Thermo-elasto-plasticity and thermo-mechanical creep for energy pile systems

In this study, a newly developed rate-dependent thermo-plastic constitutive model was enhanced to incorporate thermally accelerated creep and implemented into the Plaxis finite-element code, enabling the simulation of the behaviour of a well-instrumented energy pile in multilayered soft soils under thermomechanical loads. First, the model was validated against non-isothermal laboratory tests on soils surrounding the pile, and then against simulations of field tests. The results revealed that the inclusion of thermally accelerated creep improves the prediction of irreversible pile settlement, which is primarily attributed to the accumulation of volumetric contraction in the surrounding soil after each thermal cycle. The analysis also distinguishes between drag down effects resulting from thermo-elastic and thermo-plastic behaviour, as well as those induced by long-term creep.