Restriction function of lithology and its composite structure to deformation and failure of mining coal seam floor

In order to research the relationship between deformation and failure depth and lithology and its composite structure, in situ test data on the deformation and structure variation of rocks in different depth of the coal seam floor were utilized on Xinglongzhuang Coal Mine and Baodian Coal Mine in Yanzhou Mining Area by strain testing system and ultrasonic imaging technology in the fully mechanized top-coal working face, and the data on the East Main Haulage of -300 m lever in Peigou Coal Mine in Zhengzhou Mining Area in China were also used. There are obviously different deformation and failure characteristics of similarly homogeneous floor and soft-hard composite structure rocks floor under the mining pressure, which are based on the in situ test data. The research shows that the law of deformation and failure of similarly homogeneous floor is relatively simple; the deformation and failure depth are restricted by the strength of floor rock and has a gradual variation from top to bottom. But the deformation and failure of the interbedded soft-hard rock mining floor are more complex; this kind of structure has a obviously restricting function on the failure depth and deformation degree of the mining floor, and the weak intercalation has a strong constraint effect to the depth of floor failure which implies that the soft rocks have a cushion effect on the overlying hard rocks and a stress diffusion effect on the underlying hard rocks.