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218 Analysis and Design of Energy Geostructures

Figure 5.4 Effect of temperature on the apparent preconsolidation stress. Redrawn after Laloui, L.,
Cekerevac, C., 2003. Thermoplasticity of clays: an isotropic yield mechanism. Comput. Geotech. 30 (8),
649 660.

Cui et al., 2000; Laloui and Cekerevac, 2003). In general, these formulations link the
0
isotropic preconsolidation pressure, p c , that is the maximum mean effective stress that
the soil has ever supported, and the temperature, T (cf. Fig. 5.5).
Soils under NC conditions are characterised by a stress temperature state that lies
on the yield surface (state A in Fig. 5.5). In other words, the current mechanical pres-
sure, p A , applied to the material at a temperature T 0 coincides with the preconsolida-
0
0
tion pressure, p c . Because of the considered stress temperature state, drained heating
up to a temperature T 1 . T 0 from the initial state under a constant mean effective
stress induces thermoplastic strain (i.e. path A A ). Upon thermal unloading under a
0
constant mean effective stress, the material becomes OC and strains are only partly
recovered. For this reason, heating fine-grained soils under NC conditions leads to a
so-called thermally induced overconsolidation (Di Donna and Laloui, 2013). Because
heating under NC conditions causes plasticity and induces an increase in the elastic
0
domain (i.e. path A A in Fig. 5.5), strain hardening is produced. Strain hardening
can also be caused by isothermal mechanical loading (i.e. path A Av in Fig. 5.5).
This phenomenon is the inverse of the thermal softening that involves the shrinkage
of the elastic domain with an increase in temperature. Based on the previous