Difference Analysis of Disaster Types and Grading Control Technologies for Risk of Caving of Coal Roadway Roof

Table 1

Grading and characteristics of roof stability.

Grade	Height of fractured roof	Difficulty in controlling roof caving
I	≤1.5 m	Easy	Under general conditions, the support requirements can be met by using conventional anchor bolts alone
II	≤3.5 m	Difficult	Use of conventional anchor bolts alone does not work, and they need to be combined with anchor bolts longer than 4 m or anchor cables to strengthen support
III	≤5.5 m	More difficult	Use of conventional anchor bolts alone does not work, and they need to be combined with anchor cables longer than 6 m to strengthen support; anchor cables are locally broken
IV	Undetermined	Extremely difficult	When combining anchor bolts with cables for supporting the roof, the probability of breakage is so high that it is very difficult to prevent the roof from caving