The foundations for most dams more than 15 m high built on rock and, for some which are smaller, are treated by grouting. Grouting consists of drilling a line or lines of holes from the cutoff level of the dam into the dam foundation and forcing cement slurry, or chemicals under pressure into the open defects in the rock, that is open joints, fractures, bedding partings and faults. Figure 18.1 shows an example:

The grouting is carried out to:

– Reduce leakage through the dam foundation, i.e. through the defects. – Reduce seepage erosion potential.