Abstract: A series of laboratory experiments is conducted to study the changes in soil particles and pores under freezing and thawing cycles. The results show that during cyclic freezing-thawing processes, grain breakages occur within the soil particles, leading to a progressive increase in plastic limit, plasticity index and specific surface area of the soil. Meanwhile, the pore size distribution, tested by mercury intrusion porosimetry (MIP), is also changed in the processes as macro pores increase, small pores reduce and micro pores almost remain unchanged. All the structural indexes, including particle composition, pore distribution specific surface area, tend towards stable after 15 freezing and thawing cycles. The intrinsic influence of soil’s three-phase components during freezing and thawing cycles is discussed; and it is considered as the fundamentals of the water phase change and moisture migration among soil particles. Correspondingly, the reaction of water phase change and migration on soil particles and pores is considered to be the primary cause of the change of soil structures.

Key words: freezing and thawing cycles, soil structure, experimental study