Numerical investigations on effects of mechanical and geometrical characteristics on thermally induced group behavior of field-scale energy piles

Abstract

Energy pile groups generally exhibit different thermomechanical behavior from single energy piles. Aiming to investigate the group behavior of energy piles, three-dimensional numerical models were developed and validated against field test data for a 2 × 2 energy pile-raft foundation. The validated models were subsequently adopted to comparatively analyze the thermomechanical behavior of pile groups operating either partially or fully. The results highlighted that the group action effects would induce lower thermal stress and greater head displacement imposed upon piles. Partially operating grouped piles exhibited differential displacement, thus inducing group tilt in the raft. Besides, parametric studies were made to evaluate the effects of mechanical and geometrical parameters on the group behavior of energy piles. The effects of soil thermal expansion were directly correlated with the heating extent of the soil. Under geological conditions with high soil thermal expansion coefficients, heating-induced tensile stresses and excessive head displacements could occur during the long-term operation of multiple piles. Higher soil elastic modulus resulted in higher restrictions on the thermal movement of piles, thus reducing the head displacement and group tilt, which was considered beneficial in practice. Special attention should be paid to the group action effects for closely-spaced energy pile-raft foundations.