寒区地下冻土层水理性质及其对融雪水入渗的影响机理研究

Snowmelt infiltration into the frozen layer is considered as one of the particular phenomena in the hydrological cycle of the cold region. The existence of low temperature and frozen soil complicates both mechanisms and influencing factors of this process, where regular seepage theory is unsuitable for a reasonable interpretation. The previous research on frozen soil or frozen layer were mainly focused on its physical or mechanical properties and a prospect which sees the frozen soil as temporary porous media under exceptional condition (low temperature) has never been brought out. Therefore, the research on the special hydraulic characteristics of frozen soil and its seepage theory are not sufficient so far. Firstly, this project is intended to summarize a series of concepts for hydraulic characteristics of frozen soil, including permeability, water content, water retention capacity and water yield capacity in accordance with their parameters, including the Hydraulic conductivity, moisture content, specific water retention and specific yield. Secondly, by choosing and then monitoring these parameters of a typical frozen layer, the boundaries of parameters are confirmed. Thirdly, a series of laboratory experiments to quantify the example, the Hydraulic conductivity, and to analyze the impact drawn by its influencing factors which mainly include the porosity and ice content of the frozen soil and the environment temperature. Based on the data, the single influencing and couple influencing mathematical model will be built to calculate the total quantity of snowmelt infiltration in the research area during the whole melting period. The results of this project are expected to provide scientific references to the calculation and prediction of snowmelt infiltration and runoff, the evaluation of groundwater resources in cold region, parameters of soil infiltration as well as the mechanism research on groundwater contamination transport in the cold region.

春季融雪水在包气带冻土层的入渗是寒区水循环的特有现象之一，由于低温冻土层的存在，其入渗机理及影响因素更加复杂，用非寒区常规渗流理论解释这个过程效果较差。本项目拟从分析寒区地下冻土层的水理性质(容水性质、持水性质、给水性质、透水性质)及其特征参数出发，监测典型区包气带地下冻土层水理性质的主要影响因素即结构特征（孔隙度、含冰率、冰/土比）及其环境特征（温度、融雪水量）。以监测数据为控制范围，在室内开展不同结构、不同环境条件下的冻层水理性质参数测定试验，据之得到孔隙度、含冰率、冰/土比、温度对冻层水理性质参数的影响作用，构建冻土层水理参数与融雪水入渗量之间的函数关系；最后结合实测数据，揭示冻土层水理性质参数对融雪水地下渗流过程的影响机理，为寒区冻融作用下地下水与溶质迁移、寒区渗流理论等研究提供理论依据。

本项目针对融雪水在包气带冻土层的入渗机理及影响因素展开了系统的研究。首先对土壤的物理性质、土壤水理性质及与水热储容及运移有关的性质进行梳理，结合分析寒区冻层土壤特征，选定对冻层土壤的水热迁移较重要的典型水热参数。开展低冰点惰性液体的冰点测定试验与融冰性试验确定出可用于冻土水理参数测定试验的液体。设置冻结和非冻结对比监测试验场，同时段、同频率、同埋深（间隔20cm土层）进行土壤结构、水热及环境参数监测。最后从积雪、融雪及入渗等方面对寒区春季融雪入渗规律进行监测分析，探讨融雪水的入渗时期与入渗深度的相关性，对积雪融渗阶段的划分。取得成果如下：（一）冻层水理性质研究：采用室内试验与野外监测相结合的方式进行冻结土壤水/热物理特征参数测定。设计制作了语音式低温地温计测定1m内的冻层土壤内部温度，完成土壤含水量与温度的同步监测。利用SPSS软件对测定的土壤水热参数进行相关性和回归分析，地表土壤含水率受到日照、风等影响明显，0-60cm土层受到外界因素影响，土壤含水率与土壤温度相互之间并没有显著的相关性，直至土壤埋深80cm以下土壤水热参数才表现出线性关系。通过分析寒区地下冻土层的水理性质(容水性质、持水性质、给水性质、透水性质)及其特征参数，选择特殊的低冰点惰性液体，即浓度为20%的乙二醇溶液对冻土层水理特征参数进行测定。选取地表以下100cm的土壤为研究对象，进行冻结土壤和非冻结土壤墒情对比监测。根据冻深实测数据和研究区冻深资料将冻层生消过程分为初冻期、冻结期、稳定冻结期和融化期四个阶段，冻结条件下土壤水分重新分布，在水土势的作用下由非冻结区向冻结区迁移，冻结土壤含水率均大于非冻结土壤，二者含水率的差值随埋深和冻融阶段的推移而加大，差值量最大可达6.4%-7.8%。（二）融雪入渗研究：利用自动测量仪、示踪剂和墒情自动化监测设备等装置对春季积雪、融雪及入渗规律进行监测和试验。根据监测数据得到融雪入渗的轨迹曲线，并对积雪融渗阶段划分成三个阶段—入渗初期、入渗中期、入渗后期。冻结期，土壤的含水量呈微弱减小趋势，完全冻结期深层土含水量保持在25%左右。在融化期，融雪水流入地表基本补给40cm左右及以上的土壤。