Abstract: Aiming at the problem of roof cutting support crushing disasters caused by roof step convergence along the coal wall during the periodic weighting in shallow seam mining, based on the nonlinear variation characteristics during unstable failure of immediate roof under the abutment pressure, a system mechanics model composed by the main roof-immediate roof-powered support-waste rock was established. In addition, the instability mechanisms of the system under the loads were studied by catastrophic theory. The necessary sufficient condition for instability failure of the system and the formula of the jump value of displacement of immediate roof were gained, and the main factors for instability failure of the system were analyzed. The results show that the unstable failure of immediate roof leads to the roof cutting, the failure of the system is not only related to the stiffness ratio of the powered support, the immediate roof and the material parameters, but also related to the upper load and the cycle weighting interval. The rationality of the theoretical derivation has been verified by engineering example, some suggestions were given to the mining face.

Key words: shallow seam, catastrophic theory, immediate roof, roof cutting, instability mechanism