A THERMO-ELASTO-VISCOPLASTIC MODEL FOR SOFT SEDIMENTARY ROCK

In this paper, a new thermo-elasto-viscoplastic model is proposed, which can characterize thermodynamic behaviours of soft sedimentary rocks. Firstly, as in the Cam-clay model, plastic volumetric strain which consists of two parts, stress-induced part and thermodynamic part, is used as hardening parameter. Both parts of the plastic volumetric strain can be derived from an extended e-ln p relation in which the thermodynamic part is deduced based on a concept of 'equivalent stress'. Secondly, regarding soft sedimentary rocks as a heavily overconsolidated soil in the same way as the model proposed by Zhang et al. (2005), an extended subloading yield surface (Hashiguchi and Ueno, 1977; Hashiguchi, 1980; Hashiguchi and Chen, 1998) and an extended void ratio difference are proposed based on the concept of the equivalent stress. Furthermore, a time-dependent evolution equation for the extended void ratio difference is formularized, which considers both the influences of temperature and stresses. Finally, it is proved that the proposed model satisfies thermodynamic theorems in the framework of non-equilibrium thermodynamics.