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土样，考察了冻结方法、覆岩压力、土层差异、供水条件等因素对土体稳定性的影响。结果表明：1)试验认为冻胀对冻融处理后渗透率的提高影响很小。也就是说，渗透系数的增加程度与降温速度、温度梯度、冻结速度和/或供水条件无关。2)冻融处理后，除土体性质外，影响渗透系数增加的因素还包括降温温度和覆岩压力。至于冷却温度，如果采用-5~-7℃左右的温度冻结土壤，则没有进一步的影响。对于覆盖层压力，该方法至少在地表以下10~20米处是有效的。3)认为渗透性增加的原因与地表的变化有关。这是因为冻融处理试件和未处理试件的重塑土无侧限强度存在差异。此外，渗透性冻融处理的土壤与烘干的土壤有相似之处。

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.