Question

In an opencast bench two geologically disturbed planes intersect each other. The type of bench failures likely to takes place

• A. Circular failure
• B. Wedge failure
• C. Planar failure
• D. Toppling failure

Hint:

Remember the geometric cause of each failure type:
- 1 Plane $\rightarrow{}$ Planar Failure - 2 Intersecting Planes $\rightarrow{}$ Wedge Failure - No Dominant Planes (weak mass) $\rightarrow{}$ Circular Failure - Steeply Dipping Layers $\rightarrow{}$ Toppling Failure

Answer 1

The Correct Option is B

Step 1: Count how many discontinuity planes are involved.
The question tells us two geologically disturbed planes cross each other in the bench, so right away we know the failure mode must involve two structures acting together, not just one.
Step 2: Eliminate the single plane and non structural modes.
Planar failure needs only one continuous plane dipping out of the face, so it does not fit two intersecting planes, circular failure happens in weak fragmented rock or soil with no controlling structure, and toppling failure needs steeply dipping layers parallel to the face, none of these describe an intersection of two planes.
Step 3: Visualise what two intersecting planes create.
When two discontinuities cross each other and their line of intersection daylights out of the slope face, they carve out a wedge shaped block of rock that can slide down along that line of intersection like a block sliding down a groove.
Step 4: Name the failure.
This sliding of a wedge shaped block bounded by two intersecting planes is exactly what is called wedge failure.
\[ \boxed{\text{Wedge failure}} \]