Modelling the thermo-mechanical volume change behaviour of compacted expansive clays

TL;DR

This paper develops a coupled thermo-hydro-mechanical model for compacted expansive clays, validated against experimental data, to predict volume changes under conditions relevant for radioactive waste disposal.

Contribution

It introduces a new constitutive model combining existing hydro-mechanical and thermo-mechanical models for expansive clays, validated with MX80 bentonite data.

Findings

Model accurately predicts volume change behaviors.

Heating can cause expansion or contraction depending on conditions.

Mean yield stress varies with suction and temperature.

Abstract

Compacted expansive clays are often considered as a possible buffer material in high-level deep radioactive waste disposals. After the installation of waste canisters, the engineered clay barriers are subjected to thermo-hydro-mechanical actions in the form of water infiltration from the geological barrier, heat dissipation from the radioactive waste canisters, and stresses generated by clay swelling under almost confined conditions. The aim of the present work is to develop a constitutive model that is able to describe the behaviour of compacted expansive clays under these coupled thermo-hydro-mechanical actions. The proposed model is based on two existing models: one for the hydro-mechanical behaviour of compacted expansive clays and another for the thermo-mechanical behaviour of saturated clays. The elaborated model has been validated using the thermo-hydro-mechanical test results on the compacted MX80 bentonite. Comparison between the model prediction and the experimental data show that this model is able to reproduce the main features of volume changes: heating at constant suction and pressure induces either expansion or contraction; the mean yield stress changes with variations of suction or temperature.