| With the development of social economy and the need for traffic construction,there are more and more tunnels built in permafrost areas.Subject to the harsh climate environment and construction technology,there appear more and more frost heave disasters in the tunnels,which is mainly due to the existence of the tunnel lining behind the melting plates.In this paper,the melting plate in the tunnels is defined first,and the forming mechanism of the melting plate is described from the basic properties of permafrost.Next,from the perspective of the temperature field,the influencing factors of the formation of the molten disc are analyzed by the freezing and thawing test of the test soil.Based on that,through the tunnel test,the influence of the ground temperature on the tunnel melting plate is analyzed.Finally,together with the finite element method under the phase transition transient temperature field,under the condition of the average ground temperature,the influence of the change of the temperature in the tunnel on the formation of the melting plate is calculated,including the temperature control of the tunnel after the laying of the insulation material effect.Through the experimental analysis and numerical simulation obtained:①the formation of permanent melting plate is closely related to the annual mean ground temperature and tunnel wall temperature.The higher ground temperature is more conducive to the formation of the melting plate.Therefore,only when the average temperature of the tunnel wall is at above O℃ will a permanent melting plate be formed.Plus,the higher the temperature is,the faster the melting plate develops around the lining.②The presence of wind in the tunnel can increase the range of seasonal melting and the annual temperature difference is more obvious.The laying of thermal insulation material can effectively reduce the disturbance of the external temperature to the surrounding rock,as well as prevent the formation of the melting plate.③ Under the same external disturbance conditions,the maximum melting range of the high temperature permafrost area(-0.8℃)is one fourth of that of the low temperature permafrost(-2℃)and the highest temperature in the cold season is higher than that in the low temperature permafrost.The melting plate in the high temperature permafrost area disappears earlier than the low temperature permafrost area.④The water content of the surrounding rock and the ventilation in the tunnel are also directly related to the formation of the melting plate.The water content and the wind speed are larger.Under the same external conditions,the melting area around the lining will increase. |
