Study on the Migration Law of Overlying Strata of Gob-Side Entry Retaining Formed by Roof Cutting and Pressure Releasing in the Shallow Seam

Table 1

Rock layer mechanical parameters.

Strata	Thickness (m)	Internal friction angle (°)	Density (g · cm^−3)	Tensile strength (MPa)	Elasticity modulus (GPa)	Poisson’s ratio
Siltstone	4.0	30	2.552	2.80	32	0.28
Fine sandstone	4.0	30	2.550	2.80	32	0.28
Mudstone	1.0	30	2.301	3.53	23	0.28
12 upper coal	2.0	30	1.462	0.60	15	0.35
Siltstone	2.0	30	2.511	2.30	35	0.25
Siltstone	4.0	30	2.550	2.80	32	0.28
Fine sandstone	4.0	30	2.514	2.30	35	0.25