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Slope Stability and Mesh Fineness

Hello,

I want to run slope stability analysis for a slope using COMSOL. The slope dimensions and the soil properties are obtained from an example discussed in the Griffiths and Lane’s paper. The FS in the mentioned paper and from the limit equilibrium method are obtained as 1.40 and 1.38, respectively. The issue is that the FS based on COMSOL results is highly dependent on mesh resolution. For direct solver, Constant Newton method, and quadratic triangle mesh with maximum element size of 4m and 0.2m, the FS is computed as 1.4, and 1.0 (finer mesh results in wrong FS). Could you please let me know why by using the finer mesh incorrect results are obtained? What solving method should be used for finer mesh? When the FS parameter is gradually increasing in this method, do the results (deformation, stress) of new FS depend on the results of previous FS? (i.e. is there any searching procedure with respect to strength reduction factor?)

The model is attached.

Thanks a lot in advance. Amin

3 Replies Last Post Mar 15, 2019, 8:08 PM EDT

Posted: 6 months ago

Hi Amin,

What you see is a 'numerical' formation of artificial shear bands.

There are some remedies:

• You can change the discretization to use linear shape functions (which of course allows you to use even more elements). Since linear shape functions imply constant stress within the element, the possibility to form this kind of pattern is reduced.
• Use a less regular mesh. Change the method to Delauney in the Free Triangular node. It will be more difficult to form this kind of patterns in an unstructured mesh.
• More advanced: Add some kind of stabilization equation which penalizes either gradients within elements or gradients over a certain distance. This is the same kind of techniques as is used in the Damage feature (new in version 5.4).

Regards,
Henrik

Posted: 6 months ago

Thanks a lot Henrik for the percise response! It resolved the issue.

Amin