Effect of capillary cohesion and ice cementation on strength and deformation of unsaturated frozen silty clay
LIU Zhenya1,LIU Jiankun1,LI Xu1,2,FANG Jianhong2
(1. Key Laboratory for Urban Underground Engineering of Ministry of Education,Beijing Jiaotong University,Beijing 100044,China;2. Qinghai Research and Observation Base,Transportation Industry Laboratory of Highway Construction and Maintenance Technology in Permafrost Regions,Qinghai Research Institute of Transportation,Xining,Qinghai 810001,China)
Abstract:The strength increase and volume shrinkage during freezing of unsaturated soil may relate to the capillary cohesion and ice cementation. In this paper,shear strength,three dimensional deformation and compaction characteristics of compacted,frozen and air-dried samples were experimental studied using silty clay. The saturation degree and void ratio were considered as variable parameters. The contributions of ice cementation and capillary cohesion to strength were investigated experimentally. The experimental results demonstrate that the strength increase of unsaturated frozen silty clay is due to the capillary cohesion enhanced by suction increase and ice cementation. The capillary cohesion is remarkable in frozen soil with low initial degree of saturation,and the ice cementation is major source of cohesion in frozen soil with increasing of the initial degree of saturation. The volumetric ice content has a linear relationship with ice cementation on the assumption that capillary cohesion of frozen soil equals to that of unsaturated soil at the same matric suction. For the silty clay used,the samples with degree of saturation lower than 0.75 shrink upon frozen while the samples with degree of saturation higher than 0.75 swell. So,the sum of shrinkage induced by cohesion and expansion induced by icing are the total deformation of unsaturated frozen soil. Such shrinkage strain can be inferred from the curve of soil compression. The expansion induced by transformation from water to ice has a linear relationship with volumetric ice content on the assumption that compression caused by load equals to shrinkage caused by increasing of capillary cohesion.
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