Analysis and application of sheared and fallen roof structure during shallowly buried fully mechanized mining under thick loose bed and thin base rock

Severe ground pressure problem during shallowly buried fully mechanized mining under thick loose bed and thin base rock is increasingly prominent, which has seriously threatened safety and efficient production in coal mine. This study took 22614 working face in Shendong mining field as engineering background, adopted the combination research method of field monitoring, similar experiment and mechanical modeling to analyze the characteristics of its strong ground pressure, to reveal cause of mining-induced roof broken and instability, to build mechanical model of roof broken structure, to determine working resistance of hydraulic support in working face, and finally to perform field example application. The study results showed that: based on field monitoring, the average roof broken length of 22614 working face was 11.2 m; the average working resistance of hydraulic support was 8 450.1 kN, and the maximum working resistance was 11 857 kN. In similar materials simulation experiment, the average caving length was 12.5 m, and roof sheared and broke as short suspension beams, crack extended to surface, which led to the whole sheared roof falling behind coal wall. As well plane mechanical model of sheared and fallen roof structure was established, then the structure instability criterion was put forward, the positive correlation between instability coefficient and roof sheared and fallen angle, bearing capacity of hydraulic support was pointed out. Certainly, working resistance calculation formula of hydraulic support in working face was given and calculated average bearing capacity of hydraulic support was 8 364.22 kN, which is in good agreement with the field monitoring results. The results provided important theoretical basis for support selection and roof control of shallowly buried fully mechanized mining under thick loose bed and thin base rock in China.