Rational Boreholes Arrangement of Gas Extraction from Unloaded Coal Seam

Table 1

Mechanical properties of overlying strata.

No.	Lithology	Elastic modulus (GPa)	Compressive strength (MPa)	Poisson’s ratio	Friction angle (°)	Density (kg·m^−3)	Thickness (m)
1	Sandy mudstone	38	63	0.4	29	2400	10
2	Coal seam C13	10	15	0.4	30	1400	5
3	Sandy mudstone	26	33	0.3	32	2400	8.5
4	Medium-grained sandstone	28	76	012	30	2600	11
5	Speckled mudstone	57	50	0.12	26	2600	7
6	Fine sandstone	47	50	0.4	21	2500	13
7	Sandy mudstone	38	37	0.38	26	2400	16
8	Fine sandstone	20	48	0.4	24	2500	2.5
9	Sandy mudstone	38	37	0.26	37	2400	6
10	Coal seam B11	10	20	0.4	30	1400	2
11	Sandy mudstone	38	70	0.26	26	2400	14