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

Table 13

Calculation formula for the and assignment.

Threat level

Safe (I)

Low threat (II)

Medium threat (III)

Relatively high threat (IV)

High threat (V)

Note: and are the mean and standard deviation of the index factor, respectively; when or is less than 0, its value is 0.