本文關鍵詞： 道路工程 多年凍土 片塊石路基 溫度場 數值模擬　出處：《西安科技大學》2015年碩士論文　論文類型：學位論文

【摘要】：“溫室效應”和人類工程活動加速了多年凍土的退化,導致多年凍土區(qū)的工程建設更加困難。為了增強多年凍土區(qū)公路路基的穩(wěn)定性,保護路基下部多年凍土,片塊石路基作為一種主動降溫措施得到了廣泛應用。但是,目前片塊石路基邊坡未進行覆蓋處理,減弱了片塊石路基對多年凍土的保護作用;其次,針對片塊石路基降溫效果的大規(guī)�，F場測試工作開展的較少,尤其缺乏對其長期作用效果的有效監(jiān)測。本論文通過片塊石路基降溫效果的室內模型試驗,結合野外試驗路路基溫度場實測數據,并選取適當的模型對片塊石路基的溫度場進行數值模擬,探討片塊石路基溫度場變化特征,揭示片塊石路基的降溫機理。為多年凍土區(qū)路基的設計、施工與維護提供科學依據,更好地保護路基下部多年凍土,減少多年凍土地區(qū)路基病害的發(fā)生,具有較高的學術價值和重要的工程意義。主要研究內容和結論如下:(1)為了探索片塊石層的傳熱特性,通過室內模擬試驗,對相同粒徑的片塊石層在不同的上邊界條件下降溫機理和降溫效果進行了研究。研究結果表明,在風的作用下,封閉邊界的片塊石層對外界的溫度變化不夠敏感,降溫速度較開放邊界要慢,此時主要以自然對流為主,依靠內部空氣自然對流傳熱來實現對其底部土層的降溫效果;開放邊界條件下,片塊石內部主要以強制對流為主,依靠外界負溫環(huán)境下風的作用在其內部形成強制對流,以強制對流傳熱的方式來實現降溫的。(2)依托青藏公路五道梁段片塊石路基實體觀測工程,對比分析了片塊石路基和普通路基的溫度場變化過程,驗證了片塊石路基的主動降溫效果。監(jiān)測結果表明,相對于一般填土路基而言,片塊石路基很好地發(fā)揮了“熱二極管”效應,寒季能增加路基的蓄冷量,暖季可以有效阻止外界熱空氣進入路基,對于防止多年凍土融化、主動保護凍土起到了積極有效的作用。(3)基于多孔介質不可壓縮流體的對流理論,建立了多年凍土區(qū)片塊石路基的對流換熱數值計算模型,并與野外實測數據進行對比驗證,證明該模型是合理可靠的。利用該模型對片塊石路基的速度場和溫度場進行數值模擬。數值計算結果表明,寒季片塊石層內自然對流最強烈,內部存在對流渦包,降溫效果顯著,可以大量引入外界冷能進入路基體;暖季,片塊石層內部未見空氣流動,自然對流消失,片塊石層起到保溫隔熱作用,能阻擋外界熱量進入路基內部。對片塊石路基的長期熱穩(wěn)定性研究表明,片塊石路基在短期內降溫效果明顯,從長遠分析,綜合考慮全球氣候變暖和瀝青路面的強吸熱性,片塊石單獨應用于多年凍土地區(qū)公路路基中難以發(fā)揮主動降低地溫、保護多年凍土和維護路基熱穩(wěn)定性的作用,必須進行補強。
[Abstract]:"Greenhouse Effect" and human engineering activities have accelerated the degradation of permafrost, making it more difficult to build permafrost regions. As a kind of active cooling measure, the slice block roadbed has been widely used. However, at present, the slope of the block stone roadbed has not been covered, which weakens the protective effect of the block stone roadbed on permafrost. Secondly, The large scale field test for the cooling effect of rock subgrade is less, especially the effective monitoring of its long-term effect. In this paper, the laboratory model test of the cooling effect of rock block roadbed is carried out. Combined with the measured data of roadbed temperature field in field test road, and selecting appropriate model to simulate the temperature field of rock block roadbed, the variation characteristics of temperature field of rock block roadbed are discussed. This paper reveals the mechanism of cooling of subgrade with block rock, provides scientific basis for the design, construction and maintenance of embankment in permafrost region, better protects the permafrost in the lower part of roadbed, and reduces the occurrence of roadbed disease in permafrost region. It has high academic value and important engineering significance. The main research contents and conclusions are as follows: 1) in order to explore the heat transfer characteristics of the lamellar layer, the laboratory simulation test is carried out. The cooling mechanism and cooling effect of the lamellar layer with the same diameter under different upper boundary conditions are studied. The results show that the lamellar layer with closed boundary is insensitive to the outside temperature change under the action of wind. The cooling rate is slower than the open boundary. At this time, the natural convection is the main factor, and the internal natural convection heat transfer is relied on to realize the cooling effect on the bottom soil layer; under the open boundary condition, the internal convection is mainly forced convection. Relying on the action of wind in the negative temperature environment to form forced convection in its interior and to realize cooling by forced convection heat transfer. (2) relying on the solid observation project of block rock subgrade in the section of five beams of Qinghai-Tibet Highway, The variation process of temperature field of block rock subgrade is compared with that of ordinary subgrade, and the active cooling effect of block stone subgrade is verified. The monitoring results show that, compared with general fill subgrade, the temperature field of block rock subgrade is different from that of normal embankment. The "thermal diode" effect is well played by the block rock subgrade. In the cold season, the storage capacity of the roadbed can be increased, and the warm season can effectively prevent the external hot air from entering the roadbed, thus preventing the permafrost from thawing. Based on the convection theory of incompressible fluid in porous media, a numerical calculation model of convection heat transfer of a piece of rock subgrade in permafrost region is established and compared with the field measured data. It is proved that the model is reasonable and reliable. The velocity field and temperature field of rock subgrade are numerically simulated by using the model. The numerical results show that the natural convection is strongest and the convection vortices exist inside the subgrade in cold season. The cooling effect is remarkable, the external cold energy can be introduced into the roadbed in large quantities; in the warm season, there is no air flow inside the lamellae, the natural convection disappears, and the lamellae plays the role of heat preservation and insulation. The study on the long-term thermal stability of the block subgrade shows that the cooling effect of the subgrade is obvious in the short term. In the long run, considering the strong heat absorption of the global climate warming and asphalt pavement, It is difficult to take the initiative to reduce the ground temperature, protect the permafrost and maintain the thermal stability of the roadbed.
【學位授予單位】：西安科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：U416.1

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