Effects of moisture content and freeze-thaw cycles on the compression and pore structure characteristics of expansive soils

This paper presents experimental and theoretical studies to investigate the effects of humidity and freeze-thaw (FT) cycles on the compression and pore structure characteristics of a compacted expansive soil. Compacted specimens were equilibrated to different moisture content and then subjected to FT cycles and saturation process. Constant water content compression tests and consolidation tests were conducted to determine the compression curves for unsaturated and saturated compression curves, respectively. Mercury intrusion porosimetry tests were performed to determine the meso-structural characteristics of the soil. Experimental results indicated that (i) within the elastic range, the recompression index (Ce) is insensitive to moisture content but increases significantly after FT cycles; (ii) within the elastoplastic range, the preconsolidation pressure increases while the compression index (Cc) decreases as the moisture content decreases. Both the preconsolidation pressure and Cc decrease after FT cycles; (iii) under different humidity and FT conditions, there exists a unique linear relationship between the Ce and the void ratio of macropores (el) and a unique relationship between the Cc and a factor that is composed of el, void ratio of medium pores (em) and humidity factors. Based on the testing results, a model was proposed to describe the compression curves of expansive soils considering the effects of humidity and FT cycles. The model was found capable of suitably describing the void ratio-stress-moisture content relationships for compacted expansive soils.