ABSTRACT
A canal is designed to transport water; however, on many occasions, water is precisely its worst enemy. Yet in this case, the water causing the damage is not that circulating through the canal, but instead, that which filters into the ground. It can often occur that there are high groundwater layers which, if the
canal is emptied, can lead to the lining being uplifted and damaged. Similar effects are often caused by rain water which infiltrates through the ground and on other occasions, the actual canal filtrations through the joints and cracks in the lining. However, the canal designer has to be able to achieve stability not only
of the actual lining itself, but also of the underlying geometric shape, which comes from either the excavation of the natural ground or the backfilled soil. It is a well-known fact that moisture can often produce a lubricating effect in the ground, reducing its cohesion and fostering slope sliding. This sliding can affect the slopes on the side where the canal is located or even the actual side slopes of the canal itself. However, if the moisture and, even worse still, the underground current
lines are harmful to the slopes in excavation, they are even more so for the backfills. It often occurs that the water filtering through a canal lining in a backfilled section has a gradient that is much stronger than a stripping excavation. This can cause higher filtration speeds leading to siphoning and washing away of the backfill, followed by collapsing and serious flooding. In the ground with more gypsum content, a well-designed drainage system
can be an element providing a significant contribution to a canal’s stability (Chapter 12). All this requires the designing engineer to carry out a painstakingly
detailed study of the type and number of drains necessary to achieve a high level of probability that the canal will be stable.
