Effects of humidity and freeze-thaw cycles on compression and pore structure characteristics of expansive soils

Through the experimental and theoretical studies, the effects of humidity and freeze-thaw (FT) cycles on the compression and pore structure characteristics of a compacted expansive soil have been investigated. The compacted specimens are equilibrated to different moisture contents and then subjected to the FT cycles and saturation process. The constant water content compression tests and consolidation tests are conducted to determine the compression curves for unsaturated and saturated specimens, respectively. The mercury intrusion porosimetry tests are performed to determine the pore structure characteristics of the soil. The experimental results indicate that: (1) Within the elastic range, the recompression index (C_e) is insensitive to the moisture content but increases significantly after the FT cycles. (2) Within the elastoplastic range, the preconsolidation pressure increases while the compression index (C_c) decreases as the moisture content decreases. Both the preconsolidation pressure and C_c decrease after the FT cycles. (3) Under different humidity and FT conditions, there exists a unique linear relationship between C_e and the void ratio of macropores (e_l) and a unique relationship between C_c and mesoscopic parameter that is composed of e_l, void ratio of medium pores (e_m) and humidity conditions. Based on the test results, a model is proposed to describe the compression curves of expansive soils considering the effects of humidity and FT cycles. The model is found to be capable of suitably describing the void ratio-stress-moisture content relationships for compacted expansive soils.