Mechanism of dynamic load of longwall mining under shallow room mining goaf

In order to explore the control mechanism of pressure appearing in the lower coal seam of shallow-buried coal bed with room mining goaf, to reduce the dynamic pressure of the working face through the room mining goaf, and to mitigate the risk caused by the coal pillar due to removal of hydraulic support, dynamic pressure characteristics of the 3^-1 coal bed working face with longwall mining under the 2^-2 coal bed room mining goaf are studied. The overburden structure of 3^-1 coal seam is divided into four types. The theoretical analysis and simulation of similar materials are adopted to analyze the structure and motion models for the overlying strata under dynamic load, and to reveal the mechanism of dynamic pressure. Conclusions are as follows: with the stability of the room goaf, the double cantilever beam structures easily lead to the upper and lower key layers, and the fracture of the key stratum is the main reason for the formation of dynamic load. The unstable masonry beam structure with the instability of the main roof and the room pillars near the large coal pillar are not unstable. The instability of the structure is caused by the collapse of the lower coal seam, resulting in the dynamic ground pressure. The key block firstly slides due to instability, and two key blocks without force and trapezoidal weight of rock pillar above the coal pillar are directly applied on the working face, which causes the roof to fall behind. When the coal pillar cannot effectively support the above inverted trapezoidal rock pillar, the instability of trapezoidal rock pillar and crack movement of roof collapse cause dynamic load in common.