Investigating the time-dependent behaviour of Boom clay under thermo-mechanical loading

TL;DR

This study investigates the long-term thermo-mechanical behaviour of Boom clay using high-pressure triaxial tests, revealing significant effects of temperature and loading rates on volume change and consolidation over time.

Contribution

It provides new insights into the time-dependent volume change behaviour of Boom clay under combined thermal and mechanical loading conditions.

Findings

Temperature and loading rates significantly affect volume change.

High loading and heating rates cause notable volume changes.

Full consolidation of Boom clay requires long periods due to low permeability.

Abstract

Among the various laboratory studies to investigate the Thermo-Hydro-Mechanical (THM) behaviour of Boom clay, relatively few were devoted to the time dependent behaviour, limiting any relevant analysis of the long-term behaviour of the disposal facility. The present work aims at investigating the time-dependent behaviour of Boom clay under both thermal and mechanical loading. High-pressure triaxial tests at controlled temperatures were carried out for this purpose. The tests started with constant-rate thermal and/or mechanical consolidation and ended with isobar heating and/or isothermal compression at a constant stress rate or by step loading. Significant effects of temperature as well as of compression and heating rates were observed on the volume change behaviour. After being loaded to a stress lower than the pre-consolidation pressure (5 MPa) at a low temperature of 25\degree C and at a rate lower than 0.2 kPa/min, the sample volume changes seemed to be quite small, suggesting a full dissipation of pore water pressure. By contrast, after being subjected to high loading and heating rates (including step loading or step heating), the volume changes appeared to be significant, particularly in the case of stresses much higher than the pre-consolidation pressure. Due to low permeability, full consolidation of Boom clay required a long period of time and it was difficult to distinguish consolidation and creep from the total volume change with time.