Evolution Mechanism of Interconnected Vertical Fractures in the Overburden of Longwall Coal Mining

Table 1

Proportion of the similar simulation materials.

Rock strata	Thickness (cm)	Material ratio	Similar materials			Water (kg)
			Sand (kg)	CaCO3 (kg)	Gypsum (kg)
Soft rock	8	473	38.4	6.72	2.88	4.8
Primary key stratum	12	437	30	2.25	5.25	3.75
Soft rock	6	473	28.8	5.04	2.16	3.6
Soft rock	6	473	30	5.25	2.25	3.75
Soft rock	6	473	28.8	5.04	2.16	3.6
Soft rock	6	473	40	7	3	5
Soft rock	8	473	38.4	6.72	2.88	4.8
Soft rock	6	473	30	5.25	2.25	3.75
Soft rock	6	473	28.8	5.04	2.16	3.6
Soft rock	6	473	30	5.25	2.25	3.75
Soft rock	6	473	28.8	5.04	2.16	3.6
Soft rock	6	473	75	13.125	5.625	9.375
Hard rock	15	455	72	9	9	9
Key stratum 2	14	455	40	5	5	5
Soft rock	8	473	38.4	6.72	2.88	4.8
Soft rock	6	473	30	5.25	2.25	3.75
Soft rock	6	473	28.8	5.04	2.16	3.6
Soft rock	6	473	55	9.625	4.125	6.875
Key stratum 1	11	455	52.8	6.6	6.6	6.6
Soft rock	6	473	20	3.5	1.5	2.5
Immediate roof	4	473	19.2	3.36	1.44	2.4
Coal seam	7	773	82.03125	8.203125	3.515625	9.375
Floor	15	455	72	12.6	5.4	9