Study On The Changing Law Of Water Pressure Reduction Cofficient Of High Water Pressure Subway Tunnel Lining

In order to meet the needs of urban economic development,the proportion of subways in the urban transportation system has increased sharply as a transportation mode with the advantages of shortening transportation distance,relieving traffic pressure and improving transportation capacity.A considerable proportion of subway tunnels will inevitably pass through water-rich strata,especially subway tunnels under high water pressure environment are prone to water inrush,leakage and other problems during the construction and operation stages,which will cause harm to the safety of people’s lives and properties.a huge threat.At present,the research on the initial seepage field of the tunnel is rarely involved.The research on the influence of the groundwater tunnel lining mainly focuses on the distribution law of the tunnel seepage field and the influencing factors of the lining water pressure.There are many theoretical analysis methods,but there are few literatures.Method for deviation analysis,the calculation of lining water pressure in engineering design still follows the calculation method of lining water pressure for hydraulic tunnels.Therefore,this paper will use the concept of tunnel lining water pressure reduction coefficient to study the reduction degree of circular tunnel lining water pressure on the basis of hydrostatic pressure.The influencing factors of lining were studied in detail,and the variation law of lining water pressure reduction coefficient with various influencing factors was analyzed,and the following conclusions were drawn:(1)distribution law of the initial seepage field is analyzed through the conformal transformation theory in the complex function.It is found that when the groundwater level line is parallel to the horizontal plane,the pore water pressure in the seepage field is equal to the hydrostatic pressure;when the groundwater level line has an inclination angle with the horizontal plane,There is a certain relationship between the pore water pressure and the inclination angle.The larger the inclination angle,the smaller the lining water pressure.(2)based on the conformal transformation theory,the axisymmetric theory and the mirror image method,respectively,deduced the water pressure reduction coefficient of the tunnel lining,the calculation formula of the tunnel drainage and the water inflow,and carried out the error analysis of the results obtained by the three theoretical methods.The results show that the deviation of the calculation formula of the lining water pressure reduction coefficient derived by the three theoretical methods is not more than 3%.The deviation of the tunnel water inflow and discharge calculated by the conformal transformation method and the mirror method is not more than 2%,but the deviation of the tunnel water inflow and discharge calculated by the axisymmetric method and the other two theoretical methods is greater than 20%,and with the tunnel tunnel This gap will gradually decrease as the head height increases.(3)Based on theoretical analysis,numerical simulation and model test,it is found that the reduction coefficient of lining water pressure decreases with the increase of the ratio of the permeability coefficient of the lining and the surrounding rock,and as the ratio of the permeability coefficient of the lining and the grouting circle increases.It decreases with the increase of the tunnel head height.Grouting is an effective method to reduce the water pressure of lining in engineering.This method can effectively prevent groundwater from infiltrating behind the lining through the grouting ring by reducing the permeability coefficient of the surrounding rock.However,it is found that the effect of grouting on reducing the water pressure of the lining is limited.Yes.It is worth noting that the effect of grouting on reducing the lining water pressure is based on the premise of tunnel drainage.When the tunnel is not drained,grouting can hardly reduce the lining water pressure.(4)The flow state of groundwater can affect the water pressure of the lining.Through literature research,theoretical analysis and model tests,it is found that when the tunnel is excavated,the dynamic balance of groundwater around the tunnel is broken,and groundwater is discharged into the tunnel.When the tunnel is lined,the lining water pressure of the drainage tunnel is less than the hydrostatic pressure at the corresponding location.The reduction of lining water pressure caused by tunnel drainage depends on the size of the drainage volume,which is related to the drainage system.