多年冻土区铁路路基导热系数监测与分析

为分析冻融过程、 道砟覆盖及降雨对多年冻土区铁路路基土体导热系数的影响， 对青藏高原多年冻土区铁路路基试验段和天然地表土体开展导热系数、 温度、 水分原位监测。结果表明： 融化期导热系数波动均明显大于冻结期， 天然场地导热系数在冻结期大于融化期， 而无道砟覆盖路基土体和道砟覆盖路基土体的导热系数在冻结期小于融化期， 与通常的认知和温度场模拟取值相反； 道砟层的保温和阻水效应导致道砟覆盖路基土体含水量和导热系数均小于无道砟覆盖路基土体， 冻结期路基土体导热系数有减小趋势， 道砟覆盖路基土体尤为显著； 降雨入渗增大土体导热系数， 低含水量的道砟覆盖路基土体导热系数对降雨的响应最强烈。寒区路基工程数值模拟时， 应考虑水热变化对导热系数的影响， 不宜采用固定相变区间的分段函数或阶跃函数预估导热系数。

Monitoring and analysis of the thermal conductivity of railway subgrade in the permafrost regions

In order to analyze the effects of freezing and thawing process， ballast cover and rainfall on thermal conductivity， the in-situ monitoring of thermal conductivity， temperature and moisture of subgrade and natural soil in the test section of permafrost railway roadbed was carried out in the Qinghai-Tibet Plateau. The results show that the fluctuation of thermal conductivity during the melting period is more obvious than the freezing period. The thermal conductivity during the thawing period is larger than the freezing period in natural site， but the thermal conductivities of gravel soil subgrade and ballast covered subgrade during the freezing period are smaller than the thawing period. The monitoring results of subgrade soil are contrary to the general cognition and simulation value of temperature field. Moisture content and thermal conductivity of gravel soil subgrade are higher than ballasted subgrade soil due to the thermal insulation and water blocking effects of ballast layer. Meanwhile， the thermal conductivity of subgrade soil during freezing period tends to decrease， especially for the ballast subgrade soil. The rainfall infiltration increases the thermal conductivity of the soil. And the thermal conductivity of the low water content ballast subgrade has a considerable response to rainfall. In the numerical simulation of railway subgrade engineering in cold area， the influence of hydrothermal change on thermal conductivity should be considered. It is not appropriate to use the piecewise function or step function of the fixed phase change interval to estimate the thermal conductivity.