basic tutorial 7_2d slope stability analysis srm

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Basic Tutorial 7

2D Slope Stability Analysis

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GTS Basic Tutorial 7


Contents

Starting GTS 1

Create Analysis Data 4

2D Geometry Modeling 9

Polyline 9

Intersect 10

2D Mesh Generation 11

Display Mesh Seed and Size Control 11

Specify size control for the Edges. 11

Auto Mesh Planar Area 13

Mesh Set Operation 14

Change Parameter 14

Analysis 15

Supports 15

Generate boundary conditions. 15

Self Weight 17

Generate Self Weight of the model. 17

Analysis Case 18

Solve 21

Post Processing, Result Display and Control 22

Displacement Contour 23

Maximum Shear Strain 25


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On general civil construction sites, serious accidents occur that can cost a significant

amount of money and time. Sometimes even many workers lives are lost due to the failure

at the inclination of the slope. Therefore, careful study of slope stability must be completed

before carrying such type of civil construction. This tutorial will analyze the example of

slope stability for a 2D ground, which includes a soft layer of ground (strata) in the middle.

In this case, the Strength Reduction Method will be used since it describes failure behavior

more accurately than the traditional Limit Equilibrium Method. After the slope stability

analysis is completed, we will check the safety factor and the maximum shear failure plane

from the resultant contours.

Starting GTS

Start the program.

1. Run GTS.

2. Start a new project by clicking File > New button.

3. Project Setting dialog box will appear.

4. Enter ‘Basic Tutorial 7’ in Project Title.

5. Select ‘2D’ in Model Type.

6. Select ‘X-Y Plane’ in Analysis Constraint.

7. Make sure that ‘Y’ is selected in Gravity Direction.

8. Click on button to the right of Unit System.

9. Select ‘kN (ton)’ in Force (Mass) in Unit System.

10. Make sure that ‘m’ is selected in Length and ‘hour’ is selected in Time in Unit System.

11. Click in Unit System dialog box.

12. Use default values for rest of the inputs.

13. Click in Project Setting dialog box.


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Preview

In this tutorial, the slope stability analysis will be performed on a model that contains a

single soft layer of ground (strata). The model will be directly created in GTS by using its

built-in functions.

GTS Basic Tutorial 7 - 1


Two different materials are assigned to the general ground elements and the soft ground

elements. These elements are grouped together by its material, so that it is convenient for

later use. The name of each Mesh Set are as follows:


Clay

Thin Layer


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The Attributes of Mesh Sets are defined as follows:

Mesh Set Name Attribute Name

(ID) Material Name (ID)

Property Name

(ID)

Clay Clay (1) Mat Clay (1) ㅡ

Thin Layer Thin Layer (2) Mat Thin Layer (2) ㅡ

GTS Basic Tutorial 7 - Table 1

The Material Properties of Ground are defined as follows:

Material ID 1 2

Name Mat Clay Mat Thin Layer

Type Mohr Coulomb Mohr Coulomb

Modulus of Elasticity (E) [KN/m2] 1.0e5 1.0e4

Poisson’s Ratio () 0.3 0.3

Unit Weight () [KN/m3] 20 20

Unit Weight (Saturated) [KN/m3] 20 20

Cohesion (C) [KN/m2] 50 30

Friction Angle () 5 3

Tensile Strength [KN/m2] OFF OFF

Dilatancy Angle [deg] OFF OFF

Coefficient of Lateral Pressure (K0) 1 1

GTS Basic Tutorial 7 - Table 2


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Create Analysis Data

Attribute

We will now define the Attributes of the ground. In a two dimensional model, the type of

ground is always Plane.

1. Select Model > Property > Attribute… in the Main Menu.

2. Click button which is placed to the right of button in the

Attribute dialog box.

3. Select ‘Plane’.

4. Make sure that Attribute ID is ‘1’ in the Add/Modify Plane Attribute dialog box.

5. Enter ‘Clay’ in Name.

6. Select ‘Plane Strain’ in Element Type.

7. In order to create Material, click button at the right of Material.

In a 2D model, the Attribute of Plane type represents Ground. The material of the Ground

can be specified by clicking the Add button after choosing proper element type.

GTS Basic Tutorial 7 – 4

8. Make sure that Material ID is ‘1‟ in the Add/Modify Ground Material dialog box.

9. Enter ‘Mat Clay’ in Name.

10. Select Color as .

11. Select ‘Mohr Coulomb’ in Model Type.


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12. Enter ‘1.0e5’ in Modulus of Elasticity (E) of Material Parameters.

13. Enter ‘0.3’ in Material Parameters of Poisson‟s Ratio ().

14. Enter ‘20’ in Material Parameters of Unit Weight ().

15. Enter ‘20’ in Material Parameters of Unit Weight (Saturated).

16. Enter ‘30’ in Material Parameters of Cohesion (C).

17. Enter ‘20’ in Friction Angle () of Material Parameters.

18. Enter ‘1’ in K0 of Material Parameters of Initial Stress Parameters.

19. Enter ‘1.0e7’ in Tensile Strength in Parameters of Constitutive Model.

20. Make sure that „Drained‟ is selected in Drainage Parameters.

21. Click button.


22. Make sure that „Mat Clay‟ has been generated in Material in the Add/Modify Plane


23. Click button.

24. Make sure that „Clay‟ has been generated in the Attribute dialog box

25. Close the Add/Modify Plane Attribute dialog box.


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26. Click button which is placed to the right of button in the


27. Select ‘Plane’.

28. Make sure that Attribute ID is ‘2’ in the Add/Modify Plane Attribute dialog box.

29. Enter ‘Thin Layer’ in Name.

30. Select ‘Plane Strain’ in Element Type.

31. In order to create Material, click button at the right of Material.

32. Add properties of “Thin Layer” in the Add/Modify Ground Material dialog box as

shown in GTS Basic Tutorial 7 – 9. These values are obtained from GTS Basic


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Tutorial 7 - Table 2.

33. Repeat the procedure given in Steps 8~25.

34. Click button in Attribute dialog box.




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9

2D Geometry Modeling

Polyline

Create the Geometry of a Polyline.

1. Select Geometry > Curve > Create on WP > Polyline (Wire)… in the Main Menu.

2. Make sure that Single Location is selected in the Polyline dialog box.

3. Make sure that it says ‘Input Start Location’ in the Polyline dialog box.

4. Make sure that the Method is set to „ABS x, y‟.

5. Enter ‘0, 0’ in Location, and press Enter key.

6. Make sure that it says ‘Input Next Location (RB to Stop)’ in the Polyline dialog box.

7. Make sure that the Method is set to „Rel dX,dY‟.



10. Enter ‘20, -10’ in Location, and press Enter key.



13. Enter ‘-60, 0’ in Location, and press Enter key.

14. Make sure that Polyline is generated under Geometry > Curve in the Works Tree.




18. Make sure that it says ‘Input Next Location (RB to Stop)’ in the Polyline dialog box.





23. Click the right button of the mouse to complete the Polyline.




27. Make sure that it says ‘Input Next Location (RB to Stop)’ in the Polyline dialog box..



If any mistake has been

made during the input,

click button to

undo the mistake.

Once a closed wire is

formed, as is shown in

this case, the Polyline

will be created

automatically.


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32. Click the right button of the mouse to complete the Polyline.

33. Click button in the Polyline dialog box.


Intersect

In order to generate the mesh properly, all the Edges must be broken at locations where they

intersect with the other Edges. After breaking the Edges using the Intersect tool, we will

delete the unnecessary Edges, if any.

1. Click Zoom All in the Dynamic View Toolbar of the Work Window to view all

the generated Edges.

2. Select Geometry > Curve > Intersect… in the Main Menu.

3. Select all the edges by clicking Displayed button in the Selection Toolbar.

4. Click button.

5. Click to close the dialog box.


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2D Mesh Generation

Display Mesh Seed and Size Control

In order to obtain more accurate results around the Thin Layer, finer elements will be

generated in that region. We will specify proper mesh size on the Edges for Mapped Mesh

Generation, and set up the display to view the Mesh Seed.


2. Select Mesh > Size Control > Display Mesh Seed…in the Main Menu.

3. Make sure that „Show Mesh Seed‟ is selected in the Display Mesh Seed dialog box.

4. Click button.

Specify size control for the Edges.

5. Select Mesh > Size Control > Along Edge… in the Main Menu.

6. Select Polygon in the Selection Toolbar.

7. In button, select the Edges shown in GTS Basic

Tutorial 7-12 using the Polygon.

8. Select Seeding Method as ‘Interval Length’.

9. Enter ‘0.45’ in Interval Length.

10. Click (Preview) button to check if the seeding would be distributed correctly.

11. Click button.

12. Select Pick/Window Select in the Selection Toolbar.

13. In button, select the Edges „A‟ and „C‟ shown in

GTS Basic Tutorial 7 - 12.

14. Select Seeding Method as ‘Linear Grading (Length)’.

15. Enter ‘1’ in SLen.

16. Enter ‘0.45’ in ELen.


18. Click button.

19. In button, select the Edges „B‟ and „D‟ shown in

GTS Basic Tutorial 1 - 12.

20. Enter ‘0.45’ in SLen.

A total of 8 Edges

should be selected. To

complete the Polygon

Selection, double-click

the mouse at the final

location.


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21. Enter ‘1’ in ELen.


23. Click button.

The defined Size Control items are registered under Mesh > Size Control in the Works Tree.

This mesh seeding information will be stored and applied to every mesh generation until it

is deleted by the user.



25. Select Mesh > Size Control > Display Mesh Seed… in the Main Menu.

26. Make sure that „Hide Mesh Seed‟ is selected in the Display Mesh Seed dialog box.

27. Click button.

C D

A B


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Auto Mesh Planar Area

We will generate Mesh Sets using the Auto Mesh Planar Area feature.

1. Select Mesh > Auto Mesh > Planar Area… in the Main Menu.

2. In button, click Displayed to select all the Edges.

3. Make sure that ‘Loop Mesher’ is selected in Mesher.

4. Make sure that ‘Quadrilateral’ is selected in Type.

5. Make sure that Generate Offset Elements and Include Interior Edges are selected.

6. Make sure that Element Size in Mesh Size is selected and enter ‘1.2’.

7. Select Attribute ID ‘1’ - ‘1:Clay’.

8. Delete ‘Auto-Mesh (P.A.)’ in Mesh Set and enter ‘Clay’.

9. Select Mesh Set in Add to in Mesh Set.

10. Make sure that Merge Nodes is selected.

11. Select Generate Mid-side Nodes.


13. Click button.

By using Auto Mesh Planar Area, user does not require to generate surfaces for each

meshed area. Elements will be automatically generated in the closed areas defined by the

selected boundary edges. Please refer to the Online Manual for detailed information on the

options in the Auto Mesh Planar Area dialog box.

GTS

Basic Tutorial 7 - 13

Analysis will be

performed using higher

order quadratic elements.


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Mesh Set Operation

We will merge the Mesh Sets having the same material properties and rename the Mesh Sets.

1. Select Mesh in the Works Tree.

2. Select Mesh Set and click on button to the left of Mesh Set.

3. Select Mesh > Mesh Set > Clay #1 in the Works Tree.

4. Press F2 key on the keyboard.

5. Rename Clay #1 as ‘Thin Layer’ and press Enter key.


7. Clicking on the left button of the mouse, ‘drag and drop’ the ‘Clay #3‟ Mesh Set into

the ‘Clay #2’ Mesh Set.

8. Click in Merge the selected mesh set(s)?


10. Press F2 key on the keyboard.

11. Rename Clay #2 as ‘Clay’ and press Enter key.

Change Parameter

While generating Mesh Sets using the Auto Mesh Planar Area command, we defined the

Attribute of the thin ground layer as „Clay‟. Using the Change Parameter command, we

will change the Attribute of the thin ground layer Mesh Set to „Thin Layer‟.

1. Select Model > Element > Change Parameter… in the Main Menu.

2. Select ‘Mesh(M)’ in the Selection Filter of Selection Toolbar.

3. In button, select Mesh > Mesh Set >Thin Layer

in the Works Tree.

4. Make sure that ‘2D’ is selected in Attribute.

5. Make sure that Attribute ID ‘2’ – ‘2: Thin Layer’ is selected.

6. Click button.


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Analysis

Supports

Generate boundary conditions.

1. Select Mesh > Mesh Set in the Works Tree.

2. Invoke the Context Menu by right-clicking the mouse.

3. Select Show All.

4. Click Zoom All in the Dynamic View Toolbar.

5. Select Model > Boundary > Supports in the Main Menu.

6. Enter ‘Support’ in BC Set in the Supports dialog box.

In order to apply a boundary condition in the model, it is necessary to create a Boundary Set

first. Either select Model > Boundary > Boundary Set or click button to the right of

BC Set in the dialog box of each boundary condition function (Model > Boundary >

Supports). In addition, if the name of the Boundary Set is directly entered in the BC set box

in the boundary condition function dialog box (Model > Boundary > Supports), the

program will automatically create the Boundary Set.

7. Select ‘Curve’ in Type of Object in the Supports dialog box.

8. In button, select Edges ‘A’ and ‘B’ as shown in GTS

Basic Tutorial 7 –14.

9. Make sure that ‘Add’ is selected in Mode.

10. Select ‘UX’ in DOF.

11. Click button.

12. In button, select Edge ‘C’ as shown in GTS Basic

Tutorial 7 – 14.

13. Make sure that ‘Add’ is selected in Mode.

14. Select ‘UX’ and ‘UY’ in DOF.

15. Click button.


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Boundary Conditions can be applied directly to the model geometry if the Type is selected

as Curve or Surface. The assigned geometric boundary conditions will be transferred to the

relevant nodes and elements for the analysis.

The user can Add, Replace or Delete the constraints by selecting the appropriate Mode. The

applied constraints cannot be deleted with respect to each degree of freedom, but all the

constraints of each node can be deleted. By selecting Fixed, Free, Pinned or No Rotation,

the relevant degrees of freedom will be selected automatically.


A

B

C


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Self Weight

Generate Self Weight of the model.

1. Select Model > Load > Self Weight… in the Main Menu.

2. Enter ‘Self Weight’ in Load Set.

3. Enter ‘-1’ for Y Self Weight Factor.

4. Click button.

The sequence of applying Loads is the same as the sequence for applying Boundary

Conditions. A Load Set must be first created before assigning the Loads. The method of

creating a Load Set is identical to the method for creating a Boundary Set.


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Analysis Case

We will create an Analysis Case for performing analysis.

1. Select Analysis > Analysis Case… in the Main Menu.

2. Click in the Analysis Case dialog box.

3. Enter ‘Basic Tutorial 7’ as Name in the Add/Modify Analysis Case dialog box.

4. Enter ‘2D Slope Stability’ in Description.

5. Enter ‘Slope Stability’ in Analysis Type.

6. Click button in Analysis Control.

In Analysis Control, we will define specific options for the Slope Stability Analysis.

7. Enter ‘1’ in Initial Safety Factor.

8. Enter ‘0.1’ in Increment of Safety Factor/Step.

9. Enter ‘30’ in Maximum Number of Steps.

10. Enter ‘50’ in Maximum Number of Iterations.

11. Make sure that ‘Force Norm’ is selected in Convergence Criteria and enter ‘0.03’.

12. Make sure that Initial Water Level is ‘0’ and selected.

13. Click button.


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GTS Basic Tutorial 7 -15

14. Make sure that ‘All’ is selected in Initial Element of Analysis Model.

15. Make sure that ‘All’ is selected in Initial Boundary of Analysis Model.

16. Select Load > ‘Self Weight’ in Set Tree of Add or Modify Initial Model.

17. Clicking on the left button of the mouse, ‘drag and drop’ the ‘Self Weight’ from the

Add or Modify Initial Model box to the Activated box.

18. Click button in the Add/ Modify Analysis Case.

19. Click button in the Analysis Case dialog box.


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Solve

We will now perform analysis.

1. Select Analysis > Solve… in the Main Menu.

2. Click in the Solver Manager dialog box.

All the messages during the analysis will be shown in the Output Window. Especially, one

needs to be very cautious about warning messages, because these messages indicate that the

analysis results may not be correct. The model is automatically saved before the analysis.

The result is saved as a binary file (*.TA*) in the same folder as the model. The detail

analysis information is also saved in a text file (*.OUT).



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Post Processing, Result Display and Control

Once the analysis is completed, we will start Post-Processing. In this tutorial we will study

various methods of checking analysis results.

1. Select Boundary in the Works Tree.


3. Select Hide All.

4. Select Load Works Tree.


6. Select Hide All.

7. Select Geometry in the Works Tree.


9. Select Hide All.

10. Invoke the Context Menu in the Work Window by right-clicking the mouse when no

entity is selected.

11. Select Turn off All Triads.

12. Invoke the Context Menu in the Work Window by right-clicking the mouse when no

entity is selected.

13. Select Toggle Grid.

In order to have a clean view of results, it is better to hide all the load labels, boundary

labels and other symbols.


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Displacement Contour

We will first check resultant Displacements.

1. Select the Post-Works Tab in the Works Tree.

2. Confirm that CO : Basic Tutorial 7 > Slope Stability > Safety Factor in the Works

Tree is ‘1.6625’.

3. Double-click CO : Basic Tutorial 7 > Slope Stability > Displacement > ‘DXYZ(V)’ in

the Works Tree.



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We will check the Deformed Shape.

4. Select Mesh Shape in the Post Data Tab to control deforming displays.

5. Select Deformed + Undeformed.

6. Click button in the Post Data Tab.

7. Select ‘Deform’ in the Properties Window.

8. Select ‘Feature Edge’ in the Undeformed Shape Type.

9. Click button in the Properties Window.



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Maximum Shear Strain

We will check the Maximum Shear Strain in the model.

1. Select CO : Basic Tutorial 7 > Slope Stability > Plane-Strain Strains > ‘HO-Plstrn

Max Shear’ in the Works Tree.

2. Select the Post Command Tab.

3. Select ‘No Edge’ in Edge Type.


HO represents the

results of high order

elements.

In order to obtain accurate results of Slope Stability Analysis

using the Strength Reduction Method, the following

procedure is performed by MIDAS/GTS:

- The analysis is started with the initial factor of safety (FOS).

- If the result converges correctly, the increment is added to

the initial FOS and the analysis is performed once again.

- If the result does not converge, the increment is subtracted

from the initial FOS and the analysis is performed once

again.

- If analysis convergence is not monotonic, the increment is

reduced to half and the analysis is performed once again.

- The above process is repeated until the change in FOS is

less than 0.01.

basic tutorial 7_2d slope stability analysis srm

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