Effect of thermal cycles on sand-concrete interface under constant shear stress

Energy geostructures provide a profitable solution for structural support as well as the heating and cooling of buildings. However, their activation can produce in structure and its surrounding soil thermally-induced stresses and strains with a crucial role played by the soil-structure interface which is the thin layer that transmits the thermal and mechanical loads. In the present work, the thermo-mechanical behaviour of the soil–structure interface is investigated using a temperature-controlled direct shear box. Tests were conducted on loose and dense sands in contact with a concrete plate representing the structure's surface. After applying the normal stress (25, 50, or 100 kPa), a shear stress was increased up to 45% of the shear strength. This stress state was then maintained while 20 cycles of temperature varying between 13 °C and 34 °C at the soil-concrete interface were applied. The obtained experimental results reveal that temperature cycles lead to irreversible cumulative displacements in both normal and shear directions. These displacements were found to be more significant in loose sand compared to dense sand. Additionally, under higher stress levels, greater displacements were observed for both soil densities.