基于热参数和土水势变化的冻土冻结势研究
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摘要
针对冻土热参数、土水势在不同温度条件下的变化趋势缺乏统一表述的问题,提出了冻土冻结势概念。为通过不同温度下的热参数和土水势变化率得到冻结势的表达式,首先,基于Johansen法反演不同温度下的冻土未冻水含量,根据未冻水含量计算出冻土热参数理论值,得出热参数在不同温度下的变化率;其次,通过土水特征曲线研究了冻土土水势随未冻水含量的变化关系,得出了冻土土水势在不同温度下的变化率;最后,根据以上计算结果拟合出了冻结势函数。研究结果表明:热参数及土水势在不同温度下产生不均匀变化的根本原因是未冻水含量的不均匀变化;随着土体温度的降低,未冻水含量、土水势、热参数先发生剧烈变化,随后变化趋势减缓并趋于某一数值;在温度为0～-5℃时,冻土冻结势急速发展,当温度低于-5℃时冻结势发展趋缓,由此得出0～-5℃是重塑冻土热参数和土水势性质的剧变区间。在此基础上,依据冻结势函数拟合出一种考虑温度变化的导热系数计算方法,该计算方法能较好地预测不同温度下冻土的导热系数。
The concept of frozen soil freezing potential was put forward in view of the lack of a unified estimating standard for the variation trend of the thermal parameters,soil-water potential of frozen soil at different temperatures.In order to obtain the expression of freezing potential according to the thermal parameters and the change rates of soil-water potential at different temperatures,firstly,based on the Johansen method,the unfrozen water contents of frozen soil at different temperatures were obtained,and the theoretical values of the thermal parameters of frozen soil were calculated through the unfrozen water contents,and the change rates of the thermal parameters at different temperatures were obtained; secondly,the relationship between the soil-water potential of frozen soil and the content of unfrozen water was studied by SWCC,and the change rates of soil-water potential of frozen soil at different temperatures were obtained; finally,the freezing potential function was fitted according to the above calculation results. The results showed that the fundamental reason for the variation of thermal parameter and soil-water potential at different temperatures was the variation of unfrozen water content; with the freezing temperature decreasing the content of unfrozen water in frozen soil,the water potential of frozen soil and the thermal parameters of frozen soil changed rapidly at first,then the change trend slowed down and tended to a certain value. When the freezing temperature was at 0 ℃ to-5 ℃,the freezing potential of frozen soil varied rapidly,and when the freezing temperature was lower than -5 ℃,the freezing potential slowed down. From that,it was concluded that 0 ℃ to -5 ℃ was the sharp variable range of remolded frozen soil thermal parameters and soil-water potential properties.According to the freezing potential function, a method for calculating the thermal conductivity of frozen soil considering the change of freezing temperature was proposed,which could be used to predict the thermal conductivity of frozen soil at different temperatures.
The concept of frozen soil freezing potential was put forward in view of the lack of a unified estimating standard for the variation trend of the thermal parameters,soil-water potential of frozen soil at different temperatures.In order to obtain the expression of freezing potential according to the thermal parameters and the change rates of soil-water potential at different temperatures,firstly,based on the Johansen method,the unfrozen water contents of frozen soil at different temperatures were obtained,and the theoretical values of the thermal parameters of frozen soil were calculated through the unfrozen water contents,and the change rates of the thermal parameters at different temperatures were obtained; secondly,the relationship between the soil-water potential of frozen soil and the content of unfrozen water was studied by SWCC,and the change rates of soil-water potential of frozen soil at different temperatures were obtained; finally,the freezing potential function was fitted according to the above calculation results. The results showed that the fundamental reason for the variation of thermal parameter and soil-water potential at different temperatures was the variation of unfrozen water content; with the freezing temperature decreasing the content of unfrozen water in frozen soil,the water potential of frozen soil and the thermal parameters of frozen soil changed rapidly at first,then the change trend slowed down and tended to a certain value. When the freezing temperature was at 0 ℃ to-5 ℃,the freezing potential of frozen soil varied rapidly,and when the freezing temperature was lower than -5 ℃,the freezing potential slowed down. From that,it was concluded that 0 ℃ to -5 ℃ was the sharp variable range of remolded frozen soil thermal parameters and soil-water potential properties.According to the freezing potential function, a method for calculating the thermal conductivity of frozen soil considering the change of freezing temperature was proposed,which could be used to predict the thermal conductivity of frozen soil at different temperatures.
引文
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[2]曹元兵.季节冻土区铁路路基冻胀研究进展[J].铁道工程学报,2017,34(4):6-9,20.
[3]栗晓林,王红坚,邹少军,等.循环荷载下冻土变形特性研究现状及冻土开挖问题[J].冰川冻土,2017,39(1):92-101.
[4]张蔚,何元庆,刘婧.深季节冻土区路基防冻胀道砟碎石排水盲沟热状况的数值分析[J].冰川冻土,2015,37(4):991-1001.
[5]陈之祥,李顺群,夏锦红,等.基于未冻水含量的冻土热参数计算分析[J].岩土力学,2017,38(增刊2):67-74.
[6]李顺群,王杏杏,夏锦红,等.基于混合量热原理的冻土比热容测试方法[J].岩土工程学报,2018,40(9):1684-1689.
[7]徐斆祖,奥利奋特J L,泰斯A R.土水势、未冻水含量和温度[J].冰川冻土,1985,7(1):1-14.
[8]徐斆祖,王家澄,张立新.冻土物理学[M].北京:科学出版社,2010.
[9]马田田,韦昌富,陈盼,等.Na Cl溶液对土体持水特性影响的试验研究[J].岩土力学,2015,36(10):2831-2836.
[10]DROTZ S H,TILSTON E L,SPARRMAN T,et al.Contributions of Matric and Osmotic Potentials to the Unfrozen Water Content of Frozen Soils[J].Geoderma,2008,148(3):392-398.
[11]ALEKSYUTINA D M,MOTENKO R G.The Effect of Soil Salinity and the Organic Matter Content on the Thermal Properties and Unfrozen Water Content of Frozen Soils at the West Coast of Baydarata Bay[J].Moscow University Geology Bulletin,2016,71(3):275-279.
[12]JOHANSEN O.Thermal Conductivity of Soils[D].Norway,Trondheim:University of Trondheim,1975.
[13]王彦洋.冻土的热参数与土冻结过程的热力耦合分析[D].天津:天津城建大学,2015.
[14]陈之祥,李顺群,王杏杏,等.热参数对冻土温度场的影响及敏感性分析[J].水利水电技术,2017,48(5):136-141.
[15]宁英成.非饱和土土水特性曲线与渗透系数试验研究[D].大连:大连理工大学,2014.
[16]KAIIUZHUYI I L,MOROZOVA N S,PAVLOVA K K.Determining Soil-Water Potentials of Low-Moisture Frozen Soil[J].Leningrad Gasudarstvenny Gidrologicheskii Institute,1980(264):71-78.
[17]WILLIAMS P J,PERFECT E.Investigation of Water Movement Through Frozen Soils[R].Final Report for Dept.Energy,Mines and Resources Mines Branch.Canada Ottawa:Dept.Energy,Mines and Resources Mines Branch,1979.
[18]邓友生,徐斆祖.全量程(多分子层到饱和)土壤持水曲线变化规律初探[J].冰川冻土,1990,12(1):48-54.