Mechanical Modeling of Roof Fracture Instability Mechanism and Its Control in Top-Coal Caving Mining under Thin Topsoil of Shallow Coal Seam

Table 2

Mechanical parameters of different rock blocks.

Lithology	Thickness (m)	Bulk modulus (: GPa)	Shear modulus (: GPa)	Tensile strength (MPa)	Cohesion (C: MPa)	Internal friction angle (j: °)
Loess layer	30	0.10	0.08	0	0.05	20.0
Medium grain sandstone	7	10.22	3.96	4.30	13.7	35.1
Sandy mudstone	3	6.73	2.59	1.33	2.6	15.7
3# coal	5	3.21	9.65	0.72	1.27	17.8
Sandy mudstone	20	8.95	3.66	2.71	7.57	19.6