Fracture Development and Multifield Coupling Evolution Law of Soft Overburden Rock in a Medium-Thick Coal Seam Mine

Table 1

Physical and mechanical parameters of coal strata.

Rock layer	Density (kg·m^-3)	Bulk modulus	Tensile strength (MPa)	Internal cohesion (MPa)	Angle of internal friction (°)
Fine sandstone	2750	29.50	2.03	3.64	39.69
1 coal	1420	34.20	1.20	0.90	20.00
Mudstone	2360	8.50	4.60	2.66	38.60
Muddy siltstone	2570	30.10	3.64	1.55	39.40
Siltstone	2760	35.90	2.42	4.20	41.20
Chalky clay	1820	0.001	0.00	0.03	23.00