Study On The Disaster-causing Mechanism Of Water-rock Coupling In Thin Bedrock Stope Under Thick Unconsolidated Aquifer

It is a common phenomenon that the upper part of the East China mining area is covered by the Cenozoic thick unconsolidated confined aquifer,and the thickness of bedrock above the coal seam is thin and weathered seriously,many disaster-causing accident occurred in the process of mining near thick unconsolidated aquifer,and roof pressure is abnormal released during the period of the stope pressure change.Taking Mining Group Gubei Mine 1202(3)working face as the research object,and mining working face specific hydrogeological data based on combining research methods of theoretical analysis,similar simulation,numerical simulation and field practice,the thick loose aquifer and thin bedrock stope water rock coupling mechanism was studied.(1)The structural mechanics model of thin bedrock under thick unconsolidated aquifer is established,the total weight of overburden of the hydraulic support is obtained.By using the similar simulation test,the displacement and deformation characteristics of the overlying strata and the evolution law of the bearing pressure of the stope are analyzed and compared.Thin bedrock stope under the action of non confined aquifer,the weight of the loose layer and the applied load are not all downward transfer.The front collapse angle of the overlying rock is always less than the latter.In contrast,Confined aquifer plays an important role in the large-scale migration of overlying strata,the front collapse angle of the overlying rock is less than the latter in initial production stage,the front collapse angle of overlying rock increases suddenly.The overlying strata of the stope show the trend of whole fracture,and the fracture shape is cut along the coal wall,and the compaction effect of overburden rock is obvious.(2)Two numerical models of fluid solid coupling and non coupling are established,under the condition of no coupling,the maximum principal stress in the loose layer decreases significantly with the coal seam excavation,the front maximum principal stress value increases slowly.Under the condition of fluid solid coupling,the stope is affected by the seepage field and the stress field,the degree of stress concentration in coal and rock is improved,the maximum principal stress value is approximately linear growth.(3)Engineering practice of thin bedrock stope under thick unconsolidated aquifer shows that roadway deformation and support resistance with the rapid growth of the advancing distance increases during the initial mining stage.The abnormal release of roof pressure causes the hydraulic support to be affected by the instantaneous impact load,the support is unable to support the weight of the unstable rock at first weighting.In conclusion,mining under the condition of single critical layer of thin bedrock under thick unconsolidated aquifer,the load transfer of confined aquifer increases the stress concentration of the surrounding rock,the weight of the whole broken bedrock block and the overlying load will exceed the bearing capacity of the support,which is the main cause of disaster-causing accident.The results of this study can be used for reference in coal mining under similar conditions.