The Study on Large-Diameter Drilling Prevention Method of Rock Burst in the Xinxing Coal

Table 3

Experimental results of coal sample firmness coefficient.

Sampling location	Sample No.	Number of impacts	Measuring cylinder reading l/mm	Test piece firmness factor f	Average value of sample firmness coefficient
58th floor of the sixth mining area	1	3	67.5	1.888888889	1.90
	2	3	65.5	1.916030534
	3	3	67.0	1.895522388
65th floor of the sixth mining area	1	3	70.0	1.857142857	1.87
	2	3	65.0	1.923076923
	3	3	72.0	1.833333333