Effects of specimen preparation method on the volume change of clay under cyclic thermal loads

Previous investigations of the volume change of soil with different fabric patterns have been mostly carried out at a constant temperature. To investigate the influence of the specimen preparation method on the volume change of saturated clay under cyclic thermal loads, reconstituted, intact and recompacted specimens were tested. Thermal axial strains of these specimens in a normally consolidated state were measured using a temperature-controlled invar oedometer apparatus. The soil fabric of each specimen was evaluated using a scanning electron microscope (SEM) and a mercury intrusion porosimeter (MIP). All specimens showed continuous contraction as the number of thermal cycles increased, albeit at a decreasing rate. After five heating and cooling cycles with temperatures ranging from 15 to 70°C, the accumulated plastic axial strain of the reconstituted specimen was 38% and 68% larger than those of the intact and recompacted specimens, respectively. The SEM visualisations and MIP measurements demonstrate that these observed differences can likely be attributed to different distributions of clay particles in the soil specimens (with a 28% clay content). In the intact and recompacted specimens, most of the clay particles formed silt-size aggregates. In the reconstituted specimen, the clay particles filled the spaces between silt particles and the soil fabric was homogeneous overall.