10/22/2010
Case Studies of Support of Open Excavations and Distressed Retaining Walls in Malaysia Ir. Liew Shaw Shong
1
Type of Case Studies
1 : Jack-In Pipe Anchorage
2 & 3 : Excavation in Fill Ground
2
10/22/2010
Case Study 1
3
Building Boundary
Soldier Pile Wall (9 rows of JackIn Anchors)
CBP Wall
Soldier Pile Wall
(5 rows Ground Anchors)
4 (9 rows of JackIn Anchors)
10/22/2010
Case Study 1
3
Building Boundary
Soldier Pile Wall (9 rows of JackIn Anchors)
CBP Wall
Soldier Pile Wall
(5 rows Ground Anchors)
4 (9 rows of JackIn Anchors)
10/22/2010
Jack-In Anchor Installation Ground Anchors
Tunnel Construction in progress
Building
Jack-In Anchors
CBP Wall
Tunnel Construction in progress 5
GEOLOGY & SUBSOIL CONDITIONS Meta-sedimentary Kajang Kajang formation overlain by b y some alluvial deposits consisting of sandy clayey silts and fill 0
5
Layer 1 Fill (Clayey Silt)
10
) m ( h 15 t p e D 20
25
Layer 2 Clayey Silt Layer 3 Sandy Silt
Layer 4 Sandy Silt
Legend LL PL MC
6
30 16
17
18
19
20
0
Bulk Unit Weight (kN/m 3 )
10
20
30
SPT'N
40
0
20
40
60
80
0
400 00
80 000
Atterberg Limits Young Modulus (kPa) (kPa)
10/22/2010
Pull Out Tests for Instrumented Jack-In Anchor 18m VWSG - A 0.6m
1.6m VWSG - C
VWSG -B 3.0m
VWSG - C 6.0m
VWSG - D 9.0m
250
200
) N k ( d 150 a o L t u 100 O l l u P
VW SG - E
V WS G - F
12.0m
15.0m
7.6m VWSG - E
250
Jacked Anchor at Level 4
10.6m VWSG - F
Jacked Anchor at Level 7
200
) N k ( d 150 a o L t u 100 O l l u P
Pull-Out Test Test 1 ( 5 Days) 15-Jan-2002 Test 2 (14 Days) 25-Jan-2002 Test 3 (21 Days) 1-Feb-2002
50
4.6m VWSG - D
Pull-Out Test Test 1 ( 6 Days) 04-Mar-2002 Test 2 (14 Days) 12-Mar-2002 Test 3 (24 Days) 22-Mar-2002
50
0
0 0
) 2 m / N k ( e c n a t s i s e R t f a h S
10
20
0
30
10
Head Displacement (mm) ) Pipe Shaft Resistance Test 1 :A-B Test 1 :B-C Test 1 :C-D Test 1 :D-E Test 1 :E-F Test 2 :A-B Test 2 :B-C Test 2 :C-D Test 2 :D-E Test 2 :E-F Test 3 :A-B Test 3 :B-C Test 3 :C-D Test 3 :D-E Test 3 :E-F
40
80
120
20
30
Head Displacement (mm)
2 m / N k ( 40 e c n a t s i s e R 80 t f a h S
Pipe Shaft Resistance Test 1: C-D Test 1: D-E Test 1: E-F Test 2: C-D Test 2: D-E Test 2: E-F Test 3: C-D Test 3: D-E Test 3: E-F
9
120
Jack-in Anchor Load with Time 150
Loading at Jacked Anchors Level 3
140 130
Level 5 Level 7 Level 9
120 110
Level 3 - FEM Results Level 5 - FEM Results
7th layer : 22/02/2002 Load cell : 6/03/2002
Level 7 - FEM Results Level 9 - FEM Results
100 90
5th layer : 19/01/2002 Load cell : 29/01/2002
80 a 70 o 60
9th layer : 27/03/2002 Load cell : 28/03/2002
50 40
3rd layer : 5/01/2002 Load cell :12/01/2002
30 20 10 0 0
50
100
150
Time (Days)
200
250
10
300
10/22/2010
Prestressed Ground Anchor Load with Time 600 550
Load cell : 19/02/2002
500 450 400
Load cell : 20/03/2002
) N350 k ( d300 a o250 L
Load cell : 19/01/2002
Load cell : 22/02/2002
200 150
Loading at Ground Anchor Level 2 Level 3 Level 4 Level 5
100 50
Level 2 - PLAXIS Level 3 - PLAXIS Level 4 - PLAXIS Level 5 - PLAXIS
0 0
50
100
150
200
11
250
300
Time (Days)
Wall Movement Ground Anchor Wall
Jack-In Anchor Wall
Wall Movement (mm)
Wall Movement (mm) 0
10
20
30
4
1
4
3 4
7
8 8
5
9
) m12 ( h t p14 e D
F
16 18 20 22
26
30
40
50
8
1
6
8
24
20
2
6
2
6
10
10
0
0 2
0
40
Measured Wall Deflection Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage6 Stage 7 Stage 8 Stage 9 Stage 10
- Movement (Back analyses) of CBP wall for each stages
2
4
5
F
10
) m12 ( h t p14 e
3
16 18
Measured Wall Deflection Stage1 Stage2 Stage3 Stage4 Stage5 FinalStage
20 22 24 26
1
- Movement (Back analyses) 12 of CBP wall for each stages
10/22/2010
Ground Settlement behind CBP Wall 0 10 20 30 40 50 60
Jack-In Anchors Wall : dV/dH (wall) = 1.57
70 80
Ground Anchor wall : dV/dH (wall) = 3.37
90
dV : Ground Settlement Behind the Wall
Ground Settlement at
100
dH : Horizontal Wall Deflection
Jacked Anchor Wall (Measured)
110 120
Jacked Anchor Wall (FEM Results)
130 140
Ground Anchor Wall (Measured)
150
Ground Anchor Wall (FEM Results)
160 0
20
40
60
80
100
120
13
Time (Days)
BACK ANALYSES WITH FEM MODELLING
FEM Plane Strain Analysis (PLAXIS)
Hardening Soil Model
Interface Element : To model the Soil Interaction with Wall & Anchorage Elements
Temporary Wall and Jacked Anchors : Beam Element (Axial & Bending Stiffness)
Consolidate for 6 months after final excavation to model Drained Condition
14
140
10/22/2010
Typical FEM Model Beam Element (Jack-In Anchors)
Beam Element (CBP Wall and Soldier Piled Wall)
Interface Element
15
Soil Shear Strain within Jack-In Anchor Retaining System Relatively larger shear strains ranging between 0.26% and 0.38% developed along the potential slip surface
16
10/22/2010
Total Ground Displacement of Jack-In Anchor Retaining System The reinforced soil mass has more displacement at the upper portion with gradually reduced trend towards the lower portion
17
Dimensionless Ground Surface Settlement Distance from Wall / Excavation Depth 25
) 0 % ( h t p e D 0.05 n o i t a v a 0.1 c x E / t n 0.15 e m e l t t e S 0.2
20
15
10
5
0
Clough & O’Rourke (1990)
Maximum wall movement of CBP wall at final excavation is about 0.002H
18
10/22/2010
Interpreted E′ from SPT-N & Pressuremeter (PMT) Effective Young's Mudulus, E' ( kPa) 0
0.0x10
4
3.0x10
4
6.0x10
4
9.0x10
5
1.2x10
5
1.5x10
5
1.8x10
0 Legend Interpreted E' ( PMT) Interpreted E' (SPT)
5
E' After Ja cked Anchor Inclusion
10
) m ( h t 15 p e D 20
25
a) E′ for upper clayey silt = 2150 x SPT ′N b) E′ for lower sandy silt = 2600 x SPT ′N c) Back-analysed: ≈ 30% more than E′ Prestressed Ground Anchor Wall E′ Jacked Anchor Wall ≈
19
30
CONCLUSIONS FOR TYPE 1 CASE STUDY The jack-in anchor wall behaves as a semi reinforced soil wall. The mobilised shaft resistance of jacked anchor ranges from 20kPa to 30kPa. Increase in stiffness shall be considered in the design. FEM can analyze complicated interaction of the entire soil20 structure system
10/22/2010
RECOMMENDATIONS To avoid flexural effect, strain gauges shall be installed in pairs at jacked anchor section. Research on generation of excess pore water pressure & its dissipation around and along the jacked anchor shall be carried out. Locked in tensile stress under compressive injection may increase movement within reinforced earth21 mass
Case Study 2 High rise development with 5½ storey basement car park
Deep excavation: 7m-14.5m
22
10/22/2010
Plan High rise development with 5½ storey basement car park
Deep excavation: 7m-14.5m 23
Cross Section
Located at the toe of a filled slope
Soil nail stabilisation works to facilitate excavation 24
10/22/2010
TOPOGRAPHIC • Original hilly ground with natural valley & stream • Loose sandy silt overlaying a thin deposited soft compressible material at valley area
15m high filled slope
25
SUBSURFACE CONDITIONS BH-4
BH-IM4
BH-IM1
BH-SP1
BH-3
BH-2
BH-1
26
10/22/2010
SOIL NAILING DESIGN & CONSTRUCTION
6m to 12m soil nail at 1.25m c/c spacings
4V : 1H reinforced gunite facing
sufficient weepholes / subsoil drains
27
Additional Strengthening Works at the Valley Area
12m long FSP IIIA sheet pile wall 2 rows of 18m long soil nail anchorage
3 rows of subsoil drains
Permanent RC props against basement structure 28
10/22/2010
INSTRUMENTATION MONITORING
29
Lateral Ground Displacement SPT-N Value 0
5
10
15
20
25
30
35
40
45
50
5
10
15
20
25
30
35
40
45
50
0
0
-2
-2
-4
-4
-6
-6
-8
-8
-10
-10
-12
-12
-14
-14
-16
-16
) -18 m ( h -20 t p e D-22
-18 -20 -22
-24
-24
-26
-26
-28 -30 -32 -34 -36 -38
-28
Legend 20/9/2004 23/10/2004 04/11/2004 09/11/2004 24/11/2004 21/12/2004 24/01/2005 21/02/2005 22/03/2005 12/11/2005 SPT-N
IM-01
-30 Legend 09/11/2004 24/11/2004 21/12/2004 21/02/2005
10
20
30
40
50
60
70
80
90
100 110
-36
22/03/2005 12/11/2005
IM-04
SPT-N
30 0
-34
24/01/2005
-40 -10
-32
0
10
20
30
40
Ground Lateral Displacement (mm)
50
60
70
80
90
100 110
-38 -40
10/22/2010
Ground Settlement 01/08/04
10/09/04
20/10/04
29/11/04
08/01/05
17/02/05
29/03/05
08/05/05
17/06/05
10
10
0
0
-10
-10
-20
-20
-30
-30
-40 ) m -50 m ( t -60 n e m -70 e l t t e -80 S d -90 n u o r -100 G -110
-40 -50 -60
Legend SM01 SM02 SM03 SM04 SM05 SM06 SM07 SM08 SM09 SM10 SM11 SM12
-120 -130 -140
-70 -80 -90 -100 -110 -120
Sheet Pile Installation
-130 -140
Construction
-150
Post-Construction
-150
-160
-160 01/08/04
10/09/04
20/10/04
29/11/04
08/01/05
17/02/05
29/03/05
08/05/05
17/06/05
31
Date
Groundwater Table 0 1/0 8/0 4 2 0/ 09 /0 4 0 9/1 1/ 04 2 9/1 2/0 4 1 7/0 2/05 0 8/0 4/05 28 /0 5/0 5 17 /0 7/0 5 50 49 48 47 46 45 44 43 42 41 50 49 48 47 46 45 44 43 42 41 40
SP 01 ) m L R ( e l b a T r e t a w d SP n u o r G
03
Sheet Pile Installation Construction
Post-Construction 32
50 49 48 47 46 45 44 43 42 41 50 49 48 47 46 45 44 43 42 41 40
0 1/0 8/0 4 2 0/ 09 /0 4 0 9/1 1/ 04 2 9/1Date 2/0 4 1 7/0 2/05 0 8/0 4/05 28 /0 5/0 5 17 /0 7/0 5
10/22/2010
Back Analysis
• FEM plane strain analysis • Hardening soil model • Coupled consolidation undrained analysis • Initial stresses were calculated by gravity loading33
Soil Parameters Layer
Material
Ave SPT-N
γ γb
(kN/m3)
Su (kPa)
c’ (kPa)
φ’ ( ) ◦ ◦
E’ (kPa)
E’ur (kPa)
Back Analysed E’ (kN/m2)
RL57m – RL49m
Sandy Silt (Fill)
12
18.5
-
5
32
30,000
90,000
18,000
RL49m – RL43m
Sandy Silt (Fill)
9
18.5
-
5
32
22,500
67,500
16,200
RL43m – RL40m
Sandy Clay (Weak Zone)
2
18
40
0.5 (5)#
20
32,500
97,500
32,500
RL40m – RL37m
Sandy Silt
10
18.5
-
5 (10) #
32
25,000
75,000
25,000
RL37m – RL21m
Sandy Silt
20
18.5
-
5 (10) #
32
50,000
150,000
50,000
Below RL21m
Gravelly Sand
50
19.5
-
7
32
125,000
375,000
125,000
# Improved apparent cohesion adopted in FE back analysis at the last few stages.
34
10/22/2010
Lateral Ground Displacement 0
10
20
30
40
50
10
20
30
40
50
60
70
10
20
30
40
50
60
70
10
20
30
40
50
60
70
60
60 12m Soil Nail
55
55 Shotcrete
50 50
45 45 ) m40 L R ( h t p e 35 D
18m Soil Nail
40
Sheet Pile
35 30
30
Legend Legend Measured Measured Back-analysed Back-analysed
25
25
20
Stage: Progressive nailing
Stage: Completion of excavation and soil nail stabilisation
Stage: Post-installation
of sheet piles with first row of 18m soil nails
15
20
35 0
10
20
30
SPT'N'
40
50
10
20
30
40
50
60
70
10
20
30
40
50
60
70
10
20
30
40
50
60
70
Lateral Ground Displacement (mm)
INTERPRETATION
• Young’s modulus (E’) E’ = 1500 to 1800 x SPT’N’ ..for upper loose fills E’ = 2500 x SPT’N’ ..for weathered Granitic Residual subsoil
• Unloading/reloading stiffness, E’ ur = 3 x E’ 36
10/22/2010
Ground Settlement 30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
10
10
0
0
-10
-10
-20
-20
-30
-30
) m -40 m ( t n e-50 m e l t t -60 e S
-40 -50 -60
-70
Legend Back-Analysed Measured
-70
-80
Stage: Progressive nailing
-80
Stage: Post-installation of sheet piles with first row of 18m long soil nails Stage: Completion of excavation and soil nail stabilisation
-90 -100
-90 -100
-110 30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
37
-110
0
Distance From Excavation Face (m)
INTERPRETATION Larger ground settlement as compared to FE back-analysis
Possible reasons: • High compressed air flushing the soil to form open hole (micro tunneling) • Excessive ground loss and stress relief • Ground deformation continues at a decreasing rate 38
10/22/2010
Subsidence Trough at Active Wedge
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
10
10
0
0
-10
-10
-20
-20
-30
-30
) m -40 m ( t n e-50 m e l t t -60 e S
-40
-50
-60
Legend Back-Analysed Measured
-70
-80
-70
-80
Stage: Progressive nailing Stage: Post-installation of sheet piles with first row of 18m long soil nails Stage: Completion of excavation and soil nail stabilisation
-90
-100
-90
-100
-110
-110 30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
39
0
Distance From Excavation Face (m)
INTERPRETATION OF FEM • Large shear strain developed along the potential slip surface immediately behind the reinforced soil mass • Settlement trough profile at active wedge • Band of potential slip surface running through the soft clayey deposit – reinforced soil mass slides laterally • Soil nails have restricted the development of 40 active zones within the reinforced soil mass
10/22/2010
CONCLUSION FOR CASE STUDY 2 • Successful stabilisation of loose fill by soil nailing technique. • Excessive ground loss due to open-hole drilling in loose fill should be carefully considered. • FE analysis provides good insight view of the inherent failure mechanism in investigating the distresses and back calculated operating engineering parameters. 41
42
10/22/2010
Case Study 3
Investigation of Soil Nailed Slope Distress at Fill Ground & Remedial Solution
43
Site Location
44
10/22/2010
Site Layout
45
Introductions 4V:1H soil-nailed slope Entire stretch is approximately 60m at uncontrolled fill over a valley Existing 8m to 11 m high Reinforced Soil wall was 23m away from soil-nailed slope
46
10/22/2010
Localised Surface Slips
47
Localised Surface Slips
48
10/22/2010
Pocket Pilecap Excavation Project Site Heterogeneous Fill
49
Tension Cracks
50
10/22/2010
Subsoil Profiles
Decayed Wood
• �������� ������ ������� �� ������ ���� ��� ����� ���� ���� ����� ������� ���� � �� ��
51
Instrumentation Schemes Two (2) inclinometers (namely IN-1 & IN-2) to monitor the nailed slope performance Ten (10) ground settlement markers were installed An additional inclinometer (IN5) was installed
52
10/22/2010
Instrumentation Layout
GSM - 3
GSM - 1
GSM - 2
****GSM-1 (WILL BE BOLD )
53
Groundwater Level Two (2) observational wells (SP-1 and SP-2) to measure groundwater level during period of unexpected prolonged rain storm between March and April 2008 Groundwater fluctuated drastically between August and December 2008 during construction of soil nailing work 54
10/22/2010
Rain Hyetograph (Kuala Lumpur Rain Gauge Station) Sheet Pile Installation & Top Row Anchored Nail Installation
Abnormal storm
01/04/2008 – First Surface Collapse
Passive Berm Bottom Row Waler Beam Excavation Anchored Installation Nail & Horizontal Drain Installation
08/07/2008 – SP1 Installation
55
Inclinometers Results Section A-A Towards RS Wall 0
50
Cumulative Displacement (mm)
1 00
0
87
87
86
86
85
85
84
84
83
83
82
82
81
81
) 80 m ( l 79 e v e 78 L d e 77 c u d 76 e R
80
75
75
74
74
73
73
72
72
71
71
70
70
69
69
Towards Excavation Side
50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850
79 78 77 76
68
SOIL NAILED SLOPE WITH TOE LEVEL AT RL74.0m
68
IN-1
IN-2
25.04.2008 (Collapsed of loose shallow slip of soil nail slope) 25.05.2008 (Pilecap pocket excavation) 25.06.2008 26.07.2008 25.08.2008 (Nearby piling work, sheet pile installation & heavy downpour) 25.09.2008 (Rectification work of localised collapse) 23.10.2008 (Sheet pile machine broke down & heavy downpour) 27.11.2008 24.12.2008 22.01.2009
56
10/22/2010
Inclinometer Results Towards RS Wall
IN-5
Towards Excavation Side
Cumulative Displacement (mm)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 0 2 4 6 8 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5
83 82 81 80 79 78 77 76 75 ) 74 m ( l 73 e v 72 e L 71 d e 70 c u 69 d e 68 R 67 66 65 64 63 62 61 60 59
SOIL NAILED SLOPE WITH TOE LEVEL AT RL 74.0m Permanent Sheet Pile (12 ~ 15m Length)
16.07.2008 (Installation of IN-5) 15.08.2008 25.08.2008 (Heavy downpour) 03.09.2008 (Extraction of temporary sheet pile) 25.09.2008 13.10.2008 23.10.2008 11.11.2008 (Maximum monitoring result) 04.12.2008 (Tie back after the installation of anchored nail) 17.12.2008 (Reading had been stabilised) 24.12.2008 (Final measurement before IN-5 was spoiled)
57
Remedial Solutions Instrumentation Monitoring (During & After Slope Distress) Additional ten (10) numbers of displacement markers were installed; 5 numbers were located near the crest of slope while the rest of 5 number were positioned at lower tier of RS wall 58
10/22/2010
Displacement Markers (DSMs) Monitoring Results & Tension Cracks Settlement Markers at Lower Tier of RE Wall DSM-5
) m m ( t n e m e c a l p s i
DSM-4
0
15
DSM-3
DSM-2
30
DSM-1
45
60
0
50
D
1 3. 05 .2 00 8
1 4. 05 .2 00 8
1 7. 05 .2 00 8
2 3. 05 .2 00 8
2 6. 06 .2 00 8
0 8. 08 .2 00 8
1 4. 08 .2 00 8
Settlement Markers at the Soil Nailed Slope Crest DSM-6
DSM-7
DSM-8
DSM-9
DSM-10
0
50
100
) m m ( t n e m e c a 150 l p s i D
200
250 2 3. 06 .2 00 8
2 6. 06 .2 00 8
3 0. 06 .2 00 8
0 2. 07 .2 00 8
3 0. 07 .2 00 8
1 4. 08 .2 00 8
1 8. 08 .2 00 8
59
Ground Settlement Markers (GSMs) Monitoring Results
60
10/22/2010
Typical Cross Section
61
Monitoring Results for Instrumented Anchor Nail MOBILISED FORCE RESULT OF ANCHORED NAIL 0
25
50
75
Elapsed Days 125 150
100
175
200
225
250
275 220
220 200
Passive Berm Excavation
Sheet Pile Installation & Top Row of Anchored Nail Installation
180
Bottom Row Anchored Nail & Horizontal Drain Installation
Waler Beam Installation
200 180 160
160
) N k ( 140 d e r r 120 e f s n a r 100 T d 80 a o L
140 120 100 80
60
60
40
40
20
20
0
0 8 0 / 7 0 / 8 0
8 0 / 8 0 / 7 2
8 0 / 9 0 / 6 1
8 0 / 0 1 / 6 0
8 0 / 0 1 / 6 2
8 0 / 5 1 / 1 1
8 0 / 2 1 / 5 0
8 0 / 2 1 / 5 2
9 0 / 1 0 / 4 1
9 0 / 2 0 / 3 0
9 0 / 3 2 / 2 0
9 0 / 3 0 / 5 1
9 0 / 4 0 / 4 0
Date
Level A
Level B
Level C
62
10/22/2010
Finite Element Method (FEM) Analyses Hardening soil model Anchor nails with little bending stiffness and modelled as geotextile element Sheet piles modelled as plate element
63
Soil Material Properties in FEM Analyses Material
Average SPT ‘N’
Bulk Density, γ γb (kN/m3)
Effective Cohesion, c’ (kN/m2)
Effective Friction Angle, φ’ (o)
Loose Fill Material
8
17
0
18
Original Granitic Residual Soils
20
20
5
31
Very Hard Weathered Granite
100
20
0
40 64
10/22/2010
Finite Element Method (FEM) Analyses Loose Fill: E’ = 1500~1800 × SPT ‘N’ (kN/m2) Original granitic residual soil: E’ = 2500 × SPT ‘N’ (kN/m2) Interpreted effective residual strength: c r’ = 0 kPa and φr’ = 18o
65
Potential locations of tension cracks and slip surface
Tension Cracks Surface Slippage
66
10/22/2010
Back Analysis of Potential Failure Slip Inherent failure mechanisms : TENSION CRACKS become APPARENT during PILECAP EXCAVATION FEM results confirmed high shear strain in SEMI-CIRCULAR failure and cutting through the installed nails
67
5.0 Conclusions
It is IMPERATIVE to study original topography and normally, natural valley has high potential of retaining SOFT deposit. Drilling method using HIGH COMPRESSED AIR as flushing medium shall be carefully assessed in loose fill ground PROPERLY & WELL-PLANNED instrumentation scheme shall be carried out prior to the commencement of excavation & nailing works FEM is GOOD geotechnical assessment tool 68
