3415
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Field investigation of a geothermal energy pile: Initial observations
Essai sur site d’un pieu géothermique
: Observations initiales
B. Wang, A. Bouazza, R.M. Singh & D. Barry-Macaulay
Monash University, Melbourne, Australia
C. Haberfield & G. Chapman
Golder Associates Pty Ltd, Melbourne, Australia
S. Baycan
Vibropile Pty Ltd, Melbourne, Australia
ABSTRACT: Shallow geothermal energy techniques integrated in structural pile foundation have the capability of being an efficient
and cost effective solution to cater for the energy demand for heating and cooling of a building. However, limited information is
available on the effects of temperature on the geothermal energy pile load capacity. This paper discusses a field pile test aimed at
assessing the impact of coupled thermo-mechanical loads on the capacity of a geothermal energy pile. The full-scale in situ
geothermal energy pile equipped with ground loops for heating/cooling and multi-level Osterberg cells for static load testing was
installed at Monash University in a sandy profile. Strain gauges, thermistors and displacement transducer were also installed to study
the behaviour of the energy pile during the thermal and mechanical loading periods. Thermal behaviour of the surrounding soils was
also examined during the heating and cooling cycles of the energy pile. It has been found the pile shaft capacity increased when the
pile was heated and returned to the initial capacity (i.e initial conditions) when the pile was cooled. Thus indicating that no loss in pile
shaft capacity was observed after heating and cooling cycles.
RÉSUMÉ : Les pieux géothermiques ont la capacité d'offrir une solution efficace et rentable capable de réduire la demande d'énergie
nécessaire pour le chauffage et le refroidissement des bâtiments. Cependant, peu d'informations sont disponibles sur les effets de la
température sur la capacité de charge de ce type de pieux. Cet article présente les résultat
s d’essais in
-situ de chargement visant à
évaluer l'impact du couplage des charges thermomécaniques sur la capacité d'un pieu géothermique. Un pieu géothermique, équipé de
tubes en polyéthylène pour la circulation du liquide nécessaire pour le chauffage/refroidissement du pieu ainsi que des cellules
Osterberg multi-niveaux, a été installé dans du sable sur une profondeur de 16 m. En outre, ce pieu a été équipé de jauges de
contrainte, thermistances et de capteurs de déplacement pour étudier son comportement pendant les périodes de chargement
thermiques et mécaniques. Le comportement thermique des sols environnants a également été examiné lors des cycles de chauffage et
de refroidissement du pieu. Ces essais ont montré que le frottement latéral du pieu augme
nte après qu’il
ait été chauffé et retourne à la
capacité initiale (c.-à-conditions initiales) après
qu’il
ait
été refroidi. Ceci indique qu'aucune perte de la capacité n’a été observée
après des cycles de chauffage et de refroidissement.
KEYWORDS: Energy piles, shaft resistance, Osterberg cells, thermal properties, in-situ pile load test, sustainable development
1 INTRODUCTION
Energy foundations widely known as energy piles can be
defined as dual-purpose structural elements. They utilise the
required ground-concrete contact element and the shallow solar
energy flux, found within 100 m of the ground surface, to
transfer the building loads to the ground as well as acting as
heat exchanger units. Energy piles may be driven, bored or
augered. Reinforced concrete piles have been found to be
advantageous due to the material’s high thermal storage
capacity and enhanced heat transfer capabilities (Brandl, 1998).
Geothermal energy piles bring another dimension to pile
design. The principle of energy piles is that energy is extracted
from or sunk into the ground by a fluid, circulating via a
Ground-Source Heat Pump (GSHP) similar to vertical borehole
GSHP systems. The difference is where the energy pile
foundation serves as an integral support to the superstructure in
addition to heating and cooling the built structure (Bouazza et
al., 2011). The advantages of energy piles are the cost saving
over installing additional vertical boreholes and additional land
areas generally required outside the perimeter of the built
structure to accommodate other shallow vertical and horizontal
GSHP systems.
Physical testing of pile foundations have been well
documented on assessing the pile shaft and base capacity
installed in various ground conditions with or without the
influence of groundwater. However, the relatively new concept
of energy pile foundations has introduced new parameters to be
considered into pile design, to accurately predict the pile
behaviour and reliability in modern structures.
2 BACKGROUND
Austria, Switzerland and Germany can be regarded as the
pioneering countries that have investigated this technology for
decades. Extensive use of energy geostructures have been
featured in Austria. Brandl (2006) reported that more than
25,000 energy foundations (piles, etc.) were in use in Austria
with installations dating as early as the 1980’s.
Over the past five years, the installation of thermo active pile
foundations has grown exponentially in the UK (Amis et al.
2008). There were approximately ten times more thermo-active
foundations installed in 2008 than in 2005. The reason for this
rise in production is mainly driven by the code for sustainable
buildings that requires the construction of zero-carbon buildings
by 2019 (Bourne-Webb et al. 2009). The implementation of the
thermo active pile technology in the USA is very limited by
comparison to Europe. Traditionally, reliance was on the use of
ground source heat pumps (GSHPs) to reduce building energy
consumption for heating and cooling (McCartney et al., 2010).
Recently, the USA is experiencing a renewed interest in the use
of energy piles as they have been identified as being a more cost
effective solution compared to the use of other GSPHs systems
Baycan S.
Haberfi ld C., Chapm n G.
Wang B. Bouazza A. Singh R.M., Barry-Macaulay D.
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