First Asian Experienced Plaxis User Course 2003 -2

1st Asian Course for Experienced

Plaxis Users

Dates

: 31 July to 2 August 2003

Location

: National University of Singapore

Course leader : Associate Professor Harry Tan, National University of Singapore

INTRODUCTION: This course will follow in the tradition of the International Course for Experienced Plaxis Users, held annually in The Netherlands. The course is scheduled to be held 4 days before the 12th Asian Regional Conference on Geotechnical Engineering in Singapore, so as to allow for maximum participation of Plaxis users in Asian countries. COURSE CONTENT: It is aimed to teach the use of advanced soil models and advanced features in the new Plaxis V8, and an introduction of the 3D Tunnel programs. The basic course covers the Mohr-Coulomb model, attention is now focused on the Hardening Soil model and the Soft Soil Creep model. These model and advanced features of Plaxis V8 are employed in handson practice in practical problems of excavations,

ratory soil investigations. As before, lectures will be followed by related exercises, which are real case studies. Also the 3D tunnel program will be introduced. • Deep excavations - Prof H. Tan • Consolidation in excavations and cut slopes Prof H. Tan • Tunneling - Prof P.A. Vermeer • Modeling of shield tunnels - Prof P.A. Vermeer • Introduction to 3D aspects of NATM tunneling Prof P.A. Vermeer The third day focused on the Soft Soil Creep model and its applications to embankments on weak foundations improved with PVD and geosynthetics. • Soft Soil Creep model - Prof P.A. Vermeer • Embankments on weak foundation with PVD and geosynthetics - Prof H. Tan SOFTWARE: Exercises and case studies are based on the PLAXIS computer program V8, which is used by geotechnical engineers worldwide. This user-friendly code has been developed for deformation analyses, stability

embankments, slopes and tunnels. The course provides both the knowledge and hands-on experience in using advanced soil models and new Plaxis features. The theoretical knowledge is provided in lectures, whereas the experience can be obtained from the exercises and case studies. Some of the main lectures concentrate on various aspects of excavations, embankments, slopes and tunnels, whereas others go into details of advanced modeling features. LECTURES: Experts with theoretical background and an extensive experience in practical computer modeling give lectures and prepare exercises of case studies. On the first day of the course the Hardening Soil model will be introduced and the effect of groundwater flow will be considered in detail. The specific areas of lectures are:

Organizers

: PAC, Faculty of Engineering, National University of Singapore PLAXIS BV Consoft International Pte Ltd

• • • • • •

Concepts of plasticity - Prof H. Tan Soil stiffness - Prof P.A. Vermeer Hardening Soil model - Prof P.A. Vermeer Drained and undrained behavior - Prof H. Tan Parameters of the HS model - Prof P.A. Vermeer Pore pressures and groundwater flow - Prof H. Tan

During the second day, the focus is on advanced engineering in the field of deep excavations and tunnels, and the determination of parameters from in-situ and labo-

assessment, groundwater flow and consolidation. It contains special options for soil-structures involving retaining walls, ground anchors,geosynthetics, tunnels linings, etc. The latest V8 has a fully automatic mesh generator based on graphical input of soil-layer geometries, and several new features to facilitate input and analysis of complex situations. Amongst other things, Plaxis V8 allows for fully coupled deformation-consolidation during staged construction. FORMAT: The course begins with registration on Thursday morning and ends on Saturday afternoon. Each session begins with 60 minutes of lectures followed by an application exercise of about the same length. Lectures are in English, and individual assistance will be provided by graduate students during exercises. COST: The cost of the course is $1200 per participant. This includes a full set of instruction manuals and the use of a computer. The fees also covers all lunches and two tea-breaks per day.

Prof Harry Tan - Department of Civil Engineering, NUS (course

Prof Pieter Vermeer - Professor of Geotechnical Engineering,

leader)

University of Stuttgart (Germany)

Harry teaches basic and graduate course in Geotechnical Engi-

Pieter teaches both basic courses on Soil Mechanics and special

neering at NUS. He has been a Plaxis user over the last 10 years,

courses of Geotechnical Engineering at the University of

and has taught Plaxis courses in Singapore, Malaysia and Korea

Stuttgart in Germany. He has been involved in constitutive mod-

over the last 3 years. He is involved in geosynthetics and earth

elling and finite element analysis since the early seventies and

reinforcement research, and is very much involved in consulting

initiated the development of the Plaxis code. His interests range

for industry in Singapore and Malaysia using the Plaxis pro-

from field and laboratory testing of soils and rocks up to the

gram. He is currently the Director of Centre for Soft Ground Engi-

analysis of geotechnical structures.

neering at NUS.

The Lecturers

SCHEDULE 1st Asian Course for EXPERIENCED PLAXIS USERS Dates: 31/07, 1/08 and 2/08 2003 Thursday, 31 July 2003 0900-0915 0915-1000 1000-1015 1015-1100 1100-1200 1200-1300 1300-1345 1345-1415 1415-1515 1515-1530 1530-1615 1615-1700

CG01 Opening CG02 Concepts of Plasticity Break CG03 Stiffness of Soils CG04 Foundation (Exercise) Lunch CG05 Hardening Soil Model CG06 Drained and Undrained Soil Behavior CG07 Pile Loading Test (Exercise) Break CG08 Selection of Parameters for HS CG09 Pore Pressures and Groundwater Flow

Tan SA Tan SA Vermeer

Vermeer Tan SA

Vermeer Tan SA

Friday, 1 August 2003 0900-0945 0945-1015 1015-1030 1030-1200 1200-1300 1300-1400 1400-1500 1500-1515 1515-1630 1630-1700

CG10 Deep Excavations CG11 Consolidation Break CG12 New OG Excavation (Exercise) Lunch CG13 Tunnel Heading Stability CG14 Settlements due to Tunneling Break CG15 Shield Tunneling (Exercise) CG16 Plaxis 3D Tunnel (Demonstration)

Tan SA Tan SA

Vermeer Vermeer

Saturday, 2 August 2003 0900-0945 0945-1030 1030-1045 1045-1200 1300-1400 1400-1415

CG17 Soft Soil Creep CG18 Embankment Modeling Break CG19 Muar Test Embankment (Exercise) Lunch CG20 Closure

Vermeer Tan SA

Vermeer/Tan

1ST Asian Course for

EXPERIENCED PLAXIS USERS 31ST JULY to 2ND AUGUST 2003

THURSDAY, 31ST JULY 2003

CG02 CONCEPTS OF PLASTICITY

Concepts of Plasticity Ronald Brinkgreve Plaxis BV / Delft University of Technology

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Contents • Aspects of real soil behaviour • Stresses and strains • Stress paths in standard soil tests • Standard drained triaxial test (CD-test) • Oedometer test • Consolidated undrained triaxial test (CU-test)

• Basic concepts of the Mohr-Coulomb model • Elastic strains, plastic strains • Yield function, plastic potential • Parameters

• Possibilities and limitations of the M-C model PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

2

1

Aspects of real soil behaviour • • • • • • • • • •

Elasticity (reversible deformation; limited) Plasticity (irreversible deformation) Failure (ultimate limit state or critical state) Presence and role of pore water Undrained behaviour and consolidation Stress-dependent stiffness Time-dependent behaviour (creep, relaxation) Compaction en dilatancy Memory of pre-consolidation pressure Anisotropy (directional strength and/or stiffness)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

3

Stresses and strains • Stresses Cartesian stresses: σ = σ xx σ yy σ zz

[

σ xy σ yz σ zx ]T

σ = σ '+σ w σ = total stresses σ’ = effective stresses σw = pore pressure (isotropic): • Hydrostatic (constant head) • Non-hydrostatic (variable head → groundwater flow) • Excess pore press. (undrained behaviour → consolidation) PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

4

2

Stresses and strains • Stresses Principal stresses: σ 1 = s * −t *

(

s * = 12 σ ' xx +σ ' yy

σ 2 =σ zz σ 3 = s * +r *

t*=

1 4

)

(σ 'xx −σ ' yy )2 + σ xy2

Stress invariants (p and q):

(

)

p=

1 1 σ xx + σ yy + σ zz = (σ 1 + σ 2 + σ 3 ) 3 3

q=

1 2 2 (σ xx − σ yy ) 2 + (σ yy − σ zz ) 2 + (σ zz − σ xx ) 2 + 6σ xy + 6σ 2yz + 6σ zx 2

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

5

Stresses and strains • Strains

[

Cartesian strains: ε = ε xx Normal strains ∂ ux ∂x ∂ uy ε yy = ∂y

ε xx =

ε zz =

∂ uz ∂z

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

ε yy ε zz γ xy γ yz γ zx ]T Shear strains γ xy =

∂ ux ∂ u y + ∂y ∂x

∂ u y ∂ uz + ∂z ∂y ∂u ∂u γ zx = z + x ∂x ∂z

γ yz =

Concepts of Plasticity

6

3

Stresses and strains • Visualisation of stresses: -σ1

-σ1 p-axis

q-axis

√2

Rendulic plane q-axis

p-axis 1

-σ3 σ2= σ3

-σ2

-σ3√2

Principal stress space PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Rendulic plane Concepts of Plasticity

7

Stresses and strains • Visualisation of stresses:

-σ1

-σ1 p-axis Deviator plane -σ3

-σ2

-σ3

-σ2 Principal stress space

Deviator plane (π-plane) (p = constant)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

8

4

Stress paths in standard soil tests • Standard drained triaxial test (CD test) Stress-strain and strain diagram: σ1 εv

⏐σ1-σ3⏐ ⇓ ε1

σ3

σ3

-ε1

εv

-ε1

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

9

Stress paths in standard soil tests

Loose sand PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Dense sand Concepts of Plasticity

10

5

Stress paths in standard soil tests • Standard drained triaxial test (CD test) Stress paths: σxy -σ’1 Axial loading

-σ3

σn -σ3

-σ’3

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

11

Stress paths in standard soil tests • Consolidated undrained triaxial test (CU test) Stress-strain diagram: σ1 ⏐σ1-σ3⏐ εv ≈ 0 σ3

⇓ ε1 σ3

pw

-ε1 -ε1

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

12

6

Stress paths in standard soil tests

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

13

Stress paths in standard soil tests • Consolidated undrained triaxial test (CU test) Stress paths: -σ’1 Axial loading

-σ3 -σ3

-σ’3

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

14

7

Stress paths in standard soil tests • Oedometer loading test Stress-strain diagram:

σ1

σ1 -ε1 ln σ1

⇓ ε1

-ε1 PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

15

Stress paths in standard soil tests • Oedometer loading test Stress paths: -σ’1

Axial loading

-σ’3 PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

16

8

Stress paths in standard soil tests • Simple shear test Stress-strain diagram: dσxy

σxy

⇒ dγxy γxy εv γxy PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

17

Stress paths in standard soil tests • Simple shear test Stress paths:

-σ’1 Shearing

-σ’3 PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

18

9

Basic concepts of the M-C model • Division of strains and strain increments: ε =ε e + ε p

(strains)

dε = dε e + dε p

(strain increments)

Strains (or increments) are divided into elastic strains and plastic strains A soil model relates increments of stress to increments of strain

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

19

Basic concepts of the M-C model • Elastic strain increments: e ⎡ d ε xx ⎢ ⎢ ⎢dε e ⎢ yy ⎢ ⎢ e ⎢ d ε zz ⎢ ⎢ e ⎢ d γ xy ⎢ ⎢ ⎢ d γ eyz ⎢ ⎢ ⎢dγ e ⎣ zx

⎤ ⎡ 1 ⎥ ⎢ ⎥ ⎢ ⎥ ⎢− ν ⎥ ⎢ ⎥ ⎢ ⎥ ⎢− ν ⎥ 1 ⎢ ⎥ = ⎢ E ⎢ ⎥ ⎥ ⎢ 0 ⎥ ⎢ ⎥ ⎢ ⎥ ⎢ 0 ⎥ ⎢ ⎥ ⎢ ⎥ ⎢⎣ 0 ⎦

From Hooke’s law:

−ν

−ν

0

0

1

−ν

0

0

−ν

1

0

0

0

0

2 + 2ν

0

0

0

0

2 + 2ν

0

0

0

0

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

⎤ ⎡ d σ ' xx ⎥⎢ ⎥⎢ 0 ⎥ ⎢ d σ ' yy ⎥⎢ ⎥⎢ 0 ⎥ ⎢ d σ ' zz ⎥⎢ ⎥⎢ ⎥⎢ 0 ⎥ ⎢ d σ ' xy ⎥⎢ ⎥⎢ 0 ⎥ ⎢ d σ ' yz ⎥⎢ ⎥⎢ 2 + 2ν ⎥⎦ ⎢⎣ d σ ' zx 0

⎤ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥⎦

20

10

Basic concepts of the M-C model • Plastic strain increments: d ε p = dλ

From flow rule:

∂g ∂σ '

dλ = magnitude of plastic strains (multiplier) dg/dσ’ = direction of plastic strains (vector) g = plastic potential (function) Classical plasticity: g = f

(associated plasticity)

For soils in general: g ≠ f

(non-associated plasticity)

f = yield function PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

21

Basic concepts of the M-C model • When do plastic strains occur? Determination on the basis of a yield function f = f(σ’,ε) • If f < 0 • If f = 0 and df < 0 • If f = 0 and df = 0 • f>0

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Pure elastic behaviour Unloading from a plastic state (= elastic behaviour) Elasto-plastic behaviour Non-acceptable stress state

Concepts of Plasticity

22

11

Basic concepts of the M-C model • Yield function: Can be represented as a contour in (principal) stress space σ1 f>0

Not acceptable

f=0

Plasticity

f 20

Boulder clays (e.g. Teeside, Cheshire) and very stiff ´blue´ London Clay, Oxford Clay, Keuper Marl

Low compressibility

0.05 – 0.10

10 – 20

Upper ´blue´London Clay, weathered ´brown´ London Clay, fluvio-glacial clays, Lake clays, weathered Oxford Clay, weathered Boulder Clay, weathered Keuper Marl, normally consolidated clays (at depth)

Medium compressibility

0.10 – 0.30

3 – 10

Normally consolidated alluvial clays (e.g. estuarine clays of thames, Firth of Forth, Bristol Channel, Shatt-al-Arab, Niger Delta, Chicago Clay), Norwegian ´Quick´Clay

High compressibility

0.30 – 1.50

0.7 - 3

Very high compressibility

Above 1.5

< 0.7

Very organic alluvial clays and peats

Note: Tomlinson does not indicate a stress level, but data seem to correspond to pref = 100 kPa. Tomlinson (1995): Foundation Design and Construction, Pitman Publishing Inc.

IGS, University of Stuttgart

12

Cone Penetration Testing in Geotechnical Practice. Book by Lunne et al. (1997), Blackie Academic & Professional Quote from the CPT-book: Most correlations between CPT results and the drained constrained modulus, M, refer to the tangent modulus, as found from oedometer tests. The reference value of M is normally based on the effective vertical stress, σ′v 0 , before the start of the in situ test; this value is denoted M0. Based on a review of available calibration chamber tests, Lunne and Christophersen (1983) recommended that an estimate of M0 for NC unaged and uncemented predominantly silica sands can be obtained from:

M0 = 4qc

for qc < 10 MPa

M0 = 2qc + 20 (MPa)

for 10 MPa < qc < 50 MPa

M0 = 120 MPa

for qc > 50 MPa

Lunne and Christophersen also included OC sands in their study and recommended as a rough guideline to use:

M0 = 5qc

for qc < 50 MPa

M0 = 250 MPa

for qc > 50 MPa

For an additional stress ∆σ′v , Lunne and Christophersen recommended Janbu´s (1963) formulation to compute M for the stress range σ′v 0 to σ′v 0 + ∆σ′v :

M = M0

σ´v 0 + ∆σv´ / 2 σv´0

Lunne, T. and Christophersen, H. P. (1983): Interpretation of cone penetrometer data for offshore sands. Proceedings of the Offshore Technology Conference, Richardson, Texas, Paper No. 4464.

IGS, University of Stuttgart

Part 3 The logarithmic compression law as a special case for m=1

m=1 :

Literature :

dε ≡

pref dσ dσ = Eoed Eref oed σ′

∆e = − CC ∆ log σ′

∆ε´ =

pref ∆ ln σ′ Eref oed

∆ε´ =

CC ∆ ln σ′ 1 + e0 ln10

Eref oed = (1 + e 0 ) ln 10

pref CC

CC = Compression Index e0 = Initial Void Ratio

IGS, University of Stuttgart

13

Results of an oedometer test on a reconstituted clay sample: m=1 e

e

1,4

ε =

− ∆e 1 + eo

1,4

Cc

1,2

1,2

1,0

1,0

0

200

400

600

1

800

10

100

σ´ [kPa ]

1000

σ´ [kPa ]

Data from an oedometer test on a reconstituted clay sample (kaolin), wL = 69%, wP = 38%

after: Wood (1990), Soil Behaviour and Critical State Soil Mechanics, Cambridge University Press.

IGS, University of Stuttgart

The logarithmic law (m=1) is accurate for soft soils, but not for coarse grained soils and neither for heavily overconsolidated soils

normally consolidated clay from Drammen site

1.4

logarithmic law

m=1

void ratio e

1.2 0.9 loose Hostun sand m reasonable value for saturated soil nK ' 1+ Kw

Example 2: E´ = 3 000 kPa,

ν´ = 0.45,

→ K´ = 10 000 kPa,

νu = 0.495

Ktotal = 103 103 kPa → Kw/n = 93 103 kPa

B = 0.903 > poor value for saturated soil

UNDRAINED BEHAVIOUR WITH PLAXIS Method A (analysis in terms of effective stresses): type of material behaviour: undrained effective strength parameters c´, ϕ´, ψ´ effective stiffness parameters E50´, ν´ Method B (analysis in terms of effective stresses): type of material behaviour: undrained undrained strength parameters c = cu, ϕ = 0, ψ = 0 effective stiffness parameters E50´, ν´ Method C (analysis in terms of total stresses): type of material behaviour: drained total strength parameters c = cu, ϕ = 0, ψ = 0 undrained stiffness parameters Eu, νu = 0.495

7

UNDRAINED BEHAVIOUR WITH PLAXIS Notes on different methods: Method A: ƒ recommended ƒ soil behaviour is always governed by effective stresses ƒ increase of shear strength during consolidation included ƒ essential for exploiting features of advanced models such as the Hardening Soil model, the Soft Soil model and the Soft Soil Creep model Method B: ƒ only when no information on effective strength parameters is available ƒ cannot be used with the Soft Soil model and the Soft Soil Creep model Method C: ƒ NOT recommended ƒ no information on excess pore pressure distribution (total stress analysis)

UNDRAINED STRENGTH FROM MOHR CIRCLE Consider fully undrained isotropic elastic behaviour (Mohr Coulomb in elastic range) ∆pw = ∆p > ∆p´ = 0 → centre of Mohr Circle remains at the same point cu =

(

)

1 'o σ x + σ 'yo sin ϕ' + c' cos ϕ' 2

Fig.6 Mohr Circle for evaluating undrained shear strength (plane strain)

8

INFLUENCE OF CONSTITUTIVE MODEL ref

Model Number

Eur

E50

kN/m

2

ref

kN/m

ref

φ

Ψ

c

2

°

°

kN/m

Eoed

2

kN/m

nc

υur

p

-

kN/m

0.0

0.2

100

0.75 0.426 0.9

2

ref

2

m

K0

-

-

Rf -

HS_1

30 000 90 000

HS_2

50 000 150 000 50 000 35

0

0.0

0.2

100

0.75 0.426 0.9

HS_3

15 000 45 000

15 000 35

0

0.0

0.2

100

0.75 0.426 0.9

HS_4

30 000 90 000

40 000 35

0

0.0

0.2

100

0.75 0.426 0.9

HS_5

30 000 90 000

15 000 35

0

0.0

0.2

100

0.75 0.426 0.9

HS_6

50 000 150 000 30 000 35

0

0.0

0.2

100

0.75 0.426 0.9

30 000 35 0 / 10

Table 1 Parameter sets for Hardening Soil model

Parameters for MC Model E = 30 000 kN/m

2

υur = 0.2 φ = 35° Ψ = 0° and 10°

see also Schweiger (2002)

COMPARISON MC – HS / INFLUENCE ψ 300 275 250 225

2

q [kN/m ]

200 175 150 125 100 75

MC non dil MC dil HS_1 non dil HS_1 dil

50 25 0 0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

ε1 [%] Fig.7 Simulation of undrained triaxial compression test – MC / HS model - q vs ε1

9

COMPARISON MC – HS / INFLUENCE ψ 300 MC non dil MC dil HS_1 non dil HS_1 dil total stress path

275 250 225

2

q [kN/m ]

200 175 150 125 100 75 50 25 0 0.00

25.00

50.00

75.00

100.00 125.00 150.00 175.00 200.00 225.00 250.00 2

p' [kN/m ] Fig.8 Simulation of undrained triaxial compression test – MC / HS model - q vs p´

COMPARISON MC – HS / INFLUENCE ψ 100 90

MC non dil MC dil HS_1 non dil HS_1 dil

2

excess pore pressure [kN/m ]

80 70 60 50 40 30 20 10 0 -10 -20 0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

ε1 [%] Fig.9 Simulation of undrained triaxial compression test – MC / HS model - ∆pw vs ε1

10

COMPARISON MC – HS / INFLUENCE ψ 1.0 0.9

MC non dil MC dil HS_1 non dil HS_1 dil

0.8 0.7 0.6

parameter A

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

ε1 [%] Fig.10 Simulation of undrained triaxial compression test – MC / HS model - A vs ε1

PARAMETER VARIATION – HARDENING SOIL 150

125

2

q [kN/m ]

100

HS_1 HS_2 HS_3 HS_4 HS_5 HS_6 total stress path

75

50

25

0 0.00

25.00

50.00

75.00

100.00

125.00

150.00

2

p' [kN/m ] Fig.11 Simulation of undrained triaxial compression test – HS model - q vs p´

11

PARAMETER VARIATION – HARDENING SOIL 150

125

2

q [kN/m ]

100

75

50

HS_1 HS_2 HS_3 HS_4 HS_5 HS_6

25

0 0.00

1.00

2.00

3.00

4.00

5.00

6.00

ε1 [%] Fig.12 Simulation of undrained triaxial compression test – HS model - q vs ε1

PARAMETER VARIATION – HARDENING SOIL 80

2

excess pore pressure [kN/m ]

70 60 50 40 30 HS_1 HS_2 HS_3 HS_4 HS_5 HS_6

20 10 0 0.00

1.00

2.00

3.00

4.00

5.00

6.00

ε1 [%] Fig.13 Simulation of undrained triaxial compression test – HS model - ∆pw vs ε1

12

PARAMETER VARIATION – HARDENING SOIL 0.8 0.7

parameter A

0.6 0.5 0.4 0.3 HS_1 HS_2 HS_3 HS_4 HS_5 HS_6

0.2 0.1 0.0 0.00

1.00

2.00

3.00

4.00

5.00

6.00

ε1 [%] Fig.14 Simulation of undrained triaxial compression test – HS model - A vs ε1

Factor of Safety of Embankments Critical FS is Shortterm loading condition, undrained strength is key parameter for safe design

13

Factor of Safety of Cuts/Excavations Critical FS is Longterm unloading condition, For permanent cuts drained strength is key parameter for safe design For temporary cuts, need to consider if undrained or partially drained condition

SUMMARY

ƒ

Undrained analysis should be performed in effective stresses and with effective stiffness and strength parameters

ƒ

Undrained shear strength is result of the constitutive model

ƒ

Care must be taken with choice of value for dilatancy angle

ƒ

Note that for NC-soils in general ƒ factor of safety against failure is lower for short term (undrained) conditions for loading problems (e.g. embankments) ƒ factor of safety against failure is lower for long term (drained) conditions for unloading problems (e.g. excavations)

14

REFERENCES Atkinson, J.H., Bransby, P.L. (1978) The Mechanics of Soils, An Introduction to Critical State Soil Mechanics. McGraw Hill Ortigao, J.A.R. (1995) Soil Mechanics in the Light of Critical State Theories – An Introduction. Balkema Schweiger, H.F. (2002) Some remarks on pore pressure parameters A and B in undrained analyses with the Hardening Soil Model. Plaxis Bulletin No.12 Skempton, A.W. (1954) The Pore-Pressure Coefficients A and B. Geotechnique, 4, 143-147 Vermeer, P.A., Meier, C.-P. (1998) Proceedings Int. Conf. on Soil-Structure Interaction in Urban Civil Engineering, Darmstadt, 177-191

15

1ST Asian Course for

EXPERIENCED PLAXIS USERS 31ST JULY to 2ND AUGUST 2003

THURSDAY, 31ST JULY 2003

CG07 Pile Loading Test

Simulation of a Pile load test

CG07 SIMULATION OF A PILE LOAD TEST

Course for Experienced PLAXIS Users

Course for Experienced PLAXIS Users

1

Simulation of a Pile load test

INTRODUCTION An extensive research program related to bored piles in overconsolidated clay was conducted by Sommer & Hambach (1974) to optimize the foundation design of a highway bridge in Germany. Load cells were installed at the pile base to measure the loads carried directly by pile base. Figure 1 gives the layout of the pile load test arrangement. The upper 4.5 m subsoil consist of silt (loam) followed by tertiary sediments down to great depths which are more or less overconsolidated stiff plastic clay similar to the so-cal1ed Frankfurt clay. Therefore this pile load test is often used to verify the numerical modeling of the pile behavior in Frankfurt overconsolidated clay. The groundwater table is about 3.5 m below the ground surface. The considered tested pile has a diameter of 1.3 m and a length of 9.5 m. It is located completely in the overconsolidated clay. The loading system consists of two hydraulic jacks working against a reaction beam. The reaction beam was supported by 16 anchors. The anchors were installed vertically at a depth between 15 and 20 m below the ground surface at a distance of about 4 m from the tested pile to minimize the effect of the mutual interaction between the tested pile and the reaction system (Fig 1.a). Vertical and horizontal loading tests were carried out. The loads were applied in increments and maintained constant till the settlement rate was negligible. Both the applied loads and the corresponding displacements at the tested pile head were measured. Additionally the soil displacements near the pile in different depths were measured using deep settlement points (Fig 1.b).

Figure 1: Lay of the pile load test and the measured points

AIM The purpose of this case study is to simulate the pile-loading test, create about the same amount of settlement and compare the simulation results with the results of Sommer & Hambach (1974).

Course for Experienced PLAXIS Users

3

Simulation of a Pile load test

GEOMETRY OF THE MODEL • • • • •

Create an axisymmetric geometry with 15-noded elements. The dimensions are 4 m width x 15 m depth. The first 4.5 m of the soil consists of silt (loam) The following layer consists of overconsolidated stiff plastic clay, similar to the socalled Frankfurt clay, which extends to great depths. The groundwater table is located at a depth of 3.5 m below the ground surface. The boundaries are sufficiently far away to apply the standard fixities.

A A

(0.65,15) (0,15)

(4,15) loam

concrete pile water table (4,10.5)

(0,10.5)

clay

(0,5.5)

(0.65,5.5) (0.65,5.0) y

(4,0)

(0,0) 0

• • •

4

x

The pile has a diameter of 1.3 m and a length of 9.5 m. Create an interface at the right side of the pile. Extend the interface for half a meter to allow for sufficient flexibility around the pile tip. Apply a distributed load (system A) to the pile or a prescribed displacement. When accurately modelled, both should give the same results.

Course for Experienced PLAXIS Users

Simulation of a Pile load test

MATERIAL PROPERTIES The required soil parameters were determined based on the conducted laboratory and in-situ tests as well as on experience gained in similar soil conditions (see Table 1). The parameters for the concrete pile are also given in Table 1. Parameter

Symbol

Material model

Model

Silt (Loam)

OCR Clay

MohrCoulomb Drained 19 19 10E+3 0.3 5 27.5 0

HardeningSoil Drained 20 20 ?** ?** 0.7 0.2 100 20 20 2

Concrete Pile Linear Elastic Non-Porous 25 30E+6 0.2 -

Type of behaviour Type Dry weight γunsat Wet weight γsat Young's modulus Eref/50 Oedometer modulus Eoed Power M Unloading modulus Eur Poisson's ratio ν Reference stress pref Cohesion c Friction angle ϕ Dilatancy angle ψ Interface strength 1.0 (rigid) 1.0 (rigid) 1.0 (rigid) Rinter reduction POP POP 200 OCR OCR Table 1: Geotechnical parameters for the 2 layers and the concrete pile.

Unit kN/m3 kN/m3 kN/m2 kN/m2 kN/m2 kN/m2 kN/m2 ° ° kN/m2 -

The remaining parameters for the clay (E50ref and Eurref) shall be determined from the following results of Triaxial tests by Amann (1975).

**

Course for Experienced PLAXIS Users

5

Simulation of a Pile load test

1 kp/cm² = 100 kPa

Figure 2: Triaxial Tests with Frankfurt clay (σ3 = const.)

6

Course for Experienced PLAXIS Users

Simulation of a Pile load test •

Do not assign the concrete material properties to the pile yet, but instead assign the loam and clay material properties to the clusters of the pile. Initial stresses are not correctly calculated if the pile is alread in place. The material properties of the pile will be assigned in the first calculations phase. Create a water table at a depth of 3.5 m and generate water pressures. Generate initial stresses (assign a value for POP to the clay layer).

• •

CALCULATIONS •

In the first phase, ‘activate’ the pile by assigning the material property of concrete to the pile clusters. In the second phase the pile load is activated or a prescribed displacement of 35 mm is applied. In the third phase the pile load is increased until a settlement of about 35 mm is observed (ignore this phase if prescribed displacement is used).

• •

OUTPUT Figure 3 shows the results of the observed pile load settlement behavior by Sommer & Hambach (1974). Load [kN] 0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

3500

0.00 Total load Skin friction

5.00

Base load

Settlement [mm]

10.00 15.00 20.00 25.00 30.00 35.00 40.00

Figure 3: Observed pile load settlement behavior. •

In addition to the total load, check the skin friction (total amount of friction along the surface of the pile) and the base load of the pile (total load at the base-surface op the pile).

Course for Experienced PLAXIS Users

7

Simulation of a Pile load test

Plate element with negligible stiffness for the determination of normal force in pile.

Figure 4a: Effective Stresses

Figure 4b: Deformed Mesh

REFERENCES Amann, P., Breth, H., Stroh, D. (1975) „Verformungsverhalten des Baugrundes beim Baugrubenaushub und anschließendem Hochhausbau am Beispiel des Frankfurter Tons.“ Mitteilungen der Versuchsanstalt für Bodenmechanik und Grundbau der TH Darmstadt, Heft 15 El-Mossallamy, Y. (1999) “ Load settlement behavior of large diameter bored piles in overconsolidated clay.” Proceedings NUMOG VII Graz, Balkema Rotterdam Sommer, H. & Hambach, P. (1974) „Großpfahlversuche im Ton für die Gründung der Talbrücke Alzey.“ Der Bauingenieur, Vol. 49, pp. 310-317

8

Course for Experienced PLAXIS Users

Simulation of a Pile load test

SOLUTIONS TO THE SIMULATION OF A PILE LOAD TEST

Course for experienced PLAXIS users

Course for Experienced PLAXIS Users

9

Simulation of a Pile load test

From the Triaxial tests on the Frankfurt clay in figure 2 an E50ref of 20.000 kN/m2 and an Eurref of 72.000 kN/m2 was found. A Triaxial test of the Frankfurt clay was simulated with PLAXIS to compare and test the chosen parameters with the Triaxial tests of Amann (1975). The results are shown in figure 5 and match with the results of Amann (figure 2). (sig'yy - sig'xx)/2 [kN/m2] -200

-160

-120

-80

p=300 kN/m2

-40

p=200 kN/m2 p=100 kN/m2 0 0

-0.01

-0.02

-0.03

-0.04

eps-1

Figure 5: Results of the Triaxial test in PLAXIS of the Frankfurt Clay. With the chosen E50ref and Eurref the pile load test was calculated with a prescribed displacement of 35 mm applied to the top of the pile. The Total load – settlement curve is shown in figure 6. When using Traction loads, the Total load is obtained by multiplying the traction loads in Load System A by πr2, i.e. the cross section area of the pile. When Prescribed displacements were used, the total load is obtained by multiplying the vertical reaction force of the axisymmetric analysis (Force-Y) by 2π, i.e. the full circle. For an axissymmetric problem the Base Load can be calculated as follows: In output a cross-section of the total stresses is made just below the base of the pile (figure 6). This cross-section represents the total stresses over the radius of the pile. To obtain the total base load we need to integrate the total stresses over the total cross section of the pile (~ average total stress * πr2). To obtain a correct Base Load value we need to substract the Initial Load of the pile. The calculated Base Load is plotted in figure 8.

10

Course for Experienced PLAXIS Users

Simulation of a Pile load test x 0.341

0 0.033

0.65

X [m]

Y [m]

)n [kN/m2]

0.000 0.033 0.341 0.650

5.475 5.475 5.475 5.475 Average σ'n Base Load [kN] Initial Load [kN] Base Load – Initial Load[kN]

-898 -911 -1004 -1442 -1064 1412 248

)n

Figure 6 and Table 1: Total stresses 2.5 mm below the base of the pile.

1164

The Skin Friction of an axissymmetric problem can be calculated from the shear stresses in the interface of the pile (figure 7). The shear stresses shown in figure 7 and table 2 are the shear stresses along the perimeter of the pile. To obtain the skin friction of the pile the shear stresses have to be integrated over the total skin surface of the pile (skin surface=length*circumference=L*2πr). The calculated Skin Friction is plotted in figure 8. 0 )s

y

X [m]

Y [m]

)s [kN/m2]

0.650005 0.650005 0.650005 : : 0.650005 0.650005 0.650005 0.650005

5.50 5.64 5.78 : : 14.58 14.72 14.86 15.00 Average σs Skin Friction [kN]

-89 -91 -98 : : -20 -13 -12 -14 56 2183

Figure 7 and Table 2: Shear stresses at the interface of the pile.

Course for Experienced PLAXIS Users

11

Simulation of a Pile load test Load [kN] 0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

3500

0.00 Total load

5.00

Skin friction Base load Total Load with Plaxis

10.00

Base load with Plaxis Skin Friction with Plaxis

Settlement [mm]

Base load - Initial Load with Plaxis

15.00

20.00

25.00

30.00

35.00

40.00

Figure 8: Results of the Pile load test.

12

Course for Experienced PLAXIS Users

1ST Asian Course for

EXPERIENCED PLAXIS USERS 31ST JULY to 2ND AUGUST 2003

THURSDAY, 31ST JULY 2003

CG08 Selection of Parameters for HS Model

1

2

3

4

5

6

7

8

9

10

11

12

13

1ST Asian Course for

EXPERIENCED PLAXIS USERS 31ST JULY to 2ND AUGUST 2003

THURSDAY, 31ST JULY 2003

CG09 Groundwater Flow and Pore Pressures

Pore pressures and groundwater flow presented by Tan SA National University of Singapore Ronald Brinkgreve Plaxis BV / Delft University of Technology

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Contents • Water pressures (general) • Water pressure generation: • • • • • •

Using ‘phreatic levels’ Cluster pore pressure distribution Steady-state groundwater flow calculation Transient flow calculation: PlaxFlow Parameters for transient flow Time-dependent conditions

• Example: Embankment subjected to tidal movements Example: Dewatering of an excavation

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

2

1

Water pressures (general) • Water pressures • External water pressures (loads on boundaries) • Internal water pressures (pore pressures)

σ ' = σ −σ w • Total stress: From weight and external load • Pore pressure: σ w = σ w, steady + σ w, excess

• Effective stress analysis

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

3

Water pressures (general) •

Excess pore pressures σw,excess • •

•

Generation in plastic calculation for undrained materials Dissipation or generation in consolidation analysis

‘Steady-state’ pore pressures σw,steady A. Generation from phreatic levels B. Generation by groundwater flow calculation

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

4

2

Water pressure generation • General phreatic level • To generate pore pressures in soil clusters (also for inactive clusters) (A+B) • To generate external water loads when outside the mesh (A+B) • To generate boundary conditions for groundwater flow calculation (B)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

5

Water pressure generation • General phreatic level (example)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

6

3

Water pressure generation • Cluster pore pressure distribution

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

7

Water pressure generation • Cluster pore pressure distribution (example: General boven, interpolate midden, cluster onder) Layer 1 General phreatic level Interpolate from adjacent clusters or lines

Cluster phreatic level

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

Layer 2

Layer 3

8

4

Water pressure generation • Steady-state groundwater flow calculation based on Darcy’s law Specific discharge:

qx = -kx ∂h/∂x qy = -ky ∂h/∂y

Hydraulic head:

h = y + σw /γw

Continuity condition:

∂qx /∂x + ∂qy /∂y = 0

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

9

Water pressure generation • Steady-state groundwater flow calculation Required input: • Permeabilities • Water weight • Boundary conditions for flow • Prescribed hydraulic head (h given) • Closed flow boundary (qx = 0 or qy = 0)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

10

5

Water pressure generation • Steady-state groundwater flow calculation

(example: boundary conditions)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

11

Concepts of Plasticity

12

Flow Field

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

6

Head and Flownet

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

13

Water pressure generation • Steady-state groundwater flow calculation Results: • • • • •

Flow field Groundwater head distribution Pore pressure distribution Degree of saturation (around phreatic surface) Total discharge through cross section

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

14

7

Water pressure generation • Steady-state groundwater flow calculation (example: screen, drain, well)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

15

Concepts of Plasticity

16

Flow Field

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

8

Head and Flownet

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

17

Water pressure generation • Transient flow calculation: PlaxFlow Special relations around phreatic level:

Permeability as a function of pressure

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Saturation as a function of pressure

Concepts of Plasticity

18

9

Water pressure generation • Transient flow calculation Parameters: selection from predefined data sets

Material input window

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

19

Water pressure generation • Transient flow calculation Special conditions: • Impermeable screens (qn = 0) • Drains (σw = 0) • Wells • Sink (Q < 0) • Source (Q > 0)

• Precipitation (infiltration) (qn > 0) PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

20

10

Water pressure generation • Transient flow calculation Time-dependent conditions: • Head • Precipitation (infiltration)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

21

Example: Embankment subjected to tidal movements

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

22

11

Example: No Dewatering of Excavation BS8004

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

23

Concepts of Plasticity

24

Flow Field

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

12

Head and Flownet

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

25

Pore Pressures on Wall

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Concepts of Plasticity

26

13

1ST Asian Course for

EXPERIENCED PLAXIS USERS 31ST JULY to 2ND AUGUST 2003

Friday, 1ST AUGUST 2003

CG10 Deep Excavations

Deep Excavations New OG Basement by Tan SA National University of Singapore

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

1

General Site Condition • Upper Cross Street • T-shaped in plan • Excavation is performed in 5 stages, supported by 4 levels of struts

• Majestic Theatre

• Food Centre

• The control of ground movements induced by the excavation is a crucial issue

• Yu Hua Building PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

2

1

Excavation Support System • Grout Mixed Pile wall is used in the original design • Due to underground obstructions, FSP III sheet piles are installed at some sections • Excavation support system consists of alternating grout mixed piles and sheet piles PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

3

Grout Mixed Pile Wall

• Overlapping φ700mm and φ620mm grout piles • Deep Cement Mixing Method • I-beam is installed in each grout pile PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

4

2

Excavation Support System 102.2m

• First level strut: H350x350x12x19

101.2m

• Other struts: 2H400x400x13x21

99.0m 96.5m 94.5m

• Struts are preloaded to 30% of their design strut loads

91.5m

•The first 4 excavation stages are carried out to 0.5m below the struts

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

• Total depth of excavation is 10.7m Deep Excavations

5

Excavation Zones C A

B

Food Court

D

Zone 1

• At each excavation stage, Zone 2 is excavated before Zone 1 and Zone 3

Zone 2 E

Majestic Theatre

F

G

Zone 3 Yu Hua Building

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

• The excavated area is divided into three zones

H

Deep Excavations

• Note

Heavy Struts to Restraint Out of Plane Movements 6

3

Excavation Zones Y2

C

D

X2 A

B

Zone 1

• These two sections would probably satisfy Plane Strain condition

Zone 2 F

E

• Section X1-X2 and Section Y1-Y2 will be analysed

Zone 3

X1 G

H

Y1

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

7

Deep Excavations

Extent of Site Investigation Y2

C

D

BH1 C6 X2

A

C7

NB2

B

C3

C5

C2

C4

C1

C9

NB3

E

BH2

X1

F

NB1

Borehole Position Cone Penetration Test Position

G

C10

C8

H

Y1 BH3

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

8

4

Retaining Wall Embedment Depth C 13.7m

A

B

16.0m

D

Zone 1

Zone 2 18.0m

E

F

Zone 3

G

21.0m

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

H

• Retaining walls along CD, EF and GH consist of majority of grout mixed piles • Retaining wall along AB consists of majority of sheet piles • Retaining walls were terminated at different depths 9

Deep Excavations

Soil Profile At Section X1-X2 X1

X2

0.0

0.0

Fill -4.2

-5.7

Marine Clay

Depth (m)

-12.8 -14.5

Stiff Clay

-14.5

-18.0

Siltstone

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

10

5

Soil Profile At Section Y1-Y2 Y1

Y2

0.0

0.0

Fill -5.0

-5.7

Marine Clay

Depth (m)

-10.0 -13.0

-17.0

Stiff Clay

-23.5

Siltstone

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

11

Deep Excavations

Finite Element Model At X1-X2

X1

• As the soil layers are not uniform and the walls at X1 and X2 have different properties, symmetry cannot be assumed

X2

Fill Marine Clay Stiff Clay Siltstone

• The whole excavation has to be modelled

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

12

6

Finite Element Model At X1-X2

X1

• The soil layers are modelled as MohrCoulomb material

X2

• The retaining walls are modelled as beam elements

Fill Marine Clay Stiff Clay Siltstone

• X1:

Grout mixed pile wall

• X2:

Sheet pile wall

• The struts are modelled as node-to-node anchors PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

13

Deep Excavations

Finite Element Model At Y1-Y2

Y1

Y2

Fill Marine Clay Stiff Clay

Grout mixed pile wall

• Y2:

Grout mixed pile wall

• Bored piles, installed within Zone 1 and Zone 3, are modelled as beam elements

Siltstone

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

• Y1:

Deep Excavations

14

7

Excavation Sequence Excavation Sequence In Zone 2

Consider the time required for: • Excavation • Installation and preloading of struts • Periods between two excavation stages

Strut 1

-2

Strut 2

-4

Strut 3

-6

Strut 4

-8 -10 -12 -14 -16 0

20

40

60

80

100

120

Excavation Sequence In Zone 1 And Zone 3

Time (Day) 0

Depth of Excavation (m)

Depth of Excavation (m)

0

Strut 1

-2

Strut 2

-4

Strut 3

-6

Strut 4

-8 -10 -12 -14 -16 0

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

20

Deep Excavations

40

60

80

Time (Day)

100

120

15

Calibration of Finite Element Model • Some of the soil properties can be obtained from the soil investigation works • Important parameters are calibrated using: – Consolidated undrained triaxial test results ƒ Marine Clay – Instrumentation results

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

16

8

Calibration Using Instrumentation Results • Section X1-X2 is analyzed • The analytical wall deflections at every stage of the excavation are compared with the measured wall deflections

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

17

Deep Excavations

Calibrated Soil Properties Soil Type

γ (kN/m3)

φ’ (o )

c’ (kN/m2)

Eur’ (kN/m2)

Increment of Eur’ (kN/m2/m)

kv (m/day)

kh (m/day)

Fill

18

30.0

0

6000

-

8.64E-3

8.64E-3

Marine Clay

15

21.5

0

7127

718

1.14E-4

3.81E-5

Stiff Clay

18

30.0

10

32000

-

8.64E-3

8.64E-3

Siltstone

20

35.0

20

600000

-

8.64E-3

8.64E-3

Marine Clay:

Eu = 300 Cu 1+υ, E' = = Eu 1 + υu

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

Eur’ = 2 E’ 18

9

Wall Deflection At X1 X1

Plot of Measured and Analytical Wall Deflection On Day 10

Plot of Measured and Analytical Wall Deflection On Day 31

Lateral Deflection (mm) -20

0

20

40

60

Lateral Deflection (mm) 80

-20

0

20

40

60

Lateral Deflection (mm) 80

-20

0

0

0

2

2

2

4

4

4

6

6

6

10 12

0

20

40

60

80

8 Depth (m)

8 Depth (m)

8 Depth (m)

Plot of Measured and Analytical Wall Deflection On Day 45

10 12

10 12

14

14

14

16

16

16

18

18

18

20

20

20

22

22

22

Measured

FEM Analysis

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

19

Deep Excavations

Wall Deflection At X1 X1

Plot of Measured and Analytical Wall Deflection On Day 59

Plot of Measured and Analytical Wall Deflection On Day 66

Lateral Deflection (mm) 0

20

40

60

Lateral Deflection (mm) 80

-20

0

20

40

60

Lateral Deflection (mm) 80

-20

0

0

2

2

2

4

4

4

6

6

6

8

8

8

10 12

Depth (m)

0

Depth (m)

Depth (m)

-20

Plot of Measured and Analytical Wall Deflection On Day 73

10 12

0

20

40

60

80

10 12

14

14

14

16

16

16

18

18

18

20

20

20

22

22

22

Measured

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

FEM Analysis

Deep Excavations

20

10

X2

Wall Deflection At X2 Plot of Measured and Analytical Wall Deflection On Day 10

Plot of Measured and Analytical Wall Deflection On Day 31

Lateral Deflection (mm) -50

0

50

100

Lateral Deflection (mm) 150

-50

0

50

100

Lateral Deflection (mm) 150

-50

0

0

0

2

2

2

4

4

4

6

6

6

10 12

10 12

14

16

16

16

18

18

18

20

20

20

22

22

22

21

Deep Excavations

X2

Wall Deflection At X2 Plot of Measured and Analytical Wall Deflection On Day 66

Lateral Deflection (mm) 50

100

Plot of Measured and Analytical Wall Deflection On Day 73

Lateral Deflection (mm) 150

-50

0

50

100

Lateral Deflection (mm) 150

-50

0

0

2

2

2

4

4

4

6

6

6

8

8

8

10 12

Depth (m)

0

Depth (m)

Depth (m)

0

10 12

50

100

150

12

14

14

16

16

16

18

18

18

20

20

20

22

22

22

FEM Analysis, With Preload

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

0

10

14

Measured

150

FEM Analysis, No Preload

FEM Analysis, With Preload

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

-50

100

12

14

Plot of Measured and Analytical Wall Deflection On Day 59

50

10

14

Measured

0

8 Depth (m)

8 Depth (m)

8 Depth (m)

Plot of Measured and Analytical Wall Deflection On Day 45

FEM Analysis, No Preload

Deep Excavations

22

11

Calibration Using Instrumentation Results • Section Y1-Y2 is analyzed • Soil parameters calibrated in Section X1X2

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

23

Deep Excavations

Wall Deflection At Y2 Plot of Measured and Analytical Wall Deflection On Day 13

Plot of Measured and Analytical Wall Deflection On Day 27

Lateral Deflection (mm) 0

10

20

30

40

Plot of Measured and Analytical Wall Deflection On Day 34

Lateral Deflection (mm) 50

-10

0

10

20

30

40

Lateral Deflection (mm) 50

-10

0

0

2

2

2

4

4

4

6

6

6

8

8

8

10 12

Depth (m)

0

Depth (m)

Depth (m)

-10

Y2

10 12

0

10

20

30

40

50

10 12

14

14

14

16

16

16

18

18

18

20

20

20

22

22

22

Measured

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

FEM Analysis

Deep Excavations

24

12

Wall Deflection At Y2 Plot of Measured and Analytical Wall Deflection On Day 55

Plot of Measured and Analytical Wall Deflection On Day 69

Lateral Deflection (mm) -10

0

10

20

30

40

Plot of Measured and Analytical Wall Deflection On Day 83

Lateral Deflection (mm) 50

-10

0

10

20

30

40

Lateral Deflection (mm) 50

-10

0

0

0

2

2

2

4

4

4

6

6

6

12

8

0

10

20

30

40

50

8 Depth (m)

10

Depth (m)

8 Depth (m)

Y2

10 12

10 12

14

14

14

16

16

16

18

18

18

20

20

20

22

22

22

Measured

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

FEM Analysis

25

Deep Excavations

General Site Condition

Y2

• Restraints provided by diagonal bracings • Plain strain condition cannot be assumed at Section Y1-Y2 • 3D Effects are significant

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

26

13

Ground Settlement At X1

X1

Plot of Ground Settlement With Time At X1 0

S ettlement (mm)

-20

-40

-60

-80

-100 0

20

40

60 Time (Day)

80

100

M easured FEM Analysis

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

27

Deep Excavations

Site Condition At X1 X1

• Additional settlement induced by excavation and construction works at the Majestic Theatre

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

28

14

X2

Ground Settlement At X2 Plot of Ground Settlement With Time At X2 0

S ettlement (mm)

-20

-40

-60

-80

-100 0

20

40

60 Time (Day)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

80

100

M easured FEM Analysis, With Preload FEM Analysis, No Preload

29

Deep Excavations

Ground Settlement At Y1

Y1

Plot of Ground Settlement With Time At Y1 0

S ettlement (mm)

-20

-40

-60

-80

-100 0

20

40

60 Time (Day)

80

100 M easured FEM Analysis

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

30

15

Y2

Ground Settlement At Y2 Plot of Ground Settlement With Time At Y2 0

S ettlement (mm)

-20

-40

-60

-80

-100 0

20

40

60 Time (Day)

80

100 M easured FEM Analysis

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

31

Deep Excavations

Site Condition At Y2

Y2

• Settlement Point on Pile Supported floor slab

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

32

16

Parametric Study • Examine the influence of various parameters on the response of the excavation support system at Section X1-X2 of Zone 2, in particular:

• Influence of Wall Embedment Depth • Influence of Excavation Width • Influence of Wall Stiffness and Struts Stiffness • Influence of Wall Type PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

33

Deep Excavations

Influence of Wall Embedment Depth Influence of Embedment Depth of Wall On Maximum Wall Deflection At X1

Influence of Embedment Depth of Wall On Maximum Wall Deflection At X2

600

600

500

500

400

400 / o x 100%

/ o x 100%

Marine Stiff Clay Clay

Siltstone

Stiff Clay

Marine Clay

300

300

200

200

100

100

0

Siltstone

0 10

15

20

25

30

10

Embedment Depth of Wall (m)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

15

20

25

30

Embedment Depth of Wall (m)

Deep Excavations

34

17

Influence of Width of Excavation Influence of Excavation Width On Maximum Wall Deflection At X2

180

180

160

160

140

140

/ o x 100%

/ o x 100%

Influence of Excavation Width On Maximum Wall Deflection At X1

120

120

100

100

80

80 0.0

1.0

2.0

3.0

4.0

5.0

0.0

1.0

Excavation Width Multiplier

2.0

3.0

4.0

5.0

Excavation Width Multiplier

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

35

Deep Excavations

Comparison Between Influence of Strut and Wall Stiffness Influence of Strut Axial Stiffness And Wall Bending Stiffness On Maximum Wall Deflection At X1

Influence of Strut Axial Stiffness And Wall Bending Stiffness On Maximum Wall Deflection At X2

500

500 Axial Stiffness of Struts

Bending Stiffness of Wall

400

300

/ o x 100%

/ o x 100%

Axial Stiffness of Struts

Bending Stiffness of Wall

400

300

200

200

100

100

0

0 0

2

4

6

8

10

12

0

2

Stiffness Multiplier

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

4

6

8

10

12

Stiffness Multiplier

Deep Excavations

36

18

Influence of Different Wall Types Influence of Different Wall Types On Maximum Wall Deflection At X1

Influence of Different Wall Types On Maximum Wall Deflection At X2

175

175

150

150

125

125 Maximum Deflection (mm)

Maximum Deflection (mm)

Sheet Pile Wall

100

75

Grout Mixed Pile Wall 50

100

Sheet Pile Wall 75

Diaphragm Wall

50

Diaphragm Wall 25

25

0

Grout Mixed Pile Wall

0

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+03

1.0E+04

2

1.0E+05

1.0E+06

1.0E+07

1.0E+08

2

Bending S tiffness (kNm /m)

Bending S tiffness (kNm /m)

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

37

Deep Excavations

Wall Deflection Using Sheet Pile Walls Wall Deflection At X1 (Sheet Pile Wall)

Wall Deflection At X2 (Sheet Pile Wall)

Deflection (mm) -50

0

50

100

Deflection (mm) 150

200

-200

-150

-100

-50

0

0

0

2

2

4

4

6

6

10

8

Maximum

Depth (m)

Depth (m)

8

50

Maximum

10

12

12

14

14

16

16

18

18

20

20

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

38

19

Wall Deflection Using Diaphragm Walls Wall Defection At X1 (2.0m Diaphragm Wall)

Wall Defection At X2 (2.0m Diaphragm Wall)

Deflection (mm) -50

0

50

100

Deflection (mm) 150

200

-200

-150

-100

-50 0

2

2

4

4

6

6

50

8 Depth (m)

8 Depth (m)

0

0

10

10

12

12

14

14

16

16

18

18

20

20

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

39

Wall Deflection Using Diaphragm Walls Wall Defection At X1 (2.0m Diaphragm Wall) Deflection (mm) -50

0

50

100

150

200

• Retaining wall at X1 is a fixed earth support system

0 2

Maximum 4

6

• There is sufficient wall embedment in Stiff Clay Layer

Depth (m)

8 10 12 14

16

• Retaining wall rotates about its toe and the maximum deflection occurs at the top of the wall

18 20

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

40

20

Wall Deflection Using Diaphragm Walls • Retaining wall at X2 is a free earth support system

Wall Defection At X2 (2.0m Diaphragm Wall) Deflection (mm) -200

-150

-100

-50

0

50

0

• There is insufficient wall embedment in Stiff Clay Layer

2 4

6 8 Depth (m)

• Retaining wall kicks out at its toe and the maximum deflection occurs at the toe of the wall

10 12 14

Maximum 16 18 20

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

41

Lessons Learnt • • • •

2D FEM can model X1-X2 well, as problem is plane strain 2D FEM cannot model Y1-Y2 well, as problem is 3D Beware of Limitation of FEM modeling For good FEM model, need: • • • • •

Correct Geometry Correct Soil Layers Correct Soil Parameters Correct Construction Sequence Undrained plus Consolidation Effects

PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES

Deep Excavations

42

21

1ST Asian Course for

EXPERIENCED PLAXIS USERS 31ST JULY to 2ND AUGUST 2003

Friday, 1ST AUGUST 2003

CG11 Consolidation

PLAXIS Experienced Users Course, March 2003

CONSOLIDATION

presented by Tan SA National University of Singapore

Helmut F. Schweiger Institute for Soil Mechanics and Foundation Engineering Graz University of Technology, Austria

CONTENTS

ƒ

1D theory of Terzaghi

ƒ

Influence of constitutive model and parameters • • •

Influence of compressibility of water Influence of void ratio dependent permeability Influence of constitutive model

ƒ

Study on effect of vertical drains and equivalent permeabilities after CUR

ƒ

Practical example: application of vertical drains

ƒ

Summary

1

1D CONSOLIDATION initial ground surface

apply surcharge load ∆σ rapidly

soft clay layer fully saturated

D

pw = pw, o

pw = pw, o + ∆pw, t=o

σ´ = σο´

∆pw, t=o = ∆σ

z

t=0

σ´ = σο´

rigid impermeable layer

rigid impermeable layer

consolidation process completed

consolidation takes place

settlement ∆s

settlement ∆st

t=

pw = pw, o σ´ = σο´ + ∆σ

pw = pw, o + ∆pw, t

0