Lecture 1

finite element for soil and rock analyses 15‐JUNE‐2007

PLAXIS SEMINAR‐HO CHI MINH 1

Plaxis Vietnam Seminar

No Title Time

1 The Plaxis Approach‐Geotechnics, Deep Excavation, Foundations and etc

2 Soil Models and Structural Elements

3 Geometry, Model Space, Mesh and Initial Stresses

4 Notes on usage of Plaxis Codes on the modelling of Excavations and Tunnels

FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

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f i n i t e e l e m e n t c o d e f o r s o i l a n d r o c k a n a l y s e s

C t ti l G h i i R ti G t h i l A l i

PLAXIS SEMINARKUCHING 2008

Malaysia

THE PLAXIS APPROACH

Computational Geomechanics in Routine Geotechnical Analysis

V I S U A L I S E A N A L Y S E O P T I M I S E > T H E W A Y F O R W A R D

William W.L. CHEANG

Regional Technical ManagerPlaxisAsia (Plaxis BV)

Contributed

Ir. Erwin BEERNINKIr. Dennis WATERMAN

Dr. Erick SEPTANIKADr. Ronald BRINKGREVE

Dr. Siew Wei LEEDr. Andy PICKLES

Prof. Pieter .A.VERMEERPROF. Yasser EL. MOSSALLAMY

LAXIS PROFESSIONAL vers ion 8 .5 - PLAXFLOW vers ion 1 .5 - DYNAMICS module - 3-D FOUNDATION vers ion 2 .0 – 3-D TUNNEL vers ion 2 .0 – 3-D GEOTHERMIE vers ion 1 .

SEMINAR1. GEOTECHNICAL ENGINEERING2. GEOTECHNICAL ANALYSISG O C C S S3. MODELLING OF SOIL‐STRUCTURE

INTERACTION PROBLEMS WITH PLAXIS4. REAL CASE HISTORIES5. CONCLUSIONS

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1. TUNNELLLINGEXCAVATION

1 GEOTECHNICAL ENGINEERING

2. EXCAVATION3. FOUNDATIONS4. LAND RECLAMATIONS5. SLOPE (EMBANKMENT) STABILITY AND

REINFORCEMENT

1.GEOTECHNICAL ENGINEERING

TUNNELLING

NEW AUSTRIAN TUNNELLING

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SHIELD TUNNELLING



The design of sequential excavations depends on the quality of the ground

The smaller the

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excavated area the smaller the settlements.

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Case study: Heinenoord tunnel near Rotterdam

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EXCAVATIONS

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FOUNDATIONS

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PILED RAFTS FOUNDATIONS

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LAND RECLAMATION

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Soft CLAY

Sandfill

Sandy SILTPVD

W.T.

Deformed mesh at completion of staged reclamation (exaggerated scale)



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2 GEOTECHNICAL ANALYSIS2.GEOTECHNICAL ANALYSIS

2.GEOTECHNICAL ANALYSIS

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GEOMETRY SPACE1. 2‐D Plane Strain Space

2. Axi‐symmetric space

3. 3‐D Space

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45 m45 m

8 m

30 m



AXI-SYMMETRY AND NON AXI-SYMMETRY

AX I - S Y M M E T RY N O T AX I - S Y M M E T RY

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3 SOIL STRUCTURE INTERACTIONPlaxis Finite Element Codes

3.SOIL‐STRUCTURE INTERACTION

3.FINITE ELEMENT ANALYSIS WITH PLAXIS

“REALITY OR VIRTUAL DREAM ?”

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FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

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PLAXIS FINITE ELEMENT CODES

Overview of current products:

CURRENTSUITE OF PROGRAMS + ADD‐ONS MODULES

PlaxisVersion 8.6 Dynamics

Plaxis PlaxFlow Version 1.5 (VI Package)Plaxis PlaxFlow Version 1.5 (VI Package)

Plaxis 3D Tunnel Version 2.2

Plaxis 3D Foundation Version 2.1

P L A X I S V 8 3 D T U N N E L 3 D F O U N D A T I O NP L A X F L O W

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PLAXIS PROGRAMS AND ANALYSIS TYPEAnalysis Type Product (Code)

2D Analysis Stress ‐Deformation Plaxis Professional Version 8.6

1.Stress –Deformation2.Dynamic Problems

Combine Plaxis Professional Version 8.6 + Dynamics module

1 Stress‐Deformation Combine Plaxis Professional Version 8 6 + 1.Stress‐Deformation2.Transient Flow Problems

Combine Plaxis Professional Version 8.6 + PlaxFlow

3D Analysis Tunnels*ExcavationSlopeReinforced Wall

Plaxis 3D Tunnel Version 2.4

Foundations*Piled Foundationsl d f d

Plaxis 3D Foundation Version 2.1

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Piled Raft FoundationsExcavations

PLAXIS DEVELOPMENT TIME-LINE

1 6 0 9

3D Tun

nel

Version 1

987

989

990

991

993

995

998

002

001

000

Version 2

Version 3

Version 4

Version 5

Version 6

Version 7

Version 8

Dyn

amics

003

Plax

Flow

004

005

3D Fou

nd v1

3D Fou

nd v1.

007

3D Fou

nd v2.

2D Version 9

008

19 19 19 19 19 19 19 202020 20 20 20 20 20

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PROGRAMS (CODES): 2D AND 3D

PLAXIS 2D PLAXIS 3D

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PLAXIS PROFESSIONAL v8.6

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Excavations

PLAXIS V8

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Soil reinforcement

PLAXIS V8

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Tunnels

PLAXIS V8

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PLAXIS PROFESSIONAL VERSION 8.5

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MOVIE1



PLAXIS PLAXFLOW v1.5

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PLAXFLOW

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PLAXFLOW + PLAXIS 8

Deformations Ground waterheads

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RAIN WATER INFILTRATION ON PARTIALLY SATURATED SLOPE

MOVIE 1

MOVIE2

DYNAMICS MODULE

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PLAXIS DYNAMICS MODULE

For vibrations and earthquake simulation1. Single‐source vibrations

2. Earthquake analysis

3. Absorbing boundaries

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MOVIE

S T R O N G M O T I O N I N P U T F R O M S M C

PLAXIS 3D TUNNEL v2.2

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PLAXIS 3D TUNNEL

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PLAXIS 3D TUNNEL APPLICATIONSMODELLING OF SHIELD TUNNELLING PROCESS

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PLAXIS 3D TUNNEL APPLICATIONSSIMULATION OF SOIL‐STRUCTURE INTERACTION: EFFECT OF TUNNELLING ON STRUCTURE

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MOVIE

PLAXIS 3D TUNNEL APPLICATIONSTWIN TUNNELS

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PLAXIS 3D FOUNDATION v2.1

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PLAXIS 3D FOUNDATION: PILES

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PLAXIS 3D FOUNDATION: PILED FOUNDATIONS

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STRUCTURE ON SLOPE

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PLAXIS 3D FOUNDATION: PIERS

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COMPLEX SOIL STRUCTURE INTERACTION MODEL

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MULTI-SUCTION BUCKETS (OFFSHORE)

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TANK ON PILED RAFT FOUNDATION

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COMPLEX SOIL STRUCTURE INTERACTION PROBLEMS

MOVIE E X C AVAT I O N S

MOVIE C O F F E R D AM

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DEVELOPMENTS

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RECENT DEVELOPMENTS – 3D FOUNDATION

Plaxis 3D Foundation Version 2

Embedded piles

Ground anchorsGround anchors

Phi‐c reduction

Simulation of soil tests

Small‐strain stiffness (HS‐small)

User‐defined soil models

Grouping of elements

N O t t

10115

14

13

6

5

4

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New Output program

103

102

12

11 10

9

8

7

6

3

2

1

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QUAY WALLS

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ANCHORING OF QUAY WALLS

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MICROPILES

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1. Constitutive Soil Models

1. Linear Elastic

2. Linear Elastic Perfectly Plastic :

• Mohr‐Coulomb

3. Isotropic Hardening Models:

• Hardening Soil Model ( Failure Criterion, MC, Lade & Matsuoka‐Nakai)

• Double Hardening

• Cam‐Clay Class of models (Soft‐soil & Soft soil creep)

S th l t th t b i t tSome other elements that may be important:

• Anisotropy

• Small‐strain stiffness effects

• Cyclic effects

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4 REAL CASE HISTORIES

2‐D MODELLING OF EXCAVATIONS3‐D MODELLING OF EXCAVATIONS3‐D PILED RAFT FOUNDATIONS

4. REAL CASE HISTORIES




APPLIED 1 EXCAVATION

OVAL COFFERDAMNICOLL HIGHWAY INVESTIGATIONEFFECT OF TENSION PILES EFFECT OF PASSIVE PILES

APPLIED 1: EXCAVATION

Oval Cofferdam Structure Details

Plan View Cross Section32m

32m

27m

24m

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Oval Cofferdam Details

• Excavation for a pumping station

• Ground conditions: Fill, Clay, Alluvium, CDG, Rock

• Oval cofferdam size 24 m × 32 m (plan view)

• 27 m deep excavation in 6 stages

• DWall thickness 1.2 m

• Ring beams size 0.8 m × 1.8 m

O i i l d i d 2D d lli

69

• Original design used 2D modelling

• Struts size 305 × 406 × 287 (necessary?)

• 3D modelling explores early struts removal

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Designer’s Original Analysis in 2D

70

• Model plane strain excavation

• No consideration of hoop force in ring DWalls and ring beams

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3D Analysis

Plaxis 3D Foundation

71

Mesh size 200×170×40m

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Retaining System for Oval Cofferdam

SpringVolume element

Deformation(150x)

72

Pile with Shell

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Stress in Ring Beams & Force in StrutsMean stress in ring beams

(kPa)Layer 2D (kN) 3D (kN)

1st str t 2064 1083

Strut Forces

1st strut 2064 1083 (52%)

2nd strut 4200 1577 (38%)

3rd strut 4552 1584 (35%)

4th strut 7856 1503 (19%)

73

(19%)5th strut 6784 2285

(34%)6th strut 5848 2271

(39%)

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Comparison of 2D & 3D Deformations

Parameter 2D 3D

Max. ground settlement 31 mm 10 mm

Max. wall deflection 64 mm 25 mm

• Bottom-up construction on-going

74

• Bottom-up construction on-going

• Field measurements close to 3D predictions

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Check for One Strut Failure

• BS8002:1994, Cl. 4.5.2.2.1 states

The design should also accommodate the possible failure of an individual strut tie rod or anchor.individual strut tie rod or anchor.

• CIRIA C580, Cl. 5.6.3, Accidental Load Case considers

… loss of a prop (partial support) to the wall, …

• Ensure failure of one strut would not lead to collapse

• Removal of one strut in 2D analysis

1. removes a whole row of struts into-the-plane

75

1. removes a whole row of struts into the plane

2. does not consider redistribution of soil stresses and strut forces in 3D space

• Carry out 3D analysis using 3D Tunnel/Foundation

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Check for One Strut FailurePlaxis 3D Tunnel

Increase in adjacent strut forces due to one strut removal

One strut removed

30m

76

One strut removed16%5% 17% 6%

47%18% 18%

• Strut vertical spacing 3m, horizontal spacing 4m

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Check for One Strut Failure

Increase in wall horizontal deflection contours

Wall bending moment contours

Strut removed (10mm increase) 45m

77

1400 kNm/m increase

32m

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Modelling of a Gap in Wall

Wall GWall panel

Gap in wall

Wall panel

Gap panel

78

• Gap in wall for utility crossing

• Modelled by PLAXIS 3D Tunnel

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Modelling of a Gap in Wall

Wall

Wall deflection contours

Grouted slab

Wall Wall

160mm deflection

79

Gap infilled by grout • Panel filling gap as excavating downward

Panel 0.8m thk Panel 1.0m thk Panel 0.8m thk

Gap below final exc.

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Idealisation of Individual Piles as Walls

DWall+96

+103

Singapore

1.8mØ pile

1.0mØ pile

(13m c/c)

(6.5m c/c)

24m

+81

8.5m

12.5m

80

DWall

• 22m deep top down exc. in soft clay

• 1.0 and 1.8m Ø pile installed within cofferdam

+50+45

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3D Modelling of Individual Piles

Slab

PLAXIS 3D Foundation

DW

all

+50m

81

1.0mØ pile (+50m)

1.8mØ pile (+45m)

Models half geometry

DWall

1.8mØ

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Comparison of Wall Deflection

2D 3D

95

100

105

95

100

105

45

50

55

60

65

70

75

80

85

90

mR

L

45

50

55

60

65

70

75

80

85

90

mR

L

2D predicts smaller DWall deflections, as soil is not allowed to flow between piles

82

Diaphragm wall deflection

0.00

0

0.00

5

0.01

0

0.01

5

0.02

0

0.02

5

0.03

0

0.03

5

0.04

0

0.04

5

0.05

0

0.05

5

Wall horizontal disp. (m)

0.00

0

0.00

5

0.01

0

0.01

5

0.02

0

0.02

5

0.03

0

0.03

5

0.04

0

0.04

5

0.05

0

0.05

5

Wall horizontal disp. (m)

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Comparison of Tension Force in Piles

1.0m Ø pile at 6.5m c/c 1.8m Ø pile at 13m c/c

9095

100

9095

100

3D gives

45505560657075808590

Leve

l (m

RL)

45505560657075808590

Leve

l (m

RL)2D gives

10000 kN

3D gives 3000 kN

2D gives 20000 kN

3D gives 1400 kN

83

• Tension force (+ve) in piles due to ground heave in cofferdam

-500

0 0

5000

1000

0

1500

0

2000

0

Compression/tension force in pile (kN)

-500

0 0

5000

1000

0

1500

0

2000

0

Compression/tension force in pile (kN)

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Notes on Individual Piles as Walls

• Widely spaced individual piles within cofferdam modelled as continuous walls in 2D analysis would predict:

1 Smaller deflection of retaining wall Continuous wall does not allow1. Smaller deflection of retaining wall. Continuous wall does not allow flow of soil between piles, i.e. wall too rigid.

2. Larger tension force in the continuous wall. Larger surface area of wall for mobilisation of shaft resistance.

• Consequences might be:

1. under-design of retaining wall

84

2. unnecessary sleeving/coating of individual piles in cofferdam

• Discrepancy between 2D and 3D prediction increases with the increase of individual piles spacing into-the-plane.

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Effect of Excavation on Piles

Macau

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Effect of Excavation on Piles

• Piles for supporting high-rise

• “Dido” pile external dia. 0.6 m, internal dia. 0.3 m

• Pile spacing 3 - 8 m, length ~ 45 m

• Ground conditions: fill, soft clay, stiff soil

• Excavation 3 - 4 m for construction of pile caps

• 3D analysis to investigate

86

1. effect of excavation on pile deflection

2. contribution of piles to FOS of excavation slope

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3D Analysis

Individual piles

65m

• Individual piles modelled by8m

87

• Individual piles modelled by “plate” element

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Deformation of Excavation

Piles resist deformation

88

20x • Localised deformation around piles

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Deformation of Piles

160

180

200CB

20

40

60

80

100

120

140

160

Pile

hea

d de

flect

ion

(mm

) A

AB

C

Soft soil

Stiff soil

89

0Exc to+2.5

Exc to+1.3

Exc to+0.8

Back excto +2.5

Back excto +4.5

• Measured pile deflection: order of 100 mm

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Phi-c Reduction to Determine FOS

Remember to input moment capacity of piles Mp!

Plastic hinge

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FOS for Different Excavation Depths

2.20

2.40

1.20

1.40

1.60

1.80

2.00

FOS

piles

no piles

91

1.00Exc to+2.5

Exc to+1.3

Exc to+0.8

Back excto +2.5

Back excto +4.5

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APPLIED 2 FOUNDATIONS

1.EFFECT OF BARRET PILES ON ADJACENT INFRASTRUCTURE2.PILED FOUNDATION ANALYSIS3. CALIBRATION TEST: NUMERICAL AND CENTRIFUGE

APPLIED 2:FOUNDATIONS



Foundation System for a High-rise

(12m)

Tunnel

• High-rise above an existing tunnel

• Barrettes straddle tunnel

Singapore

High-rise footprint

Barrettes straddle tunnel

• Barrettes 1.5m thick, 100 m deep

• Tunnel settlement criteria 15 mm

• Ground conditions: 35 m soft clay underlain by stiff soil

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soil

• 2D & 3D analyses to optimise barrette geometries

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Geometry of Existing Tunnel

Bored pile

• Supported by three row of bored piles 1.2 - 1.5m Ø @ 4 - 8 m c/c

• Bored piles ~60 m long

T l idth 12 h i ht 6

94

• Tunnel width 12 m, height 6 m, floor/wall thickness 1 m

• Tunnel 5 m below ground surface

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2D Analysis

High-rise loading tunnel

Barrette

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Limitations of 2D Analysis

• Line load applied on barrettes is uniform into-the-plane

• In real situation

1 li l d i li d ithi th b ildi1. line load is applied within the building area

2. barrette section further away from building boundary helps shed load through skin friction

• Existing bored piles supporting the tunnel are modelled as “wall” into-the-plane

• Changes of axial force in existing piles may not be reliably

96

Changes of axial force in existing piles may not be reliably predicted

• Cannot give settlement profile of the tunnel into-the-plane (for structural calculation of tunnel deflection/distortion)

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3D Analysis

Pile-soil area60m Line load on barrette

Plaxis 3D Foundation - half problem modelled

152mTunnel

Symmetry plane

97

160m

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Structural Items in 3D AnalysisLine load on barrette

TunnelVolume element: barrettes, transfer beams & piles

“Floor” element: tunnel roof and floor slab

Transfer beam Piles“Wall” element: tunnel walls

Interface element: on barrettes, transfer beams, wall & piles

98

Barrette(100 m)

Building load(equivalent raft foundation)

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3D Analysis Results

Settlement Deformation

500x

Settlement of tunnel

roof

Settlement of tunnel

floor

99

walls

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3D Analysis Results

0 10 20 30 40 50 60

Distance in longitudinal direction of tunnel (m)

Increase of Axial Force in Tunnel Piles

Longitudinal Settlement Profile of Tunnel

90

95West pile

Set

tlem

ent (

m)

West sideEast side

50

55

60

65

70

75

80

85

Ele

vatio

n (+

mR

L)

Middle pileEast pile

Soft soil

Stiff soil

100

35

40

45

50

Increase of axial force in pile (kN)

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Summary of Barrette Foundation Analysis

• 3D analyses predict smaller tunnel settlement than 2D, reduction by 3 - 5 times

• 3D analyses model better

1. stress bulb of building load

2. load shedding through skin friction in barrettes

3. increase of axial force in tunnel piles

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4. longitudinal settlement profile of tunnel

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APPLIED 3 DEFORMATION

1.SETTLEMENT OF STRUCTURE DUE TO CONSOLIDATING GROUND & THE EFFECT OF NEGATIVE SKIN FRICTION2.EFFECT OF EMBANKMENT ON SERVICE PIPE

APPLIED 3:DEFORMATION ANALYSIS

Settlement at a Depot SiteTaiwan

• Two-storey depot supported by 0.5m Ø driven piles in alternating layers of clay and sand with pile toes founded in sand

Plan view area 280m×130m

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and sand, with pile toes founded in sand

• Consolidation settlement occurring due to placement of 2-3m surface fill onto near surface clay layer

• Concern for negative skin friction induced on pile groups

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SETTLEMENT AT A DEPOT SITE

FILL+21.5 mRL

+19.5 mRL

2.5m

Model ¼ pile group

Point load1.25m

Upper CLAY

SAND

Lower CLAY

+10 mRL

+0 mRL

Model ¼ pile group

PLAXIS 3D Foundation16m

37m

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Lower SAND-10 mRL

-15 mRL

15m15m

0.5m dia. pile

Toe +5.5 mRL

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Settlement at a Depot Site

• Modelling sequences

1. Initial equilibrium

Excess pwp contours

2. 2-3 m Fill placement (epwp)

3. Install pile cap and piles

4. Apply building load 600 kN to ¼ of pile cap (epwp)

5. Consolidation (dissipation of epwp)

Clay

Clay

110

Dissipation of epwp

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130mm

Consolidation settlement

100mm

111

Pile toe

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SETTLEMENT AT A DEPOT SITE

0.0000 100 200 300 400 500 600 700 800 900 1000

Time (Day)

F 29 F 30 F 31 F 32

-0.100

-0.080

-0.060

-0.040

-0.020

Settl

emen

t (m

)

F-29 F-30 F-31 F-32

PLAXIS

Hand calc.

(kclay=1×10-8 m/s)

112

-0.160

-0.140

-0.120

25/4/066/5/04

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220 50 100 150 200 250 300 350 400 450 500 550 600 650 700

Axial force down the corner pile (kN)

10

12

14

16

18

20

met

re R

educ

ed L

evel

Bldg. load

NSF

NSF: Negative skin friction

113

4

6

8

m

Bldg. load + consolidation

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8. Lateral Movement of Buried Service Pipe

Service pipeEmbankment

Australia

15m Service pipe

Cone

Cone

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Lateral Movement of Buried Service Pipe

• 10 m high embankments and 18 m high cone to be built adjacent to an existing service pipe

S i i 0 4 Ø d b i d 1 d• Service pipe 0.4 m Ø and buried 1 m deep

• Loading from embankments and cone may deform the pipe laterally

• Ground conditions: fill, soft clay, stiff clay, residual soil

• 3D analysis to predict the deformation magnitude and

115

profile of the pipe

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3D Analysis

Embankment load

Plaxis 3D Foundation

Cone load

Alignment of buried pipe35m

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3D Analysis Results

Deformed Pipe

Deformation at Depth 1 m Below Ground Surface (50x)

117

Pipe modelled by “beam” element

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3D Analysis Results

0

-0.0

30

-0.0

25

-0.0

20

-0.0

15

-0.0

10

-0.0

05

0.00

0

0.00

5

Lateral movement of pipe (m)• A simple 3D loading scenario modelled by 3DF

• Model the soil-structure i t ti ff t20

40

60

80

100

120

140ngitu

dina

l dis

tanc

e (m

)_

Cone

Emb.

interaction effect

• Give pipe deflection, shear force & bending moment in 3D

118

140

160

180

200

Lo

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General Notes for FE Analysis• Soil input parameters and modelling techniques continually

refined as more field data is available

• A series of sensitivity analyses are necessary to cover• A series of sensitivity analyses are necessary to cover possible field scenarios

• Use of numerical modelling in practice requires:

1. A good knowledge of soil mechanics and finite element/difference principles

120

2. An understanding of the programme/model limitations

3. Careful checking of numerical results by competent engineers

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ReferencesBreth, H. and Chambosse, G. (1975). Settlement behaviour of buildings above subway tunnels in Frankfurt clay. Proc. Conf.

Settlement of Structures, Cambridge, April 1974, London: Pentech Press, 329 ‐ 336.

Boscardin, M. D. and Cording, E. J. (1989). Building response to excavation‐induced settlement, ASCE, J. Geotech. Engrg., 115(2), 22 ‐28.

CIRIA (2003). Embedded retaining walls ‐ guidance for economic design. Construction Industry Research and Information Association, Report C580.

Davies, R. V. and Henkel, D. J. (1980). Geotechnical problems associated with the construction of Charter Station, Hong Kong.Proc. of the Conf. on Mass Transportation in Asia, Hong Kong, paper J3, 31 p.

Dickin, E. A. and Nazir, R. (1999). Moment‐carrying capacity of short pile foundations in cohesionless soil. J. Geotech. & Geoenv. Engrg. ASCE, 125(1), 1‐10.

Franzius, J. N., Potts, D. M. and Burland, J. B. (2006). The response of surface structures to tunnel construction. GeotechnicalEngineering, Proc. of ICE, 159(1), 3‐17.

Morton, K., Leonard, M. S. M. and Carter, R. W. (1980). Building settlements and ground movements associated with construction of two stations of the modified initial system of the Mass Transit Railway, Hong Kong. Proc. of 2nd Int. Conf. on Ground Movements and Structures, Cardiff, UK, 708‐802; 946‐947, Discussion (published under the title Ground Movement and Structures, Geddes, J. D., eds., Pentech, London, 1981).

Morton, K., Cater, R. W. and Linney, L. (1980). Observed settlements of buildings adjacent to stations constructed for the modified initial system of the Mass Transit Railway, Hong Kong. Proc. of 6th Southeast Asian Conf. on Soil Engineering,

121

modified initial system of the Mass Transit Railway, Hong Kong. Proc. of 6 Southeast Asian Conf. on Soil Engineering, Taipei, 415‐429.

Prasad, Y. V. S. N. and Narasimha Rao, S. (1994). Experimental studies on foundations of compliant structures – I. under static loading. Ocean Engineering, 21(1), 1‐13.

PLAXIS (2002). Users forum – beam to pile properties. PLAXIS Bulletin, June, 2002, p.22, http://www.plaxis.com/upload/bulletins/12%20PLAXIS%20Bulletin.pdf.

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Thank you

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Lecture 1

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Transcript of Lecture 1