Numerical Analysis Of Influence Of Partial Tunnel Leakage On Surrounding Environment Under Hazards Condition

Most of the shield tunnels which are the carriers of the subway lines are leaking.There is more and more accident of loss of water and soil of tunnel which is caused by leakage at home and abroad.Leakage of tunnel has evoked much attention of scholar in domestic and abroad.But the current research is mainly about long-term water seepage problem of tunnel by using two-dimensional model of tunnel,few studies have investigated the case of large tunnel leakage.A three dimensional numerical model of tunnel was established with FLAC^3D program.The equivalent leakage method was adopted to simulate the local leakage of the tunnel,and the influence of water leakage on the surrounding pore pressure,the surface and the deformation and internal force of the tunnel were studied by the fluid-structure coupling model.Settlement of tunnel and ground are studied preliminarily considering deterioration development between the tunnel deformation and the water leakage.The main contents and conclusions are as follows,The pore water pressure in the vicinity of the leaking area is obviously lower than the static pore water pressure.With downwards of leaking position,pore pressure decrease.The position is the main factor to decrease the pore water pressure.When the leaking position was closer to the top of the tunnel,the time of stabilization of surface subsidence was shorter,the surface subsidence was deeper.When tunnel leaking occurs,the settlement of tunnel will develop rapidly within 20 days.When the leaking location is closer to the bottom of the tunnel,the longer the equilibrium time is,the bigger the settlement will be,and the ratio of the maximum settlement between tunnel and surface will be 0.33⁸0.The local leakage of the tunnel will make the longitudinal settlement of the tunnel uneven,enlarging the joint opening of the adjacent segments.The lower leakage position are,the greater the joint opening which leading to larger leakage is.As a result,the mechanism of coupled development between leakage and deformation of tunnel.When the coupling deterioration between tunnel deformation and leakage is taken into account,The maximum settlement of the tunnel and the surface will increase.For the tunnel accident caused by water leakage,soil erosion and sand and water loss in water-rich sand stratum,in order to quantify risks tunnels suffer,a new shield tunnel seepage simulation test device was developed considering the interaction between elastic sealing gasket,soil and water.The state of soli loss of Fujian standard sand under different gap widths and water pressure were studied through experiments.Leakage mechanism due to invasion of sand was revealed and proved by test results,which showed that the traditional test methods would overestimate the waterproof property of elastic sealing gaskets without considering the influence of soil.Estimation formula of critical gap width of soil erosion was derived,which is verified by test results.The critical gap width of soil erosion is proportional to the vertical stresses and soil thickness and is inversely proportional to soil porosity and hydraulic pressure around gap.For Fujian standard sand,a practicable assessment method of state of soil loss is put forward considering pressure and segment gap.