Effects of freeze-thaw cycles on the moisture sensitivity of a compacted clay

This study investigates the influence of freeze-thaw (FT) cycles on the (i) microstructure, (ii) soil water characteristics, and (iii) sensitivity of the volumetric strain and mechanical properties to moisture content for a compacted clay. The mechanical properties herein include resilient modulus (M-R), unconfined compression strength (q(u)), and reloading modulus (E-1%) and stress (S-u1%) at 1% strain. Specimens were compacted at optimum moisture content and subjected to different FT cycles (i.e. 0, 1, 3, and 10 cycles). Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were performed to reveal the evolution of the microstructure during FT cycles. Specimens were then wetted or dried to different suction (s) and degree of saturation (S-r) values to obtain the (i) soil water characteristics using filter paper method and (ii) M-R, q(u), E-1%, and S-u1% using cyclic and static triaxial tests. Experimental results demonstrate that FT cycles induce cracks that are tens of microns in dimension, which reduce specimens' water retention capacity and the volumetric strain upon wetting and drying. Mechanical properties also reduce significantly and become less sensitive to the s and S-r after FT cycles. A model was used to predict the variation of the M-R, q(u), E-1% and S-u1% with s and S-r for specimens subjected to different FT cycles. An attenuation coefficient chi(FT) was proposed to describe the FT-induced degradation in the q(u), E-1%, S-u1%, and M-R. It was found that the chi(FT) for different mechanical properties are consistent. The evolution of their chi(FT) with FT cycles can be described by a uniform empirical equation. The study presented in this paper is useful for the rational understanding and prediction of the hydromechanical behaviors of compacted clay taking account of the influence of FT cycles.