Study On The Effect Of Tunnel Construction On Groundwater Environment

With the extension of the railway and road networks from eastern and central areas to eco-flimsily western mountainous areas,as well as the rapid development of hydraulic engineering,the ratio of tunnels in lines is greatly increased,and a large number of tunnels with characteristics such as ultra-long tunnel line,largely buried depth,high geo-stress,high water pressure,and large water inflow appear successively.However,the loss of groundwater caused by tunnel construction will break the balance of groundwater resources in the tunnel site,which will cause a series of negative environmental effects.If reasonable eco-control measures of groundwater are taken,the groundwater circulation system in the tunnel site will again reach a new dynamic balance.Therefore,how to clarify the influence mechanism between tunnel construction and groundwater environment is a key technical problem to be solved in the tunnel construction in eco-flimsily areas.This paper was funded by a major research project such as “Study on the effect of long tunnels and tunnel groups of the high-speed railway on groundwater environment and its control technology”,which was supported by the high-speed railway and natural science united foundation.Taking the mountain tunnel in the offshore section of the Shantou-Shanwei high-speed railway and the Banzhulin tunnel of the newly-built Xuyong-Bijie railway as engineering backgrounds,the effect of the tunnel construction on the groundwater environment was studied by comprehensive means of data investigation,theoretical analysis,numerical simulation,and model test.The main works and research results are as follows:(1)Based on the Dupuit assumptions and the integral method,the approximate analytical solutions for the steady-state water inflow and water table of the single-tube drained tunnel in a single-stratum phreatic aquifer,a vertically stratified phreatic aquifer,and a horizontally stratified phreatic aquifer are derived respectively.Based on the approximate analytical solutions of the steady-state seepage field of the single-tube drained tunnel in a phreatic aquifer,combined with the superposition method,the approximate analytical solutions for the steadystate water inflow and water table of the double-tube drained tunnels in a single-stratum phreatic aquifer,a vertically stratified phreatic aquifer,and a horizontally stratified phreatic aquifer are derived respectively.The relative error,the application condition,and the error source for the approximate analytical solutions are given.The factors influencing the steadystate water inflow and water table of the single-tube and double-tube drained tunnels in a phreatic aquifer,such as the horizontal distance from the center of the tunnel to the lateral boundary of water replenishment,the height of water replenishment in a phreatic aquifer,the vertical distance from the center of the tunnel to a horizontal impervious base,the radius of the tunnel,the coefficient of permeability,and the clear spacing of the tunnel,are analyzed.The parameters of the core influencing the steady-state water inflow and water table of the single-tube and double-tube drained tunnels in a phreatic aquifer are clarified.The influence mechanism of the construction of the single-tube and double-tube drained tunnels in a phreatic aquifer on the groundwater environment is revealed.(2)Taking the mountain tunnel in the offshore section of the Shantou-Shanwei high-speed railway as the engineering background,a set of tunnel seepage model test system that can measure the water table is developed.For the single-tube tunnel,the double-tube tunnels with the same height,the double-tube tunnels with the non-same height,with the water table and water inflow of the tunnel as the evaluation index,the influence of tunnel construction on the groundwater environment,and the effect of the grouted zone of the tunnel on the control of groundwater environment are revealed through model tests under the conditions for different permeability coefficients of the grouted zone,different heights of water replenishment,and different horizontal distances of the single-sided water replenishment.(3)Taking the Banzhulin tunnel of the newly-built Xuyong-Bijie railway as the engineering background,in order to ensure that the dynamic changes in the physical and mechanical parameters of the surrounding rock during tunnel construction and their influence on the seepage field are more realistic,the ridge regression method is introduced into the back analysis of the initial geo-stress field of rock masses.Combined with the change equations of physical and mechanical parameters of the surrounding rock such as permeability coefficient,void ratio,elastic modulus,and cohesion under different stress states,the seepage-stressdamage coupled model that can consider the mechanical behavior of rock masses during the change of elastic deformation,plastic deformation(damage),and fracture failure is established.Through the seepage-stress-damage coupled model,the dynamic changes in the physical and mechanical parameters of the surrounding rock during tunnel construction and their influence on the seepage field are revealed.