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Thermohydromechanical behaviour of soils and soil structure interfaces 221

Figure 5.7 Thermal cyclic effects on normally consolidated (A) illite and (B) carbonate clay.
Redrawn after Campanella, R.G., Mitchell, J.K., 1968. Influence of temperature variations on soil behav-
ior. J. Soil Mech. Found. Div. 94 (SM3), 709 734 and Hueckel, T., Pellegrini, R., Del Olmo, C., 1998. A
constitutive study of thermoelasto-plasticity of deep carbonatic clays. Int. J. Numer. Anal. Methods
Geomech. 22 (7), 549 574.

and range produce small increments of irreversible deformation that decrease cycle after
cycle. This phenomenon reveals an accommodation phenomenon and a soil behaviour
that becomes progressively insensitive to temperature variations (Campanella and
Mitchell, 1968). Experimental evidence in support of the previous considerations is
presented in Fig. 5.7 with reference to the results of Campanella and Mitchell (1968)
and Hueckel et al. (1998) (the latter highlight the influence of different magnitudes of
heating thermal loads on the material response). Results are depicted in terms of the
relationship between thermally induced volumetric strain, ε v , and applied temperature
variation, ΔT.
Complementary data corroborating the previous considerations are presented in
Fig. 5.8 with reference to the study of Di Donna and Laloui (2015). Soils under OC
conditions show a reversible deformation which corresponds to the thermoelastic
expansion (and contraction) of the solid skeleton. Soils under NC conditions show a
partly irreversible deformation upon the first heating cooling cycle. Irreversible defor-
mation is accumulated in all cases during the first heating cooling cycle and then sta-
bilises showing a thermoelastic behaviour (cf. Fig. 5.9). This phenomenon is called
plastic accommodation (Di Donna and Laloui, 2015). The slope of the (unloading) curve
associated with a thermoelastic behaviour of the material can be linked to the thermal
expansion coefficient of the solid skeleton.
When cyclic thermal loading of NC soils occurs, the configuration of the solid par-
ticles becomes increasingly stable at each cycle (depending on the amount of