【正文】 中文 3990 字 A convectionconduction model for analysis of the freezethaw conditions in the surrounding rock wall of a tunnel in permafrost regions HE Chunxiong(何春雄 )， (State Key Laboratory of Frozen Soil Engineering, Lanzhou Institute of Glaciology and Geocryology, Chinese Academy of Sciences, Lanzhou 730000, China。 Department of Applied Mathematics, South China University of Technology, Guangzhou 510640, China) WU Ziwang(吳紫汪 )and ZHU Linnan(朱林楠 ) (State key Laboratory of Frozen Soil Engineering, Lanzhou Institute of Glaciology and Geocryology Chinese Academy of Sciences, Lanzhou 730000, China) Received February 8, 1999 Abstract Based on the analyses of fundamental meteorological and hydrogeological conditions at the site of a tunnel in the cold regions, a bined convectionconduction model for air flow in the tunnel and temperature field in the surrounding has been constructed. Using the model, the air temperature distribution in the Xiluoqi No. 2 Tunnel has been simulated numerically. The simulated results are in agreement with the data observed. Then, based on the in situ conditions of sir temperature, atmospheric pressure, wind force, hydrogeology and engineering geology, the airtemperature relationship between the temperature on the surface of the tunnel wall and the air temperature at the entry and exit of the tunnel has been obtained, and the freezethaw conditions at the Dabanshan Tunnel which is now under construction is predicted. Keywords: tunnel in cold regions, convective heat exchange and conduction, freezethaw. A number of highway and railway tunnels have been constructed in the permafrost regions and their neighboring areas in China. Since the hydrological and thermal conditions changed after a tunnel was excavated， the surrounding wall rock materials often froze, the frost heaving caused damage to the liner layers and seeping water froze into ice diamonds， which seriously interfered with the munication and transportation. Similar problems of the freezing damage in the tunnels also appeared in other countries like Russia, Norway and Japan .Hence it is urgent to predict the freezethaw conditions in the surrounding rock materials and provide a basis for the design， construction and maintenance of new tunnels in cold regions. Many tunnels， constructed in cold regions or their neighbouring areas， pass through the part beneath the permafrost base .After a tunnel is excavated， the original thermodynamical conditions in the surroundings are and thaw destroyed and replaced mainly by the air connections without the heat radiation, the conditions determined principally by the temperature and velocity of air flow in the tunnel， the coefficients of convective heat transfer on the tunnel wall， and the geothermal heat. In order to analyze and predict the freeze and thaw conditions of the surrounding wall rock of a tunnel， presuming the axial variations of air flow temperature and the coefficients of convective heat transfer, Lunardini discussed the freeze and thaw conditions by the approximate formulae obtained by Shamsundar in study of freezing outside a circular tube with axial variations of coolant temperature .We simulated the temperature conditions on the surface of a tunnel wall varying similarly to the periodic changes of the outside air temperature .In fact， the temperatures of the air and the surrounding wall rock material affect each other so we cannot find the temperature variations of the air flow in advance。 furthermore， it is difficult to quantify the coefficient of convective heat exchange at the surface of the tunnel wall .Therefore it is not practicable to define the temperature on the surface of the tunnel wall according to the outside air temperature .In this paper, we bine the air flow convective heat exchange and heat conduction in the surrounding rock material into one model， and simulate the freezethaw conditions of the surrounding rock material based on the in situ conditions of air temperature， atmospheric pressure， wind force at the entry and exit of the tunnel， and the conditions of hydrogeology and engineering geology. Mathematical model In order to construct an appropriate model, we need the in situ fundamental conditions as a basis .Here we use the conditions at the scene of the Dabanshan Tunnel. The Dabanshan Tunnel is lototed on the highway from Xining to Zhangye, south of the Datong River, at an elevation of m, with a length of 1 530 m and an alignment from southwest to northeast. The tunnel runs from the southwest to the northeast. Since the monthlyaverage air temperature is beneath 0`}C for eight months at the tunnel site each year and the construct