Quantitative Evaluation for the Threat Degree of a Thermal Reservoir to Deep Coal Mining

Table 9

Height calculation formula for the “upper three zones”.

Code category	Overburden lithology	Formula 1	Formula 2
Three lower code	Hard lithology
	Medium hard lithology
Mining area code	Hard lithology		—
	Medium hard lithology		—

Note: is the height of the upper three zones (m), is the cumulative mining thickness (m) (when , takes 1; when , takes 2), and the bending zone height is taken as 10 m and is directly included in the formula.