关键词: 冻融循环, 孔隙水压力, 上覆荷载, 冻胀应力

Abstract:

Due to the seasonal change of climate and day/night cycle， it is inevitably that the shallow soil is influenced by freeze-thaw cycles in cold regions. The freezing process will cause the soils to expand， and the thawing process will lead the soil to settle. At the same time， the freeze-thaw cycles can induce significant changes in the physical and mechanical property and structure of frozen soils， which will seriously threat the serviceability of some structures. The stress field of soil is one of the key factors that affects the deformation of soil during freezing-thawing process. In order to research the impact of freezing-thawing cycles on the deformation and frost heave stress characteristics of foundation soil in cold regions under different overburden pressure， the two groups frozen-thaw cycles tests are conducted. The first group tests were conducted under the constant overburden pressure in the process of freezing-thawing. In order to investigate the variation of frost heave stress in the frozen-thaw cycles process， another group were carried out under constant displacement defined. It is discovered that the freeze-thaw cycle can lead the soil expand under the 10 kPa overburden pressure， and it is compressed when the stress is 50 kPa or 100 kPa. The larger the stress is， the large settlement deformation is. The soil gradually forms a stable structure under the special stress field with increasing freeze-thaw cycles， which leads to the amount of frost heaving equal to that one of thawing settlement， namely， the coefficient of freeze-thaw stabilization is near to 1. With increasing the number of freeze-thaw cycles under the constant displacement the maximum vertical frost heave stress decreases continuously. From the measured results， it is observed that the developing trend of frost heave stress is similar with that of pore water pressure. The results indicated that frost heave stress increasing in the freezing process will compress the soils structure， which lead to the pore of the soil smaller， and it shows the pore water pressure rising. The pore of the soil will partly resilient in the thawing process， which shows the pore water decreasing. According to the principle of effective stress in frozen soil， the internal microcosmic stress mechanism of soil deformation in freezing-thawing process can be revealed by studying the distribution of pore water pressure near to the freezing-thawing interface. At the same time， the principle of frost heave stress generation in freezing process was explained under microscopic scale. Finally， through analyzing the distribution of pore water pressure under constant overburden pressure， the maximum value of frost heave stress was determined under different unfrozen water content of frozen fringe. In engineering practice， especially for water supply channels， frost heave stress is the main reason for the failure of lining structure. Therefore， the determination of the maximum frost heave stress in the process of freeze-thaw cycle is of great significance to propose a reasonable design code.

Key words: freeze-thaw cycle, pore water pressure, overburden pressure, frost heave stress