LAUSR

Abstract Expansive clay, a kind of clayey soil, is widely distributed in seasonally frozen regions. Numerous studies have attempted to explain the frost heave characteristics of clayey soils, but few of them have paid attention to the frost heave characteristics of unsaturated expansive clay, especially considering the influence of swelling properties. In this study, a series of freezing temperature tests and step-freezing tests on an unsaturated moderately expansive clay and a silty clay were conducted. The silty clay was taken as a reference. The testing program, experimental results are presented and discussed, especially to the freezing point, evolution of temperature in the specimens at different elevations, water content distributions and cryostructures after freezing, frost heave during freezing, and state paths. In this regard, a physico-empirical approach is developed to obtain the relationship between freezing point and initial water contents. Experimental data show that the freezing point of expansive clay varies greatly with initial water contents. The obvious highly exothermic phase change occurs in expansive clay during the early stage of freezing with penetration decrease lagging behind. The heave amount of expansive clay is made up of the displacement caused by increasing water content in the unfrozen zone due to freezing-induced water flux and the frost heave. The state paths show significant variation of saturation and dry density of expansive clay after freezing and have a practical advantage of indicating the extent of possible expansion while thawing. On this basis, the state and variation of pore water are highlighted as the critical primary factors in determining the frost heave characteristics of unsaturated expansive clay in open system. Overall, this study further enhances the understanding of frost heave characteristics of the unsaturated moderately expansive clay.