Centrifuge Modeling of Soil-Structure Interaction in Energy Foundations

This study presents a centrifuge modeling approach to characterize the transient thermomechanical response of energy foundations during heating-cooling cycles to provide data for calibration and validation of soil-structure interaction models. This study focuses on the response of a scale-model energy foundation installed in an unsaturated silt layer with end-bearing boundary conditions. The foundation response was assessed using embedded strain gauges and thermocouples. Other variables monitored include foundation head displacements, soil surface displacements, and changes in temperature and volumetric water content in the unsaturated silt at different depths and radial locations. Measurements during the initial heating process indicate that the thermal axial stress is greater near the toe of the foundation as a result of the restraint associated with mobilization of side shear resistance along the length of the foundation. The thermal axial strains were close to the free-expansion thermal strain near the soil surface and decreased with depth. The thermal axial displacements calculated by integrating the thermal axial strains correspond well with the independently measured head displacements. The mobilized side stresses calculated from the thermal axial stresses increased with height and were consistent with the shear strength of unsaturated silt. During successive heating-cooling cycles, slight decreases in upward thermal head displacement were observed because of changes in the stiffness of the unsaturated soil from thermally induced water flow away from the foundation and potential downdrag effects. However, little change in the thermal axial stress was observed during the heating-cooling cycles.