Study On Factors Affecting Freezing Of Drainage Channels In Cold Region Tunnels

With the continuous promotion of the "Belt and Road" initiative and the approval of the entire With the continuous advancement of the "Belt and Road" initiative and the approval of the entire Sichuan-Tibet Railway,a large number of tunnels will be constructed in cold regions of China.The problem of tunnel freezing damage is a pressing issue that needs to be addressed in tunnel engineering.The freezing damage in cold region tunnels is mostly caused by the freezing of drainage ditches.Therefore,it is of great significance to study the influencing factors of drainage ditch freezing in cold region tunnels.This paper combines literature research,on-site measurements,and numerical simulations to analyze the distribution patterns and main influencing factors of the longitudinal temperature field in cold region tunnels based on the freezing damage and measured temperature data inside tunnels.The COMSOL Multiphysics software is used to study the variations of the temperature field in drainage ditches and the freezing depth caused by external temperature,surrounding rock temperature,wind speed,and other influencing factors.The research also investigates the design of frost-resistant lengths for side drainage ditches in cold region tunnels and proposes a formula to determine the frost-resistant length of side drainage ditches,providing a reference for the design of frost damage prevention in cold region tunnel engineering.The main conclusions of this study are as follows:(1)The outlet of the drain is most prone to freezing.The temperature and the movement of water affect the process of ice formation.Flowing water does not immediately freeze at 0°C.The freezing time is influenced by the environmental temperature and water flow rate.The lower the environmental temperature and the smaller the flow rate in the drain,the shorter the freezing time.The thickness of the ice layer at the drain outlet is mainly related to the water flow rate..(2)Considering the phase change of water flow in drainage ditches,a water-heat coupling model of tunnels in cold regions is established to explore the influence of different factors on the temperature field of side drainage ditches in tunnels.The results show that the temperature of the side drainage ditch increases with the increase of external temperature,rock temperature,and rock thermal conductivity,and decreases with the increase of wind speed and lining thermal conductivity.The frozen depth of the surrounding rock at the location of the side drainage ditch decreases with the increase of external temperature,rock temperature,and rock thermal conductivity,and increases with the increase of wind speed and lining thermal conductivity.According to the sensitivity analysis results,the sensitivity of each influencing factor to the freezing depth of the side drainage ditch from high to low is: rock temperature,external temperature,lining thermal conductivity,rock thermal conductivity,and wind speed.(3)Using the method of controlling variables,when the external temperature increases by 5℃,the initial rock temperature increases by 5℃,and the rock thermal conductivity increases by 0.5W/(m·K),the bottom temperature of the side drainage ditch at the same location is raised by an average of 2.72℃,2.61℃,and 0.15℃respectively,and the frozen depth of the surrounding rock at the location of the side drainage ditch is reduced by an average of 0.3m,0.12 m,and 0.03 m respectively.When the wind speed increases by 1m/s and the lining thermal conductivity increases by0.5W/(m·K),the bottom temperature of the side drainage ditch at the same location is lowered by an average of 0.2℃ and 0.81℃,respectively,and the frozen depth of the surrounding rock at the location of the side drainage ditch is increased by an average of0.02 m and 0.25 m,respectively.(4)The temperature field of the drainage ditch is extremely complex,with the lowest temperature at the top of the ditch and the highest temperature at the bottom.The temperature on the left and right sides of the ditch wall is also different.The drainage ditch gradually freezes from top to bottom,and the latent heat released by the water-ice phase change affects the temperature field of nearby water flow.The release of latent heat from the freezing of water into ice delays the cooling process of the drainage ditch.At this time,the temperature of the drainage ditch fluctuates in a wave-like pattern.To comprehensively consider these factors,the criterion for determining the freezing of the side drainage ditch is set as the temperature of the bottom of the ditch reaches 0℃.(5)A transient coupling heat transfer model of wind flow-water flow-rock was established to study the impact of different external temperatures,rock temperatures,and wind speeds on the longitudinal temperature field of the side drainage ditch in cold region tunnels.Through calculation,it was found that external temperature,rock temperature,and wind speed have a significant impact on the freezing length of the drainage ditch.Based on data fitting,a formula for the freezing length of the side drainage ditch is proposed,which can provide a reference for the design of freezing damage prevention in cold region tunnel engineering.