Thermomechanical response of kaolin clay-concrete interface in the context of energy geostructures

The analysis and design of energy geostructures are mainly characterised by the mechanical behaviour of the soil–structure interface in non-isothermal conditions. In this study, direct shear tests are conducted to investigate the shear behaviour of soil and soil–structure interface in the practical temperature range of energy geostructures (i.e., 8–45 °C). The interface in this study is formed of kaolin in contact with concrete specimens with different roughness. Tests are performed on normally consolidated and overconsolidated interfaces following the unloading/reloading paths to better understand the impact of thermal strain on the interface behaviour. The volumetric response of the interface is observed to be highly influenced by the thermal strains experienced during heating/cooling. The soil stress level and the most recent soil stress history are identified as the primary determinants of thermally induced changes in interface shear strength. For normally consolidated interfaces, the temperature increase led to higher adhesion and slightly lower friction angle, whereas higher adhesion and identical friction angles were found for tests conducted on cooled specimens. Temperature does not seem to affect the shear strength of overconsolidated interfaces. Finally, a conceptual understanding of the temperature effect on interface shear behaviour is provided by analysing data from the literature.