Study on disaster-causing mechanism of strong mine pressure in shallow buried multi coal seam mining over overlying coal pillar

With the increasing mining depth of shallow buried multi-coal seam mines in Northern Shaanxi, strong mine pressure dynamic disaster is prone to occur when the lower working face is mined back overlying coal pillar.This imposes a potential serious threat to the safety production of the mine.In view of the problem that support crushing accident in the coal pillar exit stage of the working face of plate area 302 in Longhua Coal Mine, this study takes the working face 30208 in this plate area as the engineering background.In this study, with the combination of the theoretical analysis and numerical simulation methods, we firstly explored the overlying strata displacement field, fissure field, stress evolution law of key rock strata and the distribution characteristics of the force chain, and then clarified the characteristics of overlying strata migration over the overlying coal pillar in the working face.The control measures were carried out in the mine and the results were verified by mine pressure monitoring.The results show that the upper key layer forms a 'Tri-hinge' structure, with the overlying coal pillar acting as a 'Transfer load body' to transmit the load downwards.When the working face is out of the overlying coal pillar edge, the hinged structure of the upper key layer is damaged.The overlying caving rock strata rotary subsidence of overlying rock strata, and the internal stress of the overlying coal pillar is shifted.These induce the lower key layer to abnormal periodic breaking, and the energy of the two is instantly released to the quarry, resulting in a strong mine pressure disaster.