Reasonable Scope of Kilometer Drilling in Lower Layer of Extrathick Coal Seam: A Case Study of Tingnan Coal Mine, China

Table 2

Physicomechanical parameters of coal and rock layers.

Lithology	Thickness (m)	Bulk modulus (GPa)	Shear modulus (GPa)	Density (kg·m^−3)	Cohesion (MPa)	Internal friction angle (°)	Tensile strength (MPa)
Overlying strata 10	60	4.60	4.45	2500	3.50	38	1.35
Grit stone 9	24	4.53	4.37	2510	2.53	34	1.26
Fine-grained sandstone 8	8	4.64	4.32	2540	4.57	35	1.35
Grit stone 7	15	4.58	4.42	2530	2.57	34	1.28
Mudstone 6	2	4.54	4.31	2560	2.08	32	1.32
Upper layer of 4# coal seam 5	6	1.42	0.57	1400	1.2	28	0.64
Lower layer of 4# coal seam 4	13	1.42	0.57	1400	1.2	28	0.64
Aluminum mudstone 3	2	4.87	4.79	2420	1.76	39	1.31
Sandy mudstone 2	10	4.52	4.34	2560	2.08	36	1.35
Siltstone 1	20	4.67	4.53	2550	4.58	39	1.42