隧道与城市轨道交通工程土木外文翻译原文和译文.docx

1、隧道与城市轨道交通工程土木外文翻译原文和译文隧道与城市轨道交通工程土木外文翻译原文和译文 A convection-conduction model for analysis of the freeze-thawconditions in the surrounding rock wall of atunnel in permafrost regionsAbstractBased on the analyses of fundamental meteorological and hydrogeological conditions at the site of a tunnel in the

2、cold regions, a combined convection-conduction 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

3、 data observed. Then, based on the in situ conditions of sir temperature, atmospheric pressure, wind force, hydrogeology and engineering geology, the air-temperature relationship between the temperature on the surface of the tunnel wall and the air temperature at the entry and exit of the tunnel has

4、 been obtained, and the freeze-thaw conditions at the Dabanshan Tunnel which is now under construction is predicted.Keywords: tunnel in cold regions, convective heat exchange and conduction, freeze-thaw.A number of highway and railway tunnels have been constructed in the permafrost regions and their

5、 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 communica

6、tion 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 freeze-thaw conditions in the surrounding rock materials and provide a basis for the design，construction and maintenance o

7、f 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 connect

8、ions 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

9、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 Sham-sundar in study of freezing outside a circular tube with axial variations of

10、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 variat

11、ions 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,

12、 we combine the air flow convective heat ex-change and heat conduction in the surrounding rock material into one model，and simulate the freeze-thaw 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

13、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 ba-sis .Here we use the conditions at the scene of the Dabanshan Tunnel. The Dabanshan Tunnel is lo-toted on the highwa

14、y from Xining to Zhangye, south of the Datong River, at an elevation of 3754.78-3 801.23 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 monthly-average air temperature is beneath 0 C for eight months at the tunn

15、el site each year and the construction would last for several years，the surrounding rock materials would become cooler during the construction .We conclude that, after excavation, the pattern of air flow would depend mainly on the dominant wind speed at the entry and exit，and the effects of the temp

16、erature difference between the inside and outside of the tunnel would be very small .Since the dominant wind direction is northeast at the tunnel site in winter, the air flow in the tunnel would go from the exit to the entry. Even though the dominant wind trend is southeastly in summer, considering

17、the pressure difference, the temperature difference and the topography of the entry and exit，the air flow in the tunnel would also be from the exit to entry .Additionally，since the wind speed at the tunnel site is low，we could consider that the air flow would be principally laminar.Based on the reas

18、ons mentioned，we simplify the tunnel to a round tube and consider that the air flow and temperature are symmetrical about the axis of the tunnel，Ignoring the influence of the air temperature on the speed of air flow, we obtain the following equation:where t，x，r are the time，axial and radial coordina

19、tes; U，V are axial and radial wind speeds; T is temperature; p is the effective pressure that is，air pressure divided by air density ; v is the kinematic viscosity of air; a is the thermal conductivity of air; L is the length of the tunnel; R is the equivalent radius of the tunnel section; D is the

20、length of time after the tunnel construction;， t , t are frozen and thawed parts in the surrounding rock materials respectively; ,and , are thermal conductivities and volumetric thermal capacities in frozen and thawed parts respectively; X x , r ， t is phase change front; Lh is heat latent of freezi

21、ng water; and To is critical freezing temperature of rock here we assume To -0.1 .used for solving the modelEquation 1 shows flow. We first solve those concerning temperature at that the temperature of the surrounding rock does not affect the speed of air equations concerning the speed of air flow,

22、and then solve those equations every time elapse.2. 1 Procedure used for solving the continuity and momentum equations Since the first three equations in 1 are not independent we derive the second equation by xand the third equation by r. After preliminary calculation we obtain the following ellipti

23、c equation concerning the effective pressure p:Then we solve equations in 1 using the following procedures: i Assume the values for U0，V0; ii substituting U0，V0 into eq. 2 ，and solving 2 ，we obtain p0; iii solving the first and second equations of 1 ，we obtain U0，V1; iv solving the first and third e

24、quations of 1 ，we obtain U2，V2; v calculating the momentum-average of U1，v1 and U2，v2，we obtain the new U0，V0;then return to ii ; vi iterating as above until the disparity of those solutions in two consecutive iterations is sufficiently small or is satisfied，we then take those values of p0，U0 and V0

25、 as the initial values for the next elapse and solve those equations concerning the temperature.2 .2 Entire method used for solving the energy equations As mentioned previously，the temperature field of the surrounding rock and the air flow affect each other. Thus the surface of the tunnel wall is bo

26、th the boundary of the temperature field in the surrounding rock and the boundary of the temperature field in air flow .Therefore， it is difficult to separately identify the temperature on the tunnel wall surface，and we cannot independently solve those equations concerning the temperature of air flo

27、w and those equations concerning the temperature of the surrounding rock .In order to cope with this problem，we simultaneously solve the two groups of equations based on the fact that at the tunnel wall surface both temperatures are equal .We should bear in mind the phase change while solving those

28、equations concerning the temperature of the surrounding rock，and the convection while solving those equations concerning the temperature of the air flow, and we only need to smooth those relative parameters at the tunnel wall surface .The solving methods for the equations with the phase change are t

29、he same as in reference 3.2.3 Determination of thermal parameters and initial and boundary conditions. Determination of the thermal parameters. Using p 1013.25-0.1088 H，we calculate air pressure p at elevation H and calculate the air density using formula PGT where T is the yearly-average absolute a

30、ir temperature，and G is the humidity constant of air. Letting be the thermal capacity with fixed pressure, the thermal conductivity，and the dynamic viscosity of air flow, we calculate the thermal conductivity and kinematic viscosity using the formulas and. The thermal parameters of the surrounding r

31、ock are determined from the tunnel site.2 .3.2 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

32、wind trend and 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 bound

33、ary value based on the position of the permafrost base and the geothermal gradient of the thaw rock materials beneath the permafrost base.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 a