建筑荷载下浅埋长壁老采空区地表移动变形规律与机理

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

针对采煤塌陷地新建建筑物时老采空区覆岩活化运动导致地表移动变形并威胁建筑物安全的问题,现场勘测和物理模拟分析了浅埋长壁老采空区覆岩长期状态,数值模拟研究了建筑荷载作用下浅埋长壁老采空区地表移动变形规律,探讨了建筑荷载作用下浅埋长壁老采空区地表移动变形机理。研究结果表明:采空区边界覆岩不稳定区域在采空区封闭后长期存在;相似物理模拟实验中,煤柱长期承载失稳破坏后,煤柱支承区高度增加、宽度增加了32.5%,矸石压缩区高度增加、宽度增加了80.4%,煤壁支承区高度增加、宽度增加了67.2%,侧向裂隙区高度增加、宽度减小了23.3%。当新建建筑物位置不变时,随着荷载的增加,地表移动变形量和范围也增加。各加载位置中,侧向裂隙区地表新建建筑物导致地表移动变形量突增的荷载阈值最小,建筑物高度阈值为18层,与建筑物高度12层时相比,地表最大下沉量增幅为91.4%,地表最大水平移动量增幅为62.1%。当新建建筑物位于侧向裂隙区上方时,由于侧向裂隙区内部不稳定结构多,且建筑荷载下侧向裂隙区中关键块出现回转和滑落失稳,覆岩下沉量大,此时地表移动变形量最大;当新建建筑物位于煤柱支承区上方时,煤柱在建筑荷载作用下继续产生塑性变形,覆岩下沉量较小,此时地表移动变形值次之;当建筑荷载作用于煤壁支承区时,煤壁在建筑荷载作用下继续产生压缩变形,覆岩下沉量小,此时地表移动变形值较小;当建筑荷载作用于矸石压缩区时,覆岩下沉量小,老采空区垮落矸石在建筑荷载作用下发生二次承载压缩变形,此时地表移动变形值最小。建筑荷载宽度增加初期地表最大移动变形量呈加速增长趋势,当建筑荷载宽度大于50 m时,地表最大移动变形量呈减速增长趋势。当建筑荷载附加应力对老采空区覆岩承载结构造成影响时,老采空地表产生移动变形;当建筑荷载传递至关键块的载荷超过关键块回转失稳或滑落失稳的临界载荷时,老采空区地表移动变形产生突变。

In order to solve the problem that the activation movement of overlying strata above the abandoned gob causes 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 analyzed 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 abandoned 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 decreases 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 maximum 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 surface 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 subsidence of overlying strata is small, and the amount of surface movement and deformation is smaller. When the construction load acts on the gangue compression zones, the collapse gangue in the abandoned gob under the action of construction 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.