Experimental investigations of the soil-concrete interface: Physical mechanisms, cyclic mobilization, and behaviour at different temperatures

Behaviour of the pile–soil interface is important to correctly predict the response of floating piles in terms of displacement and lateral friction. Regarding energy piles, which couple the structural roles of deep foundations with the principle of shallow geothermal energy, the response of pile–soil interfaces is influenced by seasonal and daily cyclic thermal variations. Accordingly, the goal of this paper is to experimentally investigate the response of the pile–soil interface at different temperatures. This experimental campaign aims to analyse (i) the cyclic mobilization of the shear strength of the soil–pile interface that is induced by thermal deformation of the pile and (ii) the direct influence of temperature variations on the soil and soil–pile interface behaviour. In this study, a direct shear device was developed and calibrated for nonisothermal soil–structure interface testing. It appears that the sand–concrete interface was affected by cyclic degradation but not affected directly by temperature. Conversely, the response of the clay–concrete interface changed at different temperatures, showing an increase of strength with increasing temperature, presumably due to the effects of temperature on clay deformation.