Investigation of a field-scale energy micropile in stratified soil under cyclic temperature changes

Abstract Data regarding energy pile behavior in tropical climate regions is not as readily available as in temperate climate regions, which are generally heating dominated (i.e., focused on extracting heat from a relatively cool subsurface). Further, there has not been a major effort to understand the behavior of micropiles converted into energy piles, which may have different behavior from other energy piles due to the disturbance associated with installation, especially at the toe. This paper presents the results of a series of thermal response tests (TRTs) on a 12 m-long instrumented energy micropile installed in a sedimentary tropical soil to understand the impacts of heating and cooling cycles. Vibrating wire strain gauges embedded within the energy micropile were used to assess the mechanical performance of the pile when subject to changes in temperature. Results indicate that the temperature distribution with depth and the resulting thermal axial strains are strongly dependent on the subsoil stratigraphy and are far from being homogeneous along the length of the pile. In particular, the temperature gradients across interfaces with an organic clay deposit were found to have a major effect on the thermal axial strains. Hysteresis in the thermal axial strains during the process of heating and cooling was also analyzed and was found to represent a diminishing effect on the mobilized coefficient of thermal expansion with each cycle.