Study On Mechanism Of Preventing Water-inrush From Floor Above Confined Water By Backfill Mining With Paste

The stability of the floor rock mass mainly depends on the lithological combination of the floor and the complicated geomechanical environment.When there is a confined aquifer in the floor of a coal seam,Under the combined action of mining pressure and water pressure,it is easy to cause failure and instability of floor rock mass.The confined water gradually expands upward along the crack of the floor.When the confined water pressure breaks through the effective aquifers,It is very easy to cause water inrush accidents.In this thesis,based on theoretical analysis,numerical simulation of fluid-solid coupling,numerical simulation and field measurement,The mechanism of preventing water-inrush from floor above confined water by backfill mining with paste was studied.The main research results were as follows:(1)Based on the elastic mechanics theory and plastic slip line field theory.Theoretical analyzed the stress distribution characteristics of the floor and the process of confined water conduction by backfill mining with paste.The failure range of the plastic zone and the yield limit width of the pillar were derived.The transfer law of the floor fissure under the influence of the mining stress was analyzed.Combined with the effect of confined water on the crack expansion of the floor rock mass,the crack expansion and plastic failure range of the bottom plate were divided.The formula for the maximum rising height of confined water of the floor was derived.The probability of water inrush from the floor was predicted theoretically.(2)The fluid-solid coupling experimental material was used,The distribution characteristics of stress field,displacement field and water pressure were studied under the condition of concealed fault structure in the floor.The mechanism of fracture expansion and the law of activation of hidden faults were analyzed in the process of backfill mining with paste.The distribution characteristics of vertical stress near the hidden fault,the rising height elevation of water pressure and the state of crack propagation were studied.The breaking distance of the floor rock stratum and the variation of the stress on the hanging wall and footwall of the fault were obtained.(3)Using the fluid-solid coupling calculation model,the stress and displacement of different depths of the floor were numerical simulation analyzed.The distribution characteristics of the plastic zone in the floor under the action of water pressure were studied.The process of maximum percolation velocity change and rise mechanism of confined water at different filling stages.The maximum expansion height of the plastic zone above the concealed fault was not connected with the fracture zone of the floor.The water inrush probability of the floor was greatly reduced.(4)The in-situ strength of the filling body was studied by means of field measurement.The long-term stability and safety of the filling body were evaluated.The stress deformation characteristics of the floor in different depth range were monitored.The range of fracture development and the maximum rising height of the confined water were measured.And it forecasted the probability of water inrush from the floor.The results showed that the control structure of overlying rock can be formed with filling body as the main support body.The pressure sharing load were produced on the floor to ensure the integrity of the floor aquifers effectively.The maximum lift height of the floor failure zone did not touch the failure zone of the floor,which greatly reduces the possibility of water inrush from the floor.