隧道与城轨道交通工程土木外文翻译原文和译文

1、百度文库-让每个人平等地提升自我隧道与城市轨道交通工程土木外文翻译原文和译文A convection-con duct ion model for an alysisof the freeze-thawcon diti ons in the surro unding rock wall of atunnel in permafrost regi onsAbstractBased on the an alyses of fun dame ntal meteorological and hydrogeologicalconditions 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 surro unding has bee n con structed. Using the model, the air temperature distribution in the Xiluoqi No. 2 Tunnel has been simulatednumerically. The simulated results are in agreement withth

3、e data observed. Then, based on the in situ conditions of sir temperature, atmospheric pressure, wind force, hydrogeology and engineering geology, the air-temperature relationshipbetween the temperature on the surfaceof 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 un der con struct ion is predicted.Keywords: tunnel in cold regi ons, conv ective heat excha nge and con ducti on, freeze-thaw.A number of highway and railway tunnels have been constructed in the permafrost regions an

5、d theirneighboringareas in China. Since thehydrological and thermalconditionschanged after a tunnel wasexcavated , the surrounding wall rock materials often froze, the frost heav ing caused damage to the liner layers and seep ing water froze into ice diam onds , which seriously in terfered with the

6、com muni catio n and transportation. Similar problems of the freezing damage in the tunnels also appeared in other countrieslike Russia, Norway and Japan .Henee itis urge nt to predict the freeze-thaw con diti ons in the surro unding rock materials and provide a basis for the desig n , con struct io

7、nand maintenanceof new tunn els in cold regi ons.Many tunnels , constructed in cold regions or their neighbouring areas , pass through the part beneath the permafrost base .After a tunnel is excavated , the originalthermodynamical conditions in the surroundingsare and thaw destroyed and replaced mai

8、nly by the air connections without the heat radiati on, the con diti onsdeterm ined prin cipallyby thetemperature and velocity of air flow in the tunnel, the coefficients ofconvective heat transfer on the tunnel wall , and the geothermal heat. In order to analyze and predict the freeze and thaw cond

9、itions of the surrounding wall rock of a tunnel , presuming the axial variationsof airflow temperature and the coefficientsof convective heat transfer,Lunardini discussed the freeze and thaw con diti ons by the approximateformulae obtained by Sham-sundar in study of freezing outside a circular tube

10、with axial variati ons of coola nt temperature .We simulated the temperature conditions on the surface of a tunnel wall varying similarly to the periodic changes of the outside air temperaturen fact, thetemperatures of the air and the surrounding wall rock material affect each other so we cannot fin

11、d the temperature variations of the air flow in advanee; furthermore, it is difficult to quantify the coefficient ofconvective 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 tem

12、perature n this paper, we combine the air flow conv ectiveheat ex-cha nge and heat con duct ionin thesurro unding rock material in to one model , and simulate the freeze-thaw conditions of the surroundingrock material based on the in situconditions of air temperature, atmospheric pressure , wind for

13、ce at theentry and exit of the tunnel, and the conditions of hydrogeology andengin eeri ng geology.Mathematical modelIn order to con struct an appropriate model, we n eed the in situfun dame ntal con diti ons as a ba-sis .Here weuse the con diti ons at the sce ne of the Dabanshan Tunnel. The Dabansh

14、an Tunnel is lo-toted 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 no rtheast.Si nee the mon thly-average air temperature is ben eath O C for eig

15、htmon ths at the tunnel site each year and the con structi on would last forseveral years , the surrounding rock materials would becomecooler during the con struct ion .We con clude that, after excavati on, the patter n of air flow would depend mainly on the dominant wind speed at the entry and exit

16、 , and the effects of the temperature differe nee betwee n the in side andoutside of the tunnel would be very small .Since the dominant wind directi on is n ortheast at the tunnel site in win ter, the air flow in thetunnel would go from the exit to the entry. Even though the dominant wind trend is s

17、outheastly in summer, considering the pressure differenee, the temperature differeneeand the topography of the entry and exit , the airflow in the tunnel would also be from the exit to entry .Additi on ally,since the wind speed at the tunnel site is low, we could consider thatthe air flow would be p

18、rin cipally lami nar.Based on the reasons mentioned , wesimplify the tunnel to a round tube and consider that the air flow and temperature are symmetrical about the axis of the tunnel , Ignoring the in flue nee of the air temperature on the speed of air flow, we obta in the follow ing equatio n:wher

19、e t , x, r are the time , axial and radial coordinates; U, V arethat is , air pressure dividedaxial and radial wind speeds; T is temperature; p is the effective pressure by air density ; v is the kinematic viscosityof air; a is the thermal conductivityof air; L is the length of the tunnel;R is the e

20、quivale ntradius of the tunnel sect ion; D is the len gth of timeafter the tunnel con structi on;,t , t arefrozen and thawed parts in the surrounding rock materialsrespectively; ,and , are thermal con ductivities and volumetric thermal capacities in frozen and thawed parts respectively; X x , r, t i

21、sphase cha nge front;Lh is heat late nt of freez ing water; and To is criticalfreez ing temperature of rock here we assume ToC .used for sol ving the modelEquati on 1 shows flow. We first solve those concerning temperatureat that the temperature of the surrounding rock does not affect the speed of a

22、ir equati ons concerning the speed of air flow, and the n solve those equati ons every time elapse.2. 1 Procedure used for solvingthe continuity and momentumequati onsSince the first three equati ons in 1 are not in depe ndent wederive the sec ond equati on by xand the third equation by r. Afterprel

23、iminary calculationwe obtainthe following elliptic equation concerning the effective pressure p:The n we solve equati ons in 1 using the follow ing procedures:i Assume the values for U0, VO;ii substituting UO, VO into eq. 2, and solving 2,weobta in pO;iii sol vingthe first and sec ond equati onsof 1

24、 , weobtain UO,V1;iv solving the first and third equations of 1,we obtain U2 ,V2;v calculat ing the mome ntum-average of U1,v1 and U2 , v2, weobtain the new UO , VO;the n return to ii ;vi iterating as above until the disparity of those solutionsin twoconsecutive iterationsis sufficiently small or is

25、 satisfied , wethen takethose values of p0 , U0 and V0 as the initial values for the next elapse and solve those equati ons concerning the temperature.2 .2 En tire method used for sol ving the en ergy equatio nsAs mentioned previously , the temperature field of the surrounding rock and the air flow

26、affect each other. Thus the surface of the tunnel wall is both 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 independen

27、tly solve those equations concerning the temperature of air flow and those equati ons concerning the temperature of the surroundingrock n order to cope with this problem , wesimulta neously solve the two groups of equati ons based on the fact that at the tunnel wall surface both temperatures are equ

28、al We should bear in mind the phase cha nge while sol ving those equati ons concerning the temperature of the surrounding rock , and the convection while solving those equatio ns concerning the temperature of the air flow, and we only need to smooth those relative parameters at the tunnel wall surfa

29、ce .The sol ving methods for the equati ons with the phase cha nge are the same as in refere nee 3.Determ in atio nof thermal parameters and in itial and boun darycon diti ons.Determ in ati onof the thermal parameters. Using p H , we calculateair pressure p at elevation H and calculate the air densi

30、ty using formula P/GT where T is the yearly-average absolute air temperature, and G isthe humidity constant of air. Letting be the thermal capacity with fixed pressure, the thermal con ductivity,and the dyn amic viscosity of air flow, we calculate the thermalconductivityand kinematic viscosity using

31、 the formulas and.The thermalparameters of the surro unding rock are determ ined from the tunnel site.2 . Determ in ati onof the in itialand boun dary con diti ons .Choose theobserved mon thly average wind speed at the entry and exit as boun dary conditions of wind speed , and choose the relative ef

32、fective pressure p 0 at the exit that is, the entry of the dominant wind trend and onthe section of entry that is, the exit of the dominant wind trend,where k is the coefficie nt of resista nee along the tunnel wall, d 2R,and v is the axial average speed. We approximate T varying by the sine law acc

33、ord ing to the data observed at the sce ne and provide a suitable boun dary value based on the positi on of the permafrost base and the geothermal gradie nt of the thaw rock materials ben eath the permafrost base.A simulated exampleUsing the model and the solvingmethod mentioned above , wesimulate t

34、he 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 observed6.The Xiluoqi No .2 Tunnel is located on the Nongling railway inno rtheaster n China and passes through the

35、part ben eath the permafrostbase .It has a length of 1 160 mrunning from the northwest to the southeast, with the entry of the tunnel in the northwest , and the elevation is about 700 m. The dominant wi nd direct ion in the tunnel is from n orthwest to southeast, with a imum mon thly-average speed o

36、f 3 m/s and a minimummonthly-average speed of 1 .7 m/s . Based on the data observed, weapproximate the varying sine law of air temperature at the entry and exit with yearly averages of -5 C, C and amplitudes of C and C respectively. The equivale nt diameter is 5 .8m, and the resista nt coefficie nt

37、along the tunnel wall is e the effect of the thermal parameter of the surro undingrock on the air flow is much smaller than that of wind speed, pressureand temperature at the entry and exit , we refer to the data observed in the Daba nsha n Tunnel for the thermal parameters.Figure 1 shows the simula

38、ted yearly-average air temperature in side and at the entry and exit of the tunnel compared with the data observed .We observe that the differenee is less than 0 2 C from the entry to exit.Figure 2 shows a comparisonof the simulated and observedmonthly-average air temperature in-side distaneegreater

39、 than 100 mfromthe entry and exit thetunnel. Weobserve that the principallaw is almostthe same, and the main reason for the differenee is the errors thatcamefrom approximating the varying sine law at the entry and exit; especially , the imummonthly-average air temperature of 1979 was not for July bu

40、t for August.Comparison of simulated and observed air temperature in XiluoqiTunnel in ,simulated values;2,observed valuescomparis on of simulated and observed air temperature in sideThe Xiluoqi Tunnel in ,simulated values;2,observed valuesPredict ion of the freeze-thaw con diti ons for the Daba nsha

41、 n Tunnel4 .1 Thermal parameter and in itial and boun dary con diti onsUsing the elevation of 3 800 mand the yearly-average air temperature of -3 C , we calculate the air density p 0 .774 kg/ steam exists In theair, we choose the thermal capacity with a fixed pressure of air heatcon ductivity andand

42、 the dyn amic viscosity After calculati on we obta in the thermal diffusivity a 1 .3788 and the kin ematic viscosity,Con sideri ng that the sect ion of automobiles is muchsmaller tha n that of the tunnel and the auto-mobiles pass through the tunnel at a low speed, we ignore the piston effects, comin

43、g from the movement of automobiles ,in the diffusi on of the air.Weconsider the rock as a whole component and choose the dry volumetric cavity content of water and unfrozen water W3%and W1%, and the thermal con ductivity ,heat capacity and ,Accord ing to the data observed at the tunnel site , the im

44、um monthly-averagewind speed is about 3 .5 m/s , and the minimummonthly-average wind speed is about 2 .5 m/s .We approximate the wind speed at the entry and exit as , where t is in mon th. The in itial wind speed in the tunnel is set to beThe initial and boundary values of temperature T are set to b

45、ewhere f x is the dista nee from the vault to the permafrost base,and RO 25 m is the radius of do-main of solution T. We assume that the geothermal gradient is 3%, the yearly-average air temperature outsidetunnel the is A -3, and the amplitude is B 12.As for the boun dary of R Ro, we first solve the

46、 equationscon sideri ng R Ro as the first type of boun dary; that is we assume thatT f x 3%on R Ro. We find that, after one year, the heat flow trend willhave cha nged in the range of radius betwee n 5 and 25m in the surrounding rock. Considering thatthe rock will be cooler hereafter and it will bea

47、ffected yet by geothermal heat, we appoximately assumethat the boundary R Ro is the second type of boundary; that is , we assume that the gradient value , obtained from the calculationup to the end of the first year afterexcavati on un der the first type of boun dary value, is the gradie nt on RRo o

48、f T.Con sideri ng the surro unding rock to be cooler duri ng the periodof construction, we calculatefrom January and iterate someelapses of time under the sameboundary.Then we let the boun daryvalues vary and solve the equations step by step it can be proved that the solution will not depend on the

49、choice of initial values after many time elapses .1 The yearly-average temperature on the surface wall of the tunnelis approximately equal to the ai4 .2 Calculated resultsFigures 3 and 4 show the variationsof the monthly-averagetemperatures on the surface of the tunnel wall along with the variations

50、 at the entry and exit .Figs .5 and 6 show the year when permafrost begins to form and the imum thawed depth after permafrost formed in differe nt surro unding secti ons.mon thly-average temperature aris on of the mon thly-On the surface of Dabanshan , average temperature on the surfaceThe month,I 1

51、,2,3,12tunnel with that outside thetunn el.1,i nnertemperature on thesurface;2,outside air temperatureyear whe n permafrost imum thawed depth afterBeg ins to from in differe nt permafrost formed in differe nt yearsSecti ons of the surro undingrock4 .3 Prelimi nary con clusi onBased on the in itial-b

52、o un dary con diti ons and thermal parametersmen ti oned above, we obtai n the followi ng prelimi nary con clusi ons:r temperature at the entry and exit. It is warmer during the coldseas on and cooler duri ng the warm seas on in the internal part more tha n 100 m from the entry and exit of the tunne

53、l than at the entry and exit . Fig .1 shows that the internalmonthly-average temperature on the surfaceof the tunnel wall isC higher in Janu ary, February and December, 1Chigher in March and October, and 1 .6 C lower in June and August, and 2qC lower in July than the air temperature at the entry and

54、 exit. In othermon ths the in fernal temperature on the surface of the tunnel wall approximately equals the air temperature at the entry and exit.2 Si nee it is affected by the geothermal heat in the in ternalsurrounding seetion , especially in the eentral part, the internal amplitude of the yearly-

55、average temperature on the surface of the tunnel wall decreases and is 1 .6C lower tha n that at the entry and exit.3 Un der the con diti ons that the surrounding rock is compact ,without a great amount of under-ground water, and using a thermal in sulat ing layer as desig ned PU with depth of m and

56、 heat con ductivity W/nC, FBTwith depth of m and heat conductivity mC , in the third yearafter tunnel con struct ion , the surro unding rock will begi n to form permafrost in the range of 200 m from the entry and exit .In the first and the sec ond year after con structi on, the surro unding rock wil

57、l beg in to form permafrost in the range of 40 and 100m from the entry and exit respectively n the central part , more than 200mfrom the entry and exit, permafrost will beg in to form in the eighth year. Near the cen ter of the tunnel , permafrost will appear in the 14-15th years. During the first a

58、nd second years after permafrost formed, the imumof annual thawed depth is large especially in the cen tral part of the surro unding rock sect ion and thereafter it decreases every year. The imum of annual thawed depth will be stable un til the 19-20th years and will rema in in s range of 2-3m.4 If permafrost forms entirelyin the surrounding rock , thepermafrost will provide a water-i