Investigation on the Ground Pressure Induced by Hard Roof Fracturing at Different Layers during Extra Thick Coal Seam Mining

Table 2

Basic parameters of the physical similarity model.

Items	Parameters	Items	Parameters
Length of model	2.5 m	Mining distance	2.1 m
Thickness of model	0.2 m	Model boundary	10 cm
Height of model	1.47 m	Excavation steps	45
Coal seam thickness	13.3 cm	Excavate distance once	5 cm
Geometric ratio	150 : 1	Excavate time interval	0.5 h
Weight ratio	1.667 : 1	Excavation time	21 h
Stress ratio	250 : 1	Compensation stress	0.027265 MPa