ONE DAY SEMINAR ON GEOTECHNICAL ASPECTS IN INFRASTRUCTURE(Organized by IGS Chennai Chapter and Thiagarajar College of Engineering, Madurai)

Date: 25.01.2014

Use of Geotechnical Software in Infrastructure Projects

Dr. Subhadeep BanerjeeAssistant ProfessorAssistant Professor

Geotechnical Engineering DivisionDepartment of Civil EngineeringIndian Institute of Technology MadrasChennai 600 036, India

How to handle a geotechnical problem ?Acquire land.

Reconnaissance of the sitesite.

Geologic history.

D t il dDetail survey and leveling.

Courtesy: Burland (1987)

How to handle a geotechnical problem ?

Sched le detail soilSchedule detail soil testing.

Field: SPT, Borehole, , ,plate load test etc.

Laboratory: Index h

Courtesy: Burland (1987)

property, strength, compressibility etc.

How to handle a geotechnical problem ?

Modeling:g

physical: not always possible

analytical: difficult for complex problem

Courtesy: Burland (1987)

numerical: FEM, BEM, FDM etc.

User Programmer

Analyst Engineer

Some Common Geotechnical Analysis Software

Plaxis (FEM) Pl i i f th t l ft d b t h i l Plaxis is one of the most popular software used by geotechnical consultants. it is preferred because of its user-friendly nature.

Plaxis is quite handy for plane stress problems.

There are lot of geotechnical features (such as anchors, geogrids, tunnels etc.) in-built in Plaxis. So just click and play….

Diff t tit ti d l f i li ti Different constitutive models for various applications.

Limitations It is a “Blackbox” type software.

It is so easy to use that the person who has no proper training in geotechnical engineering may possibly run a Plaxis analysis by simplygeotechnical engineering, may possibly run a Plaxis analysis by simply following some tutorials.

It is difficult to model non-conventional geotechnical problems (such l t i bl i l t i t )as, large strain problems, irregular geometries etc.)

Flexibility in modelling is absent.

FLAC d ib li it fi it diff l ti

FLAC (FDM) FLAC describes an explicit finite difference solution.

It can be used for rock mechanics problem as well.

It also has specific features such as structural elements e g to It also has specific features, such as structural elements, e.g., to represent anchors, piles, rock bolts or tunnel support, capabilities for thermal and hydro-mechanical analysis.

It i ti l l f l f d i bl It is particularly useful for dynamic problems.

Limitations It is NOT so simple in use.

It is difficult to model complicated geometries.

Dynamic analysis may sometimes encounter convergence problem

G St di t i i k f t h i l d

GeoStudio (Limit equilibrium) GeoStudio contains various packages for geotechnical and geoenvironmental applications:

1. Slope/W (Slope stability analysis)

2. Sigma/W (Load deformation analysis)

3. Seep/W (Seepage problems)

4. Quake/W (Dynamic analysis)

5. Temp/W (Geothermal analysis)

6. Air/W (Air flow analysis)

7. CTRAN/W (Contaminant transport)

8. Vadose/W (Vadose zone and soil cover analysis)

It is based on simple limit equilibrium method.Limitations

p q

The solution sometimes overestimates soil strength.

It is difficult to model complicated geometries.

It i l FEM

ABAQUS (FEM) It is a general purpose FEM.

It can model solid and water as two phases.

ABAQUS-explicit analysis is particularly useful for dynamic problems ABAQUS-explicit analysis is particularly useful for dynamic problems.

It offers various flexibilities in modelling.

It is NOT easy to use More suited for research

Limitations

It is NOT easy to use. More suited for research.

For large problems with many nodes ABAQUS analysis may encounter memory problem.

Convergence for highly non-linear problems is not easy to achieve.

ANSYS (FEM)

It is a general purpose FEM for mostly mechanical engineering applications.

It is quite efficient in dynamic analysis.

It is NOT suited for geotechnical problems

Limitations

It is NOT suited for geotechnical problems.

Couple flow analysis can not be done.

Limited number of constitutive models.

There are few moreThere are few more,

SASSI: Useful for soil-structure interaction analysisy

LS DIANA: Particularly suited for blast loadings.

SageCrisp: Couple flow analysis can be doneSageCrisp: Couple flow analysis can be done.

There are many more…..

Modern Finite Element SoftwareModern Finite Element Software

Ease of UseEase of Use≠

Ability to Use

especially true for geotechnical softwareespecially true for geotechnical software

Consequence

There may be many more if…

Problem 1: Stability Analysis of Slopes

Problem 1: Stability Analysis of Slopes

RL 107.00RL 107.00RL 104.00

RL 100.00 RL 96.70

RL 93 40

Ash Core Ash Core

4 m

7 m `Earthen Cover

RL 93.40RL 90.00

`Fly Ash Embankment ` Earthen Embankment

2.251

4m

5 m4 m

RL 80.00

The typical section of a dyke of NALCO ashpond at Angul OdishaThe typical section of a dyke of NALCO ashpond at Angul, Odisha

Plaxis model

The analysis was carried out using PLAXIS ver. 8.

Plane strain model with 15 noded triangular elements.

The base of the embankment is assumed as fixed base. The base of the embankment is assumed as fixed base.

The sides are horizontally restrained.

Material properties

Elevation Cohesion (kPa)

Angle of friction (⁰)

Unit weight (kN/m3)

B l 80 RL (F d ti ) 50 30 18Below + 80m RL (Foundation ) 50 30 18

+80 to +90 m RL (within starter dyke) 50 20 18

+80 to +90 m RL (Ash deposit) 5 35 1380 to 90 ( s depos t) 5 35 3

+90 to +100 m RL (Ash deposit) 5 30 13

+100 to +107 m RL (Ash deposit) 0 30 13

Material properties

Calculation stages

Results

FOS

Results

Total increment

Failure surface: It is not the conventional slip circles

Problem 2: Analysis of Excavation andProblem 2: Analysis of Excavation and Support Systems

Problem statement

The excavation carried up to a depth 11m from ground The excavation, carried up to a depth, 11m from groundsurface, was roughly rectangular in plan with dimensions of100m x 26m.

The excavation area was circumference by a 5-storybuilding on the north side and roads on all other sides.g

Problem statement

The sheet piles were driven to a depth of 30m below theground surface to support the excavation.

There were six levels of internal struts of three different There were six levels of internal struts of three differentsizes.

Steel H Piles were driven down to the bedrock at Steel H-Piles were driven down to the bedrock athorizontal 1.5m grid spacing within the excavation site.

26Sh il llSix no. of struts

11

26mSheet pile wall

11m

30m

H-Piles @ 1.5mspacing

Problem statement

The soil profile consisted of six different layers,

1.5m thick layer of fill

20.50 m thick marine clay layer,

9m thick silty clay layer,

7m thick medium stiff clay layer,

7m thick sandy silt layer and 7m thick sandy silt layer and

weathered rock (~5m).

Height of sheet pile

ll 30

SHEET PILE WALL

depth of excavati

0.0-1.5

wall, 30m

excavation 11mMARINE CLAY

STRUTSNo. excavation l l i

-22

SILTY CLAY

STRUTS

levels, six-31

38

SILTY CLAY

MEDIUM STIFF CLAYH-Piles-38

-45SANDY SILT

WEATHERED ROCK

H-Piles

-50WEATHERED ROCK

Excavation stages

Stages Construction sequences

1 Pile installation considering surcharge of 10 kPa for existing structure

2 Sheet pile driving up to depth of 30 m below ground

3 Excavation up to -1.4 m and installation of strut 1 at -1.0 m with a preload of 100 kN

4 Excavation up to -4.5 m and installation of strut 2 at -3.5 m with a preload of 150 kN

5 Excavation up to -6.0 m and installation of strut 3 at -5.25 m with a preload of 200 kNof 200 kN

6 Excavation up to -7.5 m and installation of strut 4 at -7.25 m

7 Excavation up to -9.25 m and installation of strut 5 at -8.75 m

8 Excavation up to -11 m and installation of strut 6 at -10.25 m

Struts

-1 H 350x350x12x19

Ground

1

-3.5 H 350x350x12x19

H 350x350x12x19

-5.25 H 400x400x13x21

-7.25-8.25 2H 400x400x13x21

2H 400x400x13x21

-10.25

2H 400x400x13x21

Excavation level

Ground water table

The initial position of the ground water table can be taken asground itselfground itself.

However, with each stage of excavation GWT will be lowered toth ti l l th i idthe excavation level on the passive side.

Initial GWT

At excavation stages

Fill Marine Clay Silty Clay Med. Stiff Clay Sandy Silt Weathered rockrock

Type ?? ?? ?? ?? ?? ??

kN/ ³ 18 00 15 00 18 00 16 00 18 00 21 00s gunsat kN/m³ 18.00 15.00 18.00 16.00 18.00 21.00

gsat kN/m³ 18.00 15.00 18.00 16.00 18.00 21.00

Eur’ kN/m² 13000 2344 13000 18900 26000 230000pe

rtie

n 0.200 0.200 0.200 0.200 0.200 0.200

c’ kN/m² 10.00 1.00 5.00 1.00 1.00 300.00

j' ° 30 00 20 00 22 00 22 00 35 00 35 00oil p

ro

j ° 30.00 20.00 22.00 22.00 35.00 35.00

y ° 5.00 0.00 5.00 0.00 5.00 0.00

Einc’ kN/m²/ 0.00 473.00 0.00 473.00 0.00 0.00

So

m

yref m 0.000 0.000 0.000 0.000 0.000 0.000

Rinter. 0.50 0.50 0.50 0.50 0.50 0.50

esNo. Identification EA

kN/mEI

kNm²/mW

kN/m/m

1 Sh il ll 3 85E6 47196 0 00 0 15pert

ie

1 Sheet pile wall 3.85E6 47196 0.00 0.15

2 H Piles (H 344x354x131 kg/m) 2.4E6 18768 0.90 0.15

prop

No Identification EA Horizontal spacingural

No. Identification EAkN

Horizontal spacing

1 H 350x350x12x19 3599730 5.00

2 H 400x400x13x21 4527090 5.00ruct

u

3 2H 400x400x13x21 9054000 5.00Str

ResultsLateral deflection of wall

00 50 100 150 200 250

Bending moment

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

Vertical settlement

20

00 10 20 30 40

(a) (b) (c)

-10

-5

-10

-5

-60

-40

-20

-20

-15

Dep

th (m

)

-20

-15D

epth

(m)

-100

-80

Settl

emen

t (m

m)

-25

Exc. Stage 1Exc. Stage 2Exc. Stage 3Exc. Stage 4

Exc. Stage 5

-25

-160

-140

-120S

-35

-30

Deflection (mm)

Exc. Stage 6

-35

-30

Bending moment (kN-m/m)

-200

-180

Distance from wall (m)

Drain-undrain analysisDrain undrain analysis

What is drain/undrain behaviour?

• Undrain: Excess pore pressure are not allowed to dissipatep p p

• Drain: Excess pore pressure completely dissipated

How to choose drain/undrain?How to choose drain/undrain?

• Short term problem: undrainpeg. earthquake, blast etc.

• Long term problem: draineg. excavation, tunneling etc.

Analysis in PLAXIS

Undrained Behaviour

MethodPlaxis

Material Material ModelParameters Computed

Stet od ate aSetting

ate a ode StressesStrength Stiffness

A Undrained Mohr-Coulomb C', Ø' (Effective)

E', ' (Effective)

Effective stressand pore pressure

C Ø 0 E' ' Eff ti tB Undrained Mohr-Coulomb Cu, Øu = 0 (Total)

E', ' (Effective)

Effective stressand pore pressure

C Non-porous Mohr-Coulomb Cu, Øu = 0 (Total)

Eu, u = 0.495 (T t l)

Total stress(Total) (Total)

D As in Method A, for other soil models (HS, SS, SSC)

Drained BehaviourDrained Behaviour

Drained Mohr-Coulomb, other models

C', Ø' (Effective)

E', ' (Effective)

Effective stress.Pore pressure

specifiedby user

Look at a Simple Problem of Single Propped Wallp g pp

PARAMETRS Used in Method A

SWITCH SOIL TYPE: UNDRAINED (EFFECTIVE Stress Analysis)

PARAMETRS Used in Method BSWITCH SOIL TYPE: UNDRAINED (EFFECTIVE Stress Analysis)

Use Advance button, and set t thstrength

increase with depth = 3.75 kN/ 2/kN/m2/m obtained from Ko=0.5 in

)('sin2

)1( 'v

Kocu

PARAMETRS Used in Method C

SWITCH SOIL TYPE: NON-POROUS (TOTAL Stress Analysis)

Use Advance button, and set strengthstrength increase with depth = 3.75 kN/ 2/kN/m2/m obtained from Ko=0.5 in

)('sin2

)1( 'v

Kocu

Modeling of Pore Water Pressures

• Method A, Use Z-Water TableMethod A, Use Z Water Table

• Method B Use Z-Water TableMethod B, Use Z-Water Table

• Method C No Water Table place phreatic line• Method C, No Water Table, place phreatic line at the base of mesh

Modeling of Ko Condition

• Method A, For NC soils, Ko =1-sin’• For OC soils use OCRKK NC• For OC soils use • Method B, same as Method A

M th d C i T t l St

OCRKK NCoo

• Method C is Total Stresses:

uK hh 'uuK

v

h

v

hOT

'

Results of Deformed Mesh

Results of Yielded Zones

Results of Wall Deflection

Results of Wall Bending Moments

Problem 3: Three dimensional FEM:Problem 3: Three-dimensional FEM: Piles under lateral load

Problem 3: Three-dimensional FEM: Piles under lateral load

Three-dimensional (3-D) numerical model of the field pile lateral load test

(U t l 2011)(Urano et al., 2011)

The analysis was carried out using ABAQUS ver 6.10

• Soil Layer

– Hypoelastic Soil Model

RCC St l il d R ft• RCC or Steel pile groups and Raft

– Linearly elastic materials

Details of Field Test

ABAQUS Modeling

Structured mesh generated g

20-noded quadratic brick elements (C3D20R)

- Reduced integration-type elements

3-noded quadratic space beam elements (B32) 3-noded quadratic space beam elements (B32)

Used symmetry

Assigned proper boundary conditions

3D Soil-Pile-Raft Model in ABAQUS

Pile E (kN/m2)

Depth (m)

Soil Profile

Eo(kN/m2) Raft E (kN/m2)

= 2 5x107

Pile E (kN/m2)= 3.9x107

1.9 Fill 69160

1.5 loam 66500

= 2.5x10

1.4 Clay 39900

2.1 Clayey sand 31920

0 9 Sandyclay 1542800.9 Sandy clay 154280

0.55 Clay 154280

2.15 Medium sand 252700

Boundary Conditions

Back Left Boundary Boundary

UY = 0

BoundaryUY = 0

Plane of RightSymmetry

UY = 0

Right Boundary

UY = 0

Bottom SurfaceUx = UY = Uz = 0

Soil Model

Hypoelastic Soil Model

Stiffness reduction curve by Vucetic and Dobry, 1991

1

0.8

0.4

0.6

G/G

max

0

0.2PI=200

. PI=100

. PI=50

. PI=30

. PI=15 PI=NP

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01

Cyclic shear strain, γ0 (%)

Pile Model

Piles were modeled using solid elements.Pile

Bending moment can not be measured from solid elements.

3-noded quadratic space beam elements.

Flexible beam

Flexural rigidity (scale down by 106)

Bending moment (scale up by 106)

Fl ibl b l thFlexible beam along thepile central axes

Input Loadp

500

600

700

200

300

400

500

oad

(KN

) Lateral Load

0

100

200

0 50 100 150 200 250

Lo

Load application point

0 50 100 150 200 250

Time (min)

point

Results and Discussion

0-200 -100 0 100 200

Bending moment (kNm)

-2

Fi ld

6

-4FieldAnalysis By Urano

et al.Analysis By

-8

-6

(m)

ABAQUS

-10

Dep

th

B di t l th il l thBending moment along the pile length

Pile–Raft–Reinforcement Body

Depth (m)

Soil Profile

Eo(kN/m2)(m) Profile (kN/m2)

1.9 Fill 69160

1 4 loam 665001.4 loam 66500

1.5 Clay 39900

2 1 Clayey fine 319202.1 sand 31920

0.9 Sady clay 1542800.55 Clay 154280

Medium

Grouted soil (Reinforcement Body)

2.15 Medium sand 252700

Pile, Raft and Reinforcement Body

Modulus of Elasticity (E0) of Reinforcement Body 1.5x106 kN/m2

With Reinforcement Body

0-200 -100 0 100 200

Bending moment (kN-m)

-2

0

A l i B U

-4

FieldAnalysis By Urano et al.

Analysis By

-6

RBy y

ABAQUS

-8

epth

(m)

-10 De

Position of Reinforcement Body

NRB

New Position for Reinforcement Body

RBReinforcement Body By

Urano et al.

Position for Reinforcement Body

New Position for Reinforcement Body

Reinforcement Body By Urano et al.

Effect of Position Grout

-200 -100 0 100 200

Bending moment (kN-m)

2

0

Analysis By ABAQUSNew Grout position

-4

-2

Test results with Old Grout position

Analysis By ABAQUSWith Old Grout position

-6

-8D

epth

(m)

-10

D