Numerical Calculation Model Of Water-thermal-force Coupling In Tunnel Section Of Cold Area

With the advancement of China's basic facilities to high-altitude and high-altitude areas,the number of completed tunnels in the seasonally frozen areas is extremely large,and tunnels built in these high-altitude areas will inevitably encounter the frost heaving problems of surrounding rocks.Compared with many literatures in the study of tunnel lining stress analysis and insulation and antifreeze,there are few analyses on the stress characteristics and freeze damage of shallow tunnel tunnels.Therefore,it is important to clarify the stress characteristics of the portal section and propose the relevant optimization of the disease management.This paper summarizes the related theories and research status of water-thermal-force coupling in cold regions and relies on a tunnel in Qinghai to study the temperature field of the three-dimensional model during the frost heaving period of a tunnel in Qinghai by finite element software ANSYS.It is found that under the double action of the external surface and the cold air in the tunnel,the frost heave of the surrounding rock is more severe.As the depth of the tunnel increases,the influence of the low temperature on the surface of each section away from the opening area is getting smaller.Through the numerical analysis of water-heat-force coupling of the tunnel portal section,the distribution of stress and deformation during the whole frost heaving period is calculated by selecting the section of 10 m,20m and 30 m from the portal section.Based on the numerical simulation,the selected section of the tunnel portal section is monitored.According to the numerical simulation,the three sections of the tunnel portal section were selected to measure the stress and deformation of each section for 6 months through the concrete surface strain gauge and the total station.The research shows that:(1)Comparing the stress values of various parts of the lining structure,the maximum value appears in the 10 m section position.The stress value of the side wall of the lining structure is the largest and the stress value at the position of the arch is second.The stress value at the position of the invert is the smallest.The maximum vertical displacement occurs at the position of the dome.The maximum horizontal deformation occurs at the side wall position.(2)Through the analysis of the stress-time curve and the displacement-time curve of simulation,it is found that the stress and deformation values at the vault and the side wall gradually decrease with the distance from the tunnel.The K36+490 section is closest to the tunnel door and the side wall has the largest frost heave force,followed by the vault position.The maximum vertical displacement occurs at the vault position.The on-site monitoring also validated the theory of numerical simulation,that is,the surrounding rock of the tunnel portal section is more frost-expanded due to the double-frozen effect than the location away from the portal section,and the damage is more serious than other sections because of the thinner overlying soil layer and complicated factors.(3)Aiming at some frost heaving damages in the tunnel portal section,the improvement measures are proposed from the aspects of heat preservation and drainage.At the same time,the design and treatment of the tunnel section of the similar cold zone are given from the aspects of the location,heat preservation,waterproof and drainage.