demo 1 - jack-in & soil nailed excavation in fills compatib

8/10/2019 Demo 1 - Jack-In & Soil Nailed Excavation in Fills Compatib

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1

Case Studies of Supportof Open Excavations andDistressed RetainingWalls in Malaysia

Ir. Liew Shaw Shong

2

Type of Case Studies

1 : Jack-In Pipe Anchorage

2 & 3 : Excavation in Fill Ground


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3

Case Study 1

4

Building Boundary

CBP Wall

(5 rows GroundAnchors)

Soldier Pile Wall

(9 rows of Jack-In Anchors)

Soldier Pile Wall(9 rows of Jack-In Anchors)


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5

Jack-In Anchor Installation

Jack-In AnchorsBuilding

CBP Wall Tunnel Construction inprogress

Tunnel Construction inprogress

Ground Anchors

6

GEOLOGY & SUBSOIL CONDITIONS

Meta-sedimentary Kajang formation overlain by somealluvial deposits consisting of sandy clayey silts and fill

0 10 20 30 40SPT'N

30

25

20

15

10

5

0

Depth(m)

16 17 18 19 20

Bulk Unit Weight (kN/m3)

0 40000 80000Young Modulus (kPa)

0 20 40 60 80Atterberg Limits

Legend

LL

PL

MC

Layer 1 -Fill

(ClayeySilt)

Layer 2 -Clayey

Silt

Layer 3 -Sandy Silt

Layer 4 -Sandy Silt


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9

Pull Out Tests for Instrumented Jack-In Anchor

JackedAnchor atLevel 4

JackedAnchor atLevel 7

0 10 20 30Head Displacement (mm)

0

50

100

150

200

250

Pull-OutLoad(kN)

120

80

40

0

ShaftResis

tance(kN/m2)

Pull-Out TestTest 1 ( 6 Days)

04-Mar-2002

Test 2 (14 Days)12-Mar-2002

Test 3 (24 Days)22-Mar-2002

Pipe Shaft Resistance

Test 1: C-D

Test 1: D-E

Test 1: E-F

Test 2: C-DTest 2: D-E

Test 2: E-F

Test 3: C-D

Test 3: D-E

Test 3: E-F

VWSG - C VWSG - D VWSG - E VWSG - F1.6m 4.6m 7.6m 10.6m

0 10 20 30Head Displacement (mm)

0

50

100

150

200

250

Pull-OutLoad(kN)

120

80

40

0

ShaftResistance(kN/m2)

Pull-Out Test

Test 1 ( 5 Days)15-Jan-2002

Test 2 (14 Days)25-Jan-2002

Test 3 (21 Days)1-Feb-2002

Pipe Shaft ResistanceTest 1 :A-B

Test 1 :B-C

Test 1 :C-D

Test 1 :D-E

Test 1 :E-F

Test 2 :A-BTest 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

VWSG - A VWSG -B VWSG - C VWSG - D VW SG - E V WS G - F

18m

6.0m 9.0m 12.0m 15.0m0.6m 3.0m

10

Jack-in Anchor Load with Time

0 50 100 150 200 250 300

Time (Days)

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

oa

Level 3 - FEM Results




Loading at Jacked Anchors

Level 3

Level 5

Level 7

Level 9

3rd layer : 5/01/2002

Load cell :12/01/2002

5th layer : 19/01/2002

Load cell : 29/01/2002

7th layer : 22/02/2002

Load cell : 6/03/2002

9th layer : 27/03/2002

Load cell : 28/03/2002


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Prestressed Ground Anchor Load with Time

0 50 100 150 200 250 300

Time (Days)

0

50

100

150

200

250

300

350

400

450

500

550

600

Load

(kN

)

Level 2 - PLAXIS

Level 3 - PLAXIS

Level 4 - PLAXIS

Level 5 - PLAXIS

Loading at Ground AnchorLevel 2

Level 3Level 4

Level 5

Load cell : 19/01/2002

Load cell : 20/03/2002

Load cell : 19/02/2002

Load cell : 22/02/2002

12

Wall MovementGround Anchor WallJack-In Anchor Wall

0 10 20 30 40 50

Wall Movement (mm)

26

24

22

20

18

16

14

12

10

8

6

4

2

0

epth(m)

Measured Wall DeflectionStage1

Stage2

Stage3

Stage4

Stage5

Final Stage

- Movement (Back analyses) of CBP wall for each stages

1

3

2 45 F

1

0 10 20 30 40

Wall Movement (mm)

26

24

22

20

18

16

14

12

10

8

6

4

2

0

Depth(m)

Measured Wall Deflection

Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

Stage6

Stage 7

Stage 8

Stage 9

Stage 10

1

23

4

5

6

7

9

8

F

- Movement (Back analyses) of CBP wall for each stages

8


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Ground Settlement behind CBP Wall

0 20 40 60 80 100 120 140

Time (Days)

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

Ground Settlement atJacked Anchor Wall (Measured)

Jacked Anchor Wall (FEM Results)

Ground Anchor Wall (Measured)Ground Anchor Wall (FEM Results)

Jack-In Anchors Wall : dV/dH (wall) = 1.57

Ground Anchor wall : dV/dH (wall) = 3.37

dV : Ground Settlement Behind the Wall

dH : Horizontal Wall Deflection

14

BACK ANALYSES WITH FEM MODELLING

FEM Plane Strain Analysis (PLAXIS)

Hardening Soil Model

Interface Element : To model the SoilInteraction with Wall & AnchorageElements

Temporary Wall and Jacked Anchors :Beam Element (Axial & BendingStiffness)

Consolidate for 6 months after finalexcavation to model Drained Condition


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15

Typical FEM Model

Beam Element (Jack-In Anchors)

Beam Element

(CBP Wall and Soldier Piled Wall)

Interface Element

16

Soil Shear Strain within Jack-In AnchorRetaining System

Relatively larger shear strains ranging between0.26% and 0.38% developed along the

potential slip surface


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17

Total Ground Displacement of Jack-InAnchor Retaining System

The reinforced soil mass has more displacementat the upper portion with gradually reduced

trend towards the lower portion

18

Dimensionless Ground Surface Settlement

0.2

0.15

0.1

0.05

0

Settlement/Excav

ationDepth(%)

25 20 15 10 5 0

Distance from Wall / Excavation Depth

Clough & ORourke

(1990)

Maximum wall movement of CBP wall atfinal excavation is about 0.002H


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21

RECOMMENDATIONS

To avoid flexural effect, straingauges shall be installed in pairs at

jacked anchor section.

Research on generation of excesspore water pressure & itsdissipation around and along the

jacked anchor shall be carried out.

Locked in tensile stress under

compressive injection may increasemovement within reinforced earthmass

22

Case Study 2High rise development

with 5 storeybasement car park

Deep excavation:

7m-14.5m


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23

High rise developmentwith 5 storey

basement car park

Deep excavation:

7m-14.5m

Plan

24

Located at the toeof a filled slope

Soil nail stabilisation worksto facilitate excavation

Cross Section


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25

TOPOGRAPHIC

Original hilly ground with natural valley & stream

Loose sandy silt overlaying a thin deposited softcompressible material at valley area

15m highfilled slope

26

SUBSURFACE CONDITIONSBH-4 BH-IM4 BH-IM1 BH-SP1 BH-3 BH-2 BH-1


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27

SOIL NAILING DESIGN & CONSTRUCTION

6m to 12m soil nail at 1.25m c/c spacings

4V : 1H reinforced gunite facing

sufficient weepholes / subsoil drains

28

Additional Strengthening Works at the Valley Area

2 rows of 18mlong soil nail

anchorage

12m long FSPIIIA sheet pilewall

Permanent RCprops againstbasementstructure

3 rows ofsubsoil drains


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INSTRUMENTATION MONITORING

30-10 0 10 20 30 40 50 60 70 80 90 100 110

-40

-38

-36

-34

-32

-30

-28

-26

-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Depth(m)

0 5 10 15 20 25 30 35 40 45 50

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

0 10 20 30 40 50 60 70 80 90 100 110

-40

-38

-36

-34

-32

-30

-28

-26

-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

5 10 15 20 25 30 35 40 45 50

Legend

09/11/2004

24/11/2004

21/12/2004

24/01/2005

21/02/2005

22/03/2005

12/11/2005

SPT-N

SPT-N Value

Ground Lateral Displacement (mm)

IM-01 IM-04

Lateral Ground Displacement


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Ground Settlement

-160

-150

-140

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

GroundSettlement(mm)

-160

-150

-140

-130

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

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

Date

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

LegendSM01

SM02

SM03

SM04

SM05

SM06

SM07

SM08

SM09

SM10

SM11

SM12

Construction Post-Construction

Sheet PileInstallation

32

Date

Groundwater Table

GroundwaterTable(RLm)

01/08/04 20/09/04 09/11/04 29/12/04 17/02/05 08/04/05 28/05/05 17/07/05

41424344454647484950

41424344454647484950

01/08/04 20/09/04 09/11/04 29/12/04 17/02/05 08/04/05 28/05/05 17/07/05

4041424344454647484950

4041424344454647484950

SP 01

SP 03

Post-ConstructionConstruction

Sheet Pile Installation


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33

FEM plane strain analysis

Hardening soil model

Coupled consolidation undrained analysis

Initial stresses were calculated by gravity loading

Back Analysis

34

Soil Parameters

Layer MaterialAve

SPT-N

b(kN/m3)

Su(kPa)

c

(kPa)

()

E

(kPa)

Eur(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

(WeakZone)

2 18 400.5

(5)

#20 32,500 97,500 32,500

RL40m

RL37m

Sandy

Silt10 18.5 - 5 (10) # 32 25,000 75,000 25,000

RL37m

RL21m

Sandy

Silt20 18.5 - 5 (10) # 32 50,000 150,000 50,000

Below RL21mGravelly

Sand50 19.5 - 7 32 125,000 375,000 125,000

# Improved apparent cohesion adopted in FE back analysis at the last few stages.


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Lateral Ground Displacement

10 20 30 40 50 60 70

10 20 30 40 50 60 70

10 20 30 40 50 60 70

10 20 30 40 50 60 70

10 20 30 40 50 60 70

10 20 30 40 50 60 70

20

25

30

35

40

45

50

55

60

Legend

Measured

Back-analysed

0 10 20 30 40 50

15

20

25

30

35

40

45

50

55

60

Depth(RLm)

0 10 20 30 40 50

Lateral Ground Displacement (mm)

Stage:Progressive Stage: Post-installation Stage: Completion of

nailing of sheet piles with firstrow of 18m soil nails

excavation and soilnail stabilisation

SPT'N'

12m Soil Nail

18m Soil Nail

Sheet Pile

Shotcrete

Legend

Measured

Back-analysed

36

INTERPRETATION

Youngs modulus (E)

E = 1500 to 1800 x SPTN..for upper loose fills

E = 2500 x SPTN..for weathered Granitic Residual subsoil

Unloading/reloading stiffness, Eur = 3 x E


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Ground Settlement

30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0

Distance From Excavation Face (m)

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Settlement(mm)

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0

Legend

Back-Analysed

Measured

Stage: Completion of excavation

Stage: Post-installation of sheet piles

Stage: Progressive nailing

with first row of 18m long soil nails

and soil nail stabilisation

38

Larger ground settlement as compared to FEback-analysis

Possible reasons:

High compressed air flushing the soil to form openhole (micro tunneling)

Excessive ground loss and stress relief

Ground deformation continues at a decreasing rate

INTERPRETATION


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30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0

Distance From Excavation Face (m)

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Se

ttlemen

t(mm

)

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0

Legend

Back-Analysed

Measured

Stage: Completion of excavation

Stage: Post-installation of sheet piles

Stage: Progressive nailing

with first row of 18m long soil nails

and soil nail stabilisation

Subsidence Trough at Active Wedge

40

Large shear strain developed along thepotential slip surface immediately behind thereinforced soil mass

Settlement trough profile at active wedge

Band of potential slip surface running throughthe soft clayey deposit reinforced soil massslides laterally

Soil nails have restricted the development ofactive zones within the reinforced soil mass

INTERPRETATION OF FEM


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CONCLUSION FOR CASE STUDY 2

Successful stabilisation of loose fill by soilnailing technique.

Excessive ground loss due to open-hole drillingin loose fill should be carefully considered.

FE analysis provides good insight view of theinherent failure mechanism in investigating thedistresses and back calculated operatingengineering parameters.

42


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Case Study 3

Investigation of Soil Nailed SlopeDistress at Fill Ground & RemedialSolution

Site Location

44


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Site Layout

45

Introductions

4V:1H soil-nailed slope

Entire stretch is approximately60m at uncontrolled fill over avalley

Existing 8m to 11 m high

Reinforced Soil wall was 23maway from soil-nailed slope

46


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Localised Surface Slips

47

Localised Surface Slips

48


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Pocket Pilecap Excavation

Project Site

49

Heterogeneous

Fill

Tension Cracks

50


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Subsoil Profiles

Decayed Wood

51

Instrumentation Schemes

Two (2) inclinometers (namelyIN-1 & IN-2) to monitor thenailed slope performance

Ten (10) ground settlementmarkers were installed

An additional inclinometer (IN-5) was installed

52


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Instrumentation Layout

****GSM-1 (WILL

BE BOLD )

GSM - 1

GSM - 2

GSM - 3

53

Groundwater Level

Two (2) observational wells(SP-1 and SP-2) to measuregroundwater level during periodof unexpected prolonged rainstorm between March and April2008

Groundwater fluctuateddrastically between August andDecember 2008 duringconstruction of soil nailing work

54


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Rain Hyetograph(Kuala Lumpur Rain Gauge Station)

Sheet Pile Installation & Top Row

Anchored Nail InstallationPassive Berm

Excavation

Bottom Row

Anchored

Nail & Horizontal

Drain Installation

Waler Beam

Installation

Abnormal storm

01/04/2008 First

Surface Collapse08/07/2008 SP1

Installation

55

Inclinometers Results

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850

Cumulative Displacement (mm)

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

Towards RS Wall Towards Excavation Side

0 50 1 00

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

Red

ucedLevel(m)

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

SOIL NAILED SLOPE WITHTOE LEVEL AT RL74.0m

IN-1 IN-2

Section A-A

56


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Inclinometer Results

0 20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

Cumulative Displacement (mm)

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

ReducedLevel(m)

Towards RS Wall

Towards Excavation Side

16.07.2008 (Installation of IN-5)

15.08.2008

25.08.2008 (Heavy downpour)

03.09.2008 (Extraction of temporary sheet pile)

25.09.200813.10.2008

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)

SOIL NAILED SLOPE WITHTOE LEVEL AT RL 74.0m

Permanent Sheet Pile (12 ~ 15m Length)

IN-5

57

Remedial Solutions

Instrumentation Monitoring(During & After Slope Distress)

Additional ten (10) numbers ofdisplacement markers wereinstalled; 5 numbers werelocated near the crest of slopewhile the rest of 5 number werepositioned at lower tier of RSwall

58


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Displacement Markers (DSMs)Monitoring Results & Tension Cracks

Settlement Markers at the Soil Nailed Slope Crest

0

50

100

150

200

250

Displacement(mm)

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

DSM-6 DSM-7 DSM-8 DSM-9 DSM-10

Settlement Markers at Lower Tier of RE Wall

0

50

0 15 30 45 60

Displacement(mm)

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

DSM-5 DSM-4 DSM-3 DSM-2 DSM-1

59

Ground Settlement Markers (GSMs)Monitoring Results

60


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Typical Cross Section

61

Monitoring Results forInstrumented Anchor Nail

08/07/08

11/15/08

02/23/09

27/08/08

16/09/08

06/10/08

26/10/08

05/12/08

25/12/08

14/01/09

03/02/09

15/03/09

04/04/09

Date

0

20

40

60

80

100

120

140

160

180

200

220

Loa

dTrans

ferre

d(kN)

Level A Level B

0

20

40

60

80

100

120

140

160

180

200

220

0 25 50 75 100 125 150 175 200 225 250 275

Elapsed Days

MOBILISED FORCE RESULT OF ANCHORED NAIL

Sheet Pile Installation &Top Row of Anchored Nail Installation

Passive Berm

Excavation

Bottom Row Anchored

Nail & Horizontal

Drain Installation

Waler Beam

Installation

Level C62


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Finite Element Method (FEM)Analyses

Hardening soil model

Anchor nails with littlebending stiffness andmodelled as geotextileelement

Sheet piles modelled as

plate element

63

Soil Material Properties in FEMAnalyses

MaterialAverage

SPT N

Bulk

Density,

b (kN/m3)

Effective

Cohesion,

c (kN/m2)

Effective

Friction

Angle,

(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


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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 residualstrength:

c r = 0 kPa and r = 18o

65

Potential locations of tensioncracks and slip surface

Tension

CracksSurface

Slippage

66


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Back Analysis of Potential FailureSlip

Inherent failure mechanisms :TENSION CRACKS becomeAPPARENT during PILECAPEXCAVATION

FEM results confirmed highshear strain in SEMI-CIRCULAR

failure and cutting through theinstalled nails

67

68

5.0 Conclusions

It is IMPERATIVE to study originaltopography and normally, natural valley hashigh potential of retaining SOFT deposit.

Drilling method using HIGH COMPRESSEDAIR as flushing medium shall be carefullyassessed in loose fill ground

PROPERLY & WELL-PLANNEDinstrumentation scheme shall be carried outprior to the commencement of excavation &nailing works

FEM is GOOD geotechnical assessment tool


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Thank You

69

demo 1 - jack-in & soil nailed excavation in fills compatib

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