Modeling of Thermomechanical Energy Pile Behavior with Temperature-Induced Radial Effects

Abstract

Geothermal energy foundations or thermoactive ground structures present sustainable alternative systems for meeting heating/cooling needs of buildings in different seasons and are also cost-effective in comparison with stand-alone ground source heat pumps. In simultaneously supporting the upper structure and exchanging heat with the surrounding soil, energy piles may suffer from coupled thermomechanical loads and exhibit complex behaviors in stress and deformation. For predicting energy pile responses to the external loads, numerical models have been established with load transfer method considering the deformation and force in the longitudinal direction of the pile. In heating and cooling, the deformation may not only occur along the length of the pile, but also happen in the radial direction, which may lead to a change of ultimate lateral frictional resistance and load transfer characteristics. Very little work has been undertaken to include the radial effects in the numerical model of energy pile behavior. With the theory of geotechnical medium circular hole expansion, the elastic and elastic–plastic solutions of radial stress of energy piles caused by temperature change are derived in this work and the analytical model under joint action of axial–radial temperature effect are implemented into the numerical model with load transfer method. The results of the study indicate that the operation of energy piles not only affects lateral resistance and axial force in the axial direction but also has an impact on radial aspects due to temperature changes. This influence is primarily manifested when the energy piles are heated, resulting in radial expansion. Such expansion strengthens the soil’s constraint on the piles, thereby increasing their bearing capacity. The opposite effect occurs when cooling. The numerical calculation method established in this paper effectively captures these phenomena.