Experimental study on the remediation of contaminated soils by freezing and thawing

本研究的目的是阐明冻融修复污染土壤技术的适用性。在本研究中，研究了以下主题：冻结条件下水溶性污染物的运动，土壤类型等。在2002财政年度，研究了粘性冻易感土壤的冷却速率，温度梯度，负荷影响和供水条件。从实验结果可以看出，在所有的测试条件下，溶质都从高温侧向冷侧移动。从这一事实来看，冻融易感土壤中水分和溶质的输运方向似乎一般是由高温侧向冷侧输运。在2003财政年度，研究了基于融化后粘性土的水力导率增加的洗涤技术。试验重点研究了土体类型和荷载对水导率变化的影响。主要结果如下：首先，在一系列的实验中，在100kPa范围内观察了冻融后的水力导率的增加。其次，不同类型土壤的水力导电性变化差异较大。关东壤土的水导率可达数百倍，藤森粘土的水导率可达10倍左右。特别是关东壤土，其水导率增加到10^<-3>cm/s至10^<-4>cm/s，即砂质土的值，而未冻结状态下的水导率在10^<-6>cm/s至110^<-7>cm/s之间，即粘性土的值。冻融前后，即使孔隙比相同，其水力导率也存在差异。

The purpose of the research is to clarify the applicability of the remediation technology of the contaminated soils by freezing and thawing. In this research, the followings topics were examined: Movement of the water-soluble pollutant by the freezing condition, types of the soil, etc.In the 2002 fiscal year, cooling rate, temperature gradient, effect of the load, and the water supply conditions were examined for cohesive frost susceptible soils.From the experimental result, it was observed in all test conditions that the solute was moved to the cold side from the high temperature side in all conditions. From this fact, the direction of the moisture and solute transport in the freezing frost susceptible soils seem to be generally to the cold side from the high temperature side.In the 2003 fiscal year, the washing technique which based on increase of the hydraulic conductivity of cohesive soil after thawing was examined. Especially, the experiment focus is on the influence of the type of soils and loads in the change of the hydraulic conductivity.The main results are as follows. First, in the series of the experiments, the increase of hydraulic conductivity after freezing and thawing was observed in the range to 100kPa. Next, there is a large difference in the change of the hydraulic conductivity in the types of soils. The hydraulic conductivity increased to several hundred times in Kanto loam, and to about 10 times in Fujinomori clay. Especially, in case of the Kanto loam, the hydraulic conductivity increased to 10^<-3>cm/s to 10^<-4>cm/s that is the value of sandy soil, though hydraulic conductivity in the unfrozen condition is in the range between 10^<-6>cm/s to 110^<-7>cm/s that is the value of cohesive soil. In addition, the hydraulic conductivity differed even in equal void ratio in before and after of freezing and thawing.