Tension Crack

If you are performing a Probabilistic analysis with SWedge, and your model includes a Tension Crack, you can define the orientation of the Tension Crack as a Random Variable, as follows:

1. Select Input Data and select the Tension Crack tab in the Probabilistic Input Data dialog.
2. Select the Tension Crack check box.
3. Select the Orientation Definition Method. There are two methods of defining the variability of the Tension Crack orientation:
   1. Dip / Dip Direction
   2. Fisher Distribution

See below for information about these options.

4. Enter or import the Tension Crack mean orientation and statistical parameters, as described below.

Dip / Dip Direction

If the Orientation Definition Method = Dip / Dip Direction, then the Dip and Dip Direction of the Tension Crack can each be assigned a statistical distribution, and are treated as independent random variables (i.e. during the statistical sampling, there is no correlation between the generated values of Dip and Dip Direction).

The Dip / Dip Direction method allows you the flexibility to choose any two distributions for the Dip and Dip Direction. This can be useful if the actual distribution of orientations you are trying to model, is asymmetric (e.g. an elliptical distribution on the stereonet). However, if your orientation distribution is approximately circular, then you should use the Fisher Distribution option.

Fisher Distribution

If the Orientation Definition Method = Fisher Distribution, then the Tension Crack orientations will be randomly generated according to a Fisher Distribution. A Fisher Distribution assumes a symmetric distribution of 3-dimensional orientations around the mean, and only requires a single parameter (Fisher K value or standard deviation) to define the variability of the distribution. Note: the Fisher K value and the standard deviation of a Fisher distribution are related, so you can use either parameter.

See the Fisher Distribution topic for more information.

Import from Dips

If the Orientation Definition Method = Fisher Distribution, then you can import the Tension Crack mean orientation and Fisher K value from a Dips .DWP file, by selecting the Import from Dips button and selecting the desired joint set from a Dips .DWP file.

See the Import from Dips topic for more information.

Comparison of Dip/Dip Direction and Fisher Distribution Methods

See the Probabilistic Joint Orientation topic for a comparison of the Dip / Dip Direction method and the Fisher Distribution method.

Minimum Tension Crack Area

You can optionally ignore the existence of a Tension Crack if the computed Tension Crack area is smaller than the specified threshold by selecting the Minimum Tension Crack Area checkbox. When Minimum Tension Crack Area is selected:

• If the Tension Crack area is larger than or equal to the specified Minimum Tension Crack Area, then the Factor of Safety computation will use the Tension Crack
• If the Tension Crack area is smaller than the specified Minimum Tension Crack Area, then the Factor of Safety computation will ignore the Tension Crack and compute as if Tension Crack is not selected.

This allows us to ignore any negligible Tension Cracks that may be formed. If wedge geometry varies in each sample, certain sampled wedges may be computed with and some without consideration of a Tension Crack.