Question

The factor of safety of a coal pillar decreases with

• A. Increase in width
• B. Increase in depth
• C. Decrease in height
• D. Increase in strength

Hint:

Increasing mining depth increases overburden stress, thereby reducing \[ \boxed{\text{Factor of Safety of the pillar}.} \]

Answer 1

The Correct Option is B

Step 1: Recall the factors affecting the safety of a coal pillar. The factor of safety (FOS) is \[ \text{FOS} = \frac{\text{Pillar Strength}} {\text{Pillar Load}}. \]

Step 2: Identify the effect of increasing depth. As the mining depth increases, the overburden load acting on the coal pillar increases, thereby increasing the pillar load. Hence, the factor of safety decreases. Therefore, \[ \boxed{\text{Increase in depth}} \] is the correct answer. Thus, \[ \boxed{(B)} \] is the correct answer.