| In recent years,China’s infrastructure construction has developed rapidly,with a sharp increase in the number of highway and railway tunnel projects,which has brought many conveniences to the national economic development.However,research has shown that the groundwater seepage into the back of tunnel lining often leads to problems such as water leakage and even deformation and cracking of the lining structure due to water pressure.Currently,researchers often assume that the seepage field of the surrounding rock is in a steady state and ignore the influence of rainwater infiltration on the seepage field when studying the external water pressure on the tunnel lining structure.In southwestern China,where there is abundant rainfall and extreme weather conditions have become more frequent in recent years,it is of great significance to study the external water pressure and its stress characteristics on the tunnel lining structure under extreme rainfall conditions.Therefore,this thesis comprehensively uses methods such as field monitoring,theoretical analysis,and numerical simulation to systematically study the external water pressure and its stress characteristics on the tunnel lining structure under extreme rainfall conditions;and explores the influence of tunnel drainage performance on the external water pressure on the lining.The main content and conclusions of this thesis are as follows:(1)Based on a tunnel in Chongqing,long-term monitoring of rainfall,external water pressure on the lining,and support pressure was carried out.By analyzing the monitoring data under different rainfall infiltration conditions,the variation patterns of external water pressure on the lining structure,support pressure,rainfall intensity,and duration were obtained.The on-site monitoring results show that rainfall infiltration in the tunnel area has a significant impact on the stress of the lining structure.(2)Based on rainfall infiltration and unsaturated seepage theory,the physical process of rainfall was explored,and the function relationship between negative pore water pressure,soil saturation,and permeability coefficient was summarized.The FISH language programming function of FLAC3 D numerical calculation software was used to develop the infiltration boundary conditions and seepage module,and finite element calculation of unsaturated seepage in tunnel engineering under extreme rainfall conditions was achieved.(3)Using the self-developed rainfall unsaturated seepage correction module and considering the fluid-solid coupling effect,the distribution patterns of the tunnel seepage field and stress field under different working conditions such as rainfall intensity,rainfall duration,and initial water level were analyzed,using the steady-state seepage field around the tunnel before rainfall as the initial condition.The results show that after rainfall,the external water pressure,stress,and displacement of the lining structure significantly increase.The external water pressure,structural stress,and displacement of the lining structure increase with the increase of rainfall intensity and duration.However,due to the limitation of soil permeability and saturation,this growth trend will not always exist.The lower the initial groundwater level before rainfall,the greater the impact on the external water pressure,structural stress,and displacement of the lining structure under extreme rainfall conditions.Based on the finite difference method,different rainfall and drainage performance conditions were calculated,and the impact of tunnel drainage performance on external water pressure of lining structure under extreme rainfall conditions was revealed.Different reasonable groundwater discharge amounts were formulated for the relying project.The results show that the setting of the tunnel drainage system has a significant weakening effect on the external water pressure of the lining structure under extreme rainfall conditions.The performance of the drainage system,rainfall intensity,and rainfall duration will all affect the amount of groundwater discharge from the tunnel.The external water pressure of the lining structure is negatively linearly correlated with the groundwater discharge from the tunnel,and the external water pressure of the lining gradually decreases with the increase of the discharge amount. |
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