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提出了应用线热源法测量冻土热参数存在的问题,冻土中未冻水含量随温度的变化是导致线热源法测量误差产生的根本原因。对二维无限大——点热源热传导方程进行简化得到一维中心对称——热流边界热传导方程。采用双针法对不同温度的环刀土样进行了测试并对冻土传热过程进行数值试算,反演得到不同温度的相变热容和未冻水含量。结果表明:当温度大于-0.7℃时,相变热容值远远大于冻土体积热容并且随温度急剧变化,线热源法测量的结果严重失真;当温度介于-0.7~-4℃时,线热源法测量结果仍有较大的误差;当温度低于-4℃时,相变热容值很小且比较稳定,线热源法测量的热参数能满足一定的精度要求。
The problems existing in the determination of the thermal parameters of frozen soil by the line heat source method are put forward. The change of the unfrozen water content in the frozen soil with temperature is the root cause of the measurement error of the line heat source method. The one-dimensional central symmetry-heat flow boundary heat conduction equation is simplified by simplifying the two-dimensional infinite-point heat conduction equation. A double-needle method was used to test the ring cutter with different temperatures. The heat transfer of the frozen soil was numerically evaluated. The phase change heat capacity and unfrozen water content were obtained by inversion. The results show that when the temperature is higher than -0.7 ℃, the heat capacity of phase transition is much larger than the volume heat capacity of permafrost and it changes rapidly with the temperature. The result of linear heat source method is seriously distorted. When the temperature is between -0.7 ~ -4 ℃ , The measured results of the line heat source method still have a large error; when the temperature is below -4 ℃, the phase transition heat capacity value is small and relatively stable, the thermal parameters measured by the line heat source method can meet certain accuracy requirements.