煤层开采诱发地表裂缝成因数值模拟

Numerical simulation for the mechanism and causes of the surface cracks due to the coal seam mining

为了通过分析地表裂缝的成因来研究采空区上覆火成岩非连续性破坏,根据现场数据和概率积分法确定了研究的岩土体范围,使用FLAC3D进行建模。布置6条监测线进行地表沉降监测,并与模拟得到的地表裂缝出现位置的变形数据进行对比,模拟得到了岩体塑性区的分布。结果表明,造成地表裂缝的主要原因是采空区上覆岩层中存在产状不均匀的火成岩,且位于松散层下方。采空区影响向上发展至火成岩底部造成火成岩边缘区域局部悬空。当采空区面积足够大时,火成岩上部拉应力超过其抗拉强度,进而发生断裂,松散层陷落导致地表裂缝。

The paper is intended to present our numerical simulation results on the exploration of the causes that may account for the surface crack of the coal seam mining. For the aforementioned purpose of the study,we have made a detailed observation and examination of the non-continuous destruction aftermath of the igneous rocks overlying the mined-out area by analyzing the scope of the rocks under study as well as the facts of the cracks by joining the field data and the probability integration method with the help of a software known as FLAC3 D. And,next,in the process of the simulated study,we have arranged six monitoring lines to trace the surface subsidence and cracks in accordance with the actual coal excavation operational sequence in imitation of the excavation situation of the relevant goaf. The maximum subsidence of the surface of the coverage area from where we get the igneous rocks accounts for 0. 25 meter,with the non-igneous rocks maximum subsidence of the surface of coverage being 2. 5 meters.Comparing the simulated data with the similar actual data obtained by our observation,we have analyzed the simulated distribution of the rock plastic or curves in the zone under study. The results of our investigation demonstrate that the cracks in the surrounding rocks turn to be accounted for by the appearance of uneven igneous lines in the rocks on the mined-out area where some kinds of igneous rocks exist beneath the loose layer. The impact of the mined-out area could then be developing to the bottom of the igneous rocks which may result in partial hanging on the edge of the said rock and lead to the state of cantilevers. And,consequently,with the gradual expansion of the mined-out area and vacant sections,the tensile stress may aggravate above the igneous rocks and gradually exceed the tensile strength,thus leading to fractures. It is just such igneous fractures that may account for the surface crack,deformation and fragmentation in the rocks. What is more dramatic,and,day in and day out,the loose layers may tend to fall into igneous fractures and lead to the surface cracks and disintegration. And,in the end,the igneous rocks can be tragitically turning to transfer the impact of the mined-out area from place to place so as to reduce the upper surface subsidence to more or less serious extent. However,in the event of breakage of igneous rocks,the surface deformation may tend to be squeezed on the crack areas,eventually falling into corresponding geological disasters.