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These tests have been modelled with a THM coupled formulation based on the macroscopic approach
developed in the context of the continuum theory for porous media by [2] and described in
[3]. The parameters used for the bentonite are given in [3]. The predictions got with this basic
model are shown in Fig. 2.1 as “Base case”. It can be observed that they overestimate the actual hydration
kinetics, especially in the case of the test performed under thermal gradient (GT40). To explain
this discrepancy non-standard processes not previously included in the model have been considered,
among which the existence of a threshold hydraulic gradient and thermo-coupling effects.
The model results obtained considering a threshold gradient of 50, a critical gradient close to 2000,
and a power law for the range of hydraulic gradient with non-Darcian flow, are shown in Fig. 2.1
with solid lines.
Although, at this stage, the new models are quite simplified, the results obtained are interesting. In
this context, this study allows comparing the measurements of actual tests with the computed response
under the hypothetical case in which some of these effects would be present. Each of these
phenomena does not exclude the others and it is possible that an explanation for the whole behaviour
of the barrier would require the combinations of some of them.
Relative Humidity (%)
100
80
60
40
20
TEST
MODEL (TG)
d=0.10m
d=0.20m
d=0.30m
Base case
0
0 10000 20000 30000
Time (hours)
Relative Humidity (%)
467
100
80
60
40
20
MODEL (TG)
d=0.10m
d=0.20m
d=0.30m
0
0 10000 20000 30000
Time (hours)
Figure 2.1. Evolution of relative humidity in three different positions along the bentonite column of
test GT40 (left) and I40 (right): the points correspond to measured vales, the discontinuous line to
the base case model, and the solid lines to the model assuming the existence of threshold gradient
2.3. Effect of temperature on hydro-mechanical properties
The swelling capacity, swelling pressure and permeability of the bentonite compacted to dry density
between 1.5 and 1.7 g/cm 3 have been determined at temperatures between 20 and 80°C [1].
The results show that the effect of temperature on the swelling capacity of the bentonite is smaller
than the effect of the vertical load applied during hydration or the effect of initial dry density. As
shown in Fig. 2.2, in which the final strains obtained in all the tests have been plotted, the effect of
temperature is higher for the higher density and is more noticeable when the load is high. The results
obtained in the swelling pressure tests confirm this trend (Fig. 2.3). On the one hand, all the
dry densities tested, including the lowest one, suffered a decrease of swelling pressure for high
temperature, what would confirm that the effect of temperature is more important as the vertical