Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
The compacted bentonites are used as buffer and backfill materials for engineering
barriers for high-level nuclear waste repositories located underground. For this
purpose, it is very important to evaluate the swelling characteristics of this clay.
The swelling capacity is one of the most important properties of the bentonite clay. The
swelling behaviour is due two mechanisms, the crystalline swelling and the osmotic
swelling. These mechanisms produce an increase in the distance between the layers of
montmorillonite which is one component of bentonite.
The result of the swelling capacity is the swelling pressure. It has been studied in
several investigations. The results of experimental tests have been collected and
compared in this thesis, considering only the Na-dominant bentonite and sand and
distilled water as test solution.
The experimental tests show that there is only an unique relation between different
bentonites in the Na-dominant bentonite and sand mixture swollen depending on its
final dry density. Also, the relation between the swelling pressure and the clay void
ratio shows the mechanism of the swelling pressure.
On the other hand, a mechanistic model is used to predict the swelling pressure of fully
saturated bentonite and sand mixture in distilled water. Firstly, it has been compared
with the results of experimental tests and it should be pointed out that the model gives
In addition, the model has been used to make sensitivity analysis with different
parameters of bentonite. The most important conclusions in this section show that the
swelling pressure mainly depends on the distance among particles. Also, the sensitivity
analyses indicate which parameters should be fitted more carefully for future studies to
validate this model with different bentonites.
2013. , 46 p.
Swelling pressure; bentonite and sand mixture; crystalline swelling; osmotic swelling; mechanistic model; montmorillonite.