Effects of soil structure on thermal softening of yield stress

Thermal softening is generally referred as the reduction of yield stress with increasing temperature. Previous experimental studies of thermal softening focus on a single type of specimen (either intact or recompacted). In this study, thermal softening of saturated intact, recompacted and reconstituted loess specimens was investigated through temperature-controlled isotropic compression tests. Scanning electron microscope (SEM) measurements were also carried out to evaluate the microstructures of these specimens. It is found when soil temperature increases from 5 to 50 °C, the yield stresses of the intact, recompacted and reconstituted specimens decreased by about 33%, 46% and 51%, respectively. The most resistant structure of intact specimen to thermal softening is mainly because its inter-particle contacts are stabilized by clay aggregates, as evident by SEM results. Reconstituted specimen has the least resistant structure to thermal softening, mainly because clay particles in reconstituted specimen float on the surface of silt particles rather than at inter-particle contacts.