wong design analysis deep excavations session03

November2009 MohrCoulombModel

WongKaiSin 1

Session 3Mohr-Coulomb Soil Model &

Design (Part 2)Time Session Topic

09:00 10:30 1 Overview10:30 11:00 Coffee Break

11:00 12:30 2 Design (Part 1)12:30 - 01:30 Lunch

1

01:30 03:00 3 Mohr-Coulomb Soil Model & Design (Part 2)

03:00 03:30 Coffee Break

03:30 05:00 4 How to reduce wall deflectionMohrCoulombModel

Thingsyoushouldknowaboutthe

MohrCoulombSoilModel

Elastic

Plastic

Elastic

MohrCoulombModel 2

ast cplastic


WongKaiSin 2

CanMohrCoulombModelsimulateRealSoilBehaviour?

El i

PlasticUUTeston

Clay

> 0

Elastic

Elasticplastic

Plastic

cu >0u =0

CDTestonClayorSand

MohrCoulombModel 3

RealSoil MohrCoulombSoil

Elastic

Sand

c' 0'>0

CanaElasticModelsimulateRealSoil Behaviour?

Shear stress produces Normal stress produces

ElasticModelShearstressproducesshearstrain:

no v

Normalstressproducesvolumetricstrain:

v

MohrCoulombModel 4


WongKaiSin 3

Can a elastic soil simulate undrained behaviour of clay?

Plastic

l i

RealSoilBehaviour

ElasticModel(=0.5)

ElasticElasticplastic

MohrCoulombModel 5

no v nov(undrained)Stressindependent

no v nov(undrained)Stressindependent

Can a elastic soil simulate undrained behaviour of clay?

Plastic

l i

ElasticElasticplastic

Yes!Ifweusecu andEu.

MohrCoulombModel 6

Canweusec' 'andE'?


WongKaiSin 4

CUTest

100

MohrCoulombModel 7porp(kPa)

ESP TSP

100

=100kPa

CUTest

ConsolidatedUndrainedTriaxialCompressionTest

2cu

Kf Kfq q

RealSoil13

curveMohrCoulomb

cu fromc' '

MohrCoulombModel 8

ESP TSP TSPESP

porp porp

c' 'overpredictedcu !!!

2cu

1

cu measured


WongKaiSin 5

RealSoil ElasticSoil

Istheporepressureresponsecorrect?

LetslookatCUtestonanormallyconsolidatedclay.

UfUf

ESP TSP TSPESP

Kf Kfq q

MohrCoulombModel 9

porp porp

Thepredictedporepressureismuchsmallerthanthemeasured!

Itoverestimatestheundrainedshearstrengthandunderestimatestheexcessporepressure ofanormallyconsolidatedclay.

EffectivestressMohrCoulombMethodusingcandMethodA

UfUf

Kf Kfq q


2cu

2cu

MohrCoulombModel 10

ESP TSP TSPESP

porp porp


WongKaiSin 6

0

5

0 20 40 60 80 100 120 140 160

Undrained Shear Strength (kPa)

(qt-po)/Nkt

Overestimationofcu ataReclaimedSite

5

10

15

20

25

30Dep

th (m

)0.22*p'o

corr. FVT

Consol tests

Cu based onphi=22 & p'o

MethodA

MohrCoulombModel 11

35

40

45

50

NicollHighway ResultsofUndrainedAnalysisusingMethodA

95

100

105

MeasuredComputedusing MethodA

65

70

75

80

85

90

Level10325 mm

Redu

cedLevel(m)

Redu

cedLevel(m)

MohrCoulombModel 12

50

55

60

0 50 100 150 200 250 300 350 400

325mm

Formation=118mmFinal=145mm WallDeflection(mm)


WongKaiSin 7

DoesMethodA alwaysoverestimatecu forNCclay?

(13)f '

13

cu

A B C

u=0

'

Thissitehasaconstantcu.

MohrCoulombModel 13

ForNCClay,itunderestimates cu atlowstressandoverestimates itathighstress.

Itforcesthesoiltofailataspecifiedundrainedshearstrength.

MethodBEffectivestressMohrCoulombMethodusingcu andu=0

Kfq

RealSoil

2c K

q

ElasticSoil

MohrCoulombModel 14

ESP TSP

porp

2cu2cu

TSPESP

Kf

porp


WongKaiSin 8

MeasuredComputedusing MethodB

NicollHighway ResultsofUndrainedAnalysisusingMethodB

MohrCoulombModel 15

CanMethodA beusedforOverconsolidatedClay?

(13)f CU

'13

B

C

=0

UU

c'

cu

A

A

B C

u=0

'

Thissitehasaconstantcu.

MohrCoulombModel 16

ForagivenlayerofOCClay,itunderestimates cu atlowstressandoverestimates itathighstress.


WongKaiSin 9

UsingMethodAforUndrainedAnalysisinOCClay

2

Kfq


Kfq 2cu

TSPESP

porp

q2cu

TSPESP

porp

q

UfUf

MohrCoulombModel 17

1.MakesurethemeasuredstresspathissimilartothatofElasticSoil.

2.Dividethestratumintosublayerswithdifferentcandforeachlayer.

3.Computecu fromcandforeachlayer.Makesurethevaluesarereasonable.

UsingMohrCoulombmodelforUndrainedAnalysis

MethodA c' and' produceswrong cu forNCclay,

butitmayproducecorrectcu forOCclay

Method B or C Forces Plaxis to use specified c

Method A Method B Method CStress Type Effective Effective Total

Strength cand cu and u cu and uM d l E E E

MethodB orC ForcesPlaxis tousespecifiedcu

MohrCoulombModel 18

Modulus E E EuPoissons Ratio = 0.35 u = 0.495

Ko or Kot Ko Ko Kot


WongKaiSin 10

CanMCmodelsimulateundrainedbehaviour ofclay?

PlasticElasticplastic

1. Itproducesthecorrectstrengthwithcu specified.

ElasticInelastic

2. Itcannotsimulatenonlinearandinelasticbehaviour.

3. Itmaynotgeneratereliableporepressureresponse.

MohrCoulombModel 19

CanMCmodelgenerateaccuratedeflectionprofilesateverystageofexcavation?

ConstantE

0

5

10

0 20 40 60 80 100

Wall Deflection (mm)

)

123

15

20

25

30

Dep

th (m4 1 42 3

MohrCoulombModel 20


WongKaiSin 11

Atearlystageofexcavation,MohrCoulomb, LinearE larger Hyperbolic, NonlinearE smaller

Et

MohrCoulombModel 21

Atfinalstageofexcavation,MohrCoulomb,LinearE smaller Hyperbolic,NonlinearE larger

Linear

Nonlinear

Et

MohrCoulombModel 22


WongKaiSin 12

MohrCoulomb

Eu/cu ~100to500

ConstantE

AdvancedSoilModelConclusionM Cmodel may not

MCmodelmaynotproducegoodmatchateverystageofexcavation.

MohrCoulombModel 23

HowreliablearetheresultsgeneratedbytheMCmodel?

Fill

Soft Marine Clay

V,MAX=33mm0

0 50 100 150

SoftMarineClay

H,MAX =28mm35

Isthemodeofdeformationreasonable?

MohrCoulombModel 24


WongKaiSin 13

ResultsusingHyperoblicModel

Fill

Soft Marine Clay

V,MAX=72mm

= 59 mm

00 50 100 150

SoftMarineClay

H,MAX =59mm35

Isthemodeofdeformationreasonable?

MohrCoulombModel 25

Fill

SoftMarineClay

Linearvs

NonLinear

0

35

0 50 100 1500

35

0 50 100 150

MohrCoulombModel 26


WongKaiSin 14

Fill

Checkplasticpointsandrelativeshearstress!

SoftMarineClay

Lessonlearned:Correctanalysismaynotproducecorrectresults.

MohrCoulombModel 27

LinearvsNonLinearModel

E2

E3 E4Mohr CoulombModel RealSoilBehaviour

E1

E2

ConstantE

MohrCoulombModel 28

Youmustunderstandtheshortcomingsofthesoilmodelused!


WongKaiSin 15

UsingMethodBatReclaimedSite

FillMethodBisaneffectivestress method.

SoftMarineClay

SandySilt

stressmethod.

Ko =1 sin'

Ifclayisstillconsolidating,thecomputedrelativeshearstresswillbe>1,i.e.theclayis in failure state prior toy isinfailurestatepriortoexcavation.

MohrCoulombModel 29

UsingeffectiveKo atasitestillundergoingconsolidation

Plasticpoints

MohrCoulombModel 30


WongKaiSin 16

85

90

95

100

105

Leve

l (m

)Fill

S ftAB

Effectiveoverburdenpressure

MethodB(cu u)andKo (1sin)

50

55

60

65

70

75

80

0 100 200 300 400 500

Current Effective Stress (kPa)

Red

uced

L SoftMarineClay

SandySilt

AB

Currenteffectivestress

Current Effective Stress (kPa)

AtA,('V 'H)='V (1 Ko)=74 kPa

AtB,('V 'H)='V (1 Ko)=37 kPa

Currentcu =22kPa

(1 3)f =2cu =44 kPa

MohrCoulombModel 31

Needtosetthecorrectinitialstresses!

Fill

SoftMarineClay

SandySilt

Checkplasticpointsaftergeneratingtheinitialstresses!

MohrCoulombModel 32


WongKaiSin 17

MohrCoulombModel 33

MohrCoulombModel 34


WongKaiSin 18

StressDependentBehaviour ofSoilunderDrainedCondition

MohrCoulombModel 35

StressPathsinanElasticMedium

KoC

D

B

C

E

F

A

1

3

E Questionable Zone

3

3

1

1

MohrCoulombModel 36

3

E QuestionableZone

F DangerZone


WongKaiSin 19

TypicalStressPathsinExcavation

A

BA

B

MohrCoulombModel 37

StressPathinZoneFunder DrainedCondition

rubber

soil

1(%)

MohrCoulombModel 38

v(%)


WongKaiSin 20

StressPathinZoneEunderDrainedCondition

MohrCoulombModel 39

1=3003=300

Whichoneiscorrect?

Adrainedanalysiscanproduceincorrectresultsundercertainstresspath.

A

BA B

Measured Computed

Lessonlearned:Correctanalysismaynotproducecorrectresults!

MohrCoulombModel 40


WongKaiSin 21

SomeproblemsmaybesensitivetoPoissonsRatio

0

5

-20 0 20 40 60 80 100


c=5kPa

=35o

E=8000kPa

10

15

20

25

Dep

th (m

)

Pois. Ratio = 0.4

Pois. Ratio = 0.2

=0.2 =0.4

Mmax ,kNm/m 298 477

Strut 1, kN/m 77 114

Strut 2 kN/m 226 335

H=9m

=0.2=0.4

25

30

Strut 2, kN/m 226 335

Strut 3, kN/m 163 178

Lessonlearned:Drainedanalysiscanproducemanysurprises.

MohrCoulombModel 41

CanMCmodelsimulatedrainedbehaviour ofsoil?

1. Itgivescorrectstrength f =c+tan

2. Modulusisnotstressdependent.

3. Itcannotsimulatenonlinearandinelasticbehaviour.

4. Itmayproducewrongresponseincertainstresspath.

5. ResultsmaybesensitivetoPoissonsratio.

MohrCoulombModel 42


WongKaiSin 22

CanMCmodelsimulatedrainedbehaviour ofsoil?

6. Itmaynotproducecorrectporepressureresponse.

Plastic

7. Whenusingc'' inconsolidationanalysis,itmaygeneratethewrongundrainedstrengthatendofconstruction.

8 There is no dilation until

Elastic

8. Thereisnodilationuntilafterthesoilreachesfailure.

MohrCoulombModel 43

v

MohrCoulombModel 44

November 2009 Excavation Design

Wong Kai Sin 1

Designing Temporary Work

Design &Analysis

ConstructionControl

InstrumentationMonitoring

Initial Design Final Design

Designing Temporary Work is a Continuous Process

Excavation Design 1

g(Working Drawings) (As-Built)

Start Finish

Excavation

Types of Analysis in TERS Design

1. Analysis for preliminary design

2 Analysis for working design to be2. Analysis for working design to be adopted in construction

3. Back-analysis

4. Re-analysis

Excavation Design 2

Working Design

Final Design(As-Built)

Start FinishExcavation

Prelim. Design Back-Analysis & Re-analysis


Wong Kai Sin 2

Analysis for preliminary design To assess feasibility of proposed

TERS configuration and construction sequence.

To assess effect of excavation on surrounding structures

To conduct analysis using moderately conservative design parameters

Excavation Design 3

Analysis for working or Final design to be adopted in construction

To conduct sensitivity studies assessing the effect of variable uncertainties

To finalise the strut forces and wall bending moments for structural design

To assess the risk of damage to adjacent structures

Excavation Design 4


Wong Kai Sin 3

Back-Analysis during Construction

To be carried out when the field performance is much better or worse than anticipatedthan anticipated.

To calibrate the design parameters against field measurements

0

5

0 20 40 60 80 100


Excavation Design 5

5

10

15

20

25

30

Dep

th (m

)

Computed

Measured

Re-Analysis during Construction

To be carried out after back-analysis

To assess potential final outcome using calibrate design parametersg p

To revise the design where appropriate

0

5

0 20 40 60 80 100 120


0

5

0 20 40 60 80 100


Excavation Design 6

10

15

20

25

30

Dep

th (m

)10

15

20

25

30

Dep

th (m

) Computed

Measured

Design

Back-Analyzed


Wong Kai Sin 4

Overview of Design Process

1. Site investigation2. Pre-construction survey2. Pre construction survey3. Evaluation of soil conditions4. Selection of TERS configuration5. Assessment of system stability6. Preparation for FEA7 Assessment of computed output

Excavation Design 7

7. Assessment of computed output

Design Step 1: Site Investigation

Plan View

1. Site investigation2. Pre-construction

survey3. Evaluation of soil

conditions4. Selection of TERS

configuration5 Assessment ofPlan View

Sectional View

5. Assessment of system stability

6. Preparation for FEA7. Assessment of

computed output

Excavation Design 8

Designer must be actively involved in the site investigation.

Get the best S.I. company to do the job!

Do enough borings and CPTs.


Wong Kai Sin 5

2. Pre-Construction SurveyTo check pre-existing conditions of surrounding structures

Things you can see ..




configuration

Cracks

Patches under new paint

Settlement of aprons & driveway

Constructions in the vicinity

configuration5. Assessment of

system stability6. Preparation for FEA7. Assessment of

computed output

Excavation Design 9

A comprehensive pre-con survey provides the designer with a proper perspective of the surrounding and issues that must be considered in the design.

Excavation Design 10


Wong Kai Sin 6

Pre-Construction Survey Pre-existing Conditions

Things you cant see ..

Ongoing movements

Seasonal fluctuations

Invest in InstrumentationSettlement marksP i

Ground settlement profile


Paper prismsWater standpipesInclinometers

3. Evaluation of Soil ConditionsThings to check ..

Fill thickness and variations

Soft clay thickness and variations




configuration5. Assessment of Soft clay thickness and variations

State of consolidation of soft clay

Depth to hard stratum & variations

Ground water table


computed output

Fill


Soft Marine

Clay

Stiff Silty Clay

Dense Silt Sand


Wong Kai Sin 7

Design Soil Profile & Parameters

Fill

Upper Marine Clay

Lower Marine Clay

Intermediate Stiff Clay


Old Alluvium

Extract only the reliable facts from Factual Report.

Is the soil condition uniform? Can we use half mesh?

Example on Idealised Soil Profile

Worst soil condition

ABH-30

ABH-32

AC 3

M3010

condition

Instrumented section


ABH-31ABH-84

AC-3

Soil Profile at ABH-32 adopted in Original Design


Wong Kai Sin 8

Example on Soil Profile -- Half-mesh based on ABH-32

Fill

E upper

RL (m)102.998.296.4

UMC

F2 upper

LMC

JGP1

JGP2

85.6

83.4

68.3


F2 lower

OA N = 35

OA N = 72

63.2

61.657.553.8

E lower

ABH-84FillE E

FillRL (m)

M3010

Example on Soil ProfileFull-mesh at Instrumented Section

UMC

F2 upper

LMC

F2 lowerF2

LMC

LMC

F2 upper

UMC

JGP1

85.4

72.169 4


F2 lowerOA N = 20OA N = 30

OA N = 70

OA N = 100OA N = 70OA N = 30OA N = 20

JGP2 JGP3 66.8

64.7

60.0

55.0

59.261.2

63.7

69.4


Wong Kai Sin 9

Example -- Results can be very sensitive to variations in soil profile

Cross-Over at Newton MRT Station

C

B

A


A B C

Results can be very sensitive to minor variations in soil profile


A

B


A B C


Wong Kai Sin 10

Results can be very sensitive to minor variations in soil profile



Design Step 4: Selection of TERS

We need to know Site constraints




configuration5 Assessment of Site constraints

DimensionsAdjacent buildingsMRT & CST tunnelsh,max allowable?



computed output


Slab elevations Ramp locations


Wong Kai Sin 11

Preliminary Design Configuration

Wall type & size

Penetration depth This is where experience


Strut size and spacing

JGP/DCM slab thickness

Preloading

experience comes in!

Need to Establish the Excavation Sequence



Wong Kai Sin 12

Design Step 5: Basic Stability Checks

Before conducting FEA, check




configuration5 Assessment of

Basal Heave Stability

Uplift or Blowout Stability

Toe Kick-in Stability



computed output


Which method should we use?

Terzaghi Bjerrum & EideEide et al.

Basal Heave Stabillity

TschebotarioffGohChangWong and GohO'RourkeSu et al.Ukritchon et al.


Plaxis

Does FOS1 mean failure?


Wong Kai Sin 13

Uplift Stability

FillE

UMCF2

B

F2

LMC

E / F2

Sand U = H B

d

Hw

R=cudW = d B

R


Sand U w Hw B

Fs = ----------------W + 2R

UCheck permeability & connectivity of sand layer!

Toe Kick-in Stability

M

PaPp

LaLp

M


How do we check toe stability?


Wong Kai Sin 14

Design Step 6: Preparation for FEA




configuration5 Assessment of

1. Selection of software2 Selection of soil models 5. Assessment of


computed output

2. Selection of soil models3. Selection of type of analysis4. Evaluation of soil parameters5. Generation of FE mesh6. Preparation of data input Plaxis?

Mohr-Coulomb?


Mohr-Coulomb?

Undrained?

Total stress?

Design Step 7: Assessment of Computed Output




configuration5 Assessment of5. Assessment of


computed output

Tons of data can be generated with a few clicks.

But what are the relevant ones?

Generating thick reports with not-so-


important graphs reflects badly on the engineer. It is a reflection of he/she not knowing whats important!


Wong Kai Sin 15

What are the relevant results?

Relevant Results

Wall deflections Wall deflections

Ground settlement

Pore pressure

Strut forces

Wall moment and shear


Plastic points

Displacement vector plots

Interpretation of Computed Output

Check Mode of Deformation

Expected Unexpected

Is the mode of deformation reasonable?Excavation Design 30


Wong Kai Sin 16

Interpretation of Computed Output

Check extend of soil yielding

Plastic point plotExcavation Design 31

Relative ShearPlastic Points



Wong Kai Sin 17

Plastic points in JGP/DCM layer

Residual stress

Lesson learned:

Plastic point and relative shear plots provide insight to the extend of soil yield and overall stability of the system.


Plot wall deflections for construction control

Max. Wall DeflectionDeflection Profiles

computed

measured



Wong Kai Sin 18

Change in Pore Pressure with Excavation Depth


Ground Settlement at End of Excavation

-100

-50

0

50

0 10 20 30 40 50 60 70 80 90

nd S

ettle

men

t (m

m)


-200

-150

Distance (m)

Gro

un


Wong Kai Sin 19

0.0

50.0

Plot ground settlement vs excavation depth at selected locations

-200.0

-150.0

-100.0

-50.0

5/24/02 9/1/02 12/10/02 3/20/03 6/28/03 10/6/03 1/14/04 4/23/04

Settl

emen

t (m

m)


-300.0

-250.0

Plot maximum strut forces with depth

FillEE

FillRL (m)

E

MC

F2

MC

F2F2

MC

LMC

F2

MC

E

JGP

85.4

72.169 4

Measured

Computed


F2 OA (20)OA (30)

OA (70)

OA (100)OA (70)OA (30)OA (20)

JGP66.8

64.7

60.0

55.

59.261.263.7

69.4


Wong Kai Sin 20

Plot development of strut forces during excavation

S1Strut Force (kN)

S1

S1

epth

bel

ow g

roun

d (m

)


De

Bending Moment at Different Stages of Excavation

1

2

4

3

5

5

4

3

21



Wong Kai Sin 21

Displacement Vectors Showing Movements at End of Excavation


FOS=1.30

Displacement Vector Plot after Strength (-c) Reduction Analysis


False alarm?


Wong Kai Sin 22

Are the computed wall deflections acceptable?


Comparison of Strut Forces with Published Apparent Pressure Diagrams

Pecks Apparent Earth Pressure Diagrams (1969)

CIRIAs Characteristic Pressure Diagrams (1996)CIRIAs Characteristic Pressure Diagrams (1996)

Local Experiences on Apparent Pressure Diagrams



Wong Kai Sin 23

E1

E2

E3 E4

Mohr-Coulomb model Cant match all stages of excavation!

0

5

0 20 40 60 80 100


12

Constant E


10

15

20

25

30D

epth

(m)3

4 1 42 3

Sensitivity Study to Finalise Design

Sand

Marine Clay

Old Alluvium

JGP

Surcharge 10 and 20 kPa

Soil Modulus (Eu/cu) 300 and 200

Over-excavation 0.5 and 1 m

JGP Thickness 1.5 and 1.0 m

JGP modulus 150 and 100 MPa


JGP modulus 150 and 100 MPa

Wall stiffness 1.0EI and 0.7EI

Modelling of bored piles Included and excluded

Preload 100, 50 and 0%


Wong Kai Sin 24

250

300

350

n (m

m)

Sensitivity Study on Wall Deflection

0

50

100

150

200

ce ca

se

20 kP

a

=200

Cu

exca

v.

P (1.0

m)

00MP

a

ad 50

%D-

Wall

odell

ed

prelo

ad

Def

lect

ion


Refer

ence

Surch

arge 2 E=

2

1.0m

over

eJG

P (

E(JG

P) =

10

Prelo

ad

0.7EI

D

Bored

pile

not m

odNo

pr

Design H,max = 200 mm

3000

3500

4000

4500

5000

nt (k

Nm

/m)

Sensitivity Study on Wall Bending Moment

0

500

1000

1500

2000

2500

3000

e cas

e

20 kP

a20

0Cu

exca

v.

(1.0m

)

00MP

ad 5

0%D-

Wall

delle

drel

oad

Ben

ding

Mom

en


Refer

ence

Surch

arge 2

0E=

20

1.0m

over

ex

JGP (

1

E(JG

P) =

100

Prelo

ad

0.7EI

D

Bored

pile

not m

odNo

pre

Design Mmax = 3400 kNm/m


Wong Kai Sin 25

2000

2500

3000

3500

ce (k

N/m

)

Sensitivity Study on Wall Shear Forces

0

500

1000

1500

2000

nce c

ase

e 20 k

Pa

E=20

0Cu

er ex

cav.

GP (1

.0m)

100M

Pa

oad 5

0%

EID-

Wall

mode

lled

prelo

ad

Shea

r For

c


Refer

enc

Surch

arge E=

1.0m

over

JGP

E(JG

P) =

1Pr

eloa

0.7EI

Bored

pile

not m No

p

Design Vmax = 2200 kN/m

Sensitivity Study - Maximum Strut Load (S1)

250300350400450500

d (k

N/m

)

050

100150200250

eferen

ce ca

se

charg

e 20 k

Pa

E=20

0Cu

m ov

er ex

cav.

JGP (

1.0m)

GP) =

100M

Pa

Prelo

ad 50

%

0.7EI

D-Wa

ll

not m

odell

ed

No pr

eload

Stru

t loa


Design S1 = 420 kN/m

Ref

Surch 1.0

mE(J

G

Bored

pile

no


Wong Kai Sin 26


600700800900

(kN

/m)

0100200300400500

feren

ce ca

se

harge

20 kP

a

E=20

0Cu

mov

er ex

cav.

JGP (

1.0m)

GP) =

100M

Pa

Prelo

ad 50

%

0.7EI

D-W

all

not m

odell

ed

No pr

eload

Stru

t loa

d (



Refe

Surch

a

1.0m

oE(

JGP P 0

Bored

p ile

n


800

1000

1200

(kN

/m)

0

200

400

600

feren

ce ca

se

harge

20 kP

a

E=20

0Cu

over

exca

v.

JGP (

1.0m)

GP) =

100M

Pa

Prelo

ad 50

%

0.7EI

D-Wa

ll

otmo

delle

d

No pr

eload

Stru

t loa

d

Excavation Design 52Design S3 = 960 kN/m

Refe

Surch

a1.0

m o

E(JGP

) P 0

Bored

pile

not


Wong Kai Sin 27


600700800900

1000

(kN

/m)

0100200300400500

eferen

ce ca

se

charg

e 20 k

Pa

E=20

0Cu

m ov

er ex

cav.

JGP (

1.0m)

GP) =

100M

Pa

Prelo

ad 50

%

0.7EI

D-Wa

ll

e not

mode

lled

No pr

eload

Stru

t loa

d



Refe

Surch 1.0

mE(J

G

Bored

pile

n


400

500

600

(kN

/m)

0

100

200

300

erenc

e cas

e

arge 2

0 kPa

E=20

0Cu

over

exca

v.

JGP (

1.0m)

P) = 1

00MP

a

Prelo

ad 50

%

0.7EI

D-Wa

ll

ot mo

delle

d

No pr

eload

Stru

t loa

d



Refer

Surch

ar

1.0m

o J

E(JGP

) Pr 0

Bored

pile

no


Wong Kai Sin 28

Best Estimates

Design Values

based on Sensitivity

St d

Best Estimates and Design Values

Study

Diaphragm Wall

Deflection mm 168 200Moment kNm/m 2980 3400Shear kN/m 2065 2200

Strut S1 Force kN/m 417 420Strut S2 Force kN/m 771 780


St ut S o ce / 80Strut S3 Force kN/m 929 960Strut S4 Force kN/m 836 880Strut S5 Force kN/m 474 550

Bending Moment and Shear Forces at Various Stages

Elev

atio

n (m

)

Elev

atio

n (m

)

56

3000 -2000 -1000 0 1000 2000 3000 4000

Bending moment (kN.m/m)Bending Moment (kNm/m)

000 -1000 0 1000 2000 3000

Shear force (kN/m)Shear Force (kN/m)Excavation Design


Wong Kai Sin 29

From the results of sensitivity studies weFrom the results of sensitivity studies, we can proceed to finalize the design:

Wall design Strut design Waler/stiffer design Set alert levels


Instrumentation plan Contingency plan Design drawings

FillE E

FillRL (m)

Analysis of Control Section for Construction Control

Use best estimated parameters to compute:

Wall deflection profilesUMC

F2 upper

LMC

F2 lowerF2

LMC

LMC

F2 lower

OA N = 20OA N = 30

F2 upper

UMC

85.4

72.1

66.864 7

69.4

Wall deflection profiles

Deflection vs Excav. depth

Strut forces

Wall bending moments

Wall shear forces

Ground settlement


OA N = 70

OA N = 100OA N = 70OA N = 30OA N = 20

64.7

60.0

55.0

59.261.263.7

Ground settlement

Pore pressures

Results are to be compared with field measurements.


Wong Kai Sin 30

How reliable is your design?

sand


Benchmarking Exercise in Germany

Benchmarking Exercise in Germany

Five worst resultswere OMITTED!

Measurement



Wong Kai Sin 31

Maximum Wall Deflectionvs

Excavation Level

Prediction Exercise in Singapore

90

92

94

96

98

100

102

Elev

atio

n Le

vel (

RL

in m

)


84

86

88

0 10 20 30 40 50 60 70 80Maximum Wall Deflection (mm)

E

Particpant # 7 Particpant # 10 Particpant # 1 Particpant # 5Particpant # 3 Particpant # 9 Particpant # 8 Particpant # 11Particpant # 12 Particpant # 6 Particpant # 13 Particpant # 4Particpant # 14 Particpant # 12 Measured

Design vs As-Built Construction Sequence

As-Built Design

62Excavation Design


Wong Kai Sin 32

Over-Excavation

(Clough & ORouke, 1990)

63Excavation Design

Excessive Surcharge

q = 20 kPa

64Excavation Design


Wong Kai Sin 33

Dont be over-confident about your analysis!

Be prepared to face a few surprises.

Implement Observational Method diligently.


If in doubt, get a second opinion.


Session 3aSession 3b

wong design analysis deep excavations session03

Documents