A continuum-based analytical model for the design of floating energy piles in generalised inhomogeneous soils

This study presents a novel continuum-based semi-analytical framework for the analysis of floating energy piles embedded in generalised inhomogeneous soils. The soil is modelled as an approximate Tajimi-type continuum. Vertical soil inhomogeneity is incorporated into the model by formulating a generalised eigenvalue problem for the evaluation of the soil modes, which are approximated through a series expansion in terms of simple trigonometric functions. The pile and the soil column beneath its tip are represented as a single axially deforming rod, and the restraint effect provided by thermally inactive piles connected to the same cap is accounted for through a concentrated spring at the pile head. In this way, a unified framework in which continuous and piecewise functions, or arbitrary combinations thereof, are used to describe the variation of soil stiffness with depth, is developed to derive the axial force along energy piles. The proposed solution is also extended to include mechanical loads. The predictive capability of the proposed model is assessed through comparisons with established analytical solutions, complex fully coupled numerical analyses and data from full scale field tests on energy piles supporting a real structure. The very close agreement confirms the reliability of the proposed framework as an efficient alternative to computationally demanding numerical approaches, which can serve as a simple tool for pile design.