Research On The Mechanism Of Frost Damage, Prevention And Measures Of Tunnel In Seasonally Frozen Soil

With the development of China's transportation,railway tunnel construction is gradually extending to the seasonal frozen area.Due to the harsh natural environment in the frozen soil segion,the problem of frost damage of tunnels has gradually attracted people's attention.Based on the investigation of 60 tunnels in cold region,the temperature field of tunnel is calculated and studied by using ANSYS.The effects of different external conditions on tunnel frost damage were analyzed.Using analytic hierarchy process and fuzzy comprehensive evaluation method,the frost damage of tunnel was classified.The fitting formula of tunnel insulation length is worked out.The main tasks completed are:(1)By using analytic hierarchy process and fuzzy comprehensive evaluation method,a tunnel freezing damage evaluation system was established.Firstly,a fuzzy comprehensive evaluation model was established,and various influencing factors were analyzed by means of numerical simulation,investigation and literature review.Analytic hierarchy process was used to determine the weight of different external factors,and semi-trapezoidal function was used to determine the membership degree.Finally,the weighted average evaluation model was used to calculate the final classification.(2)The fitting formula of insulation fortification length is calculated.Using the control variable method,the ambient temperature,wind speed and temperature of surrounding rock were controlled respectively.Through numerical simulation,the relationship between the three factors and the fortification length of the insulation layer was obtained.The data of different lengths,external temperature,wind speed and surrounding rock temperature were analyzed,and finally the calculation formula of the fortification length of the insulation layer was obtained.The conclusion was verified by using shahukou tunnel.The temperature field of the insulation ditch is simulated,whitch made the temperature distribution rule of the insulation ditch get obtained.(3)Prevention and treatment measures of tunnel frost damage.According to different freezing damage levels,the main types of frost damage were analyzed,the corresponding frost damage treatment measures for tunnels with different freezing damage grades were obtained.A new tunnel and an existing tunnel were used to verify the conclusion.The research results of this paper provide theoretical support and basis for thermal insulation of the tunnel,and have certain reference significance for engineering.