Question

The CORRECT curve showing the relationship between vertical stress on a coal pillar and extraction ratio of a bord and pillar panel in a horizontal seam is 

• A. Curve A.
• B. Curve B.
• C. Curve C.
• D. Curve D.

Hint:

Pillar stress always increases with extraction ratio—never decreases—because fewer pillars must carry the same overburden load.

Answer 1

The Correct Option is C

In bord and pillar mining, as the extraction ratio increases, the load transferred to the remaining pillars increases.

Step 1: At low extraction ratios, the pillar stress increases slowly because plenty of pillars share the load.

Step 2: As extraction continues, pillar area reduces, causing a faster increase in load concentration.

Step 3: The curve should therefore show a non-linear increasing trend without sudden drops or negative slope.
Curve A rises too steeply, B rises linearly, D decreases (which is impossible).
Curve C shows the correct gradual non-linear increase in pillar stress with extraction ratio.