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234 Analysis and Design of Energy Geostructures

Figure 5.19 Shear strength at different constant temperatures of (A) overconsolidated and (B) nor-
mally consolidated fine-grained soils. Data from Hueckel, T., Baldi, G., 1990. Thermoplasticity of satu-
rated clays—experimental constitutive study. J. Geotech. Eng. 116 (12), 1778 1796, Graham, J.,
Tanaka, N., Crilly, T., Alfaro, M., 2001. Modified Cam-Clay modelling of temperature effects in clays.
Can. Geotech. J 38 (3), 608 621. and Cekerevac, C., Laloui, L., 2004. Experimental study of thermal
effects on the mechanical behaviour of a clay. Int. J. Numer. Anal. Methods Geomech. 28 (3), 209 228.

0
B Bv in Fig. 5.18), it reaches the yield limit at a lower deviatoric stress with respect
to shearing at the initial temperature (stress path B Bw in Fig. 5.18). In other words,
the material undergoes plasticity earlier than in the isothermal case (Di Donna and
Laloui, 2013). Conversely, in the case of a NC or slightly OC material, heating results
in a combination of thermal softening and strain hardening, which compensate each
other. An analysis of this phenomenon has been reported by Hueckel and Baldi
(1990). Fig. 5.19 illustrates some experimental results reported by Hueckel and Baldi
(1990), Graham et al. (2001) and Cekerevac and Laloui (2004) that corroborate the
previous considerations. Additional results have been reported, for example by
Kuntiwattanakul et al. (1995), Abuel-Naga et al. (2006) and Hueckel et al. (1998).
The initial OCR has also an effect on the shear strength of the material at ambient
temperature after the application of one or more thermal cycles (Di Donna and
Laloui, 2013). If the material is initially under OC conditions, a heating cooling cycle
0
(stress path B B B in Fig. 5.18) does not produce any plastic deformation (so that
the dimension of the elastic domain remains the same after the entire cycle) and the
response under shearing is not affected because no permanent change is induced on
the void ratio. Conversely, if an initially NC or a slightly OC material is subjected to
0
0
0
a heating cooling cycle (stress path A A A or C C Cv-C C in Fig. 5.18,
respectively), strain hardening occurs as plastic deformation is produced. The material