块石路基层中对流过程与温度特性关系试验研究

利用块石层调控路基地温是主动冷却路基的一种重要措施，块石层内部对流换热过程是冻土工程应用研究的重要内容之一，块石层中由低压或温差引起的空气流动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仪器，首次获得由温差引起的块石层空气流动特征。研究发现：块石层中对流过程和温度变化过程相互影响，在加速区和稳定区实现快速降温之后呈现缓慢降温过程；块石层内温差大于空气对流的启动温差时，自然对流速度和温差具有线性相关性；随着降温过程在相同温差条件下具有不同的对流特性；块石层上表面温度波动对内部温度波动的影响随深度而减弱，温度延迟性与深度呈线性相关性，块石层不同层位温度变化的非对称性由不同的传热方式和传热效率导致；在热传导期块石层存在热传导影响范围，为保证降温效果块石层厚度需大于热传导范围。研究成果为理论分析和数值模拟提供直接的有力支持以及对该种措施降温机制的进一步认识和改进都具有重要意义。

Experimental study of relation between convection process and temperature characteristics of block-stone layer

Active cooling roadbed employed block-stone layer in permafrost regions is an important engineering measure.Thereinto,it is one of the important contents of frozen-soils engineering applied research to study the convection heat transfer process of block-stone layer,and the actual determination of micro wind speed in block-stone layer resulting from low pressure or temperature difference has always been being one of the problems to be solved.This study has got air flow characteristics in block-stone layer for the first time by high-precision micro wind-speed detector.The results indicate that the convection process is closely related to the temperature change;the rapid cooling is completed in accelerating and stable stage,thereafter slowly cooling process;when the temperature difference in crushed-rock layer is higher than the start temperature difference,the correlation between natural convective velocity and temperature difference is linear.With the cooling process the convective characteristics is different in the same condition of temperature difference.The influence of surface temperature fluctuations on the bottom temperature along the depth direction weakened;and there is a linear correlation between retardancy of temperature and depth.The asymmetry of temperature change is caused by different heat transfer ways and heat transfer efficiencies.At the same time,there is the scope of heat conduction in block-stone layer,in order to ensuring the cooling effect thickness of block-stone layer must be greater than the scope of heat conduction.The experimental research results provide strong support for theoretical analysis and simulation and have a great significance for further understanding of cooling mechanism and improvement.