Study on the Permeability Change Characteristic of Gas-Bearing Coal under Cyclic Loading and Unloading Path

Table 1

Comparison between evaluation index and identification critical value.

Contents	Degree of coal fracturing
Criteria value	III, IV, V	≥10	≤0.5	0.74		/
N-2	V	20.5	0.492	1.61	15.6377	35

is the coal seam gas pressure, MPa; is the coal hardiness coefficient, dimensionless; is the initial gas diffusion velocity of coal, mmHg; is the coal seam gas content, m³/t; and is the coal seam temperature, °C; degree of coal fracturing is qualitative evaluation index.