Study on Occurrence Mechanism of Coal Pillar in L-Shaped Zone during Fully Mechanized Mining Period and Prevention Technology

Table 7

Prediction and prevention method of limit value of coal mines.

Critical index rate of pulverized coal	Pulverized coal		Dangerous state	Prevention method
	1∼5 m	5∼10 m
<0	<2.16	<4.86	None
0–25%	2.16∼2.7	4.86∼6.1	Weak	Enhancement of monitoring
25%–50%	2.7∼3.24	6.1∼7.3	Medium	Water injection and pressure relief by large diameter drilling
>50%	>3.24	>7.3	Strong	Cooperative support and pressure relief of the roadway gang