Impacts of Unsaturated Conditions on The Ultimate Axial Capacity of Energy Piles

¹ Ph.D Student, Department of Structural Engineering, UC San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0085, USA
² Professor and Chair, Department of Structural Engineering, UC San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0085, USA

^* Corresponding author: fnbeh@eng.ucsd.edu

Abstract

This study uses concepts from unsaturated soil mechanics to explain changes in axial capacity observed in geotechnical centrifuge experiments on semi-floating energy piles in unsaturated silt heated monotonically to different temperatures. Thermally-induced drying of the unsaturated silt surrounding energy piles was observed during heating using temperature-corrected dielectric sensor readings. An effective stress-based equation for estimating the ultimate capacity was calibrated using the load-settlement curves for a pile at room-temperature, which was then used to estimate the ultimate capacities of energy piles under elevated temperatures using measured changes in degree of saturation near the energy pile. The predicted capacity matched well with the capacity from the experimental load-settlement curves, confirming the relevance of the effective stress principle in unsaturated soils in nonisothermal conditions and the importance of considering coupled heat transfer and water flow in unsaturated soils surrounding energy piles.