Cyclic Thermal Effects on Soil-Structure Interaction in Case of Energy Piles

Abstract

This paper presents the effect of thermal and mechanical load on stress-strain response of energy piles in Ottawa Sand. The study is focussed on the thermally induced displacement of energy piles due to cyclic thermal loading. The pile response to combined thermal and mechanical loading is analysed through axisymmetric nonlinear finite element analysis procedure using Abaqus software for a single energy pile in Ottawa sand. The stress-strain response of pile is assumed as linear elastic and the stress-strain response of sand is simulated using constitutive model CASM. The CASM model is incorporated in finite element software Abaqus through user defined material subroutine. The pile base displacement-time history and shear stress in soil at pile-soil interface are analysed. The analyses are performed for 50 thermal cycles considering different pile base conditions (i) floating base pile and (ii) fixed base pile. A parametric study is carried out by varying (i) stiffness of surrounding soil and (ii) temperature change applied on the pile. It is concluded from the results that the pile response to thermomechanical loading can be attributed to stiffness of soil and the magnitude of thermal load applied on the pile. The mechanical loading of the piles causes downward displacement and thermal load causes upward displacement of pile head. Consequently, the shear stress response at pile-soil interface is altered. The negative shear stress generates in the fixed base pile in loose sand. The resultant pile displacement is controlled by the magnitude of applied thermal load. Elastic behaviour of piles is observed for the piles subjected to cyclic thermomechanical loading.