块石路基对流特性实验研究

Experimental Study of Convective Characteristics of Block-Stone Embankment

利用块石层调控冻土路基地温是冻土工程主动冷却路基的一种重要措施,并在青藏铁路重大工程建设中得到广泛应用.通过块石层中空气流动特性的深入研究,对其结构优化和效能提升具有重要意义,而不同温差条件下块石层中空气的流动特性,以及微风速的实际测定一直是其中亟待解决的问题.通过高精度微风速探测,首次获得封闭条件下块石层的空气流动特征.结果表明:在边界温度波动条件下,块石层内的降温过程与其内部自然对流过程密切相关,在对流作用下快速完成降温过程;升温过程则在相对较长时段内主要由内部的热传导换热完成,由此导致温度变化曲线非对称这一特殊现象的出现,并随深度增加而愈加明显.块石层上下端面的温差是对流发生及强度的关键控制因素,当温差达到一定量值时流速随温差的增加而加大,同时空气温度的变化也会对空气流动过程产生影响;块石层内整个空气流动过程是一个传递过程,也是热量传递的过程.该实验研究结果将对该种工程措施机理的进一步认识和改进、相关模拟计算参数的选取,以及在冻土区高等级公路等重大工程建设中的进一步有效应用均具有重要意义.

Active cooling embankment made of block-stone in permafrost regions is an important engineering measure,which has been widely used in national key projects,such as Qinghai-Tibet Railway.So it is great significant to study air flow characteristics for its structural optimization and performance improvement,and air flow characteristics in block-stone due to temperature difference and micro wind speed are always the problems that need to be solved.In this study,air flow characteristics in block-stone are got at the first time by high-precision macro wind-speed detector.It is found that the cooling process is closely related to the process of natural convection in block-stone in the condition of boundary temperature fluctuating and rapidly completing in the convective process;warming-up process is largely aroused by the heat conduction,which results in asymmetry of the temperature curve,and becomes obvious with depth increasing;however,the convective process exists only in the processes of fast cooling stage and cooling stagnation stage;temperature difference in block-stone is the key control factor of the convection and its intensity;when temperature difference reaches a certain value,convective velocity increases with temperature difference,meanwhile the change of air temperature also have an impact on the air flow process.Air flow process in block-stone is a transfer process.The experimental results have a great significance for further understanding the cooling mechanism,improving this measure and selecting the relevant simulation parameters,effectively applying to high-grade highway construction in permafrost regions as well.