多年冻土区片块石结构路基降温效果研究

发布时间：2018-02-25 04:02

本文关键词： 道路工程多年冻土片块石路基温度场数值模拟　出处：《西安科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：“温室效应”和人类工程活动加速了多年冻土的退化,导致多年冻土区的工程建设更加困难。为了增强多年冻土区公路路基的稳定性,保护路基下部多年冻土,片块石路基作为一种主动降温措施得到了广泛应用。但是,目前片块石路基边坡未进行覆盖处理,减弱了片块石路基对多年冻土的保护作用;其次,针对片块石路基降温效果的大规模现场测试工作开展的较少,尤其缺乏对其长期作用效果的有效监测。本论文通过片块石路基降温效果的室内模型试验,结合野外试验路路基温度场实测数据,并选取适当的模型对片块石路基的温度场进行数值模拟,探讨片块石路基温度场变化特征,揭示片块石路基的降温机理。为多年冻土区路基的设计、施工与维护提供科学依据,更好地保护路基下部多年冻土,减少多年冻土地区路基病害的发生,具有较高的学术价值和重要的工程意义。主要研究内容和结论如下:(1)为了探索片块石层的传热特性,通过室内模拟试验,对相同粒径的片块石层在不同的上边界条件下降温机理和降温效果进行了研究。研究结果表明,在风的作用下,封闭边界的片块石层对外界的温度变化不够敏感,降温速度较开放边界要慢,此时主要以自然对流为主,依靠内部空气自然对流传热来实现对其底部土层的降温效果;开放边界条件下,片块石内部主要以强制对流为主,依靠外界负温环境下风的作用在其内部形成强制对流,以强制对流传热的方式来实现降温的。(2)依托青藏公路五道梁段片块石路基实体观测工程,对比分析了片块石路基和普通路基的温度场变化过程,验证了片块石路基的主动降温效果。监测结果表明,相对于一般填土路基而言,片块石路基很好地发挥了“热二极管”效应,寒季能增加路基的蓄冷量,暖季可以有效阻止外界热空气进入路基,对于防止多年冻土融化、主动保护冻土起到了积极有效的作用。(3)基于多孔介质不可压缩流体的对流理论,建立了多年冻土区片块石路基的对流换热数值计算模型,并与野外实测数据进行对比验证,证明该模型是合理可靠的。利用该模型对片块石路基的速度场和温度场进行数值模拟。数值计算结果表明,寒季片块石层内自然对流最强烈,内部存在对流涡包,降温效果显著,可以大量引入外界冷能进入路基体;暖季,片块石层内部未见空气流动,自然对流消失,片块石层起到保温隔热作用,能阻挡外界热量进入路基内部。对片块石路基的长期热稳定性研究表明,片块石路基在短期内降温效果明显,从长远分析,综合考虑全球气候变暖和沥青路面的强吸热性,片块石单独应用于多年冻土地区公路路基中难以发挥主动降低地温、保护多年冻土和维护路基热稳定性的作用,必须进行补强。
[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.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U416.1

【参考文献】