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# Anisotropy - Two Planes

## 1. Introduction

This model demonstrates a simple homogeneous slope, with TWO planes of anisotropy at different orientations. The Generalized Anisotropic Strength function is used. For more details regarding definition of anisotropic plane with strength parameters, please refer to Generalized Anisotropic Overview.

## 2. Material with Two Anisotropic Planes

This model demonstrates a simple homogeneous slope, with TWO planes of anisotropy at different orientations. The Generalized Anisotropic Strength function is used.

Read in the file File > Recent > Tutorials and open the file Anisotropy – Two Planes

The model is a single material 2D slope extruded to 3D.

Select: Materials > Define Materials

Notice the 3 materials defined: anisotropic material, rock mass, and weak joint planes.

For the anisotropic material, select the Edit () button beside the Generalized Function combo box.

Make sure the following parameters are entered.

• Anisotropy Definition = Dip/DipDirection
• Two anisotropic planes are defined
• Dip = 45 Dip Direction = 45
• Dip = 45 Dip Direction = 315
• A parameter = 5 (both planes)
• B parameter = 10 (both planes)
• Base Material = “rock mass”
• Anisotropic plane Material = “weak joint planes”

Run Compute.

Select the Results tab.

Turn on the contours by selecting Show contour from toolbar. For the Bishop method, the global minimum surface should appear as follows. Safety factor = 1.56. Base Normal Stress contours are displayed in the following figure.

Change the contour data to Shear Strength.

You can clearly see the shear strength of the two planes (blue contours) which intersect to form a wedge-like failure surface. Change the contour data to Base Friction Angle. This clearly highlights the low friction angle (15 degrees) of the two weak planes (blue colour) in contrast to the higher strength of the failure surface at other orientations.

## 3. Two Planes of Different Strength

As an additional exercise, assign a higher strength to one of the two anisotropic planes. For example, define an additional material type with Cohesion = 5 and Phi = 20.

Click on anisotropic material properties, and under the Generalized function dialog, select edit and assign this stronger material to the second plane:

Note: In case if the geometry views are zoomed out, resume to zoom all view by pressing F2.

Save with a new file name and select Compute to re-run the analysis.

Notice that the critical slip surface is now slightly asymmetric, and the Bishop safety factor is slightly higher than the previous result, since we increased the strength of one of the anisotropic planes. Change the contour data to Base Shear Strength.

Change the contour data to Base Friction Angle. You can clearly see the different friction angle of the two anisotropic planes (blue = 15 degrees, light blue = 20 degrees).

This concludes the Slope with Two Anisotropic Planes tutorial.