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Thermohydromechanical behaviour of soils and soil structure interfaces 215

measure of the current void ratio, e, in relation to the maximum void ratio, e max , and
minimum void ratio, e min , and can be determined as
D R 5 e max 2 e min 3 100% ð5:3Þ
e max 2 e

Values of D R 5 0% 20% are associated with very loose coarse-grained soils.
Values of D R 5 20% 40% are associated with loose coarse-grained soils. Values
of D R 5 40% 60% are associated with medium-loose coarse-grained soils. Values of
D R 5 60% 80% are associated with dense coarse-grained soils. Values of D R 5 80%
100% are associated with very dense coarse-grained soils.

5.4 Deformation of soils under nonisothermal conditions
5.4.1 Influence of mechanical and thermal loads on soil deformation

While mechanical loads can cause both volumetric and deviatoric deformations, ther-
mal loads only induce volumetric deformations. Compressive mechanical loads cause
contractive strains. Tensile mechanical loads cause expansive strains. Heating thermal
loads induce an expansion of all of the soil constituents (i.e. solid grains and water in
fully saturated conditions) according to their thermal expansion coefficient and the
applied temperature variation. Cooling thermal loads induce a contraction of all of the
soil constituents. Nevertheless, heating thermal loads can cause both expansive and
contractive strains of soil matrices.

5.4.2 Volumetric behaviour of fine-grained soils caused
by one thermal cycle
Experimental results about the volumetric behaviour of fine-grained soils subjected
to one thermal cycle have been presented, for example by Campanella and
Mitchell (1968), Plum and Esrig (1969), Demars and Charles (1982) and Baldi
et al. (1988). Complementary results have been proposed by Towhata et al. (1993),
Burghignoli et al. (2000), Sultan et al. (2002), Cekerevac and Laloui (2004),
Romero et al. (2005) and Abuel-Naga et al. (2007). According to the previous
results, heating fine-grained soils in drained conditions can produce a contractive or
an expansive volume variation of such materials, while cooling produces a contrac-
tive volume variation. Experimental evidence supporting the previous considerations
is reported in Fig. 5.2 with reference to the results of Baldi et al. (1988), Hueckel
and Baldi (1990) and Abuel-Naga et al. (2007). Results are depicted in terms of
the relationship between thermally induced volumetric strain, ε v , and applied