Performance-based Design of Energy Pile Foundations

Abstract

Over the past twenty years, an increasing amount of research has been performed to understand the multiphysical behavior and to address the geotechnical and structural design of so-called energy piles, i.e., deep foundations that can serve any superstructure as both structural supports and geothermal heat exchangers. The coupled application of thermal and mechanical loads to energy piles, due to their multifunctional operation, represents a challenge. Currently, knowledge about the response of energy piles subjected to thermal and mechanical loads is accessible, along with some design guidance. However, this knowledge is fragmented and no recognized performance-based design framework is available. Looking at such challenge, this paper presents a theoretical and experimental analysis of the multiphysical behavior of energy piles, as well as a performance-based design framework for such foundations. The work highlights that thermal loads involve effects that can be neglected in the design of energy piles at ultimate limit states and can be considered relevant only at serviceability limit states. Based on this result, the performance-based design of energy piles at ultimate limit states reduces to a conventional pile design process while the design at serviceability limit states must account for a number of proposed verifications.

Calculation of the representative temperature change for the thermomechanical design of energy piles

“…The load transfer mechanism of the energy pile subjected to coupled thermal and mechanical effects had been studied by Bourne-Webb et al 30 and Rotta Loria et al 31 .…”

Reliability-based load and resistance factor design model for energy piles

“…Several researches have been conducted to investigate the role of thermal loading in the geotechnical design of energy piles. It was suggested that the effect of thermal loading must be considered in the analysis and design of energy piles 10 . Compared with the ultimate limit state, the performance degradation of the energy piles due to the piping need in the serviceability limit state was suggested to be more considered in the design (e.g., 6 ).…”

“…Thus, besides satisfying the design requirements for traditional piles, the thermal loading should be properly considered in the design of energy piles. Several analysis methods have been developed to investigate the thermomechanical behavior of energy piles, such as the empirical method (e.g., 8 – 10 ), load-transfer method (e.g., 11 – 13 ), and Full numerical method (e.g., 14 – 16 ). However, it is still difficult to ascertain the pile performance in the geotechnical design of energy piles due to the uncertainties in soil parameters, applied load, design model, etc.…”

Thermo-mechanical behavior of a full-scale energy pile equipped with a spiral pipe configuration

“…Appropriate selection of design temperature variations, through due account of the non-uniformity of the temperature field within energy piles (Abdelaziz and Ozudogru 2016b), is necessary for verification purposes of these and other energy geostructures (Rotta Loria 2019;Rotta Loria et al 2020).…”