【正文】 and????. The thermal parameters of the surrounding rock are determined from the tunnel site. 2 . Determination of the initial and boundary conditions .Choose the observed monthly average wind speed at the entry and exit as boundary conditions of wind speed， and choose the relative effective pressure p=0 at the exit ( that is， the entry of the dominant wind trend) and ]5[2 2/)/1( vdkLp ??? on the section of entry ( that is， the exit of the dominant wind trend )， where k is the coefficient of resistance along the tunnel wall, d = 2R， and v is the axial average speed. We approximate T varying by the sine law according to the data observed at the scene and provide a suitable boundary value based on the position of the permafrost base and the geothermal gradient of the thaw rock materials beneath the 重慶交通大學(xué)土木工程專 業(yè)（隧道與城市軌道交通工程方向）畢業(yè)設(shè)計(jì)外文翻譯 7 permafrost base. 3 A simulated example Using the model and the solving method mentioned above， we simulate the varying law of the air temperature in the tunnel along with the temperature at the entry and exit of the Xiluoqi Tunnel .We observe that the simulated results are close to the data observed[6]. The Xiluoqi No .2 Tunnel is located on the Nongling railway in northeastern China and passes through the part beneath the permafrost base .It has a length of 1 160 m running from the northwest to the southeast, with the entry of the tunnel in the northwest， and the elevation is about 700 m. The dominant wind direction in the tunnel is from northwest to southeast, with a maximum monthlyaverage speed of 3 m/s and a minimum monthlyaverage speed of 1 .7 m/s . Based on the data observed， we approximate the varying sine law of air temperature at the entry and exit with yearly averages of 5℃， ℃ and amplitudes of ℃ and ℃ respectively. The equivalent diameter is 5 .8m ， and the resistant coefficient along the tunnel wall is the effect of the thermal parameter of the surrounding rock on the air flow is much smaller than that of wind speed， pressure and temperature at the entry and exit， we refer to the data observed in the Dabanshan Tunnel for the thermal parameters. Figure 1 shows the simulated yearlyaverage air temperature inside and at the entry and exit of the tunnel pared with the data observed .We observe that the difference is less than 0 .2 `C from the entry to exit. Figure 2 shows a parison of the simulated and observed monthlyaverage air temperature inside (distance greater than 100 m from the entry and exit) the tunnel. We observe that the principal law is almost the same， and the main reason for the difference is the errors that came from approximating the varying sine law at the entry and exit。 (iii) solving the first and second equations of(1)， we obtain U0，V1。 X= (x , r)， ? (t) is phase change front。 R is the equivalent radius of the tunnel section。 p is the effective pressure(that is， air pressure divided by air density)。重慶交通大學(xué)土木工程專 業(yè)（隧道與城市軌道交通工程方向）畢業(yè)設(shè)計(jì)外文翻譯 1 A convectionconduction model for analysis of the freezethaw conditions in the surrounding rock wall of a tunnel in permafrost regions 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 重慶交通大學(xué)土木工程專 業(yè)（隧道與城市軌道交通工程方向）畢業(yè)設(shè)計(jì)外文翻譯 2 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