  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.
