Hidden Dangers in Dam Building.
In the construction of water storage dams there is an element of insecurity to be guarded against in some cases, which does not seem to have been publicly noticed. John D. Emersly, in The Mining and Scientific Press, referring to the swelling of the ground under or near the dam, considers it a source of danger.
A valley or wide ravine with a slight descent, and having side hills coming near to each other at its lower end, is economically favorable for water impounding purposes, provided that the collecting surfaces above are large enough to insure the supply required. In the arid regions such a valley is usually so dry that, on the side hills at least, the general water level can only be reached by deep sinking. If solid primary rock, with little permeability, is available in founding the dam, its bulk, when submerged, will not increase, but if dependence is placed on a stratified formation containing layers of clay, talc or shale, its expansion when exposed to pressured water must certainly be expected. Every old miner has had trouble with swelling or “creeping” ground, and builders of escarpment walls are aware how hard it is to keep some kinds of rock in place during wet weather.
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