Research On Heat Transfer Characteristics And Selection Of Thermal Insulation Lining Of Tunnel With High Geotemperature

In recent years,the construction of railway lines in western China are in full swing,but there are a large number of high geo-temperature areas along these railway lines,which have caused serious heat damage to the tunnel structure.For example,the high geo-temperature in the surrounding rock will generate a lot of thermal stress in the tunnel structure.Therefore,it is usually necessary to consider the coupling of temperature field and stress field when carrying out mechanical research on tunnels in high geo-temperature areas.However,there are a large number of hot springs in the high geothermal areas along the railway lines in western region.The seepage process of high-temperature groundwater will accelerate the heat transfer and further aggravate the impact of heat damage on the tunnel.Therefore,the influence of the seepage field on the temperature field should not be ignored.This paper analyzes the temperature field distribution of a railway project in a high geo-temperature area,and studies the influence relationship between different physical fields under the coupling conditions of temperature field,stress field and seepage field.The main contents of the paper are as follows:(1)Based on the basic theory of heat transfer and the actual engineering data of a tunnel,the causes of heat damage,the classification of heat damage,the form of heat damage and the impact of heat damage are analyzed for tunnels with high geo-temperature.On this basis,the high ground temperature conditions of a tunnel are analyzed.The main mechanism of formation and the thermal damage classification of the high geo-temperature section were carried out.(2)The mathematical model of the temperature field of the circular high ground temperature tunnel is established in polar coordinates,and the Laplace integral transformation method is used to analyze and solve it,and the solution formula of the temperature field under the three-layer structure of lining-insulation layer-surrounding rock is obtained.;After calculation,the time-space evolution law of the temperature field is obtained,and a corresponding numerical model is established to verify the reliability of the results.Six factors,including the thickness of the thermal insulation layer,were selected to carry out an orthogonal test on the maximum temperature in the lining,to determine the significance of each influencing factor,and to analyze the relationship between the maximum temperature of the lining and the four main influencing factors.(3)For the corresponding control equations of the three THM fields,the mutual influence between the two physical fields is realized through the coupling term between the physical fields.The magnitude of the mutual influence between the three physical fields is determined,and the heat transfer characteristics of the thermal insulation lining and surrounding rock are analyzed on this basis.(4)Analyze the characteristics,advantages and disadvantages of commonly used thermal insulation materials for high ground temperature tunnels,and use the fuzzy comprehensive evaluation method to compare and select,and recommend relatively good high ground temperature thermal insulation materials;numerical simulation is used to carry out the laying methods of different thermal insulation layers.For comparison and selection,the temperature value and the heat transfer of the secondary lining under different working conditions are compared,and the laying method with better thermal insulation effect and engineering economy is recommended.