The thermomechanical behaviour of horizontally loaded energy piles in saturated clay was investigated in this study. Based on model-scale tests, a model energy pile underwent 10 heating-cooling cycles. The temperature variation, pore water pressure, soil pressure in front of the pile, pile top displacement, and pile bending moment were measured. The results showed that the thermally induced pore water pressure in the upper part of the surrounding soil gradually dissipated with increasing number of thermal cycles, whereas it gradually accumulated in the lower part of the soil. The thermally induced horizontal displacement of the pile top increased with an increasing number of thermal cycles, reaching 2.28% D (D is the pile diameter) but at a decreasing rate. In addition, the maximum bending moment, which affected the failure of the pile, occurred at a depth of 0.375L (L is the effective pile length) below the soil surface and increased with increasing number of thermal cycles.

Thermally induced volumetric strain of clay is crucial for geotechnical applications involving thermal loading. The volumetric response of clay shows a ratcheting pattern during thermal cycles until reaching a thermal stabilized state. It is also affected by the stress history of soil, including over-consolidation ratio (OCR) and recent stress history (RSH). This paper introduces a new bounding surface model to capture effects of OCR and RSH on thermo-mechanical behaviour of soil. A thermal state parameter is proposed to characterize the effects of stress history and thermal history. Based on the new thermal state parameter, the commonly recognised thermal softening mechanism is modified and incorporated with a bounding surface. The newly proposed model, with only 10 parameters, can provide an elegant approach to predict the volumetric response under thermal cycles coupled with different stress histories well.