| With the process of reform and opening up,China's economic construction has developed rapidly.More and more infrastructure is being built in Western Karst areas.However,in the process of tunnel construction,water inrush and mud outburst often occur.It not only endangers the safety of tunnel construction workers,but also affects the construction schedule.Once the treatment measures is unsuitable,it may cause a lot of problems such as bad operating environment,make eco-environment deteriorate,damaging landform,even affects people's production and life.In this paper the minimum safety thickness of fractured rock between the tunnel face and the cavity was studied,and the discrete element software is used to research the changes of the displacement and seepage fields in the process of tunnel water inrush.The results are as follows:(1)The water-resistant rock mass with nonpersistent joints between karst and karst tunnel face was treated as subject investigated,The fracture failure is divided into two modes: axial penetration failure and rock bridge shear failure.Based on the theory of fracture mechanics,the critical water pressure of joint damage under the two modes was determined respectively.Then the calculating formula of the safe thickness of water-resistant rock mass was established on the basic of the critical water pressure.(2)In the model of axial penetration failure: with the increase of the water pressure,the minimum safety thickness of water-resistant rock mass with nonpersistent joints ahead of the karst tunnel is linearly increased,and the minimum safety thickness decreases with the increase of the intermittent joint spacing,with the increase of joint spacing,the decrescent rate becomes smaller.the minimum safety thickness of water-resistant rock mass first increase and then decrease with the increase of the angle between the intermittent crack and the maximum principal stress.(3)In the model of rock bridge shear failure: With the increase of the length of the main crack,the minimum safety thickness of water-resistant rock mass of the karst tunnel is gradually increased,and there is a linear relationship between main crack length and the minimum safety thickness of karst tunnel.The minimum safety thickness of Karst Tunnel increases linearly with the increase of karst water pressure in front of the tunnel.(4)The numerical model of tunnel excavation was established by using 3D discrete element software,and the evolution process of displacement field and seepage field in karst water inrush process was studied,and the influence of karst water pressure,joint inclination and cavity size on the thickness of against-inrush was analyzed.(5)With the increase of the joint angle,the crack length of rock increase,the physical and mechanical properties of rock mass reduce,so it is easy to occur water inrush,and the thickness of against-inrush increase;When the karst water pressure increases,at the same time,the displacement and water pressure of each point and the maximum flow velocity of the fluid go up,and the against-inrush is easier to damage.The larger the size of the cavity,the more inflow water through the fracture,the more extensive of fluid diffusion range,the higher of the fluid velocity and joint water pressure,and the against-inrush rock is more easier to damage. |
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