Experimental Research on Frost Heave Process by Using Digital

Abstract

Frost heave, the most important physical and mechanical phenomenon happened in the soil freezing process, is a comprehensive manifestation of the cryostructure forming, the process of water migration and ice segregation. The development of frost heave will responsible for the formation of the complex periglacial landforms such as the frost heave mounds, ice cones, non-sorted polygons, stone circles, patchy soils, and the porphyry soil. As well as it will cause some engineering accidents which includes the houses tilting, the foundation becoming uneven and the pavement appearing frost cracks, the frozen pipes and the frozen walls warped. Therefore, carrying out a real-time monitoring research on the frost heave process to investigate frost heave occurrence and development mechanism, and further establish a reasonable frost heave model to predict and eliminate frost heave is of great significance to the safe operation of engineering structures. In this research, we improved the current freeze-thaw testing machine by modifying the soil sample container and adding the digital image processing system. As for the soil sample container, a semicylindrical soil container was designed which can intuitively show the freezing process of soil sample. As for the digital image processing system, it can not only record the process of soil from an unfrozen state to completely frozen in real time, but also analyze the recorded images. By using this improved freeze-thaw experimental apparatus, a series of laboratory one-dimensional freezing experiments were taken to investigate the ice lens formation, water migration and their distribution characteristics in the Qinghai-Tibet clay. The obtained results showed that the freezing front in the samples moved rapidly when the freezing started, the moving rate becoming slow after some hours and tended to stability after 24 hours. Before that, the cryostructure of the samples has been formed. We divided the longitudinal section of the soil samples’ frozen part into three zones, which were tiny thin ice layers zone, thin ice layers zone and thick ice layer zone from cold end to freezing front. Along with the soil freezing, the ice lenses segregated in thin ice layers zone was the main reason which induced to soil frost heave, and the ice lens grown in thick ice layers zone caused the solidification of the unfrozen zone of the samples. The horizontal section cryostructure of the samples performed as polygons cracks. The edges of these polygons cracks were the passageways for water migration. The frost heave process of the whole samples experienced three stages, which were rapid frost heave stage, steady frost heave stage and linear frost heave stage. The frost heave developed in the linear frost heave stage contributed mostly to the whole sample frost heave amount. The sample with lower cold end temperature and larger intial water content had a higher degree of unfrozen part solidification accompany with soil frost heaving. Water could migrate from unfrozen part to frozen part of the samples through the warmest ice lens.