The British Dam Society
Caring for dams, people and the environment

About Dams

Back to buildingBuilding dams - Preparing the foundation

Preparation of the rock foundation for a gravity dam

The rock foundation for a gravity
dam being prepared

A dam is built on a soil or rock foundation, depending on the type of dam. The foundation must be strong enough to carry the weight of the dam, and the water pressures acting on the dam. The dam foundation is below the original ground level. It is covered by weaker soils or rock that have to be removed either by excavation or by blasting with explosives.

Sometimes, areas of weaker soils or rocks are found below the planned foundation level and these have to be removed and replaced with stronger materials

Some rock foundations have cracks and fissures in them. These have to be filled with grout to stop water leaking out from the reservoir through the cracks once the dam is completed. This is done by drilling holes down into the rock, and by pumping grout into them, which spreads outwards to fill the cracks.