Evolution of mechanical behaviours of an expansive soil during drying-wetting, freeze-thaw, and drying-wetting-freeze-thaw cycles

This paper investigates the volumetric, microstructural, and shear behaviours of an expansive soil during multiple drying-wetting (DW), freeze-thaw (FT), and drying-wetting-freeze-thaw (DWFT) cycles. Specimens compacted at natural moisture content and dry density were subjected to 1, 4, 6, and 10 DW, FT, or DWFT cycles. Volumetric changes were recorded during the treatments and mercury intrusion porosimetry, and scanning electron microscope tests were conducted to observe the soil's microstructure before and after treatments. As compacted specimens and specimens after different numbers of DW, FT, and DWFT cycles were saturated and sheared under consolidated undrained condition to determine their undrained elastic modulus (E-u), shear strength (q(u)), total cohesion (c), and friction angle (phi). Experimental results show that DW, FT, and DWFT cycles mainly influence the soil's macropores with diameters between 5 and 250 mu m. Macropores collapse during DW cycles, which lead to collapse in the soil's global volume. Cracks develop during FT cycles and result in slight swelling in the soil's volume. These two effects offset during DWFT cycles and cause an intermediate volumetric behaviour. The E-u, q(u), c, and phi decline during DW, FT, and DWFT cycles, and the reduction was most significant during DWFT cycles. They reach an equilibrium after approximately 6 cycles of treatment. A simple normalized model was developed to describe the stress-strain curves considering the influence of DW, FT, and DWFT cycles. Good agreements were achieved between the model predictions and measurements for all stress-strain curves obtained in this study.