Variation behavior of pore-water pressure in warm frozen soil under load and its relation to deformation

Containing a considerable amount of unfrozen water, frozen soil may produce excess pore-water pressure under external load, especially at temperatures near the thawing point. The variation of the pressure has a capability in influencing the deformation of frozen soils. In order to investigate the variation behavior of pore-water pressure in frozen soils and its relation to deformation, a series of pore-water pressure tests were conducted at subzero temperatures. A total of 13 frozen specimens were tested at various temperatures, and the pore-water pressures as well as the displacement were recorded. Then, variation behaviors of pore-water pressures and their effect on deformation were discussed. Results indicated that when a frozen soil sample is subjected to load, it responds with a slow increase in pore-water pressure in the early test stage up to a peak value, followed by subsequent extremely slow dissipation. The characteristic of pore-water pressure variations recorded in this study are closely correlated with temperature, soil type, and moisture content. Generally, the variation in pore-water pressure in frozen soils is caused by the coupled action of two opposing processes: an increasing process induced by solid matrix compression and a decreasing process induced by unfrozen water drainage. Thus, consolidation can be shown to occur as a component of compression and plays a significant role in the total deformation of warm frozen soils, although this effect decreases as decreasing soil temperature. However, it is difficult to distinguish the consolidation deformation from the creep deformation when taking into account the continuous variation in pore-water pressure throughout the test period.