Preparation of the foundations is an essential stage of the site work. For earth-fill dams, the main problem is that of good sealing, particularly if silt is involved. In such a case, the sealing characteristics have to be improved by using injection technology.
Equally, there may be a decision to build a wall in the foundations themselves which would be designed to stop infiltration of water, either fully or partially. This is a variant of injection technology, called diaphragm wall technology.
For concrete dams, the rock must always be improved, as it is never fully impervious. In addition, explosives used to remove the poorest rocks also contribute to making it worse. As a result, a line of injections is performed with the aim of reducing infiltration and leakage under the dam foundations.
For earth-fill dams as well as concrete ones, these injections may be made:
- Either at the time when excavation is started,
- Or (and, possibly, also) at the end of construction, using a specially constructed gallery.
These injections carried out after construction on a site often turn out to be more effective as they benefit from compression by the existing structure.