Centrifuge modeling of temperature effects on the pullout capacity of jacked-in energy piles in saturated soft clay

Abstract

This study focuses on predicting the impacts of a heating-cooling cycle on the pullout capacity of energy piles installed through a soft clay layer. Geotechnical centrifuge physical modeling was used to evaluate temperature, pore water pressure, volume change, and undrained shear strength profiles in clay layers surrounding energy piles heated to different maximum temperatures to understand their impacts on the pile pullout capacity. During centrifugation at 50 g, piles were jacked-in at a constant rate of penetration into a kaolinite clay layer consolidated from a slurry in a cylindrical aluminum container, heated to a target temperature after stabilization of installation effects, cooled after completion of thermal consolidation requiring up to 30 hours (1250 days in prototype scale), then pulled out at a constant rate. T-bar penetration tests were performed after the heating-cooling cycle to assess differences in clay undrained shear strength from a baseline test. The pullout capacity of an energy pile heated to 80 °C then cooled to ambient temperature was 109 % greater than the capacity in the baseline test at 23 °C, representing a substantial improvement. The average undrained shear strength measured with the T-bar at a distance of 3.5 pile diameters from the pile heated to 80 °C was 60 % greater than at 23 °C but followed the same trend as pile capacity with temperature. An empirical model for the pullout capacity was developed by combining predictions of soil temperature, thermal excess pore water pressure, thermal volumetric strain, and undrained shear strength for different maximum pile temperatures. The empirical model predictions matched well with measured pullout capacities.