Thermomechanical Analysis and Parametric Study of Geothermal Energy Piles in Sand

Abstract

Response of geothermal energy piles in sand under combined thermal and mechanical loading was investigated in the present work using a nonlinear axisymmetric finite-element (FE) analysis procedure. In this study, the piles were considered to behave linear-elastically. The stress-strain behavior of sand was simulated using a state parameter–based constitutive clay-and-sand model (CASM), which was implemented in FE software through a user material subroutine. The geothermal energy piles of different lengths and diameters with floating and end-bearing conditions in sand were analyzed under mechanical and thermomechanical loading to study the displacements of soil and pile through axial and radial strains in the pile and axial stress in the pile. In addition, parametric sensitivity studies were carried out by varying the relative density of sand and thermal load on the pile. Results showed that the relative density of the sand, applied thermal load on the pile, and the end condition of the pile govern the relative displacement between pile and soil. Also, axial stresses under thermomechanical loading were greater than they were under only mechanical loading.