Engineering Properties of Unsaturated Cohesive Soil subjected to Freezing and Thawing

冬季路基和底基层的冻胀以及春季底基层土体抗剪强度的降低，会对路面和天沟造成破坏，针对这些现象，本研究旨在揭示路基和底基层的实际破坏情况和室内冻融条件下土体的工程特性，研究结果如下：（1）1984-1986年在秋田、岩手、福岛等县发生了多起冻害。特别是1986年，各都道府县的受灾数分别为752、1648和1958。此外，在长野县、山梨县和群马县的寒冷地区，每年都发生霜冻灾害。(2)在北海道的高地下水地区，甚至在长野县、山梨县、群马县的寒冷地区的低地下水地区，如果路基含水量高，都可能引起这些翻浆灾害。2.室内试验（1）在开放系统试验中，粉质土容易发生翻浆。而在桑迪土壤中，由于土壤渗透性强，几乎不发生这种现象。(2)在封闭系统中，非饱和土在冻结过程中体积变化，根据饱和度的不同，会产生膨胀和收缩现象，而在融化过程中则会产生收缩现象。(3)结果表明，冻融作用使非饱和土的抗剪强度降低，这是由于土颗粒间吸力减小所致。

Road pavement and gutter have been damaged due to frost heaving of the subgrade and the subbase in winter and decreasing of shearing resistance of soils of the subbase in spring.Considering those phenomena, this study aimes to make appear the actual damade conditon in field and engineering properties of soils subjected to freezing and thawing in laboratory.The results of those studies are as follows ;1.Field Resarches(1) Many frost heaving disasters occcured in Akita, Iwate and Fukushima prefectures in 1984-1986. Especially, in 1986, number of damages were 752, 1648 and 1958 in each prefectures. Also frost heaving disasters have occured every yeares at the cold region in Nagano, Yamanashi and Gunma prefectures.(2) Those frost heaving disasters were caused at the high grround water region in Hokkaido and even at the low ground water area on the cold region in Nagano, Yamanashi and Gunma prefectures if the subbase has the high water content.2.Laboratory Tests(1) In the open system tests, frost heaving occured easily in the silty soils. However, it was scarcely caused in sandy soils because those soils had high permeability.(2) In the closed system, volume changes of the unsaturated soil during freezing process resulted in expansion and shrinkage phenomenen according to the degree of the saturation of soil and during melting process shrinkage phenomena were always caused.(3) It was cleared that the shearing strength of the unsaturated soil subjected to freezing and thawing was decreased due to decreasing of the suction force between soil particles.