Parameters for Load Transfer Analysis of Energy Piles in Uniform Nonplastic Soils

This study focuses on the use of a thermomechanical soil-structure interaction (load transfer) analysis to assess the axial strains, stresses, and displacements during thermomechanical loading of energy piles in various soil deposits with different end restraint boundary conditions. After providing details of the model and its novel features, this paper presents a parametric evaluation performed to understand the roles of the soil shear strength parameters, toe stiffness, head stiffness, side shear stress-displacement curve, and radial expansion, as well as the magnitude of temperature change. This evaluation showed that the end restraint boundary conditions play the most important role in controlling the magnitude and location of the maximum thermal axial stress. The soil type also causes changes in the nonlinearity of the axial stress distribution throughout the energy pile. The radial expansion did not affect the thermomechanical soil-structure interaction for the conditions investigated in this study. The thermomechanical load transfer analysis was then calibrated to identify the parameters that match the observed soil-structure interaction responses from four case studies of energy piles in nonplastic soil or rock layers during monotonic heating, including one field study and three centrifuge studies. The ranges of calibrated parameters provide insight into the behavior of energy piles in nonplastic soils and can be used for preliminary design guidance.