered, but the deflection of the wall is likely to be large and this should be checked to ensure that serviceability criteria are not exceeded. It is further recommended that cantilever walls are not used in soft clays. When Larssen sheet piles are selected for the construction of cantilever retaining walls, the designer must satisfy himself that the section is capable of developing the required section modulus. Guidance on the selection of pile sections is given in 5.13. Cantilever walls should not be designed for permanent construction using total stress soil parameters. 1. 2. 3. 4. 5. 6.

Cantilever Cantilever Cantilever Cantilever Cantilever Cantilever

Walls Walls Walls Walls Walls Walls

-

Cohesionless Cohesionless Cohesionless Cohesionless Cohesionless Cohesionless

Soils Soils Soils Soils Soils Soils

7. Anchored Walls - Cohesionless Soils 8. Anchored Walls - Cohesionless Soils 9. Cantilever Walls - Cohesive Soils (Temporary works only) 10. Cantilever Walls - Cohesive Soils (Temporary works only) 11. Cantilever Walls - Cohesive Soils (Temporary works only)

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CORUS PILING HANDBOOK Example - Cantilevel Walls - Cohesionless soils

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CORUS PILING HANDBOOK Cantilevel Walls - Cohesionless soils

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CORUS PILING HANDBOOK Anchored Walls - Cohesionless soils



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CORUS PILING HANDBOOK Anchored Walls - Cohesionless soils



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CORUS PILING HANDBOOK Cantilevel Walls - Cohesive soils



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Cofferdams - Corus Piling Handbook

COFFERDAMS Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

Introduction Requirements of a Cofferdam Planning a Cofferdam Causes of Failure Support Arrangements Design of Cofferdams Single Skin Cofferdams Cofferdams for River Crossings Single Skin Cofferdam Design Example Design of Support System Allowable Stresses for Steel Walings Cofferdam Support Frames Strength of Walings - Universal Columns Strength of Walings - Timber Beams Safe Loads for Horizontal Box Pile Struts Safe Loads for Horizontal Universal Column Struts Safe Loads for Horizontal Universal Compound Beam Struts Safe Loads for Square Timber Struts Circular Cofferdams Reinforced Concrete Walings for Circular Cofferdams Earth Filled Double Wall and Cellular Cofferdams Double Skin/Wall Cofferdams Cellular Cofferdams Effect of Water Pressure Flow Nets Pump Sumps

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COFFERDAMS Introduction The purpose of a cofferdam is to exclude soil and water from an area in which it is required to carry out construction to a depth below the surface. Total exclusion of water is often not necessary and in some instances is not possible, but the effects of water ingress must be taken into account in any calculations. There are two principal approaches to cofferdam design. Single skin structures are most common, but for very large or deep excavations and marine works, double wall or cellular cofferdams may be preferred. The design of a cofferdam is carried out in the same manner as a retaining wall and consequently, the same design rules apply.

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COFFERDAMS Requirements of a Cofferdam The design of a cofferdam must provide the following: ● ●

●

●

●

●

●

The structure must be able to withstand the loads applied to it. The quantity of water entering the cofferdam must be controllable by pumping. At any stage in the construction, the formation level must be stable and not subject to excessive heave or boiling. Deflection of the cofferdam walls and bracing must not affect the permanent structure or any existing structure adjacent to the cofferdam. Overall stability must be demonstrated against out of balance earth pressures due to sloping ground or circular slip failure. The cofferdam must provide an appropriate size of hole to suit what is to be built inside. Temporary cofferdams must be built in such a way that the maximum amount of construction materials can be recovered.

Consideration should be given to the incorporation of piles used to form temporary cofferdams in the permanent structure as significant savings in both time and overall cost can be achieved.

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COFFERDAMS Planning a Cofferdam The designer of a cofferdam must have an established set of objectives before commencing the design. The sequence of construction activities must be defined in order that the design can take into account all the load cases associated with the construction and dismantling of the structure. From this sequence, the critical design cases can be determined and the bending moments, shear forces and minimum penetration depths calculated to determine the pile section which is required to do the job. As part of the analysis of construction activities, the designer should undertake a risk assessment of the effect of any deviation from the planned sequence. Such deviations may be in the form of over excavation at any stage, inability to achieve the desired pile penetration, installation of supports at the wrong level or the imposition of a large surcharge loading from construction plant. If any stage in the cofferdam construction is particularly vulnerable then contingency plans should be developed to minimise any risk and site staff should be informed to limit the possibility of critical conditions being realised. The majority of cofferdams are constructed as temporary works and it may be uneconomic to design for all possible loading cases. Decisions will have to be taken to determine the level of risk which is acceptable when assessing the design cases; such a situation may occur when assessing hydraulic loading on a cofferdam. Flood conditions tend to be seasonal and provision of a cofferdam which will exclude water at all times may involve a substantial increase in pile size and strength. In an extreme flood condition the design philosophy may involve evacuation of the excavation and allowing for the structure to be overtopped. Under these conditions, the designer must allow for overtopping, considering the effect of the sudden ingress of water on the base of the cofferdam and the effect that any trapped water will have on the stability of the cofferdam when the flood subsides. Prior to the commencement of construction the site area should be cleared to permit plant and guide frames to be set up. Excavation should not begin until all plant and materials for supporting the piles are readily available including pumping equipment where necessary.

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COFFERDAMS Causes of Failure There are many possible causes of cofferdam failure, but usually failure can be attributed to a relatively small number of causes. These include:● ● ●

● ● ●

● ● ●

Lack of attention to detail in the design and installation of the structure. Failure to take the possible range of water levels and conditions into account. Failure to check design calculations using information discovered during excavation. Over excavation at any stage in the construction process. Inadequate framing (both quantity and strength) provided to support loads. Loading on frame members not taken into account in the design, ie walings and struts used to support walkways, pumps etc. Accidental damage to structural elements not repaired. Insufficient penetration of piles to prevent piping or heave. Lack of communication between temporary and permanent works designers or designer and site staff.

In many cases failure may result from the simultaneous occurrence of a number of the above factors, any one of which might not have been sufficient to cause the failure itself.

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COFFERDAMS Support Arrangements The arrangement of supports to a cofferdam structure is the most critical part of a cofferdam design. The level at which support is provided governs the bending moments in the sheet piles and the plan layout governs the ease of working within the structure. Whilst structural integrity is paramount, the support layout must be related to the proposed permanent works activities causing the minimum obstruction to plant and materials access. As a general rule simplicity should always be favoured. Support frames should be located such that concrete lifts can be completed and the support loads transferred to the permanent works before the frame is removed. Clearance to starter bars for the next lift should also be considered when positioning frames. The clear space between frame members should be optimised to provide the largest possible uninterrupted area without the need for excessively large structural elements. Positioning of support members is often a matter of experience.

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COFFERDAMS Design of Cofferdams The life of the cofferdam structure must be assessed in order that the appropriate geotechnical parameters for the soils in which the cofferdam is to be constructed can be selected. In the majority of cases, total stress parameters for clay soils can be used as the cofferdam is a temporary structure. However, the susceptibility of any clay to rapid attainment of a drained state must be assessed by the designer and if there is any doubt, a check should be made on the final structure using effective strength parameters. As a rule of thumb it is recommended that cofferdams which will be in service for three months or more should be designed using effective stress strength parameters. The most economic section of sheet pile to be used will be determined by the bending moments calculated in the cofferdam design. This section must then be considered with respect to site conditions as it may be necessary to select a heavier section and/or higher quality of steel to ensure that the calculated penetration depth can be achieved. This is often the case where long piles are to be driven to deep penetrations or when hard driving conditions are expected. This topic is discussed in greater depth in Installation. In order to maximise the benefits in terms of the design from provision of a heavier section or higher quality steel, it is recommended that engineers consider driving of piles at an early stage in the planning/design process as the need for a heavy pile for driving may eliminate one or more levels of support with a consequent reduction in design effort. It is recommended that a minimum surcharge load of 10 kN/m² is adopted in design calculations to allow for the presence of plant and equipment around the edge of the excavation during construction. However, this surcharge should be increased (locally or globally) if heavy plant is to be located adjacent to the cofferdam or if excavated spoil is to be stacked before removal from the site - a 1m height of spoil will result in a surcharge load in the order of 20kN/m² . Following the guidance of BS 8002:1994 the structural design of steel piling, walings, struts and tie rods should be undertaken in accordance with BS 449: Part 2: 1969. It is recommended that, due to the degree of uncertainty in the determination of tie rod loads, an additional factor of safety is incorporated into their design as described in Retaining Walls. Timber components should be designed in accordance with BS 5268: Part 2: 1991. The application of the referenced codes to sheet pile design yields the following

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allowable stresses: Allowable stresses for sheet piles in bending

Class of Work

Contents

Steel Grade EN 10248: 1995 S270GP (N/mm²)

S355GP (N/mm²)

Permanent

180

230

Temporary

200

260

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COFFERDAMS Single Skin Cofferdams Single skin cofferdams are typically formed of sheet piles supported either by means of internal props or external anchors. The mechanics of single skin cofferdam design are those already outlined in Retaining Walls. The piles are considered to be simply supported between frames and below the lowest frame (in both temporary and final conditions) and to have either ‘fixed’ or ‘free’ earth support, depending on the type of soil and the depth of cut-off of the piles below the excavation level. Piles will need to be driven to such a level as to generate sufficient passive resistance and also to control the infiltration of water into the excavation. Records should be kept during driving for any indication of declutching of the piles. In such a case it may be necessary to grout behind the piles in order to control seepage. Cantilever pile cofferdams can be formed but have the same limitations as cantilever retaining walls particularly in terms of the achievable retained height. When the cofferdam has very large plan dimensions, but relatively shallow depth, it is often more economical to incorporate inclined struts or external anchorages similar to those described in the chapter on retaining walls. It should not however be forgotten that the installation of external anchorages requires space which is outside the cofferdam area and wayleaves may be required to install the anchors under adjacent properties. For a typical cofferdam with a depth exceeding 3m, a system of internal frames constructed from either timber or steel is normally employed. The design should be undertaken in stages to reflect accurately the construction process. Typically the sequence of operations would be to excavate and dewater to just below top frame level then install the first frame; this procedure being repeated for each successive frame. In the case of cofferdams in water, it should be noted that the stresses occurring during dewatering and installation of frames may be considerably in excess of those in the completed cofferdam. For cofferdams in water it may be preferable to employ Z-profile piles as the interlocks are located in the zone of maximum stress and therefore tend to tighten as the load is applied. If U-profile piles are employed it is advisable to investigate the use of some form of proprietary interlock sealant. When a cofferdam is to be used solely for the purpose of excluding water and the depth of soil to be excavated is only nominal, it is often more efficient to install all the framing under water before commencing dewatering. The table below shows the optimum spacing of frames for this method of construction. The spacing results in approximately equal loading on the second and successive frames. The table below also indicates the maximum spacing between the top and second insert frame for different pile sections. Maximum Depth, h, from first to second waling (top waling at water level)

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The above dimensions are based on an allowable working stress of 180N/mm² . For other stresses the dimensions may be approximated by the equation:file:///C|/Documents%20and%20Settings/bantinone/My%20...20Webs/myweb19/Cofferdams/Single_skin_cofferdams.html (2 of 3)5/26/2005 4:00:37 AM


h³ =1.56 x Z x pbc NB - For depths exceeding 7m waling loads may become excessive

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COFFERDAMS Cofferdams for River Crossings The following cofferdam arrangements may be employed when a pipeline is to be laid under a river bed and it is not possible to close off the waterway.

●

Construction of cofferdams in river banks

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COFFERDAMS Cofferdams for River Crossings Construction of cofferdams in river banks

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COFFERDAMS Single Skin Cofferdam Design Example The following example is based upon the same soil conditions as used for the earth pressure calculation example included in the Retaining Walls Chapter. The earth pressures in the final condition are those calculated in that example. In this example, the analysis of the sheet piles assumes the presence of a hinge at the lower prop position to make the problem statically determinate. The problem can, using this assumption, be treated as two single propped retaining walls. Before placing the top frame, excavation will have had to be carried out and the piles will therefore act in cantilever mode. The net pressure diagram for that case is given in the figure below.

The top frame is assumed to be 1m below the ground surface. We will assume in this example that the lower frame is positioned 5.5m below the ground surface. The excavation depth required to install the lower frame is therefore 6.1m. The net pressure diagram for this condition is given below. Pp at 6.1m below ground level in sand and gravel = 0x6.0

= 0.0 kN/m²

Pp at 11m below ground level in sand and grave = (53.9x6.0)+49.0

= 372.4 kN/m²

Pp at 11m below ground level in firm clay = 102.9+(2.3x65)

= 252.4 kN/m²

Pp at 13m below ground level in firm clay = 142.9+(2.3x65)

= 292.4 kN/m²

Net Pp at 11m below ground level in sand and gravel = 372.4-133.2

= 239.2 kN/m²

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Net Pp at 11m below ground level in firm clay = 252.4-98.2

= 154.2 kN/m²

Net Pp at 13m below ground level in firm clay = 292.4-138.2

= 154.2 kN/m²

In this condition, the piles are supported by their embedment below the excavation level at 6.1m depth and the top frame. This depth is sufficient to produce a fixed earth support to the toes of the piles. Hence the effective span of the piles may be taken as the distance from the top waling and the point ‘0’ on the diagram. Taking moments of the active pressures about the point ‘0’: kNm/m 69.6 x 1.1 x 0.5 x 0.73 = 68.7 x 2.19 x 0.5 x 1.83 =

27.94 137.66



27.1 x 2.19 x 0.5 x 2.56 =

75.97

27.1 x 1.51 x 0.5 x 3.79 =

77.55

12.0 x 1.51 x 0.5 x 4.30 =

38.96

26.2 x 1.2 x 0.5 x 5.2 =

81.74

10.2 x 1.2 x 0.5 x 5.6 =

34.27

10.2 x 1.2 x 0.5 x 6.4 =

39.17

3.3 x 1.2 x 0.5 x 6.8 =

13.46 = 526.72

The load on the top frame

= 526.72/6.2 = 84.95 kN/m

Zero shear occurs at 4.66m below ground level. (Where the area of the active pressure diagram above the level equals the top frame load) Take moments about and above the level of zero shear: kNm/m 84.95 x 3.66 =

310.92

-41.35 x 0.75 x 0.5 x 0.25 =

- 3.88

-27.1 x 0.75 x 0.5 x 0.5 =

- 5.08

-27.1 x 1.51 x 0.5 x 1.25 =

-25.58

-12.0 x 1.51 x 0.5 x 1.76 =

-15.95

-26.2 x 1.2 x 0.5 x 2.66 =

-41.82

-10.2 x 1.2 x 0.5 x 3.06 =

-18.73

-10.2 x 1.2 x 0.5 x 3.86 =

-23.62

-3.3 x 1.2 x 0.5 x 4.26 =

- 8.43 167.83

Maximum bending moment in the temporary condition = 167.83 kNm/m Lower frame is installed 5.5m below ground level. Excavate to final level. The depth of cut off is insufficient to produce ‘fixed earth support’. Check for ‘free earth support’ considering that the piles are simply supported at the bottom frame position due to the assumption of a hinge at the support position.



Moments about and below the lower frame position: kNm/m 57.3 x 0.6 x 0.5 x 0.2 =

3.44

68.7 x 0.6 x 0.5 x 0.4 =

8.24

69.6 x 1.8 x 0.5 x 1.2 =

75.17

93.0 x 1.8 x 0.5 x 1.8 =

150.66

93.0 x 1.46 x 0.5 x 2.89 =

198.89 = 436.40

Assume that the piles will be 11.75m long. Take moments of net passive pressures about and below the lower frame: kNm/m



102.4 x 1.62 x 0.5 x 4.96=

411.4 512.89

116.4 x 0.75 x 5.875=

= 924.29 Factor of safety against movement of pile toes = 924.29 436.40 = 2.12 Depth of cut off required to give a factor of safety of 1: 411.4 + 116.4x (5.5 + x/2)

= 436.4

Simplifying x² + 11x - 0.43

= 0.0

Solving for x gives x

= 0.04m

Pp when x=0.04: 102.4 x 1.62 x 0.5=

82.94 = 04.66

116.4 x 0.04=

= 87.60kNm/m Zero shear occurs 7.7m below ground level. (This is found by calculating the level at which the area of the active pressure diagram below the line equals the calculated total passive pressure Pp working up the diagram from the net zero pressure point). Take moments of pressures about and below the point of zero shear: kNm/m 90.4 x 0.2 x 0.5 x 0.07 =

0.63

93.0 x 0.2 x 0.5 x 0.13 =

1.21

93 x 1.48 x 0.5 x 0.69 =

47.49

-102.4 x 1.62 x 0.5 x 2.76 =

-228.93

-116.4 x 0.04 x 3.32 =

- 15.46 = -195.06

The maximum bending moment in the sheet piles is 195.06 kNm/m (Final condition) Take moments of the active pressures about and above the lower frame: file:///C|/Documents%20and%20Settings/bantinone/My%20D...9/Cofferdams/Single_skin_cofferdam_design_example.html (5 of 7)5/26/2005 4:00:39 AM


kNm/m 57.3 x 1.59 x 0.5 x 0.53 =

24.14

27.1 x 1.59 x 0.5 x 1.06 =

22.84

27.1 x 1.51 x 0.5 x 2.09 =

42.76

12.0 x 1.51 x 0.5 x 2.6 =

23.56

26.2 x 1.2 x 0.5 x 3.50 =

55.02

10.2 x 1.2 x 0.5 x 3.90 =

23.87

10.2 x 1.2 x 0.5 x 4.70 =

28.76

3.3 x 1.2 x 0.5 x 5.10 =

10.1 = 231.05

The load on the top frame in the final condition = 231.05/4.5 = 51.34kN/m To calculate the load on the lower frame in the final condition, take moments of the entire load system about the level where the factor of safety against rotational failure = 1 (ie 11.04m below ground level) kNm/m -116.4 x 0.04 x 0.02 =

- 0.09

-102.4 x 1.62 x 0.5 x 0.58 =

-48.11

93.0 x 1.48 x 0.5 x 2.65 =

182.37

93.0 x 1.8 x 0.5 x 3.74 =

313.04

69.6 x 1.8 x 0.5 x 4.34 =

271.86

68.7 x 2.19 x 0.5 x 5.67 =

426.53

27.1 x 2.19 x 0.5 x 6.40 =

189.92

27.1 x 1.51 x 0.5 x 7.63 =

156.11

12.0 x 1.51 x 0.5 x 8.14 =

73.75

26.2 x 1.2 x 0.5 x 9.04 =

142.11

10.2 x 1.2 x 0.5 x 9.44 =

57.77

10.2 x 1.2 x 0.5 x 10.24 =

62.67

3.3 x 1.2 x 0.5 x 10.64 =

21.07

-51.34 x 10.04 =

-515.45 1,333.55

The load on the lower frame

= 1,333.55/5.54 = 240.71kN/m

Summary of Results Maximum bending moment in the temporary condition = 167.83 kNm/m Maximum bending moment in the final condition = 195.06 kNm/m file:///C|/Documents%20and%20Settings/bantinone/My%20D...9/Cofferdams/Single_skin_cofferdam_design_example.html (6 of 7)5/26/2005 4:00:39 AM


Section modulus required = 195.06 x 1000 x 100/200 x 100 = 975.3 cm³/m Note that in the example given above it has been assumed that the construction is temporary works and a working stress in the steel piles of 200N/mm² has been used. The recommended sections for this construction are therefore: ● ●

LX 12 Frodingham 2N

(z=1208 cm³/m), or (z=1161 cm³/m)

both in S270GP steel

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CORUS PILING HANDBOOK Net Pressure Diagram

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COFFERDAMS Design of Support System The choice of timber or steel for cofferdam bracing is governed by the external loads which the piles must withstand, taking into account the most severe conditions possible and the internal dimensions of the cofferdam. The loads on the walings are obtained from consideration of the same conditions used to obtain the bending moments in the piles. It is acceptable to use good quality timber such as Douglas Fir or Pitch Pine for the lighter loadings. However, such timbers must be free from knots, splits, sloping grain and similar defects which could lead to possible failure. Heavier loadings will necessitate the provision of steel members, ie universal beams suitably reinforced by stiffeners where necessary to safeguard against buckling. Information regarding the resistance to bending and shear of timber and steel beams is given in the table below.

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COFFERDAMS Allowable Stresses The application of BS 449 : Part 2 : 1969 to the design of steel walings in universal beams and columns, channels and compound girders composed of universal beams, or plated channels yields the following allowable stresses: Action and Material Steel Grade to BS EN 10210:1995

Bending <40mm

S275 (N/mm²)

S355 (N/mm²)

180

230

<63mm

230

<100mm

165

Shear in <40mm

110

unstiffened <63mm web <100mm

Contents

215

140 100

130

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COFFERDAMS Cofferdam Support Frames Timber Framing

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Steel Framing



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COFFERDAMS Strength of Walings -- Universal Columns

The table below is based on S275 steel with an allowable bending stress of 180N/ mm² and an allowable shear stress in unstiffened webs of 110N/mm² . Webs should also be checked for buckling and bearing. When the waling is also subject to axial load the allowable bending moment should be reduced to ensure that the sum of the stress ratios does not exceed unity. Serial Size (kg)

Elastic Modulus 'X-X' axis cm³

Allowable BM 'X-X' axis kNm

Shear Value kN

254 x 146 x 31

351

63

166

305 x 165 x 40

560

100

200

356 x 171 x 45

687

123

270

406 x 178 x 60

1063

191

353

457 x 152 x 67

1263

227

453

457 x 191 x 74

1458

262

452

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533 x 210 x 92

2072

372

592

610 x 229 x 113

2874

517

741

610 x 305 x 149

4111

740

794

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COFFERDAMS Strength of Walings -- Timber Beams

The table below is based upon BS 5268: Part 2: 1991. Permissible bending moments have been calculated for Grade SS, Class SC4 timber in the wet exposure condition under medium term loading. For differing exposure/loading conditions the designer must refer to the code. When the waling is also subject to axial load the allowable bending moment should be reduced to ensure that the sum of the stress ratios does not exceed the permissible values given in the code. Basic Size

Elastic Modulus cm³

Permissible BM kN

mm

' X-X' axis

'Y-Y' axis

'X-X' axis

'Y-Y' axis

150x150

562

562

4.2

4.2

150x200

1000

750

7.5

5.6

150x300

2250

1125

16.8

8.4

200x200

1333

1333

10

10

250x250

2604

2604

19.5

19.5

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300x300

4500

4500

33.7

33.7

350x350

7145

7145

53.6

53.6

400x400

10666

10666

80

80

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COFFERDAMS Safe Loads for Horizontal Box Pile Struts

Note: Table is in accordance with BS 449 for S270GP steel. Selfweight and a 10kN accidental load at the centre of the strut has been allowed for when used with x- x axis vertical. For additional or alternate loading normal to the span of the strut, calculations must be made to establish safe axial load.

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COFFERDAMS Safe Loads for Horizontal Universal Column Struts

Note: Table is in accordance with BS 449 for S275 steel. Selfweight and a 10kN accidental load at the centre of the strut has been allowed for when used with web vertical. For additional or alternate loading normal to the span of the strut, calculations must be made to establish safe axial load.

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COFFERDAMS Safe Loads for Horizontal Universal Compound Beam Struts

Note : Table is in accordance with BS 449 for S275 steel. Selfweight and a 10kN accidental load at the centre of the strut has been allowed for when used with web vertical. For additional or alternate loading normal to the span of the strut, calculations must be made to establish safe axial load.

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COFFERDAMS Safe Loads for Square Timber Struts

Note:- Table is in accordance with BS8004 for SS Grade Class SC4 timber in the medium term condition. Selfweight has been allowed for. Particular attention must be paid to straightness of the strut, eg by limiting bow to approximately 1/ 300 of the length.

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COFFERDAMS Circular Cofferdams The table in Product Information gives the approximate minimum diameters of cofferdams constructed in LX, Larssen and Frodingham sheet piling; the approximate maximum driving lengths are also given. The table is intended as a guide as the minimum diameter will depend upon several other factors such as type of ground, length of piles and penetration required. Smaller diameters can be achieved by introducing individual bent corner piles. On site it is usual to pitch the whole circle before driving, the piles being driven in stages as the hammer works its way several times around the circumference. Earth pressures are calculated as for straight-sided cofferdams and the piles may be supported by circular ring beams, instead of walings and struts, thus leaving the central area clear of obstruction. The ring beams are normally subjected to axial loads only, which are calculated as follows: Axial load (kN) = waling load (kN/m) x radius of cofferdam (m) The following table gives an indication of suitable sizes of reinforced concrete ring beams for various cofferdam diameters and loadings. Reinforced Concrete Walings for Circular Cofferdams

Diameter of Cofferdam (metres)

Safe Waling Load (kN per metre run) Size of Waling 'd' x 'b' in mm and number of reinforcing bars 450 x 300 8 no. 12φbars

600 x 400 10 no. 12φbars

5

473

840

10

236

420

656

15

158

280

438

630

210

328

473

20

750 x 500 900 x 600 8 no. 16φbars 8 no. 20φbars

1050 x 700 10 no. 20φbars

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643


25

263

30

378

515

315

429

35

368

Note: The number and size of reinforcing bars given in the table is based on the minimum area of steel for column construction given by table 3.27 of BS8110: Part 2: 1985 and assumes the use of High Yield steel (fy = 460N/mm² ) reinforcing bars to BS4449: 1988.

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COFFERDAMS Reinforced Concrete Walings for Circular Cofferdams The tabulated safe loads are based on: 1. The permissible compressive stress in the concrete not exceeding 8.8N/ mm², assuming the use of C35 concrete. 2. W = 1.5 E I / (105 r³) Where: W = Waling Load in kN/m E = Young’s modulus for concrete = 25000N/mm² I = Moment of Inertia about ‘x-x’ in cm4 r = Radius of cofferdam in metres 3. The cofferdam diameter divided by the width of the beam (d) < 35 The above basic formula is based on Timoshenko’s work wherein the formula is given as: Wu = (k.E.I) / (R³.105) kN/m where Wu is the ultimate waling load and k is a factor, the value of which is dependent on the stiffness of the retained medium. 3 is the value for water, eg in a marine cofferdam built to facilitate construction on the sea bed. Progressively higher values are, in theory, applicable for weak/medium/strong soils. However, it is common to use the value of 3, to which a factor of safety of 2 is applied. Hence the value of 1.5 in the basic formula. The ring beam can tolerate very little distortion from a true circle before the onset of catastrophic instability. Hence the empirical rule: D/d < 35 where d is the depth of the ring beam, ie the difference between the inner and outer radii of the beam and D is the diameter of the cofferdam (ie the diameter of the inner face of the piles). If the sheet piles deflect to any great extent then the load in the walings will be concentrated at the top or bottom of the waling and will impart torsion into the beam. This condition should also be checked in the design.

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COFFERDAMS Earth Filled Double Wall and Cellular Cofferdams Earth filled cofferdams are self supporting gravity structures, either parallel-sided double-wall cofferdams or cellular coffer-dams. The stability of both types is dependent on the properties of the fill and the soil at foundation level as well as on the arrangement and type of the steel sheet piling. Typical uses are as dams to seal off dock entrances temporarily so that work below water level can be carried out in the dry and in the construction of permanent walls for land reclamation, quays, wharves and dolphins.

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COFFERDAMS Double Skin/Wall Cofferdams Double wall cofferdams comprise two parallel lines of sheet piles connected together by a system of steel walings and tie rods at one or more levels. The space between the walls is generally filled with granular material such as sand, gravel or broken rock. The exposed or inner pile wall is designed as an anchored retaining wall while the outer line of piles acts as the anchorage. U or Z-profile sheet piles are appropriate to this form of construction.

The wall as a whole should be analysed as a gravity structure and, in order to achieve adequate factors of safety against overturning and sliding, the width should be not less than 0.8 of the retained height of water or soil. When determining the resistance to sliding, the coefficient of friction m along the base may be taken as 0.5 to 0.6 but cannot exceed tanf of the strata. Resistance to sliding per unit run of wall = γ‘.h.μ. W plus the passive resistance in front of the wall, where W is the width of the structure.

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Transverse bulkheads should be provided to form strong points at the ends and at intermediate positions to assist construction and confine any damage which might occur. The strong points may comprise a square or rectangular cell tied in both directions. The water regime both inside and outside the structure is critical. It is recommended that weepholes are provided on the inner side of the structure near the bottom of the exposed portion of pile to permit free drainage of the fill material reducing the pressures on the inner wall and preventing a decrease in the shear strength of the fill with time. As complete drainage of the fill is not always practical, allowance should be made for any water pressure acting on the piles. It is essential that clay or silt is not used as fill material and any material of this type occurring above the main foundation stratum within the cofferdam must be removed prior to fill being placed. The piles must be driven into the soil below excavation or dredge level to a sufficient depth to generate the required passive resistance. In this condition the structure will deflect towards the excavated side and the lateral earth pressure on the landward side may be taken as active. When cohesionless soils occur at or below excavation level, the penetration of the piling must also be sufficient to control the effects of seepage. The bearing capacity of the founding strata should be checked against the weight of the structure and any super-imposed loading. The presence of rock at excavation level makes this type of cofferdam unsuitable, unless: ●

● ● ●

The rock is of a type that will allow sheet piles to be driven into it to an adequate penetration (see Installation). Tie rods can be installed at a low level (probably underwater). A trench can be preformed in the rock into which the piles can be placed and grouted. The pile toes can be pinned with dowels installed in sockets in the rock.

If the piles are driven onto hard rock, or to a nominal depth below dredged level, the resistance to overturning and sliding should be developed by base friction and gravitational forces alone. In this condition the lateral earth pressure on the landward side will be in a condition between at rest and active, depending on the amount of deflection. The internal soil pressures acting on the outer walls should be taken as 1.25 times active values.

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COFFERDAMS Cellular Cofferdams Cellular cofferdams are constructed using straight web sheet piles. (See figure) The piles are interlocked and driven to form closed cells which are then filled with cohesionless material. Provided that the material on which they are to be founded is solid they require only nominal penetration to be stable. Pile penetration will assist in the resistance of any lateral loads occurring during the construction phase in the vulnerable period before the fill has been placed and the cell has become inherently stable. Cellular cofferdam structures are used to retain considerable depths of water or subsequently placed fill. The straight web pile section and particularly the interlocks, have been developed to resist the circumferential tension, which is developed in the cells, due to the radial pressure of the contained fill and, at the same time permit sufficient angular deflection to enable cells of a practical diameter to be formed. In cellular construction no bending moments are developed in the sheet piles, which enables the steel to be disposed of in such a manner to enable the maximum tension to be developed across the profile. The sections have therefore very little resistance to bending and are not suitable for normal sheet pile wall construction. Since the straight web sections themselves are capable of retaining the fill, walings and tie rods are not required. U or Z-profile piles are not suitable for this application as they are not designed to act in tension in this manner. The radial pressure ‘p’ at any depth 'h' is Ko.γ'.h plus the net hydrostatic pressure at that depth. Ko is the ‘at rest’ earth pressure coefficient and is obtained from the equation Ko = 1 - sinφ. The effective or buoyant density of the fill should be used below the contained water level. In some circumstances, eg when using hydraulic fill, the contained water level may be at the top of the structure during and immediately after filling. Circumferential tension = p x radius of cell. The stability of the cofferdam is dependent, on the tensile strength of the piles, the size and shape of the cell and the properties of the fill and the foundation soil. The granular fill within the cells provides stability to the whole structure by resisting shear forces which are set up in it when external forces are applied. To provide adequate factors of safety the average width of the wall should not be less than 0.8 of the retained height. The stability calculations should include checks for sliding, overturning, bursting of interlocks, web tension, internal shear of fill, tilting and foundation failure. The ratio of ultimate interlock strength against the maximum calculated circumferential tension should not be less than 2. The disturbing forces on the landward side will be derived from the active state due to the flexibility of the cellular structure. When determining the resistance to sliding, the coefficient of friction m between the fill and the founding stratum may be taken as 0.5 to 0.6 but cannot exceed tanf of the fill. Resistance to sliding per unit run of wall = γ‘. h.μ.Wa where Wa is the average width of the cofferdam. If the structure is to be founded on clay the strata must be hard or very stiff and the resistance to sliding should be checked for shear failure within the clay. When founding on fine sand, a berm may be necessary on the inner side of the wall in order to prevent loss of stability by boiling of the natural stratum due to seepage. With a sand or gravel foundation penetration of the piles must be sufficient to prevent seepage affecting the structural stability. Rock provides a suitable base for cellular construction and penetration is generally not required for stability. Some limited file:///C|/Documents%20and%20Settings/bantinone/My%2...y%20Webs/myweb19/Cofferdams/Cellular_cofferdams.html (1 of 5)5/26/2005 4:00:48 AM


penetration is desirable in order to prevent loss of fill and water under the wall, otherwise some other means of sealing the base should be investigated such as placing mass concrete. Whatever the type of soil at foundation level all soft clays or silts must be removed prior to filling. Where there is a significant depth to the founding strata consideration should be given to removing the overlying material to reduce the driving depth. All the piles should be driven to the same nominal toe level to permit the transfer of stresses around the structure. If this is not possible eg due to the presence of a sloping rock platform, it will be necessary to relieve the load from any piles below the level of continuity. This may be achieved by the formation of a horizontal concrete infill wedge; on steeply sloping surfaces such a wedge may need to be dowelled into the rock. Where the rock profile is irregular, consideration should be given to levelling the surfaces prior to construction. Adequate drainage must be provided near the bottom of the piles on the exposed face by means of weepholes, together with filters where necessary, to improve stability. Complete drainage may not be possible, however, so the effect of water on the weight of the infill and pressures on the piles must be investigated. The usual maximum length in which straight web sections are provided is 20m. Longer lengths can be supplied by prior arrangement and splice details can be supplied on request. Due to their low bending strength, however, special care is required when handling straight web piles. Lifting beams should be employed when moving the piles horizontally between storage positions. Piles exceeding 15m in length require two or even three points of support when being raised to the vertical pitching position. An efficient, robust arrangement of temporary works and templates is fundamental to the success of a cellular cofferdam scheme. A minimum of two templates is generally required often placed at low and high water in a tidal location. During pitching it is essential that pile verticality is maintained. Driving plant should be lightweight and easy to handle to avoid causing damage to the piles and facilitate repositioning. In difficult driving conditions some form of driving assistance such as water jetting, should be investigated. Guidance on temporary works arrangements and the construction sequence is available on request.

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Frodingham Straight Web Section - Dimensions and Properties Note: *Including 4 No T-Junction Piles. All Dimensions to centre point of pile web. The practicability of radii less than 3.75m is subject to site conditions and guidance should be sought from the Corus Construction Centre. The dimensions given above are for the unloaded condition. Allowance should be made for a barrelling effect during filling as the tensile force is developed in the piles. A cellular cofferdam is a flexible structure; horizontal movements of the piles and vertical movement of the fill should be expected. As pitched, the pile interlocks are not stressed and a barrelling effect, producing movements of 150mm, is not uncommon during filling. Horizontal movements at the top of high cofferdams can be up to 500mm and fill settlements of 150mm are not unusual.



The properties of the Frodingham Straight Web Section SW-1A are shown here. The range of standard corners and junctions is also indicated. Non-standard corners and junctions can be fabricated on request. The figure below illustrates the most common type of cellular construction in circular cells.



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CORUS PILING HANDBOOK Forming Cellular Cofferdams

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COFFERDAMS Effect of Water Pressure The stability of a cofferdam can be adversely affected by the action of water pressures on the soils at formation level to the extent that collapse may occur. In granular soils, excess water pressure causes piping and in cohesive or very tightly packed soils, heave results. Piping occurs when the pressure on the soil grains due to the upward flow of water is so large that the effective stress in the soil approaches zero. In this situation, the soil has no shear strength and assumes a condition which can be considered as quicksand which will not support any vertical load. This is obviously a very dangerous situation for personnel operating in the cofferdam and will also affect the passive resistance afforded to the cofferdam wall by the soil. The likelihood of piping for a given cross section can be predicted by the construction of a flow net which will allow the engineer to calculate the exit hydraulic gradient. Comparison of the calculated value to the critical hydraulic gradient will indicate the factor of safety against piping; for clean sands this should generally lie between 1.5 and 2.0. Care should be taken when designing circular cofferdams and at the corners of rectangular structures where the three dimensional nature of the situation is more critical than in the case of a long wall. The factor of safety against piping can be increased by installing the piles to a greater depth thereby increasing the flow path length and reducing the hydraulic gradient. The table below gives an approximate guide to the safe minimum cut-off depth for a cofferdam constructed in medium uniform cohesionless soil, when the toes of the piles do not penetrate impermeable soils and excess water is pumped from sumps at excavation level.

Safe Minimum Cut Off Depth

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Width of Depth of CutCofferdam 'W' off 'D' 2H or more

0.4H

H

0.5H

0.5H

0.7H

Base heave can occur in cohesive or very tightly packed granular material, if the force exerted by water pressure acting on a block of material inside the cofferdam exceeds the bulk weight of the block. The likelihood of heave can be assessed using a flow net to calculate the average water pressure acting on the line drawn between the toes of the piles and converting this to an uplift force on the soil. This can then be compared to the weight of the soil plug within the cofferdam. The flow of water into a cofferdam may also be reduced by lowering the ground water level by means of well points outside the cofferdam. Alternatively, flow into the cofferdam can be reduced by pumping from well points located inside the cofferdam at pile toe level. It should however be remembered that, when the stability or ease of operation of a cofferdam involves pumping, reliability of the pumps is of paramount importance and back-up capacity must be available to cope with any emergencies.

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COFFERDAMS Flow Nets The preparation of flow nets is a useful tool, as it not only allows the Engineer to calculate the water pressures in a particular situation, but also provides a visual representation of the flow regime in the soil. The shape and complexity of a flow net is a function of the homogeneity and permeability of the soil and the following notes indicate how a net can be drawn for uniform soil conditions and permeability. ● ●

● ● ● ● ●

A scaled drawing of the problem should be produced. A datum level should be marked on the cross section either at an impermeable boundary or at a suitable level below the cofferdam. The flow criteria must be determined. External water level. Internal water level. Centre line of cofferdam (this is the axis of symmetry). Lines of flow must be parallel to the cofferdam walls and the impervious datum.

Using the above as guidelines, the net is produced from flow lines and equipotential lines (a stand pipe at any point on an equipotential line would register the same height H above datum level). These are at right angles to each other and form approximate squares. This process is very much trial and error but practice will enable the flow net to be produced with a reasonable degree of speed and accuracy. To calculate the pore water pressure ‘u’ at any point (using the example above)

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●

Calculate the potential head ‘H’ at the desired point (note that the potential head drop is always the same between successive equipotential lines once a square net has been formed) H = H1 - (H1 - H2 ) x n / Nd where n = number of equipotential drops to the point being considered Nd = total number of drops Hence at a point A, H = H1 - (H1 - H2 ) x 2 / 10

●

At any point H = u / γw + z where u = pore water pressure γw = density of water z = height of point above datum AsH, γw and z are known, u can be calculated, u = (H-z) x γw

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COFFERDAMS Pump Sumps Although a sheet pile wall can prevent the ingress of water into an excavation, it is not possible to give any guarantee that a cofferdam will be watertight. In order to deal with any water which enters the excavation it is often desirable to install a drainage system which can channel water to a sump from which the water can be pumped away. As the hydraulic gradient adjacent to the corner of a cofferdam is at its largest, it is advisable to place any sumps at excavation level as far as possible from any corner and wall. It should not be forgotten that pumps are able to remove soil as well as water and a suction hose laid in the bottom of a cofferdam can disturb the base of the excavation with subsequent movement of the wall if the hose is badly located. Consideration should be given to forming a sump using a perforated drum into which the hose can be fixed to limit damage.

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Bearing Piles - Corus Piling Handbook

BEARING PILES Contents 1. 2. 3. 4.

5. 6. 7. 8. 9. 10. 11.

Introduction Selection of Profiles Design and Installation of Steel Bearing Piles Testing the Load Capacity of Steel Bearing Piles 1. Maintained Load Test and Constant Rate of Penetration Test 2. Dynamic Testing 3. Pile Driving Formulae Working Stresses Splice Welds in Steel Piles Tension Piles Steel H Piles Dimensions and Properties End-Bearing Steel H Piles Non End-Bearing Steel H Piles Allowable Stress in Axial Compression for Piles Projecting Above Soil Level

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BEARING PILES Introduction Steel bearing piles can be used to support a structure where the use of shallow foundations would cause either failure of the underlying soil, or result in unacceptable settlements. The piles transmit the loads from the structure through the upper layers of soft soil to those of adequate strength at greater depth. The main advantages which steel piles have over alternative systems are as follows: ●

●

●

●

●

●

●

●

They are available in a wide range of profiles and section weights in order to allow the most economical choice of section for any particular loading condition or soil profile. They are well suited to use in cases where very soft clays or loose sands and gravels are present in the soil profile or when piles are being installed below the water table - conditions which can pose problems for cast-insitu systems. Steel piles have a very high load-carrying capacity which can be further enhanced, given suitable ground conditions, by the use of high yield strength steel. The option of using a higher grade steel is also useful when harddriving conditions are anticipated. Because they are comparatively light in weight, but very robust, they require no special handling equipment for transport and they can be supplied in long lengths (up to 26.5m for some sections). The ease with which steel piles can be extended, increasing their load carrying capacity, is of great value to the designer working with a material as variable as soil. The inherent uncertainty of a calculated pile capacity is less of a problem to the designer and the effect of unforeseen ground conditions on the construction process can be reduced. For example, to maintain load capacity if weak soils are encountered, it is a simple welding operation to extend the pile or where a pile achieves the required ‘set’ earlier than predicted it can be shortened, with the advantage that off-cuts from piles on one part of the site can be used as extension pieces for other piles. Steel bearing piles are extractable at the end of the structures life and therefore the opportunity for either re-use or recycling exists, resulting in an economic and environmental bonus. Steel bearing piles are of the low-displacement type and therefore there is no spoil to dispose of, which is of particular benefit when piles are being installed into contaminated ground. Steel bearing piles can readily be used as raking members in order to accommodate horizontal loads on structures such as bridge abutments.

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BEARING PILES Selection of Profiles Four basic types of steel bearing piles are produced by Corus:1. H-Section Universal Bearing Piles. 2. Box Piles. These are formed by welding together two or more units to form a single section and are sub-divided into the following types: 1. Larssen Box Piles 2. Frodingham Plated and Double Box Piles Types (2.1) and (2.2) are fabricated from standard sheet pile sections and the dimensions and properties of these box piles are given in Fabricated Steel Sheet Piling. 3. Tubular Piles. 4. Sheet Piles. It should be noted that as well as being widely specified for the construction of purely earth-retaining structures, sheet piling also has a significant capacity to carry axial load in addition to earth and water pressures and can be used to form structures such as bridge abutments, without modification. Basically, the choice of the most suitable profile is defined as follows: Where piles are fully embedded, ie the whole length of the pile is below ground level, an H-section pile is most suitable. This usually occurs when piles are used to support land-sited structures such as road and railway bridges and industrial buildings. Box piles are most useful when part of the pile is exposed above ground level, as in pier and jetty construction, or when hard-driving ground conditions are anticipated. They can also be incorporated into a plain sheet pile wall in order to increase its bending strength and/or axial load capacity. That these sections possess a comparatively uniform radius of gyration about each axis, and hence excellent column properties, is a particular advantage in these situations.

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BEARING PILES Design and Installation of Steel Bearing Piles The design, installation and test loading of bearing piles is a complex subject and the applicable design methods in particular, will be subject to some change in the future as the ‘limit-state’ approach given in Eurocode 7 - ‘Geotechnical Design General Rules’ is adopted. These topics are dealt with in detail in the Steel Construction Institute publication, P156 ‘Steel Bearing Piles Guide: 1997’.

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BEARING PILES Testing the Load Capacity of Steel Bearing Piles There are four categories of tests that are commonly used to determine the load capacity of steel bearing piles. These are: Maintained Load Test and Constant Rate of Penetration Test

Both these tests use similar apparatus and in both cases the test load is applied by hydraulic jack(s) with kentledge or tension piles/soil anchors providing a reaction. In the Maintained Load Test, the load is increased incrementally, and is held at each level of loading until all settlement has either ceased or does not exceed a specified amount in a stated period of time. In the Constant Rate of Penetration Test, the load is increased continuously at a rate such that the settlement of the pile head occurs at a constant rate. A rate of 0.75mm/min is suitable for friction piles in clay, whilst for end-bearing piles in sand or gravel a penetration rate of 1.5mm/min may be used. The amount of kentledge or tension resistance should always be in excess of the estimated ultimate bearing capacity of the pile and if kentledge is used, its support system and ‘foundations’ should be carefully considered well in advance of the test. Details of both these tests are given in BS8004 1986 Clauses 7.5.5 and 7.5.6. It is desirable to carry out test loading of steel bearing piles to *failure/ultimate load to determine whether the factor of safety or penetration is approximately correct and this can generally be done without affecting the piles subsequent load carrying capacity. * This is commonly defined as the load at which the total head settlement is 10% of the pile width or the load at which the net residual head settlement, after removal of all load, is equal to a specified amount eg 8mm Dynamic Testing

Using this approach, the test pile is instrumented with strain transducers and accelerometers, the pile is struck with the piling hammer and the force and velocity data recorded and analysed. Using this data, methods are available that give an onsite estimate of the pile bearing capacity, although more rigorous and detailed analysis of the recorded data can be performed using a computer program such as the Case Pile Wave Analysis Program (CAPWAP). Using the program, an engineer can determine the pile bearing capacity, in terms of shaft resistance and toe resistance and the distribution of resistance over the pile shaft. A load-settlement curve is calculated and is similar in form to traditional static load tests. It is advisable to correlate the results of dynamic pile tests with those of at least one maintained load test.

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Pile Driving Formulae

This approach, eg the Hiley formula, relates the measured permanent displacement of the pile at each blow of the hammer to the dynamic capacity of the pile, from which the static capacity can be obtained by the application of a factor of safety, normally 2.0. It should be noted that a dynamic formula should be applied only to piles founded in hard or soft rocks, sands and gravels or extremely hard clays and that it is then applicable only if a satisfactory re-drive check is obtained, ie the immediate set per blow on re-driving the pile after an interval of several hours should be either equal to, or less than, the previous final set per blow.

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BEARING PILES Working Stresses The maximum working stress should normally be limited to 30% of yield stress, ie 85N/mm² for grade S275 steel and 105N/mm² for grade S355 steel, to BS EN 10025:1993. However, when piles are driven through fairly soft soils to refusal on a sound rock stratum at a known level, then the maximum working stress can be increased to approximately 50% of yield stress, ie 140N/mm² for grade S275 steel and 180N/mm² for grade S355 steel. Where bending moments are to be resisted in addition to axial loads, the combined bending and axial stresses should not exceed 50% of yield, whilst the stress due to axial load alone must not exceed 30% or 50% of yield as explained above. For general guidance, extracts in the form of tables from the Steel Construction Institute publication ‘Steel Bearing Piles Guide:1997’ are reproduced in this chapter. These tables give the range of pile sizes available and general guidance on the selection of piles and sizes for various loads.

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BEARING PILES Splice Welds in Steel Piles Two main types of weld are used in steel piling: 1. Primary welds, used to form tubular or box piles and fabricate corners, junctions etc in sheet piles. 2. Splice Welds to connect an extra length to a pile, either before or after an initial installation to increase the overall pile length. For splice welds to steel piling, there has been no generally agreed Standard or Code of Practice stipulating the weld quality level to be used, which has led to a tendency to use a standard which is too high. Over specification leads to higher labour and welding consumable costs, increased Non-Destructive Testing costs, high rectification costs and consequent delays to the overall construction programme. Therefore, for guidance on the subject of welding sheet piles and bearing piles, reference should be made to Site Fabrication of Piles and the Corus publication ‘Splice Welds in Steel Piles’

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BEARING PILES Tension Piles Bearing Piles manufactured in steel have the advantage of being able to withstand high tensile loadings, which makes them ideal for resisting uplift forces.

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BEARING PILES Steel H Piles Dimensions and Properties

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BEARING PILES End-Bearing Steel H Piles The table below is applicable to piles founded in: 1. Hard and medium rock or equivalent,strata, such as extremely dense or partially cemented sands or gravels. 2. Soft rocks, dense sands and gravels or extremely hard clays, hardpan and similar soils. In the second case the piles will act in a combination of end bearing and friction in the founding stratum and the required penetration will be greater than that for the first case where penetration is dependent on the hardness of the rock and on any weathering of its upper surface.

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BEARING PILES Non End-Bearing Steel H Piles The following tables give some typical sizes and working loads for piles founded in: 1. Sands and gravel of medium to loose density. 2. Hard and stiff clays. The working loads given in the table are only an indication of bearing capacity in the above conditions. Reference should be made to the Steel Construction Institute publication ‘Steel Bearing Piles Guide: 1997’ in determining actual load bearing capacities of piles. Typical Working Loads

Pile Size mm x mm x kg/ m

Typical range of working loads per pile kN

356x368x109

(1140) (1040) 990

840

-

-

-

-

305x305x95

-

(990)

(890)

(790)

-

-

-

-

305x305x79

-

-

-

(820)

(720)

(620)

(520)

-

254x254x63

-

-

-

-

-

(650)

(550)

450

Note: Loads are for mild steel to BS EN 10025 Grade S275 The highest loads correspond approximately to the maximum load per pile given in this table. Selection of pile size for a given working load depends on the actual soil properties and is subject to driving and test loading of a trial pile. The highest loads in brackets may result in excessive penetrations into the founding stratum, depending on its properties, and may not necessarily result in the most economical solution.

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BEARING PILES Allowable Stress in Axial Compression for Piles Projecting Above Soil Level When a pile projects above soil level, as in a jetty or pier, the upper portion should be designed as a column. The table below gives permissible stress values for bearing piles subject to purely axial compression. If bending forces are to be resisted also, it will be necessary to check that the pile section selected is adequate to meet the requirements of BS 449 for members subject to combined axial compression and bending and that the combined stress does not exceed 0.5 x Yield Stress - see BS 8004. The effective length is based on a length ‘L’ which is defined as follows: 1. Where soft soils occur immediately below bed level, ‘L’ is the distance between the point of connection with the deck (or bracing if any) and a point which is located at half the depth of the soft stratum or three metres down from bed level whichever is the lesser. Liquid mud should be considered as being equivalent to water. 2. Where firm soils occur immediately below bed level, ‘L’ is the distance between the point of connection with the deck (or bracing, if any) and a point located at bed level. Hence, if the top of the pile is fixed in position in the orientation being considered but is not effectively fixed in direction, the effective length is ‘L’. If however, the pile is also fixed in direction in this situation the effective length should be taken as 0.75 x L. If the top of the pile is fixed in direction but not in position the effective length is L. For partial fixity in this situation the effective length should be taken as 1.5 x L. When the top of the pile is neither fixed in position, nor in direction in the orientation being examined, the effective length is 2 x L. Permissable Stress Values

Slenderness ratio I/r

Grade S275 (mild steel) N/ mm²

Grade S355 (high yield stress steel) N/mm²

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90

-

-

95

-

100

100

-

92

105

74

85

110

69

78

120

60

67

130

52

58

140

46

50

150

40

44

160

36

39

170

32

35

180

29

31

Note: l = effective length as defined above; r = appropriate radius of gyration. Where no stress is given, maximum working stress of 0.3 x minimum yield stress controls. It is emphasised that the stresses given are for axial loading only.



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Sample Specification - Corus Piling Handbook

SAMPLE SPECIFICATION Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Introduction General Quality Tolerances of LX and Larssen SSP Tolerances of Frodingham SSP Coating Protection Method Statement Handling Pitching & Driving Driving Tolerances Driving Records Cutting and Welding Walings and Tie Rods

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SAMPLE SPECIFICATION Introduction No specific mention is made in this chapter of Safety Standards, Health and Safety Legislation, C.O.S.H.H., C.D.M. etc as it is assumed that they would form the key part of any specification, without further duplication. This chapter is intended to encompass some of the main points commonly used in specifications for today’s contracts. Hence it cannot be job specific nor does it attempt to go into any great depth on any particular point.

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SAMPLE SPECIFICATION General Either: The Steel Sheet Piles shall be LX, Larssen or Frodingham, as produced by Corus or similar approved in new condition and shall be of the sections, numbers and lengths specified on the drawings complete with all necessary corners, junctions and special piles as indicated. Or: The Steel Sheet Piles shall be LX, Larssen or Frodingham, in new condition and shall have a minimum theoretical combined section modulus of..... cm³ /m run and a theoretical mass of..... kg/m³. The corners, junctions and special piles indicated on the working drawings shall be fabricated at the Sheet Pile Manufacturers premises under workshop conditions or similar approved facility with quality assurance systems operative. All such work shall comply (within the tolerances) to the standard dimensions quoted by the manufacturer, or for non standard fabrications to the approval of the Engineer. If during the course of the works a requirement for extra fabricated piles occurs, the contractor shall submit to the Engineer for approval, the proposed type and method of manufacture. Piles of the same steel grade and section size as the neighbouring plain piles shall be used, unless otherwise approved. All materials shall comply with the appropriate British Standards.

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SAMPLE SPECIFICATION Quality The quality of steel shall conform to : Either: (If Mild Steel is required) - EN 10248:1995 Grade S27OGP - BS EN 10025:1993 Grade S275 - BS EN 10025:1990 Grade Fe 430A - BS 4360:1990 Grade 43A - BS 4360:1986 Grade 43A Or: (If High Yield Steel is required) - EN 10248:1995 Grade S355GP - BS EN 10025:1993 Grade S355 - BS EN 10025:1990 Grade Fe 51OA - BS 4360:1990 Grade 50B - BS 4360:1986 Grade 50A The following clauses may be included if required: Either: The Steel shall contain 0.20% to 0.35% Copper. Or: The Steel shall contain over 0.35% to 0.50% Copper.

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SAMPLE SPECIFICATION Tolerances of LX and Larssen Steel Sheet Piling

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SAMPLE SPECIFICATION Tolerances of Frodingham Steel Sheet Piling

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SAMPLE SPECIFICATION Coating Protection Steel sheet pile coating protection, when required, shall receive the following surface preparation and take one of the following forms: Either: Light shot blast then application of Tar Vinyl (an aromatic pitch modified with suitable vinyl resins) in coat thicknesses of up to 150 microns. [Corus designation PC1] Or: Blast clean to ISO 8501-1, grade 2, then application of High-Build Isocyanate cured, Epoxy Pitch (special coal tar pitch, modified with epoxy resins, cured with isocyanate adducts) in coat thicknesses of up to 400 microns. [Corus designation PC2] Or: Similar approved. Due care and attention shall be given to the offloading, storing and installation of protected piles to prevent damage to coatings (see section 'Handling') Any remedial work to coatings shall be carried out in accordance with the manufacturer’s recommendations and to the satisfaction of the Engineer.

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SAMPLE SPECIFICATION Handling All piles shall be stacked in accordance with the manufacturer’s recommendations. The contractor shall ensure that operations involving loading, transporting, offloading, handling, stacking and pitching the piles, are carried out in such a manner as to prevent damage to the piles or their coating. Any damage that does occur shall be drawn to the attention of the Engineer and the contractor shall submit his proposals for remedial works for approval prior to commencement. The making good/replacement measures shall be carried out by the contractor at his own expense. The Engineer’s approval of the completed remedial measures will be required before inclusion into the structure can take place. Holes shall not be burnt/drilled nor lifting brackets welded to the sheet piles without the prior approval of the Engineer. All such modification shall be made good after use. Wherever possible the same pile sections, lengths and steel grades shall be stored in separate stacks clearly marked/colour coded to avoid errors in placement.

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SAMPLE SPECIFICATION Method Statement Before the commencement of any piling works, the contractor shall submit (allowing sufficient time for consideration) to the Engineer for approval a Safety Policy and a Method Statement which shall include the following information: ●

●

●

●

●

●

●

●

Program of the works detailing sequence and timing of individual portions of the works. Maximum proposed lead at any stage of driving between a pile and its neighbour and the limitations of same if hard driving is encountered. The height, spacing, stability and type of piling guidance system and the number of piles in each panel if applicable. Full details of installation plant to be utilised including manufacturers information, proof of servicing/recent upkeep and assessment of actual input energy to the piles and a definition of driving refusal for each type of plant proposed. Proposed phasing of excavation/filling operations such that designed stresses in the piles and frames/supports are not exceeded. Contingency plan in the event of encountering obstructions or reaching driving refusal to minimise disruption/delay especially when using pitch and drive methods. Acceptable noise levels agreed with the Local Authority are XXXX dB(a) between the hours of XXXX and XXXX etc, and the contractor shall submit details of the envisaged noise production and his intended method of complying with the aforementioned limits. Acceptable vibration levels are XXXX mm/sec measured at a distance of XXXX from the source of the vibration. The contractor shall submit details of the estimated vibration levels created by the works and his envisaged method of complying with the aforementioned limits.

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SAMPLE SPECIFICATION Pitching & Driving The selection of the driving and extracting plant shall be made having due regard to the ground conditions and pile type. The Engineer shall be notified of the contractor’s intention to pitch and drive piles at least 24 hours prior to commencement of the installation works. Prior to interlocking sheet piles the contractor shall ensure that the locks are undamaged clean and free from deleterious materials. Pitch and drive techniques shall be permitted if the following criteria are met: ●

●

●

The rig has sufficient height to adequately support the entire pile during driving. The driving will be relatively easy, without hard bands or obstructions which would dictate the requirement for full support afforded by panel driving techniques. The contractor can satisfy the Engineer that the sheet pile structure can be built to conform with the specified tolerances for verticality and alignment.

In all cases the piles shall be guided and held in position during pitching and driving. All piles shall be fully interlocked without exception. Overlapping of piles will not be accepted as a substitute for interlocking piles. Taper piles shall not be introduced to correct piles which have developed a lean, unless the approval of the Engineer is first obtained. Piles which reach refusal before achieving the design penetration shall not be cut off without the approval of the Engineer. In difficult driving conditions a lead in excess of XXXX m shall not be allowed to develop between the toe level of the pile being driven and the level of its neighbouring pile. [Note: the following two paragraphs, shown in italics, should only be added to the contract specification at the Engineer's discretion.] For guidance, where 15m piles are being driven in difficult driving conditions (where panel driving would be dictated), the typical leads that may be permitted for each successive drive may be 5m, 4m, 3m, 2m with the final drive having no more than 1m lead. The contractor shall do all within his power/experience to avoid driving damage or declutching. The Engineer shall be notified immediately if any of these occur.

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Percussive piling hammers shall be either freely suspended in which case they will have suitable leg guides/inserts in sound working order, or leader mounted in which case the leader must be of suitable rigidity and strength to keep the hammer stable during driving and moving operations. In all cases the hammer shall be held in position over the pile such that each blow is directed axially down the centreline of the pile/pair. (When driving high modulus units the centreline of the hammer blow shall be positioned as close to the centreline of the combined unit or between that position and the centreline of the beam unit). The anvil block shall be of sufficient plan area to cover at least 90% of the pile or piles being driven and of sufficient thickness to adequately transfer the heaviest hammer blow evenly to the pile heads. The anvil shall be flat and level, without substantial wear such that the blow is transferred axially and distributed evenly over the pile head. Where sheet piles are driven to a set to indicate vertical load carrying capacity this shall always be calibrated by maintained load testing on a representative sample of the piles. The set shall be recorded with a hammer of well defined input energy such as a gravity drop hammer or an hydraulic drop hammer. Where it is unavoidable to use hammers of less certain input energy, ie air hammers and diesel hammers, then the maximum losses must be used in the set calculation ie assuming approximately 30% hammer efficiency.

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SAMPLE SPECIFICATION Driving Tolerances The following tolerances are suitable for general site practice for permanent structures. However more lenient limits may be applied if difficult driving conditions are encountered eg obstructions or the works are only temporary: ● ● ●

Deviation perpendicular to theoretical line +/- 50mm. Deviation of verticality normal to and along the line of the piles, 1 in 100. Top of finished pile level +/- 20mm. Deviation from these tolerances will not be acceptable without written agreement from the Engineer. Forcible correction will not be permitted. The above tolerances are included for guidance purposes only and should be altered depending on site specific requirements

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SAMPLE SPECIFICATION Driving Records The contractor shall keep complete and accurate piling records. Two signed copies of these records shall be submitted to the Engineer not more than 48 hours from the date of the works detailed therein. The pile records shall always be submitted with sufficient time for the Engineer’s approval prior to the piles becoming inaccessibledue to further operations. The records shall contain the following information: ●

● ● ● ●

●

●

●

Pile reference number (correlated to previously accepted works General Arrangement drawing showing each pile position and reference). Pile type and steel grade. Pile length. Commencing surface level and final toe level. Depth driven, type of construction plant and times and dates when piles were driven. Where required the number of blows to drive each 250mm over the last 2.5m shall be recorded. Comments regarding unusual/ unexpected driving conditions (both harder, eg obstructions, or easier, eg increased penetration rates) should be included. Where changes in the pile length have occurred due to lengthening or cutting, all relevant information including offcut length or extension length, reason for change and on what authority the change was made shall be included.

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SAMPLE SPECIFICATION Cutting and Welding No cutting or welding of piles shall be carried out without prior written approval from the Engineer. All such cutting shall be carried out by means of Oxyacetylene, Oxypropane or other approved method. The remaining pile shall be of clean and even appearance with grinding tools being employed to remove splatter. Cut offs shall be marked so that it is clear from which pile they came and after agreement from the Engineer will be disposed of in the pre agreed manner. Cutting must be carried out in such a way as to prevent damage or distortion to adjacent piles. The finished level of the cut pile shall be within 20mm of the theoretical level. When it is necessary to form holes in the sheet piles, they shall be drilled or burnt using a template, and subsequently dressed flush. The hole size shall be of sufficient clearance and will include allowance for bolt/tie coatings and inclination if not horizontal. All holes not required in the finished works which are not sealed in the pile cap or other such detail, shall be sealed by welding a plate of the same grade, of thickness not less than the pan thickness to the pile. The minimum plate overlap shall be 40mm and the minimum continuous fillet weld size shall be 6mm. All holes shall be within a positional tolerance of +/-10mm. Holes formed as weep holes to avoid water build up behind the wall shall comply with the above details. Only welders who are qualified to the standard set out in the current Code of Practice/British Standard and have a proven record over the previous six months, or who have attained a similar standard, shall be employed on the works. Proof of welder proficiency shall be made available to the Engineer on request. For manual metal arc and semi-automatic welding of carbon and carbon manganese steels, welding of piles and steel framework shall be carried out in accordance with BS 5135, the standard being Quality Category D in accordance with Appendix H, tables 18 and 19. Defective welds shall be cut out and replaced. Where steel sheet piles are to be spliced by butt welding, the interlocks shall not be welded unless a sealing weld is required. Butt welding should only be carried out if the component ends have been matched together to ensure best possible fit.

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SAMPLE SPECIFICATION Walings and Tie Rods Walings shall be secured to each pair of piles with anchor bolts, washers and bearing plates. All splices, if welded or bolted, shall be at the fifth spacing between tie rods and splices in walings and shall be staggered by a minimum distance of 5m. No welding of the tie rods shall be permitted. Tie rods will not be used for earthing purposes and will be protected against welding splash. Tie rods shall be assembled with necessary taper washers, washers and bearing plates in accordance with the manufacturer’s recommendations. During installation of the tie rods precautions shall be taken to avoid the following: ● ● ●

Deflection of the tie. Local bending of tie rod on waling. Damage to the tie or its protective coating. Tensioning of ties will be by means of a turnbuckle only and the phasing of the tensioning will be agreed with the Engineer in advance. Care shall be taken to avoid damage to the tie rods during subsequent operations such as backfilling and the contractors proposed procedure to accomplish this shall be submitted to the Engineer for approval. Where settlement is expected to occur the ties should be placed inside a tube such that the tube will settle with the ground but the tie will remain in the correct position

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Formulae and Tables - Corus Piling Handbook

FORMULAE & TABLES Contents 1. 2. 3. 4. 5. 6. 7. 8. 9.

The Metric System Miscellaneous Conversion Factors and Constants Natural Trigonometrical Functions Bending Moments in Beams Properties of Sections Mensuration of Plane Surfaces Mensuration of Solids Equivalent of Metres in Feet Equivalent of Feet in Metres

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FORMULAE & TABLES The Metric System Linear Measure

1 inch

= 25.4mm

1mm

= 0.03937 inch

1 foot

= 0.3048

1cm

= 0.3937 inch

1 yard

= 0.9144m

1m

= 3.2808 feet or 1.0936 yds

1 mile

= 1.6093km

1km

= 0.6214 mile

Square Measure

1 sq inch

= 645.16mm²

1 cm²

= 0.155 sq in

1 sq foot

= 0.0929m²

1 m²

= 10.7639 sq. ft or 1.196 sq yds

1 sq yard

= 0.8361m²

1 hectare

= 2.4711 acres

1 acre

= 0.4047 hectare

1 sq mile

= 259 hectares 1 hectare = 10,000m²

1 km²

= 247.105 acres

1 cubic inch = 16.387cm³

1 mm³

= 0.000061 cubic inch

1 cubic foot

1 m³

= 35.3147 cubic ft or 1.308 cubic yds.

Cubic Measurement

= 0.0283m³

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1 cubic yard = 0.7646m³

Measure of Capacity

1 pint

= 0.568 litre

1 gallon

= 4.546 litres

1 litre

= 1.7598 pints or 0.22 gallon

Weight

1 oz

= 28.35kg

1g

= 0.0353 oz

1 pound

= 0.4536kg

1 kg

= 2.2046 lb

1 ton

= 1.016 tonnes or 1016kg

1 tonne

= 0.9842 ton

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FORMULAE & TABLES Miscellaneous Conversion Factors and Constants Section Modulus

1 inch³

= 16.39cm³

1 inch³ per foot of wall

= 53.7cm³ per m of wall

1.86 inch³ per foot of wall

= 100cm³ per m of wall

Moment of Inertia

1 inch4

= 41.62cm4

1 lb (f)

= 4.449N

1 pound per linear foot

= 1.4881 kg per linear m

1 pound per square foot

= 4.883kg per m²

0.205 pound per square foot

= 1kg per m²

1 ton (f) per linear foot

= 32.69kN per linear m

1000 pound (f) per square foot

= 47.882kN per m²

1 ton (f) per square inch

= 15.444N per mm²

1 ton (f) per square foot

= 107.25kN per m²

100 pound per cubic foot

= 1602kg per m³

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100 pound (f) per cubic foot

= 15.7kN per m³

1 ton (f) foot Bending Moment per foot of wall

= 10kNm Bending Moment per metre of wall

1m head of fresh water

= 1kg per cm²

1m head of sea water

= 1.025kg per cm²

1m³ of fresh water

= 1000kg

1m³ of sea water

= 1025kg

1 radian

= 57.3 degrees

Young’s Modulus, steel

= 210kN/mm²

100 microns

= 0.1mm = 0.004 inch

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FORMULAE & TABLES Natural Trigonometrical Functions

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FORMULAE & TABLES Bending Moments in Beams

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FORMULAE & TABLES Properties of Sections

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FORMULAE & TABLES Mensuration of Plane Surfaces

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FORMULAE & TABLES Mensuration of Solids

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FORMULAE & TABLES Equivalent of Metres in Feet

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FORMULAE & TABLES Equivalent of Feet in Metres

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References - Corus Piling Handbook

REFERENCES References BS 449: Part 2: 1969

Metric Units. BS 639: 1986

Specification for Covered Carbon and Carbon Manganese Steel Electrodes for Manual Metal-Arc Welding. BS 3580: 1964 (1985)

Guide to Design Considerations on the Strength of Screw Threads. BS 3643

ISO Metric Screw Threads. BS 4360: 1986 + 1990

Specification for Weldable Structural Steels. BS 5135: 1984

Specification for Arc Welding of Carbon and Carbon Manganese Steels. BS 5228

Noise Control on Construction and Open Sites. BS 5228: Part 4: 1992

Code of Practice for Noise and Vibration Control applicable to Piling Operations. BS 5268: Part 2: 1991

Structural use of Timber. BS 5400: Part 3: 1982

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Code of Practice for Design of Steel Bridges. BS 5930: 1981

Code of Practice for Site Investigations. BS 6349

Maritime Structures. BS 8002: 1994

Code of Practice for Earth Retaining Structures. BS 8004: 1986

Code of Practice for Foundations. BS 8081: 1989

Code of Practice for Ground Anchorages. BS EN 10025: 1993

Hot Rolled Products of Non-Alloy Structural Steels. Technical Delivery Conditions. BS EN 10210: 1995 BS EN 10248: 1996 Parts 1 & 2

Hot rolled Sheet Piling of Non-alloy Steels. British Standards Institution. Bell A L

Earth Pressures. Proceedings of the Institution of Civil Engineers. Vol. 199. 1915 Bond A J

ReWaRD User Manual 1st Edition 1992 BS Publication

Accelerated Low Water Corrosion of Steel Sheet Piles. file:///C|/Documents%20and%20Settings/bantinone/My%20Documents/My%20Webs/myweb19/References/index.htm (2 of 5)5/26/2005 4:01:04 AM


BS Publication

Splice Welds in Steel Piles. Burland J B, Potts D M & Walsh N M (1981)

The Overall Stability of Free & Propped Cantilever Retaining Walls, Ground Engineering, 14 (5), 28 - 38. Caquot A & Kerisel J (1948)

Tables for the Calculation of Passive Pressure, Active Pressure and Bearing Capacity of Foundations, Gauthier - Villars, Paris. Clough W G & O’Rourke T D (1990)

Construction Induced Movements of Insitu Walls, Proc. Speciality conf. on Design & Performance of Earth Retaining Structures, Cornell, ASCE, Geotechnical Special Publication No. 25, Lambe P C & Hansen L A (eds), 439-470. Clough W G, Smith E M & Sweeney B P (1989)

Movement Control of Excavation Support Systems by Interactive Design, Proc. ASCE Found. Engng., Current Principles & Practices, Vol. 2, 869-884. Code of Practice No. 2 (1951)

Earth Retaining Structures, Institution of Structural Engineers, London. Day R A & Potts D M (1989)

A Comparison of Design Methods for Propped Sheet Pile Walls, Steel Construction Institute (Publication 077). Eurocode 1: EN1991

Basis of Design & Actions on Structures. Eurocode 3: EN1993

Part 5 Piling. Eurocode 7: EN1997 file:///C|/Documents%20and%20Settings/bantinone/My%20Documents/My%20Webs/myweb19/References/index.htm (3 of 5)5/26/2005 4:01:04 AM


Geotechnical Design. Federation of Piling Specialists

Specification for Steel Sheet Piling. ICE Specification (1988)

Institution of Civil Engineers, Specification for Piling. Nyaoro DL (1982)

Analysis of Soil-Structure Integration by Finite Elements. Padfield C J & Mair R J (1994)

Design of Retaining Walls Embedded in Stiff Clay, Report 104, Construction Industry Research & Information Association, London 146pp. Peck R B, Hanson W E & Thornburn T H (1974)

Foundation Engineering, John Wiley, New York. Pile Buck (1987)

Steel Sheet Piling Design Manual . Pile Buck Inc. Potts D M & Burland J B (1983)

A Parametric Study of the Stability of Embedded Earth Retaining Structures, Transport & Road Research Laboratory, Supplementary Report SR 813. Potts D M & Fourie A B (1985)

The Effect of Wall Stiffness in the Behaviour of a Propped Retaining Wall, Geotechnique Vol. 35, No. 3, 347-352. Rowe P W (1952)

Anchored Sheet Pile Walls, Proc. Institution of Civil Engineers, Vol. 1. No. 1, 27-20. Steel Construction Institute (1997)



Steel Bearing Pile Guide. Steel Construction Institute (1997)

Integral Steel Bridges Design Guide. Tamaro G J & Gould J P (1982)

Analysis & Design of Cast-in-Situ Walls (diaphragm walls), Proc. Conf. on Retaining Structures, Cambridge, ICE, Thomas Telford, London (in press). Technical European Sheet Piling Association of Steel Sheet Piles. Timoshenko/Rourke

Concrete Walings. Tomlinson M J (1980)

Foundation Design & Construction, 4th Edition, Pitman, London, 793pp. Williams B P & Waite D

The Design & Construction of Sheet Piled Cofferdams, Special Publication 95, Construction Industry Research & Information Association.

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