Thermo-plasticity of clays

Characterisation of Ground Thermal and Thermo-Mechanical Behaviour for Shallow Geothermal Energy Applications

“…In normally consolidated clayey soils under constant mechanical load, heating induces thermo-plastic loading and contractive volumetric behaviour, while heavily over-consolidated clays tend to exhibit a thermo-elastic response (although according to some authors, inelastic strains can also be observed [196]). This behaviour has been successfully captured by constitutive modelling in the framework of Cam-Clay, including the thermal dependency of the soil volumetric behaviour, upon formulating a temperature-dependent hardening rule ( [24,25,[197][198][199]) followed by experimental confirmation (e.g., [198,200]). …”

“…Section 6.1), that can be easily incorporated into commercial finite element codes. Upon referring to one of the simplest such thermo-mechanical constitutive formulations, as that presented by Reference [198], it can be deduced that a basic set of parameters needed to reproduce a soil's basic thermo-mechanical behaviour (in addition to standard Cam Clay parameters) consists of: (a) volumetric thermo-elastic expansion coefficient, (b) thermo-plastic softening parameter, and possibly (c) a parameter describing thermally induced changes in the Critical State parameter M [229].…”

“…Of the above, parameter (a) is the best established and can be measured by means of different experiments, such as performing drained heating tests at constant isotropic stress in over-consolidated specimens (e.g., [198,230]). Parameter (b) describes the rate at which thermal softening occurs, i.e., the thermal dependency of the soil's apparent pre-consolidation stress, defining the 'shrinkage' of elastic domain with increasing temperature.…”

“…Figure 26. Evolution of volumetric strain with clay activity (adapted from Reference [26] using data from References [198,212,214,217,219,220,[222][223][224]). …”

A new triaxial apparatus for testing soil water retention curves of unsaturated soils under different temperatures

“…A number of constitutive models and experimental studies have been developed to analyze the behavior of saturated soils under different temperatures (Hueckel and Borsetto, 1990a;Delage et al, 2000;Cui et al, 2000;Laloui and Cekerevac, 2003;Zhou and Yu, 2005;Yao and Zhou, 2013). However, the models that consider the temperature effects on unsaturated soils are limited (Francois and Laloui, 2008;Tang and Cui, 2009;Cai et al, 2010;Zhou et al, 2014).…”