Study on Fracture and Stress Evolution Characteristics of Ultra-Thick Hard Sandstone Roof in the Fully Mechanized Mining Face with Large Mining Height: A Case Study of Xiaojihan Coal Mine in Western China

Table 1

Physical and mechanical parameters of extra-thick sandstone roof.

Item	Density (kg·m^−3)	Broken expand coefficient	Strength (MPa)			Frictional angle (°)
			Compression	Tensile	Cohesive
Parameters	2566	1.440	30.67	4.93	7.90	31.04