How Was the Hoover Dam Built?
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Design
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A key element in understanding how the Hoover Dam was built is to understand how the dam's engineering works. The dam is an arch-gravity design, combining the virtues of the arch-style and the gravity-style dam. The arch shape causes the water pressure to compress the dam and push it down, giving it greater strength. The curve also directs some water pressure away from the dam to the rock and earth banks around it. Gravity dams, on the other hand, use sheer size and weight to resist water pressure. The arch-gravity dam uses aspects of the arch design to somewhat reduce the massive amounts of reinforced concrete necessary to build a pure gravity dam design.
Site Preparation
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The first step in building any dam is to divert the flow of the river away from the proposed dam site. For the Hoover Dam, this was done by digging out four 50-foot-wide tunnels through the canyon rock. Two were at the Nevada side, and two at the Arizona side. Then the bed of the Colorado River had to be dredged to clear the work site's bedrock. Then the cracked and loose rock facades of the canyon walls and floors had to be blasted out to provide a solid foundation for the dam. Much of this work was done by a crew of men called "high scalers," who worked suspended from ropes and chipped away at the canyon walls with dynamite and jackhammers.
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Pouring Concrete
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Despite the arch element, which allowed the dam to be somewhat thinner and use less concrete, the amount of concrete poured to build the Hoover Dam was enormous. Over 3,250,000 cubic yards of concrete, weighing 6.6 million tons, was used to build the dam. When it was constructed, no structure like the Hoover Dam had ever been built before, and a problem with concrete is that it heats up as it cures. To simply pour the dam all at once would have caused it to eventually crack and collapse under the strain of its own curing. This problem was solved by pouring the concrete in interlocking stages, one block or section at a time. The cooling of the concrete was further aided by impeding steel pipes into each poured block. In total, 582 miles of pipe were embedded in the dam, and ice water was circulated through them until March 1935. However, although the concrete in the dam is solid enough for its job, it is still curing, getting harder and emitting heat.
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References
- Photo Credit Wikimedia Commons, National Archives
