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

Table 7

Mass fractions of fragments at different scales in the sandstone sample under different unloading rates.

Scale (mm)	Unloading rate (MPa/s)
	Sandstone
	0.02	0.05	0.08	0.11	0.14
0.3 ≥ d	0.0219	0.0152	0.0154	0.0134	0.0097
0.6 ≥ d > 0.3	0.0523	0.0436	0.0342	0.0335	0.0327
1.18 ≥ d > 0.6	0.0717	0.0609	0.0544	0.0570	0.0570
2.36 ≥ d> 1.18	0.1029	0.0882	0.1017	0.0950	0.0970
4.75 ≥ d > 2.36	0.1408	0.1420	0.1228	0.1229	0.1248
9.5 ≥ d> 4.75	0.1703	0.1805	0.1671	0.1687	0.1673
13.2 ≥ d > 9.5	0.1956	0.2191	0.2255	0.2291	0.2267
19 ≥ d > 13.2	0.2445	0.2505	0.2789	0.2804	0.2848