Basic Tutorial 8 - 2D Slope Stability Analysis SRM

7/30/2019 Basic Tutorial 8 - 2D Slope Stability Analysis SRM

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BasicTutorial 8

2D Slope Stability Analysis


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GTS Basic Tutorial 82D Slope Stability Analysis

Contents

Starting GTS 1

Create Analysis Data 42D Geometry Modeling 9Polyline 9Intersect 102D Mesh Generation 11Display Mesh Seed and Size Control 11Specify size control for the Edges. 11Auto Mesh Planar Area 13Mesh Set Operation 14Change Parameter 14Analysis 15Supports 15Generate boundary conditions. 15Self Weight 17Generate Self Weight of the model. 17Analysis Case 18Solve 21Post Processing, Result Display and Control 22Displacement Contour 23Maximum Shear Strain 25


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GTS Basic Tutorial 8

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GTS Basic Tutorial 82D Slope Stability Analysis

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 > Newbutton.

3. Project Setti ngdialog box will appear.

4. EnterBasic Tutorial 8in Project Titl e.

5. Select 2D in Model Type.

6. Select X-Y Planein Analysis Constraint.

7. Make sure that Yis selectedin Gravity Direction.

8. Click on button to the right ofUnit System.

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

10. Make sure that m is selected in Lengthand hour is selected in Timein Unit System.

11. Click in Unit Systemdialog box.

12. Use default values for rest of the inputs.

13. Click in Project Setti ngdialog 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 8 - 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 NameAttribute Name

(ID)Material Name (ID)

Property Name

(ID)

Clay Clay (1) Mat Clay (1)

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

GTS Basic Tutorial 8 - 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

Poissons Ratio () 0.3 0.3Unit Weight () [KN/m3] 20 20

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

Cohesion (C) [KN/m2] 50 30

Friction Angle () 5 3Tensile Strength [KN/m

2] OFF OFF

Dilatancy Angle [deg] OFF OFF

Coefficient of Lateral Pressure (K0) 1 1

GTS Basic Tutorial 8 - Table 2


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Create Analysis DataAttribute

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

ground is always Plane.

1. SelectModel > 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/Modif y Plane Attributedialog box.

5. EnterClayin Name.

6. Select Plane Strainin Element Type.

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

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 8 4

8. Make sure that Material I Dis 1in the Add/Modify Ground Material dialog box.

9. EnterMat Clayin Name.

10. Select Coloras .

11. Select Mohr CoulombinModel Type.


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12. Enter1.0e5in Modulus of Elasticity (E)ofMateri al Parameters.

13. Enter0.3inMateri al ParametersofPoissons Ratio ().14. Enter20inMateri al ParametersofUni t Weight ().15. Enter20inMateri al ParametersofUnit Weight (Saturated).

16. Enter30inMateri al ParametersofCohesion (C).

17. Enter20inFri ction Angle ()ofMateri al Parameters.18. Enter1in K0 ofMateri al ParametersofI niti al Stress Parameters.

19. Enter1.0e7in Tensile Strengthin ParametersofConstitutive Model.

20. Make sure thatDrainedis selected in Drainage Parameters.

21. Click button.


22. Make sure that MatClayhas been generated in Materialin the Add/Modify Plane

Attribute dialog box.

23. Click button.

24. Make sure that Clayhas 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

Attribute dialog box.

27. Select Plane.

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

29. EnterThin Layerin Name.

30. Select Plane Strainin Element Type.

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

32. Add properties ofThin Layerin the Add/Modify Ground Material dialog box as

shown in GTS Basic Tutor ial 8 9. These values are obtained from GTS Basic


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Tutor ial 8 - Table 2.

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

34. Click button in Attribute dialog box.




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2D Geometry Modeling

Polyline

Create the Geometry of a Polyline.

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

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

3. Make sure that it says I nput Start Location in the Polyline dialog box.4. Make sure that the Methodis set to ABS x, y.

5. Enter0, 0in Location, and press Enter key.

6. Make sure that it says I nput Next Location (RB to Stop) in the Polyline dialog box.

7. Make sure that the Methodis set to Rel dX,dY.



10. Enter20, -10in Location, and press Enter key.

11. Enter20, 0in Location, and press Enterkey.


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

14. Make sure that Polyline is generated underGeometry > Cur vein the Works Tree.

15. Make sure that it says I nput Start Location in the Polyline dialog box.

16. Make sure that the Methodis set to ABS x, y.


18. Make sure that it says I nput Next Location (RB to Stop) in the Polyline dialog box.





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

24. Make sure that it says I nput Start Location in the Polyline dialog box.

25. Make sure that the Methodis set to ABS x, y.


27. Make sure that it says I nput Next Location (RB to Stop) in the Polyline dialog box..



If any mistake has beenmade during the input,

click button to

undo the mistake.

Once a closed wire isformed, 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 I ntersecttool, we will

delete the unnecessary Edges, if any.

1. Click Zoom Allin the Dynamic ViewToolbar of the Work Window to view all

the generated Edges.

2. Select Geometry > Cur ve > I ntersect in the Main Menu.

3. Select all the edges by clicking Displayedbutton in the SelectionToolbar.

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 Seedin the Main Menu.3. Make sure that Show Mesh Seedis selected in the Display Mesh Seed dialog box.

4. Click button.

Specify size control for the Edges.

5. SelectMesh > Size Control > Along Edge in the Main Menu.

6. Select Polygonin the SelectionToolbar.

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

Tutorial 8-12using the Polygon.

8. Select Seeding Methodas Interval Length.

9. Enter0.45inI nterval L ength.

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

11. Click button.

12. Select Pick/Window Selectin the Selection Toolbar.

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

GTS Basic Tutor ial 8 - 12.

14. Select Seeding Methodas Linear Grading (Length).

15. Enter1inSLen.

16. Enter0.45inELen.


18. Click button.

19. In button, select the Edges Band D shown in

GTS Basic Tutor ial 1 - 12.

20. Enter0.45inSLen.

A total of 8 Edgesshould be selected. To

complete the Polygon

Selection, double-click

the mouse at the final

location.


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21. Enter1inELen.


23. Click button.

The defined Size Contr olitems are registered underMesh > Size Contr olin theWorks 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 HideMesh Seedis 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. SelectMesh > Auto Mesh > Planar Area in the Main Menu.

2. In button, click Displayedto select all the Edges.

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

4. Make sure that Quadrilateralis selected in Type.

5. Make sure that Generate Offset Elementsand I nclude I nteri or Edgesare selected.

6. Make sure that Element Sizein Mesh Sizeis selected and enter1.2.7. Select Attribute ID1 -1:Clay.

8. Delete Auto-Mesh (P.A.)in Mesh Setand enterClay.

9. Select Mesh Setin Add toin Mesh Set.

10. Make sure that Merge Nodesis selected.

11. Select Generate M id-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 8 - 13

Analysis will beperformed 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 Meshin the Works Tree.

2. Select Mesh Setand click on button to the left ofMesh Set.

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

4. Press F2keyon the keyboard.

5. Rename Clay #1as Thin Layer and press Enterkey.


7. Clicking on the left button of the mouse, drag and drop the Clay #3Mesh Set intothe Clay #2Mesh Set.

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


10. Press F2keyon the keyboard.

11. Rename Clay #2as Clay and press Enterkey.

Change Parameter

While generating Mesh Sets using the Auto Mesh Planar Areacommand, we defined the

Attribute of the thin ground layer as Clay. Using the Change Parametercommand, we

will change the Attributeof the thin ground layer Mesh Set to Thin Layer.

1. Select Model > El ement > Change Parameter in the Main Menu.

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

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

in the Works Tree.

4. Make sure that 2Dis selected in Attribute.

5. Make sure that Attribute ID22: 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 Al l.

4. Click Zoom Allin the Dynamic ViewToolbar.5. Select Model > Boundary > Suppor tsin the Main Menu.

6. EnterSupportinBC Setin 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 Setor click button to the right of

BC Setin 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 setbox

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

program will automatically create the Boundary Set.

7. Select Curvein TypeofObjectin the Supports dialog box.

8. In button, select Edges AandB as shown in GTS

Basic Tutorial 814.

9. Make sure that Addis selected inMode.

10. Select UXinDOF.

11. Click button.

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

Tutorial 814.

13. Make sure that Addis selected inMode.

14. Select UXandUYinDOF.

15. Click button.


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Boundary Conditionscan be applied directly to the model geometry if the Typeis selected

as CurveorSurface. The assigned geometric boundary conditions will be transferred to the

relevant nodes and elements for the analysis.

The user can Add, ReplaceorDeletethe 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, PinnedorNo 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. SelectModel > Load > Self Weight in the Main Menu.

2. EnterSelf Weightin Load Set.

3. Enter-1forY Self Weight Factor.

4. Click button.

The sequence of applying Loadsis the same as the sequence for applying BoundaryConditions. A Load Setmust be first created before assigning the Loads. The method of

creating a Load Setis 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. SelectAnalysis > Analysis Case in the Main Menu.

2. Click in the Analysis Case dialog box.

3. EnterBasic Tutorial 8 as Namein the Add/Modify Analysis Casedialog box.

4. Enter2D Slope StabilityinDescription.

5. EnterSlope Stability in Analysis Type.

6. Click button in Analysis Control.

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

7. Enter1in I niti al Safety Factor.

8. Enter0.1in I ncrement of Safety F actor/Step.

9. Enter30in Maximum Number of Steps.

10. Enter50in Maximum Number of I terations.

11. Make sure thatForce Normis selected inConvergence Cri teriaand enter0.03.

12. Make sure that I nit ial Water Levelis 0 and selected.

13. Click button.


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GTS Basic Tutorial 8 -15

14. Make sure that Allis selected in I niti al ElementofAnal ysis Model.

15. Make sure that Allis selected in I nitial BoundaryofAnal ysis Model.

16. Select Load >Self WeightinSet TreeofAdd or Modify Ini tial Model.

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

Add or Modify I nitial M odelbox to the Activatedbox.

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. SelectAnalysis > 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 theanalysis 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 Boundaryin the Works Tree.


3. Select Hide All.

4. Select LoadWorks Tree.


6. Select Hide All.

7. Select Geometryin the Works Tree.


9. Select Hide All.

10. Invoke the Context Menuin the Work Windowby right-clicking the mouse when no

entity is selected.

11. Select Turn off All Triads.

12. Invoke the Context Menuin the Work Windowby 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 Tabin the Works Tree.

2. Confirm that CO : Basic Tutor ial 8 > Slope Stabil i ty > Safety Factorin the Works

Tree is 1.6625.

3. Double-clickCO : Basic Tutorial 8 > Slope Stabili ty > Di splacement >DXYZ(V)in

theWorks Tree.



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We will check the Deformed Shape.

4. Select Mesh Shapein thePost 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 Edgein 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 Tutori al 8 > Slope Stabili ty > 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 theresults 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

a ain.

Documents

Basic Tutorial 8 - 2D Slope Stability Analysis SRM