Great changes occur both in the breaking form and structure of hard and thick overlying strata. Aiming at conditions of coal seam II2 overburden thick quartz sandstone in Rujigou coal mine by using field measurement

numerical simulation

theoretical analysis

field tests and other methods

we studied the features of fractures development

the breaking movement of rock

characteristics of strata behaviors

and technology of broken roof control of the overlying hard and thick rock

providing a basis for disaster prevention of working face with hard and thick roof. Research results show that the microstructure of this kind of quartz sandstone is compactive and completion; a large area vacant and great breaking movement appeared in the strata

which cause the strong dynamic load of support

and even result in reversed air flow in working face

and link up invisible burning area at upper mined-out areas. Obvious separate strata space generated after the rupture of hard and thick strata

and main fracture zone form at the top of working face and the middle part of mined-out areas

the height of main fracture zone is greater than the experience value; and disasters can even be caused when the upper mined-out areas meet the fracture zone. By applying deep-hole blasting at open-off cut to break roof and lowering mining height

it effectively shortens the initial breaking span of hard

and thick strata

and reduce the dynamic load in support and the height of main fracture zone.