Volume change behaviour of saturated sand under thermal cycles

The volume changes of saturated sand under heating and cooling cycles can greatly affect the serviceability of many earth structures in geo-energy and geo-environmental engineering. Up to date, this aspect of thermo-mechanical soil behaviour has not been fully understood. In this study, a temperature-controlled triaxial apparatus was developed to investigate the thermally induced volume changes of soil skeleton of saturated Toyoura sand. Soil specimens with different initial densities were isotopically compressed and then subjected to two thermal cycles in the temperature range of 23 to 50°C. During the first heating process, loose and medium dense specimens showed contractive strains of approximately 0•15% and 0•05% respectively as the temperature rose from 23 to 35°C. The observed contraction is most probably because the thermal expansion of soil particles adjusted force chains inside the specimen, inducing plastic contraction and soil hardening. Both specimens showed dilative strain of approximately 0•05% as the temperature increased further from 35 to 50°C. On the contrary, for the dense specimen with a more stable structure, only dilation was observed during heating with a volumetric strain of approximately 0•1%. During the second thermal cycle, the responses of sand specimens with different densities were almost reversible with heating dilation and cooling contraction.