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load is higher, since the load applied in swelling pressure tests is higher than that applied in swelling
under load tests. On the other hand, the effect of temperature on swelling pressure is less significant
for the lowest density, confirming the trend observed in the swelling under load tests. The
extrapolation of the logarithmic correlation towards higher temperatures would indicate that swelling
pressures higher than 1 MPa would develop even for temperatures of 100°C for the three densities
tested.
Final vertical strain (%)
-25
-20
-15
-10
-5
0
open symbols: 1.5 g/cm 3
filled symbols: 1.6 g/cm 3
5
20 40 60
Temperature (°C)
80 100
468
0.5 MPa
1.5 MPa
3.0 MPa
Figure 2.2. Final vertical strain in swelling under load tests performed with FEBEX bentonite compacted
to nominal dry density 1.6 g/cm 3 (filled symbols and discontinuous lines) and 1.5 g/cm 3
(open symbols and solid lines).
Swelling pressure (MPa)
6
4
2
0
Error bars obtained from values of
tests performed at laboratory
temperature (1.6Mg/m 3 )
Error bars obtained from values
of tests performed at laboratory
temperature (1.5 Mg/m 3 )
Dry density (Mg/m
Test Test
Model Model
3 )
1.6 1.5
20 30 40 50 60 70 80
Temperature (ºC)
Figure 2.3. Swelling pressure as a function of temperature for saturated FEBEX clay compacted to
different nominal dry densities. Experimental and modelling data
The decrease of swelling pressure and swelling capacity of the FEBEX bentonite with temperature
has been explained as a consequence of the transfer of microstructural (interlayer) water to the macrostructure
which is triggered by temperature. This process would be more significant in highdensity
samples, in which the interlayer water predominates initially over the “free”, macroscopic
water.