Study on mining failure law of the weak and weathered composite roof in a thin bedrock working face

In this paper, the occurrence characteristics of the weak and weathered overburden, and hydrogeological features, are first analyzed in a research coal field. The overburden failure law and the development of 'Three Zones' are studied through physical model tests, and the rupture pattern and rock failure are analyzed in the conditions of mining under a weakly cemented roof with longwall top coal caving. When coal mining is 5 meters thick, the developmental height of the caving zone and the water flowing fractured zone is calculated as 21 meters and 58 meters, respectively. Based on the geological and mining conditions, through discrete element numerical simulation, the overburden failure law and characteristics of strata pressure behaviors were studied under the weak and weathered composite roof during coal mining. The results show that under the conditions of the weak and weathered composite roof in a thin bedrock working face, the fracture length of old roof pressure will decrease, the abutment stress in front of the working face will distribute within a range of 15 meters, the peak point of abutment pressure in front of the working face will vary from 5 to 15 meters. This is smaller than that of the working face of thick bedrock, but the strata behaviors of the working face are obvious. Based on the field monitoring results, the overburden failure law is analyzed; the feasibility of the model test and the numerical simulation is verified. The influence degree of coal layer safety mining is evaluated; the appropriate water control measures have been submitted purposefully, in order to ensure safe mining.