Analytical Solutions for Thermomechanical Soil Structure Interaction in End-Bearing Energy Piles

Abstract

Analytical solutions for axial displacement, strain, and stress in an end-bearing energy pile subjected to a thermal load and a combined thermal and mechanical load have been derived and validated against full-scale in situ pile tests. The pile is embedded into a single layered and multilayered soil underlain by stiff bedrock. The thermoelastic constitutive law has been used to describe pile behavior, while soil–pile interface has been characterized by a linear elastic load-transfer function. In the case of thermal load, the solutions for a single-layered soil show that both the absolute minimum magnitude of axial strain and the absolute maximum magnitude of axial stress develop at the pile tip. Thus, the maximum compressive and maximum tensile stress develops at the pile tip for net heating and cooling scenarios, respectively. When subjected to combined thermal and mechanical load, the shapes of the corresponding displacement and strain and stress response curves are dominated by either the response to thermal or the response to mechanical load, depending on the ratio of the magnitudes of the temperature change and the axial force applied at the pile head. The analytical solutions provide not only a quick quantitative assessment, but also an in-depth qualitative understanding of the thermomechanical soil structure interaction in energy piles.