Incremental load transfer analysis of an energy pile under arbitrary mechanical and thermal loads

Abstract

This paper describes a new incremental approach to simulate the axial load–displacement response of energy piles. A load transfer approach is used to model the interaction of pile with surrounding soil, the underlying layers, and the superstructure. Interface springs are nonlinear–hyperbolic and Masing’s rule applies to model their hysteresis behaviour. Mechanical and thermal loads are incrementally applied to the pile using an iterative finite difference method. This strategy makes it possible for both mechanical and thermal loads to have arbitrary time histories during analysis. The self-weight of the energy pile can also be considered. The simulation results are found to compare favourably with published experimental results from field and laboratory testing of three energy piles. The effects of amplitudes of mechanical load and temperature change as well as those of the stiffness of the pile extremities on the thermomechanical response of the pile and the position of the null point are evaluated and discussed. The simulations show that the thermal-induced axial force due to a unique temperature change was greater for an energy pile under lower amounts of mechanical load. It is found that the effect of the end restraining condition on the response of the energy piles is more considerable during the heating processes than during the cooling processes. More restrained pile–superstructure connection also results in more thermal-induced axial force in the energy pile. The null point is always located closer to the stiffer extremity of the energy pile.