Compression behaviors of a freeze–thaw impacted clay under saturated and unsaturated conditions

This study investigates the influences of moisture content and freeze–thaw (FT) cycles on the compression behaviors of a compacted clay. Compacted specimens were first conditioned to different moisture contents (w) and then subjected to FT cycles. The treated specimens were either (i) directly used for constant water content (CW) compression tests or (ii) saturated and used for conventional consolidation tests to determine the compression curves under unsaturated and saturated conditions, respectively. Mercury intrusion porosimetry (MIP) tests were performed to track the evolution of the soil’s pore structure during moisture and FT conditionings. The compression indexes (including the recompression index C_r, preconsolidation pressure σ_vp or σ’_vp, and compression index C_c of the specimens) derived from the experimental results demonstrate that (i) within the initial elastic compression range, the C_r is independent of moisture content changes but increases after FT conditioning. The variations of C_r are associated with the volume of soil’s large pores (e_l), which remains constant during moisture conditioning but increases after FT cycles; (ii) within the elastoplastic compression range, the σ_vp or σ’_vp increases, while the C_c decreases as the moisture content decreases. However, the σ_vp, σ’_vp, and C_c decrease after FT cycles. The σ_vp, σ’_vp, and C_c are related to the volume of the soil’s medium pores (e_m), which decreases after moisture and FT conditionings. A few unique relationships are established to reveal the influences of pore structure changes on compression characteristics. The variations of the soil’s shrinkage curves under different external stress are also analyzed considering the effects of the changes in the pore structure. A model was proposed for the void ratio–moisture content–external stress relationships. This model was demonstrated useful for describing soils’ compression behaviors at different moisture contents and shrinkage characteristics under different external stress.