UC San Diego

This study focuses on developing an improved thermo-mechanical soil-structure interaction (i.e., load transfer) analysis to assess the axial strains, stresses, and displacements during thermo-mechanical loading of energy piles in different soils having different end restraint boundary conditions. This study builds on established analyses by (i) incorporating an algorithm to identify the location of the point of zero displacement (i.e., the null point) during changes in temperature, (ii) adding models for the ultimate side shear resistance representative of drained and undrained soils, and (iii) incorporating an unloading path for the side shear resistance curve. A parametric evaluation was 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 foundation type, mechanical load magnitude, and temperature change magnitude. This investigation showed that the end restraint boundary conditions played the most important role in controlling the magnitude and location of the maximum thermal axial stress. The soil type also caused changes in the nonlinearity of the axial stress distribution throughout the energy pile. The radial expansion did not affect the thermo-mechanical soil-structure interaction for the conditions investigated in this study. The thermo-mechanical load-transfer analysis was then calibrated to identify the parameters that match the observed soil-structure interaction responses from four case studies involving non plastic soils, including one field study and three centrifuge studies. The ranges of calibrated parameters provides insight into the behavior of energy piles in non plastic soils, and can be used for preliminary design guidance.