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General Report TCs 307+212
Thermal Geomechanics with Emphasis on Geothermal Energy
Rapport général TCs 307+212
Géomécanique thermique avec une attention particulière portée sur l'énergie géothermique
Puppala A.J.
University of Texas, Arlington, Texas, USA
Choudhury D.
Indian Institute of Technology Bombay, Mumbai, India
Basu D.
University of Waterloo, Waterloo, Canada
ABSTRACT: Thermal geomechanics is an important area of soil and rock mechanics, and has applications in important areas related
to sustainable development like energy extraction and storage, waste containment, forest fire, explosions in soil, and climate change.
In this general report, a brief overview of thermal geomechanics is presented in the context of the papers allocated to the thermal
geomechanics session of the 18
th
ICSMGE. A review of these papers is provided in the report. The topics covered by the papers can
be broadly grouped into two sub-themes: thermal geomechanics and geothermal energy. The papers in the thermal geomechanics
category focussed on the fundamental thermo-hydro-chemo-mechanical behavior of soil and rock while the papers on the geothermal
category emphasized the application of thermal geomechanics in geothermal energy extraction through ground-source heat pumps and
energy piles.
RÉSUMÉ: La thermogéomécanique est un domaine important la mécanique des sols et des roches avec des applications dans des
domaines importants liés au développement durable, comme l'extraction et le stockage d'énergie, la maîtrise des déchets, les incendies
de forêt, les explosions dans les sols et le changement climatique. Dans ce rapport général, on présente un bref aperçu de la
thermogéomécanique basé sur les articles acceptés à la session correspondante du 18
e
CIMSG. Un examen de ces documents est
présenté dans le rapport. Les sujets abordés par les articles peuvent être regroupés en deux sous-thèmes: thermogéomécanique et
géothermie. Les articles de thermogéomécanique fondamentale sont consacrés à la thermo-hydro-chimio-mécanique des sols et des
roches, tandis que les articles de géothermie traitent des applications de thermogéomécanique dans l'extraction de l'énergie
géothermique par pompes à chaleur géothermiques et pieux énergétiques.
KEYWORDS: thermo-mechanics, geothermal energy, energy pile, sustainability, renewable energy, thermal conductivity.
1 INTRODUCTION
The 18th ICSMGE is being held at an interesting time of
shifting paradigms at the backdrop of global climate change,
economic downturn, population growth, advocacy for
renewable energy use, and natural hazards. These factors have
made governing bodies all over the world rethink the ways of
day-to-day business, and the rather recent emphasis on
sustainable development, that advocates a triple bottom line
approach of balancing environment, economy and social equity,
is an obvious outcome of such efforts. Consistent with this
approach, the geotechnical profession has been motivated by the
mantra of ‘achieving maximum utilizing minimum’, which is
particularly important because the profession lies at the
interface of the natural and built environments, and can
significantly influence the economy, society and environment.
Extraction of renewable energy, safe disposal of wastes,
construction and maintenance of civil infrastructure and
lifelines, and security against natural and man-made hazards are
some of the far-reaching areas that geotechnical engineering
contributes to, and this report on thermal geotechnics and its
applications is, in part, a testimony of the variegated efforts that
geotechnical engineers have put in towards sustainable
development of civil infrastructure.
Thermal geomechanics is an important topic related to
sustainable development. Heating and cooling of buildings
using geo-structures like piles, walls and slabs, in situ burning
of oil spill, oil recovery from reservoirs at high pressure and
temperature, underground disposal of nuclear wastes, explosion
on or inside the soil mass, forest fire, and global climate change
affecting the freeze-thaw cycle of permafrost are some
examples which may cause the soil temperature to vary from
around
40
C to 300
C or more. It is well documented that
temperature fluctuations have an effect on the soil strength and
stiffness as well as on the pore pressure development. With an
increase in temperature, the initial shear modulus and
compressibility of clay increase and the drained and undrained
shear strength decrease. Therefore, temperature fluctuations in
soil may affect the stability of the civil infrastructure.
Differential settlement of buildings due to heating and cooling
using geothermal piles, changes in groundwater flow patterns
and groundwater advection caused by geothermal heat pumps,
temperature-imbalance induced seismic activities, distress in
underground pipelines due to freeze-thaw cycles, debris flow
and landslide are some examples in which the civil
infrastructure is negatively impacted by alterations in soil
temperature. It is thus imperative that research efforts are made
toward understanding soil and rock behavior influenced by
temperature change and heat flow.
An important application of thermal geomechanics is
extraction of geothermal energy. Geothermal energy is a clean
and renewable form of energy that is extracted from the deep
and near-surface soil and rock strata by various means. Shallow
geothermal energy is commonly extracted using ground-source
heat pumps (GSHPs) from the shallow depths beneath the
ground surface where the temperature remains stable within a
narrow range of 7°-21°C. A GSHP typically consists of
a heat
pump, an air delivery system, and a heat exchanger,
and uses
the ground as a heat source and sink in winter and summer,
respectively, to heat and cool buildings (Hughes 2008).
Although several research studies have been performed on
geothermal heat pumps, most of these studies focused on the
