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NF-PRO – Experimental and Modelling Studies of the THM Behaviour
of the Clay Barrier
María Victoria Villar 1 , Marcelo Sánchez 2 , Roberto Gómez-Espina 1 , Antonio Gens 3
Summary
1 CIEMAT, Spain
2 University of Strathclyde, UK
3 CIMNE, Spain
A THM mathematical formulation and a computer code to include ‘non-standard’ THM processes
and phenomena have been extended and improved. This upgraded approach has been
used to model some specifically designed laboratory tests. Among the phenomena investigated
are the parameters and processes influencing the hydration kinetics of the clay barrier,
the water flow under low hydraulic gradients similar to those expected towards the end of the
saturation process, the impact of temperature on the hydro-mechanical properties of the bentonite,
and the effect of clay fabric changes on the behaviour of bentonites submitted to heating
and hydration.
1. Introduction
The integration between the basic laboratory research and the development, application and calibration
of numerical models allows to improve the knowledge about the thermal, hydraulic and mechanical
processes (THM) –considered in a coupled way– that control the behaviour and performance
of the clay barrier under the conditions of a Deep Geological Repository (DGR). CIMNE has
extended and improved a THM mathematical formulation and a computer code to include in the
analysis ‘non-standard’ THM processes and phenomena. This upgraded approach has been used to
model some specifically designed laboratory tests performed by CIEMAT with FEBEX bentonite.
The following phenomena have been investigated:
- The parameters and processes influencing the hydration kinetics of the clay barrier, especially
with respect to the effect of thermal gradient. At advanced stages of the system, when the hydraulic
gradient becomes very small, it is possible that coupled phenomena, such as thermoosmotic
flow, could have a noticeable effect on the behaviour of the barrier, causing a trend to
slow down the hydration in the zones close to the containers.
- The water flow under low hydraulic gradients similar to those expected towards the end of the
saturation process. Under low hydraulic gradients Darcy’s simple relationship does not rule the
liquid flow in some soils, probably due to the strong clay-water interactions.
- The impact of temperature on the hydro-mechanical properties of the bentonite, since temperature
changes affect important hydraulic characteristics of compacted clays, whose knowledge is
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