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: Understanding the Question:
We need to identify the type of slope failure that is caused by the intersection of two geological discontinuity planes (like faults or joints).

Step 2: Detailed Explanation:
Slope stability in rock masses is largely controlled by the orientation and properties of geological structures (discontinuities).
Different failure modes can occur:
-

Planar Failure: This occurs when a block of rock slides down a

single, continuous discontinuity plane that is dipping out of the slope face at an angle steeper than the friction angle.
-

Wedge Failure: This occurs when

two discontinuities intersect in such a way that their line of intersection dips out of the slope face.
The block of rock defined by the two intersecting planes and the bench face (a "wedge") can slide out along the line of intersection.
This perfectly matches the condition described in the question.
-

Circular Failure: This type of failure occurs in very weak, heavily fractured rock masses or in soils.
The failure surface is curved or spoon-shaped and is not controlled by any single structure.
-

Toppling Failure: This occurs in rock masses with steeply dipping layers that are oriented parallel to the slope face.
Columns of rock can rotate and topple forwards out of the slope, like a row of dominoes.

Step 3: Final Answer:
The failure caused by two intersecting planes is a wedge failure.
This corresponds to option (B).