【正文】 2 C0 ； 3 、 11 月份高約 1 C0 ； 4 、 5 、 9 和 10 月份基本相同 ； 6 月份和 8 月份低約 C0 ； 7 月份低約 2 C0 。 4. 2 計算結(jié)果 圖 3 和圖 4 給出了我們預(yù) 測的隧道壁溫隨洞口氣溫變化的情況，圖 5 和圖 6給出了我們預(yù)測的不同部位圍巖開始形成多年凍土的起始年份和多年凍土形成后圍巖的年最大融化深度 。 3 計算實例 按以上所述的模型及計算方法，我們對大興安嶺西羅奇 2 號隧道內(nèi)氣溫隨洞曰外氣溫變化的規(guī)律進(jìn)行了模擬計算驗證，所得結(jié)果與實測值 [6]相比較 ， 基本規(guī)律一致 。 冬季祁連山 區(qū)盛行西北風(fēng)，氣流將從隧道出曰流向進(jìn)口端，夏季雖然祁連山區(qū)盛行東偏南風(fēng)，但考慮到洞口兩端氣壓差、溫度壓差以及進(jìn)出口地形等因素，洞內(nèi)氣流仍將由出口北端流向進(jìn)口端 。 especially , the maximum monthlyaverage air temperature of 1979 was not for July but for August. 4 Prediction of the freezethaw conditions for the Dabanshan Tunnel 4 .1 Thermal parameter and initial and boundary conditions Using the elevation of 3 800 m and the yearlyaverage air temperature of 3℃ , we calculate the air density p=0 .774 kg/m3 .Since steam exists In the air, we choose the thermal capacity with a fixed pressure of air ),./( 0 CkgkJC p ? heat conductivity )./( 02 CmW???? and the dynamic viscosity )../( 6 smkg???? After calculation we obtain the thermal diffusivity a= 1 .3788 sm /10 25?? and the kinematic viscosity， sm / 25???? . Considering that the section of automobiles is much smaller than that of the tunnel and the automobiles pass through the tunnel at a low speed， we ignore the piston effects， ing from the movement of automobiles， in the diffusion of the air. We consider the rock as a whole ponent and choose the dry volumetric cavity 3/2400 mkgd ?? ,content of water and unfrozen water W=3% and W=1%, and the thermal conductivity cmW ou ./?? , cmW of ./?? ,heat capacity ckgkJC oV ./? and duf W wC ????? 1 )( , duu W wC ????? 1 )( According to the data observed at the tunnel site， the maximum monthlyaverage wind speed is about 3 .5 m/s， and the minimum monthlyaverage wind speed is about 2 .5 m/s .We approximate the wind speed at the entry and exit as )/]()7(0 2 [)( 2 smttv ???? , where t is in month. The initial wind speed in the tunnel is set to be .0),0(),)(1(),0( 2 ??? rxVRrUrxU a The initial and boundary values of temperature T are set to be where f(x) is the distance from the vault to the permafrost base， and R0=25 m is the radius of domain of solution T. We assume that the geothermal gradient is 3%， the yearlyaverage air temperature outside tunnel the is A=3 C0 ， and the amplitude is B=12 C0 . As for the boundary of R=Ro， we first solve the equations considering R=Ro as the first type of boundary。 v is the kinematic viscosity of air。 R is the equivalent radius of the tunnel section。 用此模型對大興安嶺西羅奇 2 號隧道的洞內(nèi)氣溫分布進(jìn)行了模擬計算，結(jié)果與實測值基本一致 。 f? , u? 分別為凍、融狀態(tài)下的熱傳導(dǎo)系數(shù)， fC ，uC 分別為凍、融狀態(tài)下的體積熱容量， X=(x,r) ， )(t? 為凍、融相變界面 ， To為巖石凍結(jié) 臨界溫度 (這里具體計算時取 To= C0 )， hL 為水的相變潛熱 。 根據(jù)現(xiàn)場觀測資料，我們將進(jìn)出口氣溫擬合為年平均分別為 5 C0 和 C0 ，年變化振幅分別為 C0 和 C0 的正弦曲線 .隧道的當(dāng)量直徑為 m， 沿程阻力系數(shù)取為 洞口的風(fēng)速、壓力及氣溫的影響小得多，我們這里參考使用了大坂山隧道的資料 。 （ 2）由于隧道內(nèi)部（距進(jìn)出口 100 m以上，特別是靠中心地段）受地?zé)嶙饔幂^強(qiáng)，洞內(nèi)平均壁溫的年變化振幅降低 。 考慮到圍巖在施土過程中己經(jīng)預(yù)冷，我們這里從幾月份算起，在同一邊值下進(jìn)行迭代，直到該邊值下的溫度場基本穩(wěn)定后，再令邊值依正弦規(guī)律變化，逐時段進(jìn)行求解 (可以證明，很多時段后的解，將不依賴于初值的選擇 )。 進(jìn)出口氣溫年變化規(guī)律由現(xiàn)場觀測資料，用正弦曲線擬合，圍巖內(nèi)計算區(qū)域的邊界按現(xiàn)場多年凍土下限和地?zé)崽荻却_定出適 當(dāng)?shù)臏囟戎祷驕囟忍荻?。 由于大坂山地區(qū)隧道施工現(xiàn)場平均氣溫為負(fù)溫的時間每年約長 8 個月，加之施工時間持續(xù)數(shù)年，圍巖在施土過程中己經(jīng)預(yù)冷，所以隧道開通運營后，洞內(nèi)氣體流動的形態(tài)主要由進(jìn)出口的主導(dǎo)風(fēng)速所確定，而受洞內(nèi)圍巖地溫與洞外氣溫的溫度壓差的影響較小 。 (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 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 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 independently solve those equations concerning the temperature of air flow 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 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 the same as in reference [3]. Determination of thermal parameters and initial and boundary conditions Determination of the thermal parameters. Using p= H， we calculate air pressure p at elevation