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Finite Element Solutions for Geotechnical Engineering

3D Excavation and Piled-Raft Foundation

GTS NX

2

00 Overview

• This tutorial identifies the soil–

structure interaction by analyzing

construction stage of 3D retaining wall

excavation.

• It is possible to review in detail the

stress distributions on cross-sections,

which is not possible in 2D models.

• Also, interface is added between

ground and retaining wall to simulate

the ground-structure interaction more

realistically.

• The evaluation of the soil-structure

behavior is done by using pile

elements, not by simple beam

elements.

• Also, pile elements are perfect for

evaluating the soil-structure behavior

because it can consider the influence

of interface between pile and adjacent

ground.

Procedure

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01 Material & Property

Name Sand Sandy gravel Clay

Material Isotropic Isotropic Isotropic

Model Type Mohr-Coulomb Mohr-Coulomb Mohr-Coulomb

General

Elastic Modulus (E) [kN/m2] 22,300 74,300 37,150

Poisson’s Ratio (v) 0.3 0.3 0.3

Unit Weight (γ) [kN/m3] 20 20 20

Ko 0.5 0.5 0.5

Porous

Unit Weight (Saturated) [kN/m3] 21 21 21

Drainage Parameters Drained Drained Drained

Non-Linear

Cohesion (c) [kN/m2] 10 10 50

Frictional Angle (Φ) [deg] 33 36 25

[unit : kN, m] Ground

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01 Material & Property

Name Concrete-Raft Concrete-Structure

Material Isotropic Isotropic

Model Type Elastic Elastic

Elastic Modulus (E) [kN/m2] 2e+07 2e+07

Poisson’s Ratio (v) 0.3 0.18

Unit Weight (γ) [kN/m3] 24 24

Name Pile to Soil interface Pile to Raft interface

Model Type Pile Pile

Ultimate Shear Force [kN/m2] 2,000 1e+010

Shear Stiffness Modulus (Kt)

[kN/m3] 1e+06 1e+08

Normal Stiffness Modulus (Kn)

[kN/m3] 1e+07 1e+09

Tip Bearing Capacity [kN] 2,000 -

Tip Spring Stiffness [kN/m] 1e+06 -

[unit : kN, m]

[unit : kN, m]

Structure

Pile

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02 Geometry Modeling

• You can start the tutorial by opening

the start file in which basic materials

and properties have already been

predefined.

Start > Open

- ‘3D Excavation and Piled-Raft

Foundation_start.gts’

- Open

1

Procedure 1

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In GTS NX, 2 types of coordinate system are used: Global coordinate system (GCS) and Work plane coordinate system

(WCS). GCS is a fixed coordinate system indicated in red(X-axis), green(Y-axis), and blue (Z-axis) colors at the right

bottom corner on the screen. WCS is a coordinate system which locates at center of the working window and moves with the

work plane. So if the work plane changes, WCS will also change. 3D absolute coordinates are necessary to locate geometry

in the space, but practically relative coordinates are commonly used, for example to indicate length. You can process

modeling by inputting 2D coordinates (XY plane in WCS) after moving the work plane to proper location.

Keep in mind that in case of inputting direction for extruding geometry or defining load/boundary conditions, it always follows

Global coordinate system.

WCSWorkplane Coodinate System

GCSGlobal Coodinate System


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1

Geometry > Point & Curve >

Rectangle

- Location: (0,0) <60,60>

- Location: (18,21) <24,18>

- OK


Point

- Tabular Input tab

- Read From File…

- ‘Location of Piles.txt’

- OK

( ): ‘ABS x, y’

< >: ‘REL dx, dy’

2

2


Procedure

1

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1

Geometry > Transform >

Translate

- Translate tab

- Select: 24 points

- Direction: Z-axis

- Method: Copy(Uniform)

- Distance: -10.3

- OK


Line

- 3D tab

- Define Snap: Point Snap

- Use mouse to select the

corresponding nodes from top

layer to the bottom layer nodes.

2

2


Procedure

1

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1

Geometry > Protrude > Extrude

- Extrude tab

- Selection filter: Basic > Wire (W)

- Select: the highlighted wire

(as shown in the figure)

- Direction: Z-axis

- Reverse Direction: Check on

- Length: 3

- Apply

- Select: the highlighted face


- Direction: Z-axis


- Length: 4

- Apply

2

2


Procedure

1

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1



- Direction: Z-axis


- Length: 3

- Apply



- Direction: Z-axis


- Length: 0.6

- Apply

2

2


Procedure

1

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1

- Selection filter: Basic > Wire (W)

- Select: the highlighted wire


- Direction: Z-axis


- Length: 3

- Apply



- Direction: Z-axis


- Length: 15

- Apply

2


Procedure

1

2

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1



- Direction: Z-axis


- Length: 20

- OK


Procedure

1

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1

Select the highlighted solid

segments and right click on

mouse and select Transparency.

Display Mode (Geometry) >

Random Color

2

1

2


Procedure

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1


Procedure

1 Geometry > Divide > Solid

- Select: 2 boundary soil layers


- Selection filter: Basic > Solid (D)

- Dividing Tools: all the inner

solid segments

- OK

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1

Mesh > Control > Size Ctrl.

- Edge tab

- View Toolbar: Top

- Pick & Rect: Polyline

- Select: all the in-plane

boundary edges (cross the

selecting line through the

edges)

- Method: Number of Divisions

- Division: 10

- Apply

- Show only all the inner solid

segments

- View Toolbar: Front

- Pick & Rect: Polyline

- Select: the side edges

- Method: Number of Divisions

- Division: each value as shown

in the figure

- OK

03 Mesh Generation

Procedure

1

2 2

3

4

3

3

4

3

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1

Mesh > Generate > 3D

- Auto-Solid tab

- Select: the top solid segment

- Size: 1

- Hybrid Mesher

- Property: 1: Top Soil

- Mesh Set: Excav#1

- Apply

- Select: the second solid

segment

- Size: 1

- Hybrid Mesher

- Property: 2: Mid Soil

- Mesh Set: Excav#2

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

- Select: the third solid segment

- Size: 1

- Hybrid Mesher


- Mesh Set: Excav#3

- Apply

- Select: the bottom solid

segment

- Size: 1

- Hybrid Mesher


- Mesh Set: Excav#4-Raft

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

- Show all the boundary solid

segments

- Select: the top solid segment

- Division: 3

- Hybrid Mesher

- Property: 1: Top Soil

- Mesh Set: Top soil

- Apply

- Select: the second solid

segment

- Division: 5

- Hybrid Mesher


- Mesh Set: Mid soil

- Apply

03 Mesh Generation

Procedure

1

2

2

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1

- Select: the bottom solid

segment

- Division: 4

- Hybrid Mesher

- Property: 3: Bot Soil

- Mesh Set: Bot soil

- OK

Hide all mesh sets and show only

the inner solid segments.

Mesh > Element > Extract

- Geometry tab

- View Toolbar: Top

-Type: Face

- Select: the four sides where

the wall will be modelled

- Property: 5: Wall

- Mesh Set: Wall

- OK

03 Mesh Generation

Procedure

1

2

2

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1

Mesh > Element > Interface

- Plane tab


- Method: From Shell

- Select: all the wall elements

- Merge Nodes: Check on

- Select: all the bottom nodes of

wall elements (as shown in the

figure)

- Property Parameters: Wizard

- Strength Reduction Factor(R):

0.8

- OK

- Create Rigid Link Element:

Check on

- Mesh Set: Wall Interface

- OK

03 Mesh Generation

Procedure

1

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The interface material can be defined using the following equation. Using the stiffness of adjacent elements and nonlinear

parameters, the virtual thickness (tv) and strength reduction factor (R) is applied. Interface material stiffness and parameters

are applied differently according to the relative stiffness difference between neighboring ground and structural members. The

Wizard can be used to simplify this process.

The general Strength reduction factor for structural members and neighboring ground properties are as follows.

Checking the Element size consideration calculates the interface material properties considering the average length(line),

average area(face) of the neighboring ground element when creating an interface. In other words, the average length(l),

average area(A) are multiplies to the virtual thickness in the equation below to calculate the tangent, normal direction stiffness

of the interface.

If the consideration is not checked, the unit length(area) is applied. The thickness is defined separately for a line interface.

The thickness is an important element when using the interface on a ground material that displays hardening behavior.

Generally, the neighboring ground particle size is input, but if an accurate numerical value is not available, the default value

from the program is used. For a 3D model, like the 1 in the example above, the surface interface does not need a thickness.

When defining the stiffness against seepage for an interface element, the “permeability coefficient” can be defined to be the

same as the permeability coefficient of the ground. If the option is not checked, the layer is considered to be impermeable.

03 Mesh Generation

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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: 1

- Property: 6: Pile

- 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: 7: Pile to Soil

interface

- Mesh Set: Pile interface

- Apply

- Pile Tip tab


- Select: all the bottom nodes of

Pile elements (as shown in the

figure)

- Property: 9: Pile to Soil

interface

- Mesh Set: Pile Tip

- OK

03 Mesh Generation

Procedure

1

2

2

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1

- Show the solid segment for Raft

- Select it and right click on

mouse and select ‘Display

Mode > Line Only’

Mesh > Element > Parameters

- 1D tab

- Change Property

- Select: all the Pile interface

elements inside solid (as

shown in the figure)

- Property: 8: Pile to Raft

interface

- OK

03 Mesh Generation

Procedure

1

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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 nonlinear elastic behavior is divided into the yield force and the yield function assigned.

The graph bellow represents the relative displacement between the 2 bodies and the friction when yield force is defined. If the

relation is defined by a function, the relation between relative displacement and friction can be defined more precisely.

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

node. In the element coordinate system of the pile tip element regard the normal direction behavior toward the element as

rigid behavior just like a pile behavior. And, regard the tangent direction behavior as nonlinear elastic behavior.

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

For more information about entering parameters of pile element, look up [User Manual] Ch4 (General Material) or Select F1

for [Online Manual].

03 Mesh Generation

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1

Show all mesh sets.

Static/Slope Analysis >

Boundary > Constraint

- Auto tab

- Boundary Set: Ground support

- Apply

- Show only the ‘Piles’ mesh set.

- Advanced tab

- Object Type: Node

- Select: all the nodes of Pile

elements (as shown in the

figure)

- DOF: Rz

- Boundary Set: Piles

- OK

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

Show all mesh sets.

Static/Slope Analysis > Load >

Self Weight

- Gz: -1

- Load Set: Self weight

- OK

04 Analysis Setting

Procedure

1

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1

Show only the ‘Excav#4-Raft’

mesh set.

Static/Slope Analysis > Load >

Pressure

- Face tab


- Object Type: 3D Element Face

- Select: the highlighted area


- Direction Type: Normal

- P or P1: 200 kN/m2

- Load Set: Raft pressure

- OK


Boundary > Change Property

- General tab

- Select: all the Raft elements


- Property: 4: Raft

- Boundary Set: Change

Property-Raft

- OK

04 Analysis Setting

Procedure

1

2

2

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1

Show all mesh sets.


Construction Stage > Stage Set

- Add

- Stage Name: In-situ

- 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 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: Excav#1

- 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




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 Piles &

Raft

- 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: Raft+Load

- Select the highlighted mesh,

boundary and load sets. Drag and

drop them into Activated Data

from Set Data.


- Save

04 Analysis Setting

Procedure

1

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1

Analysis > Analysis Case >

General

- Title: 3D Excavation and Piled-

Raft Foundation

- 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

Raft Load > Displacement >

TOTAL TRANSLATION (V)

Result > General > Smooth:

Fringe

Result > General > Deform:

Undeformed

- Properties: Deform

Result > Show/Hide > Actual

Deformation

Result > Advanced > Probe

- Max/Min

05 Results

Procedure

1

2

2

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1

Advanced View Control: Clipping

Plane

- Define Plane

- X: 30m

- Add

- Y: 30m (Reverse)

- Close

- Always Show edges: Check off

- Plane Composite: Union

- Close

Raft Load > Displacement > TZ

TRANSLATION (V)

Result > Advanced > Cutting

Diag.

- Type: 2-Points Line

- Point 1: 0,30,0

- Point 2: 60,30,0

- Direction: (+)Z Dir.

- Reverse: Check on

- OK

05 Results

Procedure

1

2

2

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1

Raft Load > Beam Element

Forces > BENDING MOMENT Y

Result > General > No Results:

Exclude

Raft Load > Pile Force >

TANGENTIAL X

05 Results

Procedure

1

2

2

Tangential friction force between

pile and ground

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1

Raft Load > Shell Element

Forces > BENDING MOMENT

YY

Raft Load > Interface Stress >

TANGENTIAL Y

05 Results

Procedure

1

2

2

Friction force between wall and

ground

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Thank you!

3D Excavation and Piled-Raft Foundationnorthamerica.midasuser.com/web/upload/sample/3D... ·...

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Transcript of 3D Excavation and Piled-Raft Foundationnorthamerica.midasuser.com/web/upload/sample/3D... ·...