SSR Search Area

If you are carrying out a Shear Strength Reduction (SSR) analysis with Phase2, by default the SSR analysis considers the stability of the entire model when the analysis is computed. This means that the critical failure zone may occur anywhere in the model.

However, there are circumstances when you may wish to focus on the stability of a particular area of the model. This can be accomplished with the SSR Search Area option, which allows you to apply the SSR analysis to any particular region of a model.

For example:

• In a dam or embankment model, you may wish to analyze the stability of each side of the model independently (as shown in the figures below).

• In a benched slope model, you may wish to analyze individual benches or regions of the slope.

The SSR Search Area allows you to define a rectangular window over any portion of the model, and only the selected area of the model will be considered for the SSR analysis. Regions outside of the search area will not be part of the SSR analysis.

SSR Search Area to analyze left side of dam

Results of SSR analysis with SSR Search Area

The SSR Search Area can be created in two different ways: through the Project Settings dialog, or graphically with the mouse. You may use either method, the results are equivalent regardless of how you define the search area. Only ONE SSR Search Area can be defined for a model, you cannot define multiple search areas for a single analysis.

NOTE: before you can define the SSR search area, the SSR option must be enabled (i.e. the Determine Strength Reduction Factor checkbox must be selected in the Project Settings dialog).

SSR Search Area (Graphical Entry)

To graphically define the SSR Search Area:

1. Select the Define SSR Search Area option from the SSR Search Area sub-menu of the Analysis menu.

2. You will be prompted to enter two points which define the opposite corners of a rectangular search area. You may enter the points graphically with the mouse, or type in coordinates in the prompt line.

3. After you have entered the second point, the SSR Search Area will be drawn on the model as a dotted gray rectangle.

SSR Search Area (Project Settings)

To define the SSR Search Area in the Project Settings dialog:

1. Select the SSR Search Area checkbox under the Strength Reduction tab in the Project Settings dialog.

2. Select the Define button, and you will see another dialog in which you can enter two points which define the opposite corners of a rectangular search area.

3. After you have entered the points, select OK in both dialogs, and the SSR Search Area will be drawn on the model.

Resizing or Deleting the SSR Search Area

You can re-size or delete the SSR Search Area using the options in the SSR Search Area sub-menu of the Analysis menu.

You can also re-size or delete the SSR Search Area using right-click shortcuts. Right-click on the edge or corner of the SSR Search Area and select an option from the popup menu.

How does the SSR Search Area option work?

The SSR Search Area is implemented in the SSR analysis as follows:

1. A material can only fail if the Material Type = Plastic in the Define Material Properties dialog. If a Material Type = Elastic then the material cannot "fail", and the material strength parameters are not applicable.

2. In general, the SSR analysis is only applicable for materials which have Material Type = Plastic.

3. When you define an SSR Search Area, what this does is effectively make the Material Type = Elastic for all finite elements which are outside of the SSR Search Area. NOTE:

• This is done on an individual element basis. The original material properties are not actually changed. Instead, a new "elastic" version of each material is created, and assigned to each element which is outside of the SSR Search Area.

• All finite elements within OR crossing the SSR Search window, are considered to be part of the SSR Search Area. Only elements which are entirely outside of the search area are given Elastic properties.

4. Therefore, failure can only occur within the SSR Search Area, during the SSR analysis, since all finite elements outside of the search area are assumed to be Elastic.