Distribution Characteristics and Formation Mechanism of Surface Crack Induced by Extrathick Near Horizontal Seam Mining: An Example from the Datong Coal Field, China

Table 1

Material ratio table of model test.

	Rock stratum	Layer thickness (mm)	Material ratio	Sand (kg)	Lime (g)	Gypsum (g)	Water (ml) 7% calculation
			Sand : lime : gypsum
1	Loose layer	150
2	Sandy mudstone	540	120 : 4 : 6	536.3	17876.9	26815	40670
3	Fine sandstone	105	40 : 3 : 2	107.6	5377.8	8067	8470
4	Coal seam	60	20 : 3 : 7	19.5	1200.0	300	1470
5	Sandy mudstone	250	120 : 4 : 6	248.4	8280.0	12420	18837