Optimising energy piles: a multi-objective approach to cost and failure probability

This paper presents a comparative analysis of the influence of thermal loading on the design of optimally designed floating energy piles in soft consistency soils using a genetic algorithm. The nonlinear settlement of energy piles is also considered. The deterministic optimisation model (OPT-EP) includes a cost objective function constrained by design constraints and is later extended to include the probability of failure as a second objective function to perform multi-objective optimisation. This extension was undertaken because the Eurocode 7 approach only partially accounts for uncertainties in the soil, whereas the reliability-based design (RBD) approach fully exploits these uncertainties. Consequently, a multi-objective optimisation (cost vs. failure probability) was carried out in this study. The optimal designs obtained by the two different optimisation methodologies were further analysed and it was found that when the Eurocode 7 safety factor approach was used, the conditions related to thermal loading were not crucial for the design values. On the other hand, the multi-objective optimisation based on the RBD approach showed that the thermal loading affected the design, proving the usefulness of the multi-objective optimisation and the reliability-based design.