Soil-Concrete Interface Properties Subjected to Temperature Changes and Cycles Using Direct Shear Tests

Geothermal foundations (energy piles) combine the structural function of deep foundations with the ground source heat exchangers to transfer geothermal energy to superstructures. The intermittent operation of the geothermal energy pile system results in cyclic thermal loading on the soil-pile interface. To investigate the effects of cyclic thermal loading on soil-concrete interface properties, a conventional direct shear device was modified by replacing the bottom shear box with a concrete plate that has embedded aluminum tubes to heat and cool the interface. A series of tests were conducted with interface temperatures of 4.5, 22.5, and 42.5 degrees C, respectively. The normal stresses of the direct shear tests were 27.6, 41.4, and 100 kPa. The tests were performed both under cooling and heating with thermal cycle numbers of 0.5 and 10.5. The aforementioned tests were conducted at a shearing rate of 3 mm/min, and the water contents of all the samples were approximately 18.5%. The responses of soil-concrete interface at different temperatures and temperature cycles are presented in this paper.