Abstract: In view of the conditions of double hard-thick sandstone strata without immediate roof above coal seam in Working Face 1007 of one mine, an elastic thin plate model with two adjacent clamper edges, one simply supported edge, and one free edge was established as the mechanical model of hard thick strata. Stress distribution within the thin plate was then studied, and fracture step calculation formula of hard thick strata was obtained. The results show that the maximum point of tensile stress is located at (x=0，y=13b/10π) of the inclination clamper edge and the intersection of strike direction clamper edge and free edge where (x=a，y=b), while the actual position of maximum stress is affected by strata spanning modulus k. The pre-split weaken technology was carried out for the double hard-thick sandstone strata, that is, the lower hard thick stratum was weakened by fan-shaped rotation deep pre-split holes, and the upper hard thick stratum was weakened by ultramultiple-hole longhole blasting, which makes the movement step of the upper hard thick stratum decrease 25.7%, and the lower hard thick stratum changes from main roof to immediate roof. Thus, the accumulated gas ignition risk at the work face corner duo to the suddenly movement of large area hanging strata has been reduced.

Key words: hard thick strata, thin plate, fracture step, pre-split weaken