Cyclic Thermo-Mechanical Analysis of Energy Piles in Sand

Abstract

Geothermal energy piles in sand subjected to cyclic thermal loading with fifty thermal cycles and constant mechanical axial load are analyzed numerically in the present work using the nonlinear transient finite element analysis method. The resulting soil–structure interaction is investigated through these analyses. The stress–strain response of sand is simulated herein using the Mohr–Coulomb constitutive model. Mechanical behavior of energy piles is simulated using the concrete damage plasticity model. Analyses are carried out for floating and end bearing piles in both loose and dense sands subjected to different constant axial load magnitudes at the pile head. Parametric sensitivity studies are performed for different amounts of temperature variation on the pile. It is observed from the results that the mechanical load governs the response of the piles when the piles are subjected to higher mechanical loads close to the limit load value on the pile. However, at low to moderate axial load magnitudes, thermal expansion of the pile causes uplift of the piles. Due to pile uplift, negative shear forces are generated at the pile–soil interface near pile head. The radial strains induced in the pile due to thermo-mechanical loading are observed to be higher than that induced due to only mechanical loading. The axial stress in the piles also increases when pile is subjected to heating.