Load transfer analysis of driven energy pile under combined thermal and mechanical loading

Abstract

This study presents a semi-analytical analysis on load transfer mechanisms of driven energy piles in clay, with a comprehensive consideration of installation effects, reconsolidation of surrounding soils and combined thermal and mechanical loading. The installation effects of driven energy piles are modelled based on the cavity expansion theory. Analytical expressions for thermally induced displacements, including axial and radial expansion of pile, are derived. A hysteresis hyperbolic load transfer function is proposed according to the Masing’s criterion to incorporate the loading and unloading induced by temperature changes. Through numerical simulations and experimental validations, the axial strain and stress distribution within the pile under varying conditions is explored, where good agreements between the proposed theoretical method, numerical results and field tests are observed. A thorough comparison is conducted between driven energy piles and bored energy piles to assess the impact of installation effects on pile-soil relative displacement, shaft friction, and the ultimate bearing capacity. It is found that although the bearing capacity of driven energy piles is greater than that of bored energy piles, the axial stress within driven energy piles is also higher under thermal load. The findings shed light on the design and optimization of PHC energy piles in geothermal systems.