Frost Heave Characteristics And Model For Saturated Expansive Clay

China is a country with large area of frozen soil, ranking third in the world’s fourth largest countries in permafrost region. Frozen soil mainly distributes in the northeast of China, most areas of Inner Mongolia and parts of Xinjiang, Qinghai and Tibet. With the accelerating construction of common rail, high-speed rail, fast-passenger line, highway and other constructions in permafrost regions and seasonal frozen soil regions, and prevention of frost damage has aroused wide concern. Currently, large area of expansive clay has been discovered in seasonal frozen soil regions, however, there are few researches on the frost heave character of the expansive clay in cold regions. Frost heave is under the influence of climate conditions and groundwater conditions, and it is difficult to estimate the deformation amount. So it is necessary to study the impact of frost susceptibility factors on the deformation, which mainly include temperature and water supply, and provide a theoretical basis for reducing the hazard of frost heave on geotechnical structures. In this thesis, basic physical test, free expansive rate test, SWCC test and frost heave test are conducted for Yanji expansive clay, attentions are mainly paid to the frost heave characteristics and its relationship with other factors. Based on the coupled hydro-thermal theory, the computing method of frost heave is studied here. This work will contribute to the analysis of the migration laws of temperature and moisture in frozen soil, as well as prediction of the deformation of frozen soil under different boundary conditions, and provide reference for predicting the frost heave amount and preventing frost damage. The main work and major results are as follows:Firstly, the basic physical parameters of expansive clay are obtained from physical test. With the help of the self-developed freeze-thaw cycle test apparatus FTT1, frost heave experiments are conducted for both saturated and unsaturated soil under different temperature gradients, initial moisture contents and compactness, and obtain the result that temperature condition is one of the major factors that influence the temperature field, the moisture field and the deformation of the frozen soil under the open system. The temperature distribution along the height of the sample is approximately linear after stabilizing. Frost heave is mainly caused by segregated ice lenses, which mainly forms at the cold end of the frozen fringe.Secondly, based on the mass conservation, energy conservation and other fundamental laws, on the level of micro unit, the coupled hydro-thermal control equations for frozen soil are established, which include energy conservation equation, mass conservation equation and the associated equation. Coupled hydro-thermal numerical model was employed with the help of FEM software for frost heave tests of saturated soil, and take the coupling effect of water flow and heat transport into account. The comparison of simulations and experimental results verifies the correctness of the coupled hydro-thermal theory mentioned above.Finally, based on the segregation potential theory, the influence of various factors of the temperature field on the moisture migration rate has been analyzed, and discuss the relationship between the suction of the frozen fringe and temperature conditions. We describe water intake velocity under the open system by introducing the concept of segregation potential, and analyze the impact of frozen depth, freezing rate and cold side temperature on the moisture migration rate. The frost heave amount is divided into two parts: in situ frost heave deformation and migration heaving, and the latter one takes up the major part of the frost heave amount. The results are in good agreement with the experimental results.