Law and mechanism of surface movement and deformation above shallow longwall abandoned gob under building load

In order to solve the problem that the activation movement of overlying strata above the abandoned gob cau⁃ ses surface movement and deformation and then threatens the safety of buildings when new buildings are built in coal⁃mining induced subsidence land，the long⁃term state of shallow longwall abandoned gob overlying strata is ana⁃ lyzed through field observation and physical simulation. The surface movement and deformation law of shallow longwall abandoned gob under building load is studied by numerical simulation，and the mechanism of surface movement and deformation of shallow longwall abandoned gob under building load is investigated. The research results show that the overlying strata unstable zones at the gob boundary exist for a long time after the gob is closed. In the physical simulation experiment，after the destabilization damage of the coal pillar between the shallow longwall aban⁃ doned gob，the height of the coal pillar support zones increases，and the width increases by 32.5%. The height of the gangue compression zones increases，and the width increases by 80.4%，the height of the coal wall support zones increases，and the width increases by 67.2%，and the height of the strata separation zones increases，and the width de⁃ creases by 23.3%. When the location of the new building does not change，the amount and extent of surface movement and deformation increase with the increase of loading. Among the loading locations，the load threshold for the sudden increase of surface movement and deformation due to the new building in the strata separation zones surface is the smallest，and the load threshold is 18 stories. The maximum increase of surface subsidence is 91.4% and the maxi⁃ mum horizontal movement of the surface is 62.1% compared with the building height of 12 stories. When the new building is located above the strata separation zones，the subsidence of overlying strata is large，and the amount of sur⁃ face movement and deformation is the largest because there are many unstable structures inside the strata separation zones，and the key blocks in the strata separation zones under the building load appear rotary and slip instability. When the new building is located above the coal pillar supporting zones，the coal pillar continues to produce plastic deformation under the construction load. The subsidence of overlying strata is small，and the amount of surface movement and deformation is the second largest. When the construction load acts on the coal wall supporting zones，the coal wall continues to produce compression deformation under the action of construction load. The subsid⁃ ence of overlying strata is small，and the amount of surface movement and deformation is smaller. When the construc⁃ tion load acts on the gangue compression zones，the collapse gangue in the abandoned gob under the action of construc⁃ tion load will be subjected to secondary bearing compression deformation. The subsidence of overlying strata is small， and the amount of surface movement and deformation is the smallest. At the early stage of building load width increase，the maximum movement and deformation of the surface shows an accelerating growth trend. When the width of the building load is greater than 50 m， the maximum movement deformation of the surface shows a decelerating growth trend. When the additional stress of the building load affects the load⁃bearing structure of overlying strata，the abandoned gob surface produces movement and deformation. When the building load transferred to the key block exceeds the critical load of key block rotary instability or slip instability， there will be a sudden change in the movement and deformation of abandoned gob surface.