Design Review and Long-Term Thermomechanical Behavior of GSHP Energy Piles

Ground source heat pump (GSHP) energy piles serve dual functions, simultaneously providing structural support and acting as ground-coupled heat exchangers through built-in pipe circuits. This study synthesizes evidence from field monitoring, laboratory experiments, and numerical simulations to examine the design methodologies and long-term thermomechanical behavior of such foundation systems. Design parameters, such as heat exchanger layout, pile material, and operational strategy, have considerable influence, yet the primary concern remains the pile response under repeated heating and cooling cycles. With continuous cyclic thermal loading, a set of largely irreversible phenomena tends to occur, including ratcheting settlement, degradation of shaft friction, and the progressive accumulation of thermal stresses. The incorporation of phase-change materials (PCMs), when appropriately utilized, has been shown to boost heat exchange efficiency by approximately 20–30%, and to reduce thermal stresses by about 10–20%. To accurately reflect the time-dependent soil response, constitutive model that couples thermal, hydraulic, and mechanical processes, i.e., a coupled framework, is indispensable. Despite these advances, substantial gaps still exist. The absence of widely accepted design standards, the limitations of existing constitutive models in representing the full diversity of natural soils, the immature application of machine learning for performance prediction, and the lack of system-level optimization, still hinders the application of GSHP energy pile in large scale.