Study on overburden failure characteristics and fracture evolution law of shallow buried coal seam through trench mining

The overburden failure law and fracture development characteristics of shallow coal seam are the main factors affecting the mine water inflow and ventilation，especially in the surface gully area，because of the denudation，the coal seam buried depth is further reduced. In order to study the disturbance failure law and fracture development characteristics of overlying strata when mining through trench in shallow coal seam，taking the trench section of No.14213 working face of Zhangjiamao Coal Mine in Yushen Mining Area as the research object，the failure law and fracture development characteristics of overlying strata are studied by means of physical simulation and numerical simulation of similar materials. The results show that in the process of coal mining，the roof overlying rock will produce vertical fractures of interlayer separation and cut through strata. When mining to 60 m,the roof hanging area of coal seam reaches the limit and collapses. The original interlayer separation disappears with collapses. The new interlayer separation continues to develop upward. The separation space and vertical fractures develop alternately. When mining to 105 m，the vertical fractures lead to the ground:the separation structure is completely damaged，and the rock stratum is sinking as a whole. The dynamic development law of the cracks is:the width of the slope cracks increases and tends to be stable with the excavation; the width of the slope foot cracks changes from small to large，then to close，and the width of the bottom cracks changes from small to large and then to small. The evolution law of surface fractures is mainly related to the topography and surface stress state. In the shoulder and upper part of the slope，the width affected by the tensile stress of the slope increases after the formation of the mining fracture; the width affected by the compressive stress of the slope toe decreases or even closes after the formation of the mining fracture at the slope toe; the width of the compressive stress and the compaction adjustment of the slope rock block decreases after the formation of the mining fracture at the ditch bottom. The research results have important reference value for the crack control and water damage control of shallow coal mining channel.