Strong Ground Pressure Mechanism and Control at the Longwall Top Coal Caving with a Single Key Stratum in Goaf

Table 1

Lithologic features.

Rock formation	Lithology	Thickness (m)	Lithologic characteristics
Overburden	Siltstone	8.0	Gray, silty structure, semihard, homogeneous bedding, and quartz-based composition
	Sandy mudstone	12.0	Gray, argillaceous structure, and semihard
	2-2# coal	3.5	Black, blocky structure, weak bituminous sheen, and small amount of pyrite
	Sandy mudstone	19.0	Gray, argillaceous structure, semihard, and coal-bearing wire
Key stratum	Siltstone	22.0	Gray, silty structure, hard, homogeneous bedding, and quartz-based composition
Overburden	Sandy mudstone	24.0	Gray, argillaceous structure, and semihard
Coal seam	4-2# coal	6.5	Black, blocky structure, and weak bituminous sheen
Floor	Sandy mudstone	5.0	Gray, argillaceous structure, semihard, and coal-bearing wire