Investigation on the Height Calculation of Water Flowing Fracture Zone during Coal Mining under Ordovician Limestone Nappe Aquifer

Table 1

Experiential computing formula of the height of water flowing fracture zone from the “Procedures for coal pillar reservation and coal mining of buildings, water bodies, railways and main roadways.”

Dip angle of coal seam	Roof lithology	Compressive strength (MPa)	Formula (1)	Formula (2)
0∼54°	Hard	40∼80
	Medium hard	20∼40
	Soft	10∼20
	Ultrasoft	<10		—

ΣM refers to cumulative production thickness.