Hoover Dam (USA)

The two vertical foundations for each of the arch walls (the Nevada side and Arizona side) had to be founded on sound virgin rock; free of cracks and the weathering that the surface rock of the canyon walls had from thousands of years of weathering and exposure.

The men who removed this rock were called high-scalers. While suspended from the top of the canyon with ropes high-scalers climbed down the canyon walls and removed the loose rock with jackhammers and dynamite.

The first concrete was placed into the dam on June 6, 1933. Since no structure of the magnitude of the Hoover Dam had been constructed, many of the procedures used in construction of the dam were untried. Since concrete heats up and contracts as it cures, uneven cooling and contraction of the concrete posed a serious problem. The Bureau of Reclamation engineers calculated that if the dam were built in a single continuous pour, the concrete would have taken 125 years to cool to ambient temperature. The resulting stresses would have caused the dam to crack and crumble. To solve this problem the dam was built in a series of interlocking trapezoidal concrete pours. To further cool the concrete each form contained cooling coils of 1 inch (25 mm) thin-walled steel pipe. River water was circulated through these pipes to help dissipate the heat from the curing concrete. After this, chilled water from a refrigeration plant on the lower cofferdam was circulated through the coils to further cool the concrete.

There is enough concrete in the dam to pave a two-lane highway from San Francisco to New York.

The initial plans for the finished facade of both the dam and the power plant consisted of a simple, unadorned wall of concrete topped with a Gothic-inspired balustrade and a powerhouse that looked like little more than an industrial warehouse. This initial design was criticized by many as being too plain and unremarkable for a project of such immense scale, so Los Angeles-based architect Gordon B. Kaufmann, then the supervising architect to the Federal Bureau of Reclamation, headquartered in Denver, was brought in to redesign the exteriors. Kaufmann greatly streamlined the buildings, and applied an elegant Art Deco style to the entire project, with sculptured turrets rising seamlessly from the dam face and clock faces on the intake towers set for the time in Nevada and Arizona, in the Pacific Standard Time Zone or Pacific Daylight Time Zone and Mountain Standard Time Zone time zones respectively (although because Arizona does not observe daylight saving time, the two clocks show the same time during the half of the year around the northern summer).

Excavation for the powerhouse was carried out simultaneously with the excavation for the dam foundation and abutments. Excavation for the U-shaped structure located at the downstream toe of the dam was completed in late 1933 with the first concrete placed in November 1933.

Generators at the Dam’s Hoover Power plant began transmission of electricity from the Colorado River to Los Angeles, California 266 miles (428 km) away on October 26, 1936. Additional generating units were added through 1961.

Hydroelectric power plants have the ability to vary the amount of power generated, depending on the demand. Steam turbine power plants are not as easily throttled because of the amount of thermodynamic inertia contained in their systems.

There are two lanes for automobile traffic across the top of the dam. It serves as the Colorado River crossing for the highway U.S. Route 93. The two-lane section of road approaching the dam is narrow, has several dangerous hairpin turns, and is subject to rock slides.

To provide much more highway capacity, and better safety, the new Hoover Dam Bypass is scheduled to be completed in 2010 and it will divert the U.S. 93 traffic 1,500 ft (460 m) downstream from the dam. The bypass will include a composite steel and concrete arch bridge, tentatively named the Mike O’Callaghan – Pat Tillman Memorial Bridge. Once the bypass is completed, through traffic will no longer be allowed across Hoover Dam.

Additionally, in the wake of the September 11, 2001 terrorist attacks there are significant security concerns. Because of the attack, the Hoover Dam Bypass project was expedited. Traffic across Hoover Dam is presently restricted. Some types of vehicles are inspected prior to crossing the dam while semi-trailer trucks, buses carrying luggage, and enclosed-box trucks over 40 feet (12 m) long are not allowed on the dam at all. That traffic is diverted south to a Colorado River bridge at Laughlin, Nevada.

The dam, originally planned for a location in Boulder Canyon, was relocated to Black Canyon for better impoundment, but was still known as the Boulder Dam project. The Boulder Canyon Project Act of 1928 (BCPA) never mentions a proposed name or title for the dam. The BCPA merely allows the government to “…construct, operate, and maintain a dam and incidental works in the main stream of the Colorado River at Black Canyon or Boulder Canyon…” Work on the project started on July 7, 1930.

At the official beginning of the project on September 17, 1930, President Hoover’s Secretary of the Interior Ray Lyman Wilbur, announced that the new dam on the Colorado River would be named Hoover Dam to honor the then President of the United States. Wilbur followed a standing tradition of naming important dams after the President who was in office when they were constructed, such as the Theodore Roosevelt Dam, the Wilson Dam, and the Coolidge Dam. However, these dams were not named after sitting presidents, as they were completed after the presidents had left office. More tellingly, Hoover was already campaigning for re-election in the face of the Depression and he sought credit for creating jobs. A Congressional Act of February 14, 1931, made the name “Hoover Dam” official.

In 1932, Herbert Hoover lost his bid for reelection to Franklin Delano Roosevelt. Right after the new president took office, the U.S. administration initiated renaming of the dam to the previous name. This did not happen immediately, but over the following several years all references to Hoover Dam in official sources, as well as tourist and other promotional materials, vanished in favor of Boulder Dam.

Roosevelt died in 1945. On March 4, 1947 California Republican Congressman Jack Anderson submitted House Resolution 140 to restore the name Hoover Dam. Anderson’s resolution passed the House on March 6; a companion resolution passed the Senate on April 23, and on April 30, 1947, President Harry S. Truman signed Public Law 43; since then the dam bears its today’s name.

Material is taken from the Internet resource:

http://en.wikipedia.org

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