Abstract: The freeze-thaw cycles change the structure of soils and influence their physical and mechanical properties, which can in turn be closely related to the pore water pressure change. However, measuring the pore water pressure of freezing soils has always been a challenge task. Here a new pore water pressure probe is developed and used to measure variations of pore water pressures of sand and silty clay during freeze-thaw cycles, from which the pore water pressures at three different depths of a cylindrical specimen are obtained. It is found that the frozen fringe and some ice lens occur in the silty clay samples during freezing; while no frozen fringe and ice lens form in sand samples. The pore water pressure is influenced by temperature, freezing rate, freeze-thaw cycles, soil types and others. The pore water pressure experiences a periodical change during the freeze-thaw cycles. The pore water pressure decreases and suction increases gradually during freezing, whereas the pore water pressure increases during thawing. The freezing rate, freeze-thaw cycles and soil types can primarily influence the amplitude of pore water pressure drop. In addition, the pore water pressure drop and suction increase near the freezing front are the major driving force of water migration from unfrozen zone to frozen zone. The above results show that the pore water pressure probe can be effectively used to measuring the pore water pressure of frozen soils.

Key words: pore water pressure, freeze-thaw cycles, water migration, dry density