ANALYTICAL SOLUTION AND VERIFICATION ON SEEPAGE FIELD OF TUNNEL IN FINITE AQUIFER BASED ON IMAGE METHOD

The external water pressure and water inflow are the important parameters of underwater tunnel engineering. In view of the limitation of a semi-infinite aquifer model to analyze the tunnel seepage field with complex boundary conditions, which only considered the effect of a single boundary. A new seepage model of lined tunnel is firstly established, considering the finite aquifer. Based on the image method, the model is then transformed into a linear multi tunnel seepage model in infinite plane, and an analytical formula of water head and water inflow is deduced. The accuracy of the solution is verified by numerical solution and by the formula degradation. The influence of tunnel buried depth ratio (d/R₁), grouting ring parameters on water head distribution and tunnel water inflow are analyzed. The results show that: The water head at any position increases as aquifer thickness increases. The closer the tunnel is to the impervious boundary, the greater the water head difference between the upper and lower of the tunnel. When the distance between the tunnel and the impervious boundary is less than 3 times the tunnel diameter, the buried depth ratio of the tunnel has a significant impact on the water inflow and the external head of the lining, and their values drop sharply. Improving the impermeability of grouting circle can reduce the water inflow of tunnel more than increasing the thickness of grouting circle. The research results can provide a theoretical basis for the prediction of tunnel seepage field in limited aquifer area.