Strain distribution in geothermal energy piles: A parametric study

Abstract

This work emphasizes on the alteration in pile-soil interaction in case of geothermal energy piles during thermal cycle. The geothermal energy piles are investigated numerically using finite element software Abaqus. To simulate the soil mechanical and thermal response, two user defined material subroutines are used for the soil surrounding the piles. The behaviour of soil is reproduced using CASM; a soil constitutive model which is based on the concepts of critical state soil mechanics. To investigate the additional strains induced in the piles due to the thermal load, parametric analyses are carried out considering the effect of (i) different pile end restraints, (ii) relative densities of the soil, (iii) pile dimensions and (iv) lateral earth pressure coefficient. The analysis results indicate that the axial and radial strains are induced in the pile due to pile expansion during thermal loading. The increase in lateral earth pressure coefficient at interface of pile and soil can be correlated to the thermally induced radial strains. Moreover, the pile response to the thermal cycle can be considered to the governed by soil stiffness and the magnitude of thermal load applied on the pile. Analyses are also performed to investigate the influence of thermal parameters of soil and thermal load on the soil earth pressure coefficient at interface of pile and soil. The lateral earth pressure coefficient increases following the increase in magnitude of thermal load, however the effect of thermal conductivity of soil is not significant.