STUDY ON THE EFFECT OF COOLING TEMPERATURE ON DEFORMA-TION CHARACTERISTICS OF MARINE MUCK CLAY

The permeability, compressibility and consolidation characteristics of soil after freeze-thaw process are important factors that affect the deformation rate and amount of deformation after the artificial ground freezing construction. This paper aims to systematically reveal the effect of cooling temperature on deformation characteristics of coastal soft clayey soil, and carries out a series of tests include moisture content test, density test, penetration test and consolidation test on the undisturbed and frozen-thawed Shanghai Quaternary marine mucky clay at cooling temperatures of -5 to -25℃; combined with the changes in moisture content and density after freeze-thaw process at different cooling temperatures, it discusses the influence mechanism of vertical permeability coefficient and compression coefficient of soft clay. The results show that after undergoing single freeze-thaw cycle in a closed system, the moisture content and density of frozen-thawed soil decrease, while the freeze-thaw process enhances the permeability and compressibility of soil. As the cooling temperature decreases, the effect of freezing-thawing on the moisture content is weakened, while the effect on density is strengthened. The redistribution and phase conversion of water inside the samples caused by freezing-thawing are the fundamental reasons for the change of soil microstructure, which in turn leads to the differences in permeability and compressibility before freezing and after thawing. The compression coefficient and the initial void ratio of frozen-thawed soil are in an exponential relationship, suggesting that it is possible to provide the value of compression coefficient for deformation prediction by combining the laboratory test with the fitting formula. The vertical consolidation coefficient of frozen-thawed soil decreases linearly with the decrease of cooling temperature, hence the soil subjected to freezing-thawing should be temperature-zoned when calculating the amount of deformation. These findings help to promote the quantitative study of cooling temperature on the deformation characteristics of soft clayey soil, and provide some guidance for the application of artificial ground freezing method in coastal areas.