Micromechanical analysis of volume change behaviour due to cyclic temperature variations in sands

The contraction of sands subject to cyclic increases and reductions in temperature is of great practical importance; however, the effect of the initial packing condition and the mechanism underlying the behaviour are not completely understood. In this study, a thermal discrete-element method was developed by considering thermal expansion of particles and heat conduction through particles and interstitial pore fluids. Cyclic changes in temperature were simulated on samples with a variety of initial densities and degrees of anisotropy. The contraction of the soil skeleton was isolated from the thermal expansion of the particles using the ‘mechanical strain’ concept. Looser samples showed a larger mechanical strain accumulation, in line with observations in previous laboratory work. Highly anisotropic samples had a significant cyclic thermal contraction even in the case of samples with a high density. Over the duration of the thermal cycles, a continuous decrease in fabric anisotropy was observed for the anisotropic samples, which may be associated with the fundamental mechanism underlying the cyclic thermal contraction of the sands.