【作者】 卞晓琳；

【导师】 何平；

【作者基本信息】 北京交通大学 ， 岩土工程， 2012， 博士

【摘要】 抛石路基作为一种主动冷却路基的工程措施在青藏铁路建设中得到了广泛应用,其降温过程主要是通过抛石层内空气的对流换热作用实现。在青藏高原这样一个特定的气候条件下,由大气风场引起的强迫对流在抛石层内空气的对流换热过程中起主导作用。因此,研究大气风场与抛石路基内流速场、温度场的关系对明确抛石路基的降温机理、指导抛石路基的设计具有重要意义。本文在前人的研究基础上,通过室内试验、数值模拟、理论推导及现场测试等手段对抛石路基通风性能进行了系统研究,重点研究了抛石路基中强迫对流作用对抛石路基降温效果的影响。(1)对粒径分别为5-8cm,8-15cm和15-20cm的抛石组进行了系统地室内试验,研究了边界温度变化条件下自然对流的形成机制以及抛石层内风速场和温度场的变化规律,提出了抛石层内自然对流流速与对流传热温差的函数关系式。(2)对抛石护坡路基和抛石路基的通风性能进行了系统的现场试验,重点研究了块碎石护坡和块石路基两种结构在通风条件下的强迫通风特性以及抛石层内部流速场、温度场与外界大气风场的关联变化规律。此外,通过对抛石层通风性能现场试验数据的理论分析,研究提出了大气风场与强迫对流在抛石路基降温过程中所占影响权重的关系。(3)基于多孔介质中流体热对流的连续性方程、非达西流动量方程和能量方程,对强通风条件下青藏铁路典型抛石护坡路基内温度场和流速场的分布规律进行了数值模拟研究。(4)通过对抛石层通风性能现场试验数据的理论分析研究了流动阻力与流速的关系。结果表明,Ergun型方程能较好地反映抛石层中孔隙形状和粘性的影响,故可以用于抛石路基内流动阻力的分析计算。以实际工程为例计算了抛石路基的阻力系数,并对实测最大风速条件下的影响深度进行了分析,结果表明在实测最大风速情况下,大气风场对块石护坡阳坡的影响深度最大,约为47cm。更多还原

【Abstract】 Riprap embankment is widely used in Qinghai-Tibetan railway as a measure for cooling the permafrost. The cooling effect of riprap is achieved by convective heat transfer in embankment. Because of the particular weather conditions, forced convection usually plays the leading role during convective heat transfer in embankment in the Qinghai-Tibet Plateau. So, it is meaningful to make clear the relationship between atmospheric wind field and velocity and temperature fields in embankment, which will provide a useful basis for the riprap embankment engineering design in Qinghai-Tibet railway engineering.The ventilation performance of riprap embankment will be investigated in this study through multiple method including laboratory tests, in-situ tests, numerical simulation and theoretical analysis. And more attention was paid to clarify that the convection mechanism and its affect on cooling effect of riprap embankment.(1) Laboratory tests of different grain size including5-8cm,8-15cm and15-20cm were performed to study the formation mechanism of free convection and the characteristics and distributional pattern of temperature and velocity in riprap layer. The relation equation of natural convection velocity with temperature difference was proposed based the laboratory results.(2) In-situ tests of riprap cooling embankment and riprap slope embankment were also performed and compared to study the ventilation characteristics of riprap layer. The focus of this study is to make clear the ventilation characteristics of layer under forced convection condition and achieve the change rule of temperature and velocity with external wind condition of riprap layer. Wind speed and forced convection contribution on cooling process was studied based on the in-situ tests results.(3) Based on the continuity, non-Darcy momentum and energy equations for convection of incompressible fluid in porous media, and considering outside wind condition, the mathematical model of convective heat transfer for open riprap embankment in permafrost regions was established, and verified by in-situ monitoring data. Then, the velocity and temperature fields of open riprap embankments were studied numerically in permafrost regions along the Qinghai-Tibet railway.(4) According to the convection, conduction and fluid-solid coupled heat transfer theories, the important relationship between flow resistance and velocity was achieved based the theoretical analyses to in-situ monitoring data and test results. Besides, the influence depths of atmospheric wind field to riprap layer were calculated and analyzed through a practical project, and the calculation results show that the influence depths of atmospheric wind field to riprap layer was47cm. Those conclusions provide a basis for the solution of the technical problems in roadway construction in cold regions, such as choosing the reasonable embankment style, design parameters and so on.更多还原