This week, we’re discussing how to prepare a site for dam construction. According to the British Dam Society, “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” and “is covered by weaker soils or rock that have to be removed either by excavation or by blasting with explosives.”1
The photos below show explosions and construction workers removing weathered and unsound surface rock in the bottom of the Columbia River channel to provide for a watertight union of granite bedrock and whichever dam they’re working on (it is unfortunately unidentified, but it is likely the Grand Coulee Dam).
The fourth photo below shows bedrock in the old river channel and the natural water-worn rock surface as it is found under a bed of clay and boulders left in the canyon during the last ice age.
Photos courtesy of PG 94 (Army Corps of Engineers Dam Construction Photographs).