It is very difficult to control shaley roof if coal is not left with the shale why?

Solution (By Examveda Team)

Shaley Roof:
A shaley roof refers to a roof in underground mining that consists of shale, a sedimentary rock composed of fine particles. Shale is known for its layered structure, making it relatively weak and susceptible to damage under specific conditions.

Correct Answer: Option C: It has great affinity to absorb moisture and get departed from immediate roof
Reason:
Shale is a type of sedimentary rock that tends to absorb moisture easily. When a shaley roof is not supported by coal or other stronger materials, it becomes highly unstable because:
The shale absorbs moisture from the surrounding environment.
This absorption leads to the swelling of the shale, causing it to lose its structural integrity.
As a result, the shale starts to separate (or depart) from the immediate roof surface, increasing the risk of roof falls and making it challenging to control during mining operations.

Why Leaving Coal Helps:
Leaving a layer of coal with the shale provides support and reduces direct exposure to moisture. Coal acts as a protective layer, ensuring that the shale does not come into direct contact with environmental factors that might accelerate its degradation.

Other Options:
Option A: It is weak in nature
While shale is generally weaker compared to other rocks, the main challenge in controlling a shaley roof comes from its tendency to absorb moisture and separate, as stated in Option C.

Option B: It has weathering effect
Although weathering might affect shale over time, it is not the primary reason for difficulty in controlling a shaley roof in an underground mining setting.

Option D: It reacts with coaly surface
There is no significant chemical reaction between shale and the coal surface that would contribute to the instability of the roof.

Thus, the correct answer is Option C because moisture absorption and subsequent separation from the immediate roof are the primary challenges with a shaley roof in mining engineering.