Influence of Valleys Terrain on Pressure of Fully Mechanized Working Faces in Shallow Coal Seams

Table 3

Physical and mechanical properties of borehole strata.

Lithology	Poisson’s ratio	Volume (kg/m^3)	Elastic modulus (GPa)	Uniaxial compressive strength (MPa)	Internal friction angle
Mudstone	0.24	2630	21	30	33
Poststone	0.20	2700	47	40	36
Sandy mudstone	0.23	2590	20	29	29
Kern stone	0.23	2810	40	35	29
Coal	0.29	1400	20	13	30
Siltstone	0.24	2490	22	37	31