Thermo-hydro-mechanical coupling analysis of a thermal pile

The thermo-hydro-mechanical (THM) response of a 23 m long thermal pile previously tested at Lambeth College in London, UK was investigated by conducting a THM finite-element analysis using an advanced thermoelastoplastic constitutive model. It was found that the thermal conductivity of the soil and the reloading/swelling stiffness parameter of the model largely govern the behaviour of the thermal pile when the simulated results were compared to the measured data for pile head displacement, distributed strain inside the pile and ground temperatures during the cooling and heating cycles. The pile head movement is mainly affected by the thermal expansion coefficient of the pile concrete as well as the location of the neutral point, where the shaft resistance direction changes from the mechanical loading only condition. Additionally, the results show that the thermally generated axial stresses in the pile are governed by the magnitude of soil stiffness along the pile depth as well as by the relative values of thermally induced expansion/contraction of three materials (concrete, soil skeleton and pore water). The effect of the thermally induced plastic behaviour of the soil was limited in the Lambeth College case due to the heavily overconsolidated nature of London Clay.