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Thermohydromechanical behaviour of soils and soil structure interfaces 233

Figure 5.18 Thermal-stress paths in the mean effective stress deviatoric stress temperature
space. 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.

Based on the considered results, shrinkage of the yield limit with an increase in
temperature is observed. This shrinkage is not homothetic, depends on the stress his-
tory and is associated with thermal softening. The influence of thermal softening on
the variation of the yield surface of soils can be appreciated in the three-dimensional
described by coordinate axes p , q and T. An example of this representation is pro-
0
posed in Fig. 5.18 with reference to the yield surface described by the Advanced
Constitutive Model for Environmental Geomechanics-Temperature effects, that is
ACMEG-T (cf. Appendix C).

5.5.2 Shear strength
The assessment of the shear strength of fine-grained soils under nonisothermal condi-
tions necessitates the consideration of the initial and current temperature level as well
as the general loading conditions. Generalisations about the influence of temperature
of the shear strength of soils lack of any significance without the previous information.
The following aspects are worth noting with reference to the possible influence of
temperature on the shear strength of fine-grained soils.
The main consequence of thermal softening under deviatoric stress states is that if
an OC material (with a certain void ratio) is sheared at a high temperature (stress path