Study on the remediation of contaminated fine-grained soils based on the effect of permeability increase by freeze-thaw method

本研究的目的是阐明冻融效应对细粒土渗透性增加的影响。以藤森粘土和关东壤土为例，考察了冻结方式、覆盖层压力、土壤差异、供水条件等因素的影响。结果得出以下结论：(1)从试验结果来看，冻融处理后，冻胀对透气性增加的影响很小。换句话说，渗透率的增加程度与温度下降速度、温度梯度、冻结速度、供水条件等条件没有关系。2)冻融处理后渗透率增加的影响因素除土壤性质外，还包括冷却温度和覆盖层压力。对于降温温度，如果采用-5 ~ -7℃左右的温度冻结土壤，没有进一步的影响。对于覆盖层压力，该方法至少在地表以下10 ~ 20米的深度是有效的。3)认为渗透性增加的原因与土壤表面变化有关。因为冻融处理和未处理的重塑土的无侧限强度存在差异。此外，冻融土的渗透性与烘干土的渗透性有相似之处。

The purpose of this study is to clarify the influence of freeze-thaw effect on increase in permeability of fine-grained soils. With sample soils such as Fujimori clay and Kanto loam, the influence of freeze method, overburden pressure, difference of soils, water supply condition and so on is examined. As a result, the followings findings were obtained ;1)It is considered from the experiments that the influence of frost heave is very small for increase in permeability after freeze-thaw treatment. In other words, there is no relationship between the degree of permeability increase and such conditions as temperature descent speed, temperature gradient, freezing speed and or water supply condition.2)Besides the properties of soil, it was cooling temperature and overburden pressure that affected the permeability increase after freeze-thaw treatment. As for the cooling temperature, there is no further effect if the temperature around -5 to -7 ℃ is adopted to freeze the soils. As for the overburden pressure, the method might be effective at least to the depth of 10 to 20 meter below the ground surface.3)It is considered that the reason of permeability increase is something related to a change of soil surface. Because there is a difference in an unconfined strength of remolded soils of the freeze-thaw treated specimen and untreated one. In addition, there was a similarity between the permeability freeze-thaw treated soils and oven-dried ones.