Tension Crack
A Tension Crack can be included in the RocSlope2 analysis by selecting the Tension Crack Exists checkbox in the Slope Geometry dialog. By default, RocSlope2 does not consider a Tension Crack in the analysis.
By definition, a Tension Crack in RocSlope2 has zero shear strength. It does not contribute to the forces resisting wedge movement. It simply truncates the size of the wedge. However, if Water Pressure is included in the analysis, the resultant force will be applied to the Tension Crack plane, if applicable.
Tension Crack Orientation
The Tension Crack orientation is defined by the Dip and Dip Direction of the Tension Crack plane in the Slope Geometry dialog.
- The Tension Crack does not have to be vertical. RocSlope2 allows you to enter any orientation for the Tension Crack plane.
- However, if a Tension Crack is defined, RocSlope2 examines how the Tension Crack intersects the other planes, and only accepts those cases where the Tension Crack truncates the wedge in the manner shown in the figure above.
- If the Tension Crack plane does not form an acceptable wedge with the other planes, RocSlope2 will report "No Wedge Formed".
- A Tension Crack is not "interchangeable" with a joint plane in the RocSlope2 analysis (i.e. it will not be considered as a joint plane, regardless of the Tension Crack orientation).
- In a Probabilistic Analysis, you can define statistical variability of the Tension Crack orientation.
Trace Length from Crest
The location of the Tension Crack is user-defined by entering a Trace Length from Crest with respect to Joint 1. The Trace Length from Crest is the distance of the Tension Crack from the crest, measured along the trace of Joint 1 on the Upper Slope Face. See Figure 1 where Length (L) is the trace length used to specify the Tension Crack location.
Tension Crack and Basal Joint Wedges
For the Basal Joint Wedge specifically, the location of a tension crack for a basal joint wedge is defined differently than for a tetrahedral wedge. See the Basal Joint Wedge document for details.
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 Define Minimum Area checkbox. When Define Minimum Area is selected:
- If the Tension Crack area is larger than or equal to the specified Minimum Area, then the Factor of Safety computation will use the Tension Crack.
- If the Tension Crack area is smaller than the specified Minimum 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.
The existence of a Tension Crack may affect the Joint Water Pressure significantly if Filled Fissures or % Filled Fissures Pressure Distribution Model is selected. Remember that when Tension Crack is selected, the Percent Filled Water Depth is measured relative to the Tension Crack Depth, not the Wedge Depth.