Study on relationship between roof stability and recovery ratio of top coal at first weight period in fully-mechanized sublevel caving face

The first weight is the key of controlling mine pressure in fully-mechanized sublevel caving face. The course of top coal falling from beginning to end is a dynamic process. To set up the judgment rules of roof stability with the recovery ratio of top coal is an important theoretical problem. This paper establishes the mechanical model of the stability of the whole deformation of roof structure and the stability of partial contact of the main roof. Based on the structure stability theory and the strength theory, two kinds of limited convergence maintaining the stability of the whole deformation of roof structure and the stability of part contact of the main roof are obtained. According to the comparison of the two limited subsidence and the subsidence of roof caused by the movement situation of roof in the course of rotation, the unifying mechanical conditions between the stability of the whole transmutation of roof structure and the stability of part contact of the main roof are analyzed and the judgment rules of roof stability with the recovery ratio of top coal are established. Based on an example of fully-mechanized sublevel caving face, the judgment curve and method with the recovery ratio of top coal are put forward, the theoretical bases of designing the safe recovery ratio of top coal are provided for different roof, and the safe roof controlling is achieved at coal mine.