Fractal Characteristics of Coal and Sandstone Failure under Different Unloading Confining Pressure Tests

Table 8

Fractal dimension of fragmentation under different initial unloading confining pressures.

Initial unloading confining pressure (MPa)	Coal		Sandstone
	k	D	k	D
4	0.3948	2.6052	0.4913	2.5087
7	0.4835	2.5165	0.5837	2.4163
10	0.6172	2.3828	0.646	2.354
13	—	—	0.7195	2.2805
16	—	—	0.7934	2.2066
19	—	—	0.8356	2.1644