Study on Pressure Relief Technology of High-Pressure Water Jet of Residual Coal Pillar in Overlying Goaf in Close Seam Mining

Table 1

Mechanical parameters of interlayer strata.

Rock stratum	Volumetric force γi (MN/m^3)	Thickness Hi (m)	Elastic modulus Ei (MPa)
Lamprophyre	0.0266	5	3.000 × 10^4
Medium-grained sandstone	0.0263	10	3.845 × 10^4
Siltstone	0.0262	10	2.800 × 10^4