Groundwater Seepage And Control Method For Tunnel And Limiting Drainage Criterion Based On Ecological Balance

Tunnel buried under ground, and always surrounded by water, so it’s crucial to control the groundwater. Drainage water too much will lead to drawdown of groundwater table and ecological environment destruction, however plugging the water, the lining may can’t be able to bear the high water pressure, how to determine the reasonable water discharge which both to protect the environment from destruction and make the lining withstand a reasonable water pressure is the issue has not been solved.So, based on the theory of groundwater dynamics, the calculation method of water inflow for surrounding rock of tunnel was studied, then on the basis of permeability coefficient nonlinear variation with depth, the computational method of water inflow for heterogeneous isotropic surrounding rock was analyzed, and with the grouting circle and lining into consideration. The ecology and agronomy with respect to the ecological water requirement of vegetation were introduced, and the well flow theory, areal-well methods were adopt to do the research on calculation method for limiting water inflow of groundwater and limiting drainage criterion.By above theoretical analysis and case studies, we obtained the main achievements are as follows:(1) Based on the well flow theory, low of mass conservation and energy conservation, the calculation formulas of water inflow with flow velocity into consideration was deduced, and further the water inflow equation for tunnel after the grouting circle and lining were built was obtained. After consider the flow velocity, the water inflow was decrease and the water pressure of lining was increase, while the effect of flow velocity is insignificant to water inflow. The range value of permeability coefficient and thickness of grouting circle which can reduce the water inflow of tunnel cost-effective were got. The relationship between the water pressure of lining and the groundwater emission was analyzed.(2) Taken permeability coefficient nonlinear variation with depth into consideration, the computational formula of water inflow for heterogeneous isotropic surrounding rock was deduced, and the results were close to the existing methods, but the presented formula was simplicity and easy to use. The change trend and rule of water inflow after considered the nonlinear variation of permeability coefficient were obtained, which can provide the basis for the site selection of the tunnel. The calculation formula of grouting parameters for plugging water was achieved, because the permeability coefficient was decrease with depth, the changing law should be considered in grouting to avoid the design permeability coefficient of grouting circle is larger than surrounding rock of tunnel and can’t achieve the goal of water plugging.(3) From the perspective of the groundwater balance, the research of ecological water requirement in vegetation ecology and agronomy was introduced, and control the maximum drawdown of groundwater within the scope that maintain the normal growth of vegetation, the computation formula for precipitation funnel volume was deduced, combine the parameters of surrounding rock, the total discharged water was acquired, compared with the rainfall recharge, the allowed groundwater discharge for recovering the original groundwater table of tunnel site area. To operational phase of the tunnel, the anti-analytical formulas for groundwater table was deduced, based on the monitoring and collection of controlled water drainage, combined with the parameters of the surrounding rock and the first lining of tunnel such as permeability, the water table can got, which can provide the basis for real-time monitoring of groundwater table.(4) The well flow theory and areal-well method were introduced into the calculation of the groundwater table drawdown for tunnel, and the drawdown formula for arbitrary point within the scope of influence was obtained. The determination method of limiting groundwater emissions for keeping balance the groundwater was presented. Based on the groundwater drawdown superposition of two holes, the computational method of limiting drainage water for separated tunnel was achieved, and the relationship of single bore tunnel and separated tunnel was analyzed.(5) On the premise of ecological protection and groundwater balance, the permeability coefficient, specific yield and groundwater table for common geotechnical layer were selected, and employed the relationship formula between the water discharge and groundwater table drawdown to propose the limiting drainage criterion for most common mountain tunnel. For the tunnel which the groundwater can’t be blocked, the determine method of limiting drainage was presented.