deep excavations with pile walls - midas...

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Finite Element Solutions for Geotechnical Engineering

Deep Excavations with Pile Walls

Angel Francisco MartinezApplication EngineerMIDAS NY



01 Modeling of Excavations

02 3D Excavation Demo

03 Case Study

GTS NX

3

Surcharge Loading

Modeling of deep excavation

Projectexcavation

residential

school

residentialcommercial

GTS NX

4

Props and Anchor Modeling

Diaphragm wall

Barrettes

Anchors

Modeling of reinforcement

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5

Interface Behavior

• Soil‐structure interaction

➢ Wall friction

➢ Slip and gapping between soil and structure

• Soil material properties

➢ Taken from soil using reduction factor R

➢ Individual material set for interface possible

• Suggestions for R

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The behavior of pile elements can be divided into a normal behavior and a tangential behavior. First, the

normal behavior between the pile and the surrounding ground is considered as fixed and rigid, whereas the

tangential behavior is a nonlinear elastic behavior.

The graph bellow represents the relative displacement between the 2 bodies and the friction when yield force

is defined.

The Pile tip element works as solid-point interface that presents the relative behavior between the ground

elements and pile node.

To define the behavior, the material and property of a pile element can be entered based on test data, such as

Load Test.

Interface Behavior





03 Case Study

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Methodology – Ground Conditions

Material Depth (m) γ

(kN/m3)

γSat

(kN/m3)

E (MPa) φ' C’ K0 Ka Kp ν

Fill 3.5 18 20 16 30˚ 0 0.5 0.29 3.0 0.3

Sandy Gravel 1 19 21 32 35˚ 0 0.45 0.23 3.69 0.3

SAND 1.5 17 20 27 34˚ 0 0.45 0.24 5.5 0.3

SANDSTONE 25+ 23 23 52 38˚ 0 0.4 0.21 7.2 0.3

Concrete - 24 - 27,000 - - - - - 0.2

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1

Geometry > Point & Curve >

Rectangle

- Location: (0,0) <80, -80>

- OK

Geometry > Point & Curve >

Point

- Tabular Input tab

- Read From File…

- ‘Location of Piles.txt’

- OK

( ): ‘ABS x, y’

< >: ‘REL dx, dy’

2

2

02 Geometry Modeling

Procedure

1

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1

Geometry > Point, Curve > Line

- Draw lines connecting the outer

boundary of the piles

Geometry > Extrude

- Change Filter to Point

- Select the Pile Head Points

- Extrude -9m

2

2


Procedure

1

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1

- Selection filter: Basic > Wire

(W)

- Select: the highlighted wire

(as shown in the figure)

- Direction: Z-axis

- Length: -0.5

- Apply

- Select: the highlighted face


- Direction: Z-axis

- Length: -2.5

- Apply 2


Procedure

1

2

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1



- Direction: Z-axis

- Length: -0.5

- Apply



- Direction: Z-axis

- Length: -0.5

- Apply

2


Procedure

1

2

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1



- Direction: Z-axis

- Length: -.5

- Apply



- Direction: Z-axis

- Length: -0.5

- Apply

2


Procedure

1

2

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1



- Direction: Z-axis

- Length: -2

- Apply



- Direction: Z-axis

- Length: -3

- Apply

2


Procedure

1

2

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1

Geometry > Protrude > Extrude

- Extrude tab

- Selection filter: Basic > Wire

(W)

- Select: the highlighted wire


- Direction: Z-axis

- Length: -3.5m

- Apply

- Select: the bottom highlighted

face (as shown in the figure)

- Direction: Z-axis

- Length: -2.5

- Apply

2

2


Procedure

1

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1



- Direction: Z-axis

- Length: -3m

- Apply



- Direction: Z-axis

- Length: -21m

- Apply

2

2


Procedure

1

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1


Procedure

1 Geometry > Surface & Solid>

Auto Connect

- Select: all 10 solids (as shown

in the figure)

- Method: Boolean

- Click Apply

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1

Mesh > Generate > 3D

- Auto-Solid tab

- Select: the top solid segment

- Size: .75

- Tetra Mesher

- Property: 1: Granular Fill

- Mesh Set: Exca #1

- Apply

- Select: the second solid

segment

- Size: 0.75

- Tetra Mesher


- Mesh Set: Exca #2

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

- Select: the third solid segment

- Size: 0.75

- Tetra Mesher


- Mesh Set: Exca #3

- Apply

- Select: the bottom solid

segment

- Size: 0.75

- Tetra Mesher

- Property: 2: SAND

- Mesh Set: Exca #4

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

- Select: the third solid segment

- Size: 0.75

- Tetra Mesher

- Property: 2: SAND

- Mesh Set: Inner Sand

- Apply

- Select: the bottom solid

segment

- Size: 0.75

- Tetra Mesher

- Property: 3: SANDSTONE

- Mesh Set: Inner Sand Stone

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

- Show all the boundary solid

segments


- Size: 3

- Tetra Mesher


- Mesh Set: Fill

- Apply


segment

- Size: 3

- Tetra Mesher

- Property: 2: Sand

- Mesh Set: Sand

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

- Show all the boundary solid

segments


- Size: 3

- Tetra Mesher

- Property: 3: Sandstone

- Mesh Set: sandstone 1

- Apply


segment

- Size: 3

- Tetra Mesher

- Property: 3: Sandstone

- Mesh Set: sandstone 2

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

Hide all mesh sets and show only

the inner solid segments.

Mesh > Element > Extract

- Geometry tab

- View Toolbar: Top

-Type: Face

- Select: the top of exca 2

- Property: 5: base/roof slabs

- Mesh Set: roof slab

- OK

Mesh > Element > Extract

- Geometry tab

- View Toolbar: Top

-Type: Face

- Select: the top of exca 3

- Property: 5: base/roof slabs

- Mesh Set: roof slab

- OK

03 Mesh Generation

Procedure

1

2

2

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1

Hide all mesh sets and show only

the geometry lines for piles.

Mesh > Generate > 1D

- Select: all the lines

- Division: 10

- Property: 4: Piled wall

- Mesh Set: Piles

- OK

03 Mesh Generation

Procedure

1

2

2

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1

Mesh > Element > Pile/Pile Tip

- Pile tab

- Select: all the Pile elements

- Property: 8: pile interface

- Mesh Set: Pile interface

- Apply

- Pile Tip tab

- View Toolbar: Front

- Select: all the bottom nodes of

Pile elements (as shown in the

figure)

- Property: 7: Pile tip

- Mesh Set: Pile Tip

- OK

03 Mesh Generation

Procedure

1

2

2

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1

- Show only the ‘Piles’ mesh set.

Static/Slope Analysis >

Boundary > Constraint

- Advanced tab

- Object Type: Node

- Select: all the nodes of Pile

elements (as shown in the

figure)

- DOF: Rz

- Boundary Set: Piles

- OK

Show all mesh sets

Constraint >

- Auto tab

- Boundary Set: Ground support

- Apply

04 Analysis Setting

Procedure

1

2

2

Axial rotation constraints to

prevent the degree of freedom

errors for torsion of beam

elements

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1

Static/Slope Analysis > Load >

Self Weight

- Gz: -1

- Load Set: Self weight

- OK


Force

Select 8 nodes as shown

-Z : -300 kN

Load set: Column Load

Ok


Moment

-X: -20 kN/m

Load set: Column Load

Apply

04 Analysis Setting

Procedure

1

2

3

2 3

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1

Show only the Piles mesh set


Force

Select 27 top pile nodes as

shown

-Y : 50kN

Load set: Barrier load

Ok


Pressure

- Face tab

- View Toolbar: top

- Object Type: 3D Element Face

- Select: the highlighted area


- Direction Type: Normal

- P or P1: 10 kN/m2

- Load Set: Surcharge

- OK

04 Analysis Setting

Procedure

1

2

2

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1

Show all mesh sets.

Static/Slope Analysis >

Construction Stage > Stage Set

- Add

- Stage Name: Initial Stage

- Select the highlighted mesh,

boundary and load sets. Drag and

drop them into Activated Data

from Set Data.

- Show Data: Activate

- Clear Displacement: Check on

- Save

04 Analysis Setting

Procedure

1

2

2

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1

- New

- Stage Name: Install Pile Wall

- Select the highlighted mesh

sets. Drag and drop them into

Activated & Deactivated Data

from Set Data.


- Clear Displacement: Check on

- Save

04 Analysis Setting

Procedure

1

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1

- New

- Stage Name: Surcharge +

Columns

- Select the highlighted mesh set.

Drag and drop it into Deactivated

Data from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

- New

- Stage Name: Excavation 1



Data from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

- New




Data from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

- New




Data from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

- New




Data from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

- New

- Stage Name: Install Rafts

- Select the highlighted mesh and

boundary sets. Drag and drop

them into Activated Data from Set

Data.


- Save

04 Analysis Setting

Procedure

1

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1

- New

- Stage Name: Barrier Load




from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

- New

- Stage Name: Deactivate Base

Slab




from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

Analysis > Analysis Case >

General

- Title: 3D Excavation with Pile

Wall

- Solution Type: Construction

Stage

- Analysis Control

- Initial Stage for Stress Analysis:

Check on

- Initial Stage: 1:In-situ

- Apply K0 Condition: Check on

- OK

- Output Control

- Strain: Check on

- OK

Analysis > Analysis > Perform

- Analysis Case: Check on

- OK

04 Analysis Setting

Procedure

1

2

2

To plot the relative displacement

of element such as pile element

among the ground when

interfacial behavior occurs

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1

Results > Displacements

Excavation 1


Excavation 2


Excavation 3


Excavation 4

05 Results

Procedure

1

2

2

3 4

4

3

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1


➢ Total Displacements

Results > Beam Element >

Axial Forces


Shear Forces Z


Bending Moments Y

(Show piles only)

05 Results

Procedure

1

2

2

3 4

4

3





03 Case Study

GTS NX

43

Limit Equilibrium vs 2D vs 3D

FEM of Retaining Wall in

Birmingham New St. Station, UK

Abouzar JahanshahiRNP Assoc.United Kingdom

Video of original webinarhttps://www.youtube.com/watch?v=bVjgPAbIIVE

GTS NX

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Introduction – Theoretical Background

Complete Theoretical

Solution

Equilibrium

Material Constitutive Behaviour

Boundary Conditions

Compatibility

Conventional Methods

Closed Form

Simple

• Limit equilibrium

• Stress field

• Limit analysis

Numerical Methods

Beam-Spring

Full Numerical

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Introduction

Limit Equilibrium Finite Element Mesh in 3D

GTS NX

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Case Study – Attenuation Tank Construction

GTS NX

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Construction Sequence:• Construct Piles

• Install Steelworks.

• Excavate 4.0m

• Construct Slabs.

• Construct Barrier Wall

Imposed Loadings:• 10kN/m2 surcharge

• 300kN/pile at steel columns

• 20kNm/m moment at steel columns

• 50kN/m barrier line load

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Methodology – Ground Conditions

Material Depth (m) γ

(kN/m3)

γSat

(kN/m3)

E (MPa) φ' C’ K0 Ka Kp ν

Fill 3.5 18 20 16 30˚ 0 0.5 0.29 3.0 0.3

Sandy Gravel 1 19 21 32 35˚ 0 0.45 0.23 3.69 0.3

SAND 1.5 17 20 27 34˚ 0 0.45 0.24 5.5 0.3

SANDSTONE 25+ 23 23 52 38˚ 0 0.4 0.21 7.2 0.3

Concrete - 24 - 27,000 - - - - - 0.2

• Soil Profile Effect

• Sensitivity of E & φ’

• K0 = 1 – Sinø’

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Methodology – Limit Equilibrium Method

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Methodology – Limit Equilibrium Method

Temporary Conditions Permanent Conditions

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Methodology – FEM, 2D & 3D Models

Material Properties Ground Piles Slabs Interface

Model Type Mohr – Coulomb Elastic Elastic ---

2D Elements 2D Plane-Strain 1D Beam 1D Beam Interface Elements + Rigid Link

3D Elements 3D Solid 1D Beam 2D Plane-Stress Pile Interface + Rigid Link

GTS NX

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Results – Wall Bending Moment

LimitEquilibrium

FEM

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-100 0 100 200

Dep

th (

m,

BG

L)

Wall bending moment (kNm/m)

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-50 0 50 100 150 200D

epth

(m

, B

GL

)


FOS reducedfrom 3.19 to2.76

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Results – Wall Deflection

LimitEquilibrium

FEM

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 5 10 15

Dep

th (

m,

BG

L)

Wall deflection (mm)

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 5 10 15

Dep

th (

m,

BG

L)


GTS NX

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Results – Sensitivity Study

Soil

Original Scenario Stiffness variation by

±5%

Friction angle variation

by ±5%

Case 1 Case 2 Case 3 Case 4 Case 5

E (kN/m2) φ' E (kN/m

2) E (kN/m

2) φ' φ'

Fill 16000 30 15200 16800 28 32

Sandy

Gravel 32000 35 30400 33600 33 37

Sand 27000 34 25650 28350 32 36

Sandstone 52000 38 49400 54600 36 40

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Results – Sensitivity Study (Limit Equilibrium)

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 5 10 15 20D

epth

(m

, B

GL

)


-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-20 80 180 280D

epth

(m

, B

GL

)


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Results – Sensitivity Study (3D FEM)

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 5 10 15D

epth

(m

, B

GL

)


-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 50 100 150D

epth

(m

, B

GL

)Wall bending moment (kNm/m)

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Results – Deformation Shapes

3D FEM2D FEM

Roof slab in compression

Base Slab in tension

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Results – Method Comparison

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 5 10 15

Dep

th (

m,

BG

L)


-9

-8

-7

-6

-5

-4

-3

-2

-1

0

-20 30 80 130 180

Dep

th (

m,

BG

L)


TEMPORARY CONDITIONS(Cantilevered Wall)

PERMANENT CONDITIONS(Slabs act as supports)

Maximum Slab Loads (SLS)

•LE Model 106 kN/m•2D FEA Model 79.2kN/m•3D FEA Model 81.6kN/m

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Results – Modeling Time

• Ability to operate the programs

• Learning and layout of MIDAS GTS NX

• Time of 2D FEM vs 3D FEM

• 3D modeling can be challenging until the program functions are learned in depth.

• Modeling time depends on the complexity of the problem

• 3D modeling and analysis approximately 6 times longer than 2D modeling

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Conclusions

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Q & Ahttps://midassupport.jitbit.com/helpdesk/KB

http://latinamerica.midasuser.com/web/e-learning/reviewing-courses.php

deep excavations with pile walls - midas...

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