Numerical investigations of the effects of different factors on the displacement of energy pile under the thermo-mechanical loads

Abstract

The displacement characteristics of energy pile are very important for its safe and sustainable operation. In order to obtain the influences of various factors on the displacement of energy pile, a thermo-mechanical coupled numerical model of energy pile with groundwater advection was established based on COMSOL Multiphysics software. The effects of thermal load, thermo-mechanical coupling load, groundwater advection, soil type, soil stratification and cooling and heating cycle operation on the displacement variation of energy pile operated in summer and winter modes were studied. The results indicate that for thermal load alone, the pile displacement in summer mode can almost be restored to its initial state, and an irrecoverable pile head displacement will occur in winter mode. The lower the inlet temperature, the larger the displacement variation degree. For the thermo-mechanical coupling load, the change ratio of pile head displacement increases with the decrease of mechanical load and increases with the increase of inlet temperature in summer. For winter mode, it increases with the decrease of mechanical load and inlet temperature. In addition, the larger the advection velocity of groundwater, the more heat (cold) can be taken away from the pile, and thus the smaller the displacement changes. For the soil types and stratification, the pile head displacement in soft clay is the largest, followed by silty clay and hard clay, and the rock soil is the smallest. Moreover, the soil stratification and cooling and heating cycle operation has a significant effect on the displacement changes of energy piles and should be considered in the design of energy piles.