Lecture 2 - SI Interpretation

INTERPRETATION OF LABORATORY AND FIELD TEST RESULTS FOR DESIGN by Ir. Dr. Gue See Sew & Ir. Chow Chee Meng http://www.gnpgroup.com.my

G&P Geotechnics Sdn Bhd

CONTENTS 1. INTRODUCTION 2. OBJECTIVES 3. SCOPE 4. INTERPRETATION JKR PROBE SPT

5. DESIGN PARAMETERS 6. LABORATORY TESTS G&P Geotechnics Sdn Bhd

INTRODUCTION NEED Neglected topic; only briefly covered in universities Danger of using results directly without interpretation Decision on choice of values for soil parameters

SCOPE Common tests only

PROCESSES Specifications, Supervision, Presentation & Interpretation G&P Geotechnics Sdn Bhd



Proton Iswara

Ferrari G&P Geotechnics Sdn Bhd

OBJECTIVES 1) Illustrate the importance of interpretation 2) Show methods of compiling results and recognising errors


SCOPE Common field and laboratory tests

FIELD TESTS JKR/ Mackintosh probe SPT (Standard Penetration Test) Piezocone Field Vane Shear Geonor vane

LABORATORY TESTS Unconfined compression Triaxial Test (UU, CIU with pore pressure measurement & CD) Consolidation G&P Geotechnics Sdn Bhd


JKR Probes Primitive tool Limited use Shallow bedrock profile (limestone with slump zone) Weak zone at shallow depth Shallow foundation • No recent fill and future settlement • Structure of low risk • If in doubt – use borehole


• Apparatus Cased hardened steel pointer of 25mm dia. and 60o cone. 22mm outer dia. coupling

Prevent buckling during driving

28

12mm dia. HY 55C steel rod


5kg drop hammer

CONE PENETROMETER


For practical application: - Results of JKR Probe and Mackintosh Probe can be taken as equivalent - JKR Probe created as equivalent to Mackintosh Probe as Mackintosh Probe is patented in the early days


• Termination criteria 9Blows/300mm (maximum 400 blows/300mm)

9Max 15m depth

• Precautionary measures 9Free fall and consistent drop height 9Components and apparatus properly washed and oiled


• Typical test results


• Applications

Identifying localised soft/weak or slip plane. G&P Geotechnics Sdn Bhd

• Applications

Identifying localised soft/weak or slip plane. G&P Geotechnics Sdn Bhd

T T

T = compaction lift

Identifying non-compliance fill. G&P Geotechnics Sdn Bhd


Allowable Bearing Capacity V.S. J.K.R. Dynamic Cone Penetration Resistance (After Ooi & Ting, 1975) ** Conditions applied G&P Geotechnics Sdn Bhd

• Comparison between JKR probe and SPT


Depth (m)

0

100

JKR Blows 200

300

400

0

0

4

4

8

8

12

12

JKR Plot SPT'N' Plot 0

10

20

SPT'N' G&P Geotechnics Sdn Bhd

30

40

50

0

100

JKR Blows 200

300

400

0

0

2

2

Depth (m)

4

4

6

6

8

8

10

10

12

12

JKR Plot

14

14

SPT'N' Plot 16

16 0

10

20

SPT'N' G&P Geotechnics Sdn Bhd

30

40

Depth From Ground Surface In Meter (m)

Number of Blows per 300 mm


Depth From Ground Surface In Meter

Shear Strength In kPa


• Limitations Shallow depth Not for gravelly ground Human errors (e.g. wrong counting, non-consistent drop height, exerting force to the drop hammer

Misleading results at greater depth G&P Geotechnics Sdn Bhd

Standard Penetration Test (SPT) A popular test useful for pile foundation design

Common errors


AW Rod

63.5kg Hammer

760mm Free Fall

450mm

Split-Spoon Sampler G&P Geotechnics Sdn Bhd

Split-Spoon Sampler Driving Shoe

Split Barrel • OD = 50mm • ID = 35mm • Length ~ 650mm G&P Geotechnics Sdn Bhd

SPT-N Value

Seating drive


Test drive

5 - 10 - 30 - 20/30cm Seating drive

Test drive

(30 + 20) SPT-N = x 300 = 143 (75 + 30)


Soil ‘Soft rock’

Maximum blows to be applied In seating drive In test drive 25 50 25 100

BS1377: Part 9




Formation Level

CLAY

SAND

SILTY CLAY



Reduced Level (ft) G&P Geotechnics Sdn Bhd


New Technology


…automatic

Piezocone (CPTu) 1)To obtain soil profile and stiffness (strength) profile of the subsoil 2) To determine coefficient of consolidation of soil 3) Results can also be used directly for design (e.g. pile design)


Piezocone Results


Piezocone Results


Nk = 11-19 Lunne & Kleven (1981)

Nkt = 15 Gue & Tan (2000) G&P Geotechnics Sdn Bhd


Cone factors related to plasticity index of the clays (After Dobie & Wong, 1990) G&P Geotechnics Sdn Bhd

Soil Behaviour Type Classification Charts for CPT (after Robertson, 1990)

1. 2. 3. 4. 5. 6. 7. 8. 9.

Sensitive, fine grained Organic soils – peats Clays – clay to silty clay Silt mixtures – clayey silt to silty clay Sand mixtures – silty sand to sandy silt Sands – clean sand to silty sand Gravelly sand to sand Very stiff sand to clayey sand (heavily overconsolidated or cemented) Very stiff fine grained (heavily overconsolidated or cemented)




Vane Shear Test 1)Vane test in borehole 2) Geonor vane 3) Lab vane Use - To determine in-situ undrained shear strength (Suv) of soft clayey soils G&P Geotechnics Sdn Bhd


Most common errors - Computation – spring factor - Clay with organic materials Recognise errors Summarise results with Su from unconfined compression, UU and lab vane superimposed Plot Suv against PI Po’ Or Suv against Po’ then find Suv Po’ G&P Geotechnics Sdn Bhd



Depth (ft)

Shear Strength (lb/ft2) G&P Geotechnics Sdn Bhd


Design Parameters Foundation Design • Stability / Bearing Capacity • Settlement Prediction

Bearing Capacity • Su • C’ and Φ’

Settlement Prediction • e vs Log10 p’ (mv, Cc) • cv (k) G&P Geotechnics Sdn Bhd


LABORATORY TESTS - Why? - Types of Tests! - How? - Specifications? (Load, Pressure, Time)


SPECIFICATIONS A) Consolidation Test 1) Which samples are appropriate and suitable for the test? 2) For consolidation test - Load increment } 0.5P ’ – 8P ’ o o } or to - Pressure } e ~~ 0.42eo

B) Triaxial test 1) For triaxial tests - Strain rate - Back pressure

Ref: Head, K. H (1984) - Manual of soil Laboratory testing


Special Attention Triaxial Compression Test -

No/Minimum Trimming

-

No Side Drains

-

No Multistage


G&P-Form6 (Rev3)

G&P GEOTECHNICS SDN. BHD. (Geotechnical Consultants) LABORATORY TEST SCHEDULE Project No : ………………………………..

Lab. Schedule No. ………………..

Project : ……………………………………………………………………………………..…………………

BOREHOLE

SAMPLE NO.

TOT AL

Requested

DEPTH m

M/C

A.L.

B.D.

S.G.

Direct Shear Box

SIEVE ANALYSIS Mech.

Hydro.

Requested by : ……………………………………………

Date : …………………..

Reviewed by : …………………………………………...

Date : ……………………

CONSOLIDATION Std.

Rapid

S.S.

TRIAXIAL CIU

UU

CHEMICAL ANALYSIS UCT

OR GANIC CONTENT

PH

SULPH ATE CONTENT

CHLORIDE CONT ENT

Performed Note : 1) CIU

-

Isotropic Consolidated Undrained Triaxial Test with pore pressure measurements Use 70mm diameter sample (i.e. untrimmed Mazier sample) Sample should not have side filter during consolidation Shearing strain should be calculated using Cv values calculated during consolidation stage. Multi-stage testing not allowed P-Q Stress Path Plotting shall be submitted. 2) For CIU Tests, stress path and other relevant data shall be submitted in Hard Copy (Plots and Tabulated Data) and Soft Copy (Computer files data). Cell confining pressure of 0.5 σv , 1.0σ v , 2.0σv shall be adopted for the CIU test, where σ v is the total vertical in-situ stress. 3) UU Unconsolidated Undrained Test (at total overburden pressure of the sample) 4) UCT Unconfined Compression Test (untrimmed sample)

5) To determine Cv from Consolidation Tests :Use Square-Root Time Method to determine d0. Then use Log-Time Method to determine d100 6) Direct shear box test - Three (3) reconstituted specimens (60mm x 60mm x 20mm thick) shall be used. - Applied normal stress pressure of 0.5 σ v, 1.0σ v , 2.0σv shall be adopted for the shear box test, where σv is the total vertical in-situ stress. 7) All specimens for triaxial or consolidation tests shall be obtained from center of the recovered samples in UD sampler. 8) 2 moisture content tests shall be carried out on soil immediately besides the specimens retained for triaxial or consolidation tests. 9) Bulk density, particle size distribution and Atterberg Limit tests shall be carried out on every specimen after the triaxial or consolidation tests.



Consolidation Settlement

CONSOLIDATION TEST RESULTS

Void Ratio

Cv m²/year Coefficient of Volume Change Mv X 10ˉ³ m² / KN


Depth (m)

Compression Index G&P Geotechnics Sdn Bhd

Depth (m)

Coefficient of Consolidation, Ch m²/yr



NAVFA C DM7.1


Root time method Log time method


Compression index, Cc and Recompression index, Cr a) Cc = 0.009 (LL – 10%)

For inorganic soils, with sensitivity less than 4

b) Cc = 0.007 (LL – 10%)

For normally consolidated clay

c) Cc = 0.0115 Wn

For organic soils, peat

d) Cc = 1.15 (eo – 0.35)

For all clays

e) Cc = (1 + eo) [0.1 + (Wn – 25)0.006]

For varved clays

f) Cc = 0.5*PI*Gs

For OC clays

Compression index, Cc and Recompression index, Cr • For inorganic normally -consolidated Klang Clay (Tan et al., 2004): – Cc = 0.02LL – 0.87 – Cc = 0.61eo – 0.17 – Cc = 0.02 Wn – 0.37

• Cr ≈ (0.1 to 0.2)*Cc

Coefficient of secondary compression, Cα •

Cα / Cc = 0.04 ± 0.01

For inorganic soft clays

•

Cα / Cc = 0.02 ± 0.01

For granular soils including rockfill

•

Cα / Cc = 0.03 ± 0.01

For shale and mudstone

•

Cα / Cc = 0.05 ± 0.01

For organic clays and silts

•

Cα / Cc = 0.06 ± 0.01

For peat and muskeg

Interpretation of Laboratory Tests TWO Major Categories : (1) Strength Parameters : - Stability Analyses of Slopes & Embankment. -

Bearing Capacity Analyses for Foundation.

(2) Stiffness & Deformation Parameters : Prediction & evaluation of :Settlement, Heave, Lateral deformation, Volume Change. G&P Geotechnics Sdn Bhd


Conventional Foundation for Low Rise Buildings


Conventional Foundation for Low Rise Buildings (Soil Settlement)


Settling Platform Detached from Building

Settlement

Exposed Pile G&P Geotechnics Sdn Bhd

Strength Parameters TWO Conditions : (A) Total Stress : - For Short Term Conditions in Cohesive Soils. -

Little of no drainage.

(B) Effective Stress : -

For Long Term & Permanent Conditions.

-

Fully “Drained” Conditions.


Simple Check

qallow = (Nc.su / FOS) qallow = =

allowable bearing pressure (γfill.H + 10) ( in kPa)

Nc

5

e.g. : When

=

Hfailure = (5 x Su) / γfill Su = 10 kPa ; γfill = 18 kN/m3 Hfailure = (5 x 10)/ 18 = 2.8 m


Excavation: Check Depth of Excavation


Clough et al. (1989)

Total Stress Strength, su Undrained Shear Strength, su from :

(i)

Unconfined Compression Test, UCT

(ii)

Unconsolidated Undrained Triaxial Test, UU

(iii) Laboratory Vane Shear Test







Typical Set-up of Triaxial Test

a)Base b)Removable cylinder and top cap c)Loading ram d)Rubber membrane

Equipment for Triaxial Test

Effective Stress Strength Parameters c’ &

(i) (ii)

φ’ Æ Interpretation from

Isotropic Consolidated Undrained Triaxial Test,

CIU + ΔU

Isotropic Consolidated Drained Triaxial Test,

CID

(iii) Laboratory Shear Box Test (at v. slow rate)

Note : Advantage to use Stress Path G&P Geotechnics Sdn Bhd

MohrCoulomb


Stress Path Interpretation

Two types of Plot

(i)

MIT Stress Path Plot

The vertical axis :

t = (σ1 - σ3)/2

(T.W. Lambe of MIT, 1967)

= (σ’1 - σ’3)/2

The horizontal axis :

s = (σ1 + σ3)/2

s’ = (σ’1 + σ’3)/2

&

(ii) Cambridge Stress Path Plot

(Roscoe, Schofield and Wroth (1958) at the Cambridge, England) The vertical axis :

q = σ1 - σ 3

= σ’1 - σ’3

The horizontal axis :

p = (σ1 + σ2 + σ3)/3 G&P Geotechnics Sdn Bhd

&

p’ = (σ’1+ σ’2+σ’3)/3

Terminology & Interpretation

MIT & Cambridge Stress Path Plot

MIT & Cambridge Stress Path Plot Tan θ = t’ / s Tan θ = Sin φ’ K = c’ Cos φ’ K C’ = Cos φ’ Tan η = q / p’ Sin φ’ = (3 η) / ( 6 + η ) r = c’ (6 Cos φ’) / (3 – Sin φ’) C’


=

r (3 – Sin φ‘) 6 Cos φ’

For Slopes & Walls Analyses Parameter c’ and φ’ shall be Interpreted from

i) Isotropically Consolidated Undrained Triaxial Test, CIU + Δu ii)Isotropically Consolidated Drained Triaxial Test, CID iii)Laboratory Shear Box Test (at very slow rate) Note: Advantage to use Stress Path G&P Geotechnics Sdn Bhd

Large Strain


Scattered CIU Results 0

50

100

150

200

250

300

350

400

450

500

500

500

450

400

350

t' = (σ1' - σ3')/2

φ’ = sin-1 m

BH1 UD2 BH2 UD1 BH2 M1 BH3 UD2 BH4 UD1 BH5 M1 BH6 M1 BH6 M2 BH9 M1 BH10 UD1 BH10 UD3

300

c’ = a / (cos φ’) 400

350

Proposed Design Line 300

c’ = 3.5 kPa, φ’ = 32º

250

Upper Bound c’ = 5 kPa, φ’ = 39º

200

450

250

m

200

1 150

150

Lower Bound c’ = 0 kPa, φ’ = 29º

100

50

100

50

a

0

0 0

50

100

150

200

250

300

s' = (σ1'+σ3')/2


350

400

450

500

Correlations for Preliminary Assessment of φ’


φ’ Values vs Plasticity Index (after Terzaghi)

Typical PI = 30% to 70% (Malaysia Soft Clay) G&P Geotechnics Sdn Bhd

Φ’ Values vs Clay Content (Skempton, 1964)


Φ’ vs % of Fines 35 30 25

Figure 3 : φ’peak versus Percentage of Fines in Residual Soils


c’ vs % of Fines

Figure 4 : c’ versus Percentage of Fines in Residual Soils


Correct Interpretation

Undrained Shear Strength • Limitations of UU Tests: – Sample disturbance – Negative pore pressures generated during removal of sample from tube

• Undrained shear strength is best

obtained from in-situ testing such as field vane, piezocone, etc.

YOU PAY FOR SOIL INVESTIGATION WHETHER YOU CARRY OUT OR NOT G&P Geotechnics Sdn Bhd




REFERENCES ASTM, (1986) Standard Test Method for Deep Quasi-static, Cone and Friction Cone Penetration Tests of Soil, D3441-86, ASTM Committee D-18 on Soil and Rock, USA

Dobie, M.J.D., & Wong, J.T.F. (1990) “Piezocone testing; Interpretation in Malaysia Alluvial Clays” Geotechnical Aspects of the North-South Expressway, PLUS & PL, Kuala Lumpur

Fleming, W.G.K. et al (1985) Piling Engineering Survey University Press, Glasgow

Head, K. H (1984) Manual of Soil Laboratory Testing

International Society for Soil Mechanics and Foundation (1988) International Reference Test Procedure, ISSMFE Technical Committee on Penetration Testing, Proposal to ISSMFE, Orlando, USA G&P Geotechnics Sdn Bhd

REFERENCES Meigh, A.C. (1987) Cone Penetration Testing: Methods and Interpretation, Construction Industry Research and Information Association, CIRIA Ground Engineering Report: In-site Testing, London

Proceedings of 1st International Symposium on Penetration Testing/ ISOPT – I/Florida, USA, 1988

Proceedings of 2nd European Symposium on Penetration Testing/ ESOPT – II/ Amsterdam/ May 1982

Robertson, P.K. and Campanella, R.G. (1988) Guidelines for using the CPT, CPTU and Marchetti DMT for Geotechnical Design, U.S. Department of Transportation, Federal Highway Administration, Office of Research and Special Studies, Report No. FHWAPA-87-023+84-24 G&P Geotechnics Sdn Bhd

REFERENCES Sanglerat, G, (1972) The Penetrometer and Soil Exploration, Elsevier Publishing Company, Amsterdam, Netherlands

Teh, C.I. and Houlsby, G.T. (1991) An Analytical Study of the Cone Penetration Test in Clay, Geotechnique, Vol. 41, No. 1, pp: 17-34

Gue, S.S. & Tan, Y.C. (2003) Current Status & Future Development of Geotechnical Engineering Practice in Malaysia, 12th ARC on Soil Mechanics & Geotechnical Engineering, Singapore Gue, S.S. & Tan, Y.C. (2006) Landslides: Abuses of the Prescriptive Method, International Conference on Slopes, Malaysia


Lecture 2 - SI Interpretation

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