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Application of HS model to deep excavations andfoundation rafts

Andrzej TrutyZACE Services

28.08.2009

Andrzej Truty ZACE Services Application of HS model to deep excavations and foundation rafts

Major goals in modeling soil-structure interaction problems

Estimation of stress resultants in structures that interact withsoil

Assessment of deformations in the area close to theconstruction site (mainly in the urban areas)

Assessment of additional deformations due to pumping of thewater from the excavation zone


Major problems

Simple constitutive models for soils do not include the effectof small strain stiffness

Only small part of soil adjacent to the structure undergoesmoderate or larger strain amplitudes while the other remainsin the range of small or very small strains

Stiffness of soil in these zones can be very different

Hence there is a strong need to have a relatively simple butpowerful to describe basic phenomenona exhibited by soils

1 densification2 stiffness stress dependency3 plastic yielding4 dilatancy5 strong stiffness variation with growing shear strain amplitude

in the regime of small strains (γ = 10−6 to γ = 10−3)


Stiffness-strain relation for soils (G/Go (γ))

G - current secant shear modulus

Go - shear modulus for very small strains

Atkinson 1991


Notion of tangent and secant stiffness moduli

Initial stiffness modulus Eo

Unloading-reloading modulus Eur

Secant stiffness modulus at 50 % of the ultimate deviatoricstress qf

0

50

100

150

200

250

0 0.05 0.1 0.15 0.2 0.25

EPS-1 [-]

q [k

pa] 1

Eo

1E50

1Eur

qf

0.5 qf

σ3=const

q50

qun

Remark: All classical soil models require specification of Eur

modulus (Cam-Clay, Cap etc..)Andrzej Truty ZACE Services Application of HS model to deep excavations and foundation rafts

HS model

Double hardening elasto-plastic model (Schanz, Vermeer,Benz)Nonlinear elasticity for stress paths penetrating the interior ofthe elastic domain

0

100

200

300

400

500

600

0 100 200 300 400 500

p [kPa]

q [k

Pa]

Cap surface

Graphical representation of shear mechanism and cap surfaceAndrzej Truty ZACE Services Application of HS model to deep excavations and foundation rafts

Shear/cap yield surfaces in HS model


Setting initial state variables: γPSo and pco

Given: σo , OCRFind: γPS

o and pco

0

100

200

300

400

500

600

0 100 200 300 400 500

p [kPa]

q [k

Pa]Cap surface

Shear mechanism

σSR

σο

Procedure:

Set effective stress state at the SR pointσSR

y = σyo OCR

σSRx = σSR

z = σy KSRo


Setting initial state variables: γPSo and pco

Remarks

1 KSRo = KNC

o ≈ 1− sin(φ) in the standard applications(approximate Jaky’s formula)

2 KSRo = 1 for case of isotropic consolidation (used in triaxial

testing for instance)


Excavation in Berlin Sand: engineering draft

E = 20000√

y kPa for y ≤ 20m

E = 60000√

y kPa for y > 20m


Excavation in Berlin Sand: FE discretization

Interface wall-soil

Fictitious interface to modelimpermeable barrier

SeepageElements +Fluid head BC

SeepageElementsFluid head BC

x

y

30m 120m

90m


Excavation in Berlin Sand: Bending moments

-35

-30

-25

-20

-15

-10

-5

0-600 -400 -200 0 200 400

M [kNm/m]

Y [m

[] HSHS-smallMC


Excavation in Berlin Sand: Wall deflections

-35

-30

-25

-20

-15

-10

-5

0-0.04 -0.03 -0.02 -0.01 0

Ux [m]

Y [m

] HS-smallHSMCMeasurement


Excavation in Berlin Sand: Deflection after 1-st excavationstep

-35

-30

-25

-20

-15

-10

-5

0-0.005 -0.004 -0.003 -0.002 -0.001 0

Serie1


Excavation in Berlin Sand: Soil deformation in crosssection x =20m

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

00 0.01 0.02 0.03 0.04

Uy [m]

Y [m

] HSHS-smallMC

Vertical heaving of subsoil at last stage of excavation


Excavation in Berlin Sand: Settlements behind the wall

-0.02

-0.015

-0.01

-0.005

0

0.005

0.010 20 40 60 80 100 120 140

X [m]

UY

[m] HS

HS-smallMC

Settlements behind the wall at last stage of excavation


What could happen during pumping of the water (effect ofdepression curve)

-35

-30

-25

-20

-15

-10

-5

0-0.015 -0.01 -0.005 0 0.005 0.01

Ux [m]

Y [m

] HS-smallHSMC


What could happen during pumping of the water (effect ofdepression curve)

-35

-30

-25

-20

-15

-10

-5

0-500 -400 -300 -200 -100 0 100 200 300 400 500

M [kNm/m]

Y [m

[] HSHS-smallMC


Schweiger’s report: class A predictions for wall deflectionsfrom different modeling groups

H. F. Schweiger. Benchmarking in geotechnics. part i: Results of benchmarking. part ii: Reference solution andparametric study. Technical Report CGG IR006 2002, Institute for Soil Mechanics and Foundation Engineering,Graz University of Technology, Austria, March 2002.


Deep excavation problem (1) in Warsaw (Poland)

Diapraghm walls L=27m, h=80cm

Piles 10-12m φ = 0.8m


HEB profiles+temporary piles


3D view of a coarse model

RemarkOption Boreholes was used to map irregular subsoil stratigraphyonto regular continuum mesh


Temporary piles and piles under 40-story building

A B

C

A B

C


S-curve for tertiaray clays: theory vs measurements

Warstwa 11b

0

100000

200000

300000

400000

500000

600000

0.000001 0.00001 0.0001 0.001 0.01 0.1

EPS-1 [-]

E-se

cant

[kPa

]

Pomiar p'=260 kPaPomiar p'=320 kPaZ_SOIL p'=260 kPaZ_SOIL p'=320 kPa


Settlements (without piles under the 40-story building)


Settlements (with piles under the 40-story building)

RemarkTemporary piles and piles under the high building are needed alsoto prevent uplifting of the foundation raft at the early stage ofconstruction


Deep excavation problem (2) in WarsawWykop wykonany do poziomu pWykop wykonany do poziomu płłyty dennej.yty dennej.

RemarkThis analysis was carried out by MSc Agnieszka Gugulska (CracowUniversity of Technology)


Top view


3D model

Stropy rozporowe

Słupytymczasowe

Rozpory stalowe

Podkładki Ściany szczelinowe

GGłłóówne elementy konstrukcyjne podziemnej czwne elementy konstrukcyjne podziemnej częśęści wysokiego budynku. ci wysokiego budynku. Model w programie Model w programie Z_SoilZ_Soil..

Płyta fundamentowa


3D model+boreholesModel oModel ośśrodka gruntowego w programie rodka gruntowego w programie Z_SoilZ_Soil..


Calibrating HS model

Rys. 58- Zestawienie porównywanych krzywych typu S.

Podsumowanie

Z porównania krzywych wynika, że wartością parametru refurE , dzięki której otrzymano

wykres zależności ( )vE ε0 najbliższy rzeczywistemu, jest wartość ][5,31579 kPaE refur = .

3.2. Sprawdzenie poprawności wyznaczonych wartości parametrów dzięki modelowi

testu ściskania trójosiowego w programie Z_Soil.

Sprawdzenie poprawności wyestymowanych wartości parametrów używanych

w modelu HS-small polegało na porównaniu krzywych typu S, otrzymanych dzięki

modelowi testu ściskania trójosiowego wykonanego w programie Z_Soil, z krzywymi

wyznaczonymi przez firmę „Geoteko” na podstawie wyników rzeczywistych badań

ściskania trójosiowego. Test trójosiowy przeprowadzony został na trzech próbkach gruntów

warstwy geotechnicznej IIb w warunkach z odpływem przy wartościach naprężeń 3σ

równych 250, 300 i 400 [kPa]. Zestawienie odpowiednich krzywych wykonano

na rysunku 59.


Excavation up to level -1

Wykop wykonany do poziomu stropu drugiej kondygnacji podziemnej.Wykop wykonany do poziomu stropu drugiej kondygnacji podziemnej.



Wykop wykonany do poziomu stropu trzeciej kondygnacji podziemnejWykop wykonany do poziomu stropu trzeciej kondygnacji podziemnej..



Wykop wykonany do poziomu pWykop wykonany do poziomu płłyty dennej.yty dennej.


Results: bending moments


Results: Settlements of the ground surface


Results: Foundation raft settlements


Conclusions

HS is a good model to predict deformations and stressresultants in soil-structure interaction problems, especiallydeep excavations

Calibration procedures are fully documented in the coursenotes

It has been verified for several types of cohesive soils

It includes the effect of small strain stiffness that is of primaryimportance in modeling deep excavations

In the most recent Z Soil upgrade v.9.11 the model wasslightly modified by changing the form of the cap surface


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