During top coal caving mining, the essential cause of top coal crushing is ( ).
A: softening of water in roof strata
B: the stress it beared is large than its own strength
C: the gas in the top coal expands, leading to breakage
D: cracks produced by raw coal during its formation
A: softening of water in roof strata
B: the stress it beared is large than its own strength
C: the gas in the top coal expands, leading to breakage
D: cracks produced by raw coal during its formation
举一反三
- Which of the following is not a common way for coal caving? ( ) A: Top caving coal in group sequence B: Top caving coal in single cycle sequence C: Top caving coal in multiple cycles in sequence D: Top caving coal in intervals of single cycle
- While it has set targets to increase its consumption of ( ), China remains the world’s top producer and consumer of coal
- Rich in coal, abundant in oil and gas, while coal is the most important basic energy and raw material in China.
- Quantity of energy contained in the atmosphere is ______. A: smaller than that in coal alone B: smaller than that either in oil or in gas that we have on Earth C: greater than that in coal, oil and gas on Earth combined D: greater than that in coal, oil and gas on Earth, respectively
- What are the main disadvantages of fully mechanized caving technology? ( ) A: More coal loss B: Fire prone C: Big coal dust D: Gas is easy to accumulate