Page 241 - Analysis and Design of Energy Geostructures

216 Analysis and Design of Energy Geostructures

Figure 5.2 Volumetric behaviour of fine-grained soils subjected to temperature variations. Redrawn
after Di Donna, A., Laloui, L., 2013. Soil response under thermomechanical conditions imposed
by energy geostructures. In: Laloui, L., Di Donna, A. (Eds.), Energy Geostructures: Innovation in
Underground Engineering. Wiley, pp. 3 21.

temperature variation, ΔT. The theoretical relationship between ε v and ΔT for
concrete is plotted for reference.
Under NC conditions, fine-grained soils contract when heated and a significant
part of this deformation is not recovered upon cooling (Di Donna and Laloui, 2013).
According to currently available experimental evidence, thermally induced volumetric
strains of up to 6% can characterise NC soils upon heating (e.g. for temperature varia-

tions of up to ΔT 5 80 C). Such an irreversible mechanical behaviour is unusual for
any material and is associated with a thermal contraction of the soil matrix (also termed
thermal collapse).
Under highly OC conditions, fine-grained soils expand when heated and this
deformation is entirely recovered upon cooling (Di Donna and Laloui, 2013).
Thermally induced volumetric strains of up to 20.5% can characterise OC soils upon

heating (e.g. for temperature variations of up to ΔT 5 80 C). Such a reversible
mechanical behaviour is typical for most materials, such as metals and concrete.
Between the two aforementioned cases there is an intermediate one associated
with slightly OC conditions (Di Donna and Laloui, 2013). Under slightly OC condi-
tions, fine-grained soils show an initial expansion and subsequent contraction when
heated, followed by a tendency towards contraction upon cooling. This mechanical
behaviour represents a transition between the behaviour of soils under NC and OC
conditions.