Intro Tutorial 2 to GTS NX Slope Stability

Slope Stability Analysis during Excavation stages by 2 methods

Tutoria Tutoriall by Angel Angel Francisco Martinez Martinez Integrated Solver Optimized for the next generation 64-bit platform

Finite Element Element Solution s f or Geotechnic Geotechnic al Engineering Engineering

Overview

GTS NX

STEP 01 

Geometry Import

STEP 02 

Import Materials

STEP 03 

Mesh generation

STEP 04 

Boundary Conditions

STEP 05 

Load Conditions

STEP 06 

Define Construction Sequence

STEP 07 

Analysis Case

STEP 08 

Perform analysis and check result

2

Overview

GTS NX

STEP 01 

Geometry Import

STEP 02 

Import Materials

STEP 03 

Mesh generation

STEP 04 

Boundary Conditions

STEP 05 

Load Conditions

STEP 06 

Define Construction Sequence

STEP 07 

Analysis Case

STEP 08 

Perform analysis and check result

2

00 Slope Stability 

GTS NX

Overview  • 2D Slope Stability analysis during

excavations •The stability of slopes created by

embankment or excavation is greatly affected by ground water, external loadings, earthquake, etc. Shear stress inside the slope develops due to the self weight and external loadings. If the shear stress exceeds the shear strength, shear failure will take place. Using

FEM offers accurate approximate solutions that satisfy force equilibrium, compatibility,

the various proposed methods,

constitutive equations and boundary conditions at each point of the slope, which enables

numerical analysis is performed to

simulation of close to real failure shapes and reflect the site conditions to find the minimum

check the stability, and appropriate reinforcement is introduced.

safety factor against failure. Moreover, failure planes need not be assumed in advance, and the failure process can be automatically investigated.

Higher order elements will be used for better accuracy, and the safety

-Strength Reduction Method (SRM): Shear strength is gradually reduced until the

factor will be examined to determine

calculation no longer converges in analysis. At that point, slope failure is assumed, and the

the need for reinforcement.

rate of the maximum strength reduction is considered to be the minimum safety factor for the slope.

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02 Material for Soil and Structures  Name Material Model Type

GTS NX

Weathered Soil

Weathered Rock

Soft Rock

Isotropic

Isotropic

Isotropic

Mohr-Coulomb

Mohr-Coulomb

Mohr-Coulomb

General Elastic Modulus (E) (kN/m2) Poisson’s Ratio(v) Unit Weight(r) (kN/m3) Ko

36,500

150,000

1,850,000

0.33 18.5 0.5

0.30 21 0.5

0.28 24 0.5

22

25

31

33

35.5

17.5

50

180

Porous Unit Weight(Saturated) (kN/m3)

19.5 Non-Linear 

Friction Angle Cohesion (kN/m2)

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03 Property for Soil and Structure 

GTS NX

Name

Weathered Soil

Weathered Rock

Soft rock

Property

2D

2D

2D

Model Type

Plain Strain

Plain Strain

Plain Strain

Material

Weathered Soil

Weathered Rock

Soft rock

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04 Construction Sequence 

GTS NX

1. Initial state of ground 2. 1st Excavation 3. 2nd Excavation 4. 3rd Excavation

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Modeling Procedure

Integrated Solver Optimized for the next generation 64-bit platform

Finite Element Solution s f or Geotechnic al Engineering

01 Create New Project 

GTS NX

Procedure  1

Main Menu > New

2

Analysis Setting > Model

1

Type > 2D Set units to kN / m / sec 2

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02 Geometry works (Create or Import from AutoCAD  ) 

GTS NX

Procedure  1

Main Menu > Import > DXF

2

Select Slope Stability DXF>

1

DXF> Open

3

2

Select OK 

3

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03 Define Material / Property for Soil & Structures 

GTS NX

Procedure  •* You can Import from the existing

model file (Refer to Project Overview > Material / Property)

1

Mesh > Prop. > Property > Import

2

Select “2D Slope

Stability_final.gts” file 3

Select All Select OK 1

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04 Generate Mesh (2D Element) 

GTS NX

Procedure  1

Mesh > Generate > 2D > Auto -

1

Area 2

Select Edge(s) > Select 15 edges for “Embankment 3” as

highlighted in the figure. 3

Input element Size : 1 (1m between two nodes)

4

Select Property : Embankment

5

Input Mesh Set Name : Embankment 3

6

Click on the >> icon to open the Advanced Option Window

7

Select Triangle as Element Type

8

Activate Higher Order Elements

9



Click OK , then Click Apply

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04 Generate Mesh (2D Element) 

GTS NX

Procedure  Select Edge(s) > Select edges 1

for “Weathered Rock” as

highlighted in the figure. 2

Input element Size : 1 (1 m between two nodes)

3

Select Property : Weathered

1

Rock

4

Input Mesh Set Name : 2

Weathered Rock

5

Click Apply 3

4

5

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04 Generate Mesh (2D Element) 

GTS NX

Procedure  Select Edge(s) > Select edges 1

for “Weathered Rock” as

highlighted in the figure. 2

Input element Size : 1.5 (1 m between two nodes)

3

4

Select Property : Soft Rock

1

Input Mesh Set Name : Soft 2

Rock

5

Click Apply 3

4

5

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05 Define Boundary Condition (Water Level) 

GTS NX

Procedure  * Water Level Function will be

1

defined.

1

Static / Slope Analysis > Boundary > Water Level > Edge 2

2

Select Target Edge(s) > Select

Initial Water Level

edges to define water level as 3

highlighted in the figure. (Do not need to select Vertical edges) 3

Interval : 1 (m)

4

Input Name : Water Level (1)

5

4

5

Select OK 

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05 Define Boundary Condition (Ground) 

GTS NX

Procedure  1

1

Static / Slope Analysis > Boundary > Constraint > Auto

2

Boundary Set Name : Ground Boundary

2

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05 Define Boundary Condition (Ground)  Procedure  1

GTS NX

1

Static / Slope Analysis > Boundary > Slip Circular surface

2

Define Grid Points: 5 X 5 2

3

Define Tangent line of Circle:6

4

Boundary Set Name : SAM 1

3

4

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05 Define Boundary Condition (Ground) 

GTS NX

Procedure  1

Static / Slope Analysis > 1

Boundary > Slip Circular surface 2

Define Grid Points: 6 X 6 2

3

Define Tangent line of Circle:6

4

Boundary Set Name : SAM 2

3

4

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06 Load Condition (Self Weight) 

GTS NX

Procedure  1 1

Static / Slope Analysis > Load > Self Weight

2

Load Set Name : S/W

2

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07 Change Names of Mesh Sets 

GTS NX

Procedure  Change Mesh Sets in preparation for Construction stage definition. 1

Go to the Model tab in Works Tree Select the mesh set corresponding to the 1st excavation, as shown in the image. Press key F2 to change name to

1

Exca 1 Press Enter 2

Repeat for the other excavations as the 2nd image shows.

2

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08 Define Construction Stage (Create Stage Set) 

GTS NX

Procedure  * 4 Construction stage will be defined for this project.

1

1

Static / Slope Analysis > Construction Stage > Stage Set Stage Type > Stress

2

Select Add 2 3

Select Created Stage Set 4

Select Define CS… 3

4

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08 Define Construction Stage (Drag & Drop) 

GTS NX

Procedure  1

Stage 1 : Initial state of ground

2

Activated Data : All Mesh Sets

5

1

for initial state of ground (2D elements), Ground Boundary, Self Weight

3

Check “Clear Displacement”

4

Select Save

5

Select New

2

3

4

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08 Define Construction Stage (Drag & Drop) 

GTS NX

Procedure  1

Stage 2 : Exca 1

2

Deactivated Data : Mesh Sets for Exca 1

1

5

Activate SAM 1 boundary

3

Check on Slope Stability SRM

2

And SAM 4

Select Save

5

Select New 3

4

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08 Define Construction Stage (Drag & Drop) 

GTS NX

Procedure  1

Stage 3 : Exca 2

2

Deactivated Data : Mesh Set for Exca 2 and Exca 2-1

1

5

Activate SAM 2 Check on Slope Stability SRM 3

and SAM

4

Select Save

5

2

Select New 3

4

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08 Define Construction Stage (Drag & Drop) 

GTS NX

Procedure  1

Stage 4 : Exca 3

2

Deactivated Data : Mesh Set for Exca 3

3

1

5

Check on Slope Stability SRM and SAM

2 4

4

Check “Define Water Level for Global” Input 1m, Select “Water Level”

3 5

Select Close

5

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09 Analysis Case 

GTS NX

Procedure  1

Analysis > Analysis Case >

1

General 2

Title : Case Name

3

Solution Type : Construction Stage

2 5

4

5

Select Construction Stage Set Analysis Control : Select Initial

3

5 4

Stage for Stress Analysis (Initial Stage), Check Optionsfor Ko analysis.

6

Select OK 

7

Select OK 

7 6

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10 Perform Analysis and Check Results 

GTS NX

Procedure  1

Analysis > Analysis > Perform

2

Select OK 

1

2

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11 Post Processing (Pre mode vs Post mode)  2

Procedure  1*

After analysis, model view

GTS NX

2 1

2 2

will be converted to PostMode automatically, can back to Pre-Mode to change model information. 3 2 *All

results will be represented

by graphic based output, table, diagram and graph. 3

Results are given by stages and types of elements. The results are set in order, the 1s being results for STRESS analysis, the following for SLOPE STABILITY showing the FOS for the stage. The bottom of the results tab lists the FOS for all the stages in order. FOS match between SRM and SAM

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11 Post Processing (Post mode) 

GTS NX

Procedure 

1

Inspect the slope stability results for the last stage by selecting the Plane Strain Strains. Expand the results for Water Level SRM and double click

1

Plane Strain Strains. > EEquivalent to verify the line of slope failure due to the saturated ground. 2

Right click the legend and select

1

AUTO RANGE to see results more clearly. 3

2

Expand the results for Water

2

Level SRM and double click Plane Strain Stresses. > Pore Stress to verify the Pore Stress dues to change in Water Level

3

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11 Post Processing (Post mode) 

GTS NX

1

Procedure  2

1

Inspect the slope stability results for the last stage by selecting the Plane Strain Strains. Click on Results > Special Post > SAM.

2

Select Stage Exca 1 and click MIN

Select Stage Exca 3 and click MIN 3

3

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11 Post Processing (Post mode)  Procedure 

GTS NX

3 1

1

Inspect the changes in the model by navigating the stages using the bar on the bottom of the model / above the output

2

window. Press Right or Left key on keyboard to go forward and backward in the stages respectably. 2

The images shows total displacements for the 1st 4 stages of the analysis.

3

You can create a video animation of the stages by selecting Multi Stage Animation > Select All Stages > Play > Save

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