3004
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
0
1
10
100
0,1
1
10
100
PV*
SO
4
2-
(g/l)
K2SO4 H2SO4
Figure 3. Critical number of pore volumes, PV*, as a function of the
SO
4
2-
concentration in sulphuric acid and potassium sulphate solutions.
4 CONCLUSIONS
On the basis of the available results it is possible to state that
aqueous solutions of H
2
SO
4
and K
2
SO
4
may adversely affect the
hydraulic performance of CB mixture depending on SO
4
2-
concentration and pH. At concentration of the order of g/l or
more, both solutions produce an initial decrease in the k value,
followed by an increase and finally an almost constant trend of
hydraulic conductivity with curing time. Swelling and a dense
net of fixtures were detected on the samples after permeation
mainly due to ettringite formation, both in samples permeated
with the acidic and saline solutions.
The number of pore volumes of flow at which the change in the
k trend occurs is greater the higher the SO
4
2-
concentration. The
PV at which this change of trend occurs (PV*) does not seem to
be affected by the pH when SO
4
2-
concentration exceeds 1 g/l.
A correlation between PV* and SO
4
2-
concentration was found
that can be useful from the practical point of view to estimate a
cut-off wall durability on the basis of the expected flow rate
through it. This criterion is on the safe side because it is based
on the PV related to the requirement of decreasing k with time:
a constant or increasing k with time does not necessarily imply
a bad performance, at least immediately. Moreover, the
chemical conditions adopted in the tests are not expected to
occur continuously in the field if a pumping system is provided
so that there is an advective flow of groundwater and not of
pollutant across the barrier.
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