Grand Coulee Dam Starts Small to Become a Giant
Grand Coulee Dam, with more than 10.5 million cu yd of concrete, was the largest masonry structure ever built when completed in 1941 and broke a record set by the Great Pyramid at Khufu, Egypt, which stood for 47 centuries. The 550-ft-high structure, 4,173 ft long at the crest, stands across the Columbia River, 92 miles northwest of Spokane, Wash. Water stored behind the dam is pumped up 280 ft to the Grand Coulee, a 50-mile-long valley that was dammed to form a reservoir for irrigation water. President Franklin D. Roosevelt appropriated $63 million for the project, originally wanting a small dam that could be enlarged later.
It was widely believed the contract to build the dam and its powerplant would go to Six Cos. Inc., the joint venture that built Hoover Dam. But it went instead to a joint venture of Silas Mason Co. Inc., New York City; Walsh Construction Co., Davenport, Iowa; and Atkinson-Kier Co., San Francisco (MWAK). Its $29.34-million bid was $5 million less than what Six Cos. bid. According to BuRec, bidders included Hollywood star Mae West, who proposed to engineers that if they ran into trouble, they should "come up and see me sometime."
One of MWAK's first big tasks was to excavate overburden. Instead of relying on trucks, it set up a conveyor belt, a device never used on such a large scale. The 5-ft-wide, 3/4-in-thick belt extended 2 miles and carried more than 50,000 cu yd of spoil away each day. Landslides alone dropped as much as 2 million cu yd of earth and rock at one time.
Work began on the west cofferdam in early 1935. Within days of its completion in late March, the river rose, reaching 30 ft above normal by June. The Columbia, the country's second largest river, had a flow at the site that varied from 17,000 to 492,000 cu ft per second. In September, mwak began a timber crib dam to protect work on the river's east side.
By mid-1935, BuRec engineers, including Chief Design Engineer John Lucian Savage, who also designed Hoover Dam, were rethinking the low dam. It would only produce power, for which there was no market, and be of no use for irrigation. There were also doubts about the efficiency of joining a new concrete dam to an old one (ENR 8/1/35 p. 139). MWAK now had to build a foundation for the high dam and it finished work in 1938, 14 months ahead of schedule.
In late 1937, BuRec completed plans for the ultimate Grand Coulee Dam. The fast-track dam was cast in 5-ft lifts in 100 blocks. On a special day, workmen placed 20,860 cu yd in 24 hours but a cement shortage held up work for a while. When completed in 1941, the dam had two powerhouses, each housing nine 108,000-Kw generators, the world's largest hydro installation. In 1970, construction began on a third powerhouse that would have six additional units.
NEWS IN BRIEF 1940
Building for Defense
(ENR Oct. 24, 1940, p. 50)--Faced with inevitable involvement in WW II, the Army and Navy embarked on huge expansion of aviation infrastructure. Recognizing the modern aerial strategies that dominated warfare in Europe, Congress initially authorized expenditure of $66.8 million on Navy airbases. Months later, another $63 million was appropriated and $62 million more for Army airbases. In addition to the landing field and hangars, the modern airbase required shops, warehouses, magazines for storage of bombs, ammunition and detonators, photo laboratories and training facilities. ENR reporters visited a number of the fields to get a clear picture of the scale of construction work taking place.
Troubled Tacoma Wrecked by Wind
(ENR Nov. 14, 1940, p.1)--On Nov. 7, a modest wind of 42 mph ripped away nearly all of the suspended structure of the 2,800-ft span of the Tacoma Narrows Bridge, causing the towers to be bent by the unbalanced pull of the side-span cables. It was not so much the wind itself that caused the bridge to collapse, but the way the wind caused a cumulative rolling motion and a lag of phase difference between opposite sides of the bridge. This led to buckling of the stiffening girders. No one was hurt, since "abnormal twisting and waving" motions beforehand halted traffic flow. Among the few injured was a university professor who had been conducting studies on the bridge to control its ever present wavelike oscillation, which, until the collapse, no one had considered to be dangerous.
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