1. Introduction

The NLH_CSRM model will eventually replace the LKR and LETK laws of behavior. This « modernization » work is part of the development actions of the EDF -R&D project « Radioactive Waste Management » (GDR2).

The scope of use of model NLH_CSRM is currently limited to isotropic mechanical behavior. Taking into account structural anisotropy and the dependence of work hardenings on temperature — effective in the latest version of model LKR — will be the subject of future renderings; as will the dependence of the criteria on the third invariant of the stress deflector (Lode angle).

The NLH_CSRM model is part of the thermodynamic framework of generalized standard materials with two irreversible mechanisms,

• Plastic mechanism —irreversible instantaneous behavior: hardening and/or softening workings, contracting or expanding volume behavior, influence of the average stress on the fragile nature of the compression response,…;

• Viscoplastic mechanism — irreversible delayed behavior (Perzyna type): primary, secondary, and tertiary creep (ruin).

A coupling between these two mechanisms makes it possible — among other things — to represent the dependence of the maximum resistance of certain geomaterials on the stress rate.

This « modernization » work is motivated by the desire to increase the robustness and efficiency of the model used to describe the behavior of Callovo-Oxfordian argillite — host rock constituting the first geological barrier of Cigéo — in order to be able to consider its use on 3D problems requiring memory and calculation time.