Page 295 - Analysis and Design of Energy Geostructures

CHAPTER 6

Thermomechanical behaviour

of single energy piles

6.1 Introduction

Energy pile foundations, similar to conventional pile foundations, consist of two com-
ponents: a group of piles and a pile cap (the latter being intended as the general struc-
tural element connecting the piles to the superstructure). Addressing the response of
the piles in a group is crucial for a comprehensive understanding of the behaviour of
any pile foundation. At the same time, in many practical cases, considering the piles as
single isolated elements represents the starting point of any analysis and design. This
approach is considered hereafter for energy piles subjected to the mechanical and ther-
mal loads associated with their structural support and geothermal heat exchanger roles.
The application of mechanical and thermal loads to energy piles introduces novel
aspects in the mechanical response of such foundations compared to that characterising
conventional piles typically subjected to only mechanical loads because of their sole
structural support role. The reason for this is because, as a consequence of the coupling
between the heat transfer and the deformation of materials previously treated in Part B
of this book, thermal loads induce thermal expansions and contractions of both the
piles and the surrounding soil as well as modifications of the stress state. Understanding
the influence of thermal loads, applied alone or in conjunction with mechanical loads,
is key to address the thermomechanical behaviour of energy piles.
To investigate the response of single energy piles to mechanical and thermal loads,
various approaches can be employed. Full-scale in situ tests, model-scale laboratory
tests and centrifuge tests are example of experimental approaches. In general, more
remarkable financial expenditures are required to run full-scale in situ tests compared
to model-scale laboratory tests and centrifuge tests. Despite this limitation, the capabil-
ity of full-scale in situ tests to provide data unaffected by scale effects that can poten-
tially characterise the results of model-scale laboratory tests and centrifuge tests can
make such an approach preferable for analysis and design purposes.
This chapter presents an analysis of the response of single energy piles subjected to
mechanical and thermal loads based on the results of full-scale in situ tests. A focus is
devoted to energy piles subjected to mechanical and heating thermal loads, although
the influence of cooling thermal loads can be inferred from the results presented.

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Analysis and Design of Energy Geostructures
DOI: https://doi.org/10.1016/B978-0-12-816223-1.00006-0 All rights reserved. 271