The Story of Boulder Dam
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Chapter 2

THE canyon scene was an active one. Men and equipment were ferrying back and forth across the river. Batteries of vibrating drills sang out their machine-gun tune. Earth shovels roared, bucked, and swung about. Motor trucks charged up to receive their loads and swayed off. Orders were bawled, with yells of acknowledgment.

On top the canyon, high above the busy scene below, the picture assumed another perspective. The noise and activity became muffled and distant. Men became ants, and the earth shovels and trucks crept here and there on the canyon floor like slow-motion toys. Dominant over all was the great canyon and the river.

Men and machines declined to the diminutive, and the mighty Colorado seemed to surge with laughter at their puny efforts. But at intervals blasts shook the earth, and the surging waves of the Colorado changed to tremors. These Lilliputians seemed so determined . . .

Blasting out the construction road to the dam site

The Fundamental Problem

To harness the Colorado River and bring it under beneficial control Reclamation engineers faced the fundamental problem of erecting a great dam that would do three things: Stop floods, hold the spring run-off for year-round use, and create a reservoir deep enough to trap the million tons of silt swept down the river daily without impairing the efficiency of the reservoir or interfering with the generation of power. The power plant in turn had to be large enough to make full economical use of the water, and also the long drop created by a high dam, for the sale of electrical energy was counted on to repay much of the cost.

It was determined that these requirements could be met by building a dam capable of impounding 10,500 billion gallons of water in a reservoir 589 feet deep, and by constructing a power plant capable of producing 6 billion kilowatt-hours annually.

The dam would be higher—726.4 feet from bedrock to roadway crest—than any ever constructed, and the power plant larger than any ever planned to that time. The 10,500 billion gallon reservoir would be the largest artificial lake ever created by man.

In the waters of the reservoir, just upstream from the dam, would stand four tall steel and concrete towers 33 stories high. Huge 170-ton steel gates in the towers would control the release of water from the reservoir. They would have the largest valves ever designed.

The huge gates when opened would permit the water to flow through penstocks—mammoth steel pipes big enough to drive a locomotive through with plenty of room to spare—and the penstocks would guide the water into the powerhouse or past the powerhouse into the river below the dam.

Two great troughlike spillways large enough to float a battleship, one on each side of the river just above the dam, would protect the dam and powerhouse from floods. All overflow would pour into the spillways, rush around the dam through huge tunnels 50 feet in diameter and emerge below.

The gigantic dimensions of the various structures and parts of Boulder Dam made the project appear almost presumptuous. Even engineers took pause. Some said: "It can't be done." A dam of such great magnitude presented insoluble problems, they maintained. Geologic conditions would not permit its erection. It would be impossible to control the river while the dam was being built. Even if the geologic conditions permitted, amid the river were brought under control, the millions of tons of silt swept down by the river would fill the reservoir in a short time. Or if the silt were allowed to pass through it would destroy the gates, valves, and turbines.

They pointed out still other reasons for failure. No contractor would risk bidding on so large a job with such difficult construction conditions. The building site was in the lonely desert where no man could work in the summer because of the extreme heat. How could the millions of tons of construction material be transported across this blistering trackless desert and down the sheer 800-foot drop of the canyon?

But exploration and preliminary work by the Bureau of Reclamation went steadily forward. Geologic examinations had shown that the task was not impossible. The job could and would be done, as assigned.

Specifications and drawings for the dam and appurtenant structures were being prepared in the main field office of the Bureau of Reclamation in Denver, Colo. Washington flashed word to rush the blueprint work. Actual construction should start as soon as possible in order to create employment, for the trying year of 1930 was upon the land. Drafting forces were increased and designers worked night and day. The specifications were rushed to completion.

On March 11, 1931, six months ahead of schedule, the Secretary of the Interior awarded the labor contract for construction of Boulder Dam to Six Companies, Inc., of San Francisco, Calif., the lowest bidder.

The bid was $48,890,995.50, the largest labor contract ever let by the United States Government at that time.

The site of Boulder City (left); Boulder City, the model Government town (right)

The Struggle Begins

The battle with nature was on. Arrayed on the Colorado's side were cloudbursts and sudden floods, the almost unbearable desert heat, the three-dimensional difficulty of transportation over burning desert and down over the brink of the canyon rim 800 feet to the canyon floor, and the hazards of working on the sheer canyon walls.

Allied with Reclamation engineers were the experiences gained from winning many similar though smaller battles, an ideal site for the great dam, and modern construction machinery.

It was necessary to build highways and railroads; erect machine shops, air compressor plants, garages, and warehouses; to span the canyon first by bridges and then hater by heavy-duty steel wire cables half a mile long and as thick as a man's wrist; to construct a great gravel screening plant and two huge concrete mixing plants; to acquire power draglines and power shovels, trucks, cars, derricks, and cranes in great numbers. It was necessary to bring power 222 miles across the desert from San Bernardino, Calif.

Care of the workmen required earnest thought. The temperature in Black Canyon rises to 130 in the shade and the daily mean for weeks stays above 100. All summer long the walls of the canyon throw off furnacelike waves of heat. Metal left in the glare of the sun burns to the touch.

High scalers working 500 feet above the river

Drillers aloft

After studying climatic soil conditions, a location for the construction town was chosen on a ridge 7 miles from the dam site. Here the Government's engineers plotted out paved streets, comfortable modern homes with green lawns and shrubbery, and dormitories and offices.

In the fall of 1931 the site of Boulder City was raw desert waste. A year later nearly 1,000 dwellings with all modern facilities sheltered the town's 5,000 inhabitants—the project officials, workmen, service employees, and their families. Built and under construction were stores, restaurants, churches, a school, a theater, hotel, and hospital— a complete modern little city

Materials for the dam itself were required in quantities never before shipped to a single construction job in such a short time—5 million barrels of cement; 8 million tons of sand, gravel, and cobbles; 45 million pounds of reinforcement steel; 18 million pounds of structural steel; 21 million pounds of gates and valves; 840 miles of pipe. All were hauled over the railroads in the first 4 years of construction.

Features of work at Boulder Dam. (click on image for a PDF version)

Often 60 carloads of materials a day arrived on the scene. The car loads of materials totaled more than 30,000 (not counting the 145,000 carloads of sand, gravel, and cobbles used for the concrete).

The Government and contractors employed as many as 5,250 men at one time with a gross monthly payroll of more than $750,000. About 40 percent of the men were unmarried and lived in air-cooled dormitories. The workmen ate in a mess hall with a seating capacity of 1,300. Single men were charged $1.60 a day for meals, room, and transportation to and from the canyon. Married men rented modern new homes from the contractor at $15 and $50 a month unfurnished.

The jumbo drill—a battery of 30 drills ready for simultaneous action

A big hole for the river to flow through—one of the diversion tunnels

Greatest Machinery Ever Seen

Even as the structures at Black Canyon were required to be the greatest of their kind ever built, so were many of the plants and much of the equipment. It was the greatest massing of specialized equipment ever witnessed on any construction project.

Boulder Dam and Appurtenant Works.

There were huge trucks for hauling materials, some of 16-cubic yard capacity, others of 50-ton capacity, and still others which were operated as 100- and 150-man transports.

Air compressor plants of 14,500 cubic feet per minute capacity were built near the river's edge.

The sand and gravel screening and washing plant to provide the aggregate (the sand, gravel, and cobbles to be mixed with the cement and water for the concrete) was the largest of its type. It could screen, wash, and place aggregate in readiness for mixture with cement and water at the rate of more than 16-1/2 tons a minute

Blasting away the sides of the canyon

Plan of Attack

The general plan of attack in building Boulder Dam was to drill tunnels through the canyon walls around the site, to divert the Colorado through the tunnels, build cofferdams to block off the river from the dam site, excavate the site, and build the dam and power plant.

The narrowness of the canyon, the spread of activity up and down the river and the possible large fluctuation of the river's flow made the job of diverting the Colorado a ticklish one.

It had been decided to drive, four diversion tunnels (two on each side of the river) around the dam site through the solid rock of the canyon walls. Two temporary cofferdams would then be built—one would be upstream, above the site but just below the tunnel inlets; the other would be downstream, below the site but just above the tunnel outlets. These cofferdams would block off the river so that the site could be pumped dry and excavated to foundation bedrock.

The four tunnels would have another important use besides diversion of the river. After completion of the dam, they would serve to house the outlet works used in the regulation of the reservoir. The two outer tunnels would become outlets for the huge spillways. The two inner tunnels would guide the stored water from the intake towers in the reservoir to the power plant or past it to the outlet valves below the dam.

The dispatch with which the diversion tunnels were driven forecast the efficiency and speed with which the entire job would be handled.

The canyon walls were attacked first by batteries of compressed-air drills. An especially designed drilling jumbo equipped with 30 drills lumbered into action. When the drills had bitten 10 and 20 feet into solid rock a ton of dynamite was loaded into the holes. The electrically fired blast shook the walls. Power shovels moved to the tunnel face, and the broken rock was loaded into trucks. The trucks then roared up the grade to dump their loads in side canyons. Soon all was in readiness to repeat the performance.

An average blasting round broke 1,000 cubic yards of rock and advanced the heading 17 feet. Work progressed at times from 8 headings. A total length of 256 feet of tunnel was driven in 24 hours, and 6,848 feet in 1 month. Removal of the million and a half yards of rock in the 4 tunnels required 3,561,000 pounds of dynamite, or 2.38 pounds per cubic yard.

Each of the 4 diversion tunnels was holed out to 56-foot diameter—as high as a 4-story building—and lined with a 3-foot thickness of concrete. The total length of the tunnels was approximately 3 miles.

At work in the river bed

The Engineers Turn the River

As soon as the two tunnels on the Arizona side of the river were lined, a pile trestle bridge was built across the river downstream from the tunnel inlets and the temporary barriers in front of the tunnel portals were blasted away. Trucks ran out on the trestle bridge and dumped their loads of large rocks, then smaller ones, and finally sand, into the channel. Within 24 hours a temporary dike was formed, blocking the river and forcing it out of its age-old channel and into the tunnels.

Meanwhile, downstream below the dam site, a dike of tunnel muck was pushed across the river channel just above the tunnel outlets. This prevented the river from backing into the area.

The Colorado River had been diverted. With the temporary dikes in place, and the water pumps sucking the dam site clear of water, excavation proceeded swiftly for the main structure of the dam itself and the powerhouse. Safe and dry, the huge power shovels, draglines, and powerful trucks labored 24 hours a day digging down to the solid rock 135 feet below the river bed. They removed more than half a million cubic yards of muck, sand, and gravel.

Work also went ahead on the removal of loose and projecting rock from the canyon walls. To get at the desired spots the "high scalers" either climbed up ropes or were suspended from anchors sunk in the canyon rim. They swung in safety belts or bosun chairs pendulum fashion hundreds of feet above the river and gouged at weak spots or drilled blasting holes. Nine hundred and thirty thousand cubic yards of rock were dislodged from the walls.

Dumping a bucket of 16 tons of concrete

An Impasse Confronts

An impasse confronted the engineers in obtaining the steel pipe to form the penstocks inside the huge diversion tunnels. The penstocks required 2-3/4 miles of plate steel pipe nearly 3 inches ??? thick whose gross weight exceeded 44,000 tons. The penstock header lines were to be 30 feet and 25 feet in diameter, the penstocks 13 feet (except 108 feet of 9-foot diameter), and the outlet conduits 86 inches and 102 inches in diameter.

Standard railroad cars were too small to transport the larger pipe sections, which would not pass through a normal railroad tunnel. They could not be shipped, therefore, from existing rolling mills. The engineers conferred. They hit upon the solution. They would construct a plant right at the dam site and manufacture the great pipes on the spot.

The dam rises, step by step, in solid blocks of concrete

The fabrication plant was erected along the construction railroad a mile and a half from the top of the Nevada dam abutment. The flat steel plates were shipped in by rail and the pipe sections were fabricated in the plant. A section of the largest pipe when completed was over 23 feet long and weighed 175 tons.

Fabrication of a 30-foot section consisted of marking six 10-foot 6-inch by 31-foot 5-inch flat plates, cutting them to size with an acetylene torch, planing welding grooves on three sides, preparing the plates for rolling by bending the ends in a 3,000-ton press, rolling the plates in 12-foot vertical rolls, assembling and electrically welding the plates together and adding butt straps and stiffeners. All welds between the rolled plates were then X-rayed by a 300,000-volt portable machine, the film examined, all flaws chipped out and replaced with new metal, and the weld X-rayed again.

The pipe was then taken by 75-ton traveling cranes to the normalizing furnace where it was heated to a temperature of 1,150° F. It was held at this temperature for several hours, and slowly cooled to relieve the stresses set up by rolling and welding. Fabrication of the pipes required approximately 76 miles of welding and 29 miles of X-ray film.

The graceful intake towers whose gates control the release of the reservoir water

A 200-ton trailer pulled and controlled by two 60-horsepower caterpillar tractors transported the heavier pipe sections from plant to canyon rim. The 200-ton cableway transferred the pipe from canyon rim to a "car-on-a-car" at the portals of one of the construction adits whence it traveled on the double carriage through the adit to a penstock header tunnel. Finally it was pulled to its position by winches and hoists.

All pipe sections were joined within steel pins, the largest of which were 3 inclines in diameter, except the 8-1/2-foot outlet conduits, which were hot-riveted, and a few miscellaneous sections that were welded. In welding, the weld and pipe near it were stress-relieved by heating with gas rings.

The Arizona spillway—big enough to float a battleship

Meanwhile, while the engineers were surmounting the difficulty of making and installing the great penstock pipes, the main job of concrete placement for the huge structure of the dam was being carried out swiftly. On June 6, 1933, the first bucket of concrete was placed. Six months later a million yards were in place. Another million was poured in the following half year, and the third million by December 6, 1934, only 18 months after starting placement.

As soon as construction of the dam, intake towers and outlet works was sufficiently advanced, and the upstream portions of the two inner diversion tunnels plugged with concrete, a steel bulkhead gate was lowered at the inlet of the outer diversion tunnel on the Arizona side of the river.

Looking down on the lake.., the spillways, the dam

The River Harnessed at Last

This was February 1, 1935. Back of the unfinished dam, water started to rise. The Colorado had been blocked and thrown back on its haunches. By midsummer the new reservoir held more than one trillion gallons of water. And the formerly muddy brown waters of the river dropped their silt and became a beautiful deep blue.

When the newly formed Lake Mead had risen to the base of the intake towers, 260 feet above the river bed, the one remaining opening—the slide gates in the Nevada outer diversion tunnel plug—was closed to the Colorado. From that time on the river had to respond to rein. The broncho of the West was fully harnessed.

Concrete pouring continued and the crest height of the dam was reached March 23, 1935. By the following summer all the concrete—3,250,335 cubic yards, 6,900,000 tons of it—was in place, with the exception of the filling of temporary galleries.

In 21 months 1,200 men with modern equipment had built a structure whose volume was greater than the largest pyramid in Egypt, which, according to Herodotus, required 100,000 men and 20 years to build.

The dam towered to a height of 726.4 feet—more than half that of the Empire State Building in New York City; it had a base thickness of 660 feet—more than the length of two ordinary residence blocks; a crest thickness of 45 feet—room enough for 4 lanes of highway; and it was 1,244 feet long—nearly a quarter of a mile.

The Government's contract had allowed Six Companies, Inc., 7 years to complete the work, but with the aid of an efficient personnel, and the assistance of the most modern equipment, the contract was completed 2 years ahead of schedule.

Aerial view of Boulder Dam and Lake Mead

The speedy and successful completion of the Boulder Dam contract was the finest achievement of the ability and lengthy experience of a combination of grand old construction men.

One of the master strokes in the construction of Boulder Dam was the cooling of the concrete. Left to itself, the vast bulk of the dam would have taken more than a century to cool off from the heat created by the setting of the cement, shrinking as it cooled, and cracking as it shrank. The ingenious solution was to build the dam in pierlike blocks and to cool the placed concrete by running ice-cold water through pipes imbedded in the blocks. As each block contracted and left gaps between itself and adjacent blocks, engineers pumped the gaps full of special grout concrete, making the structure monolithic, of one piece.

Boulder Dam was done. A permanent asset had been added to the Nation's productive economy. The years of study and the plans and the blueprints had materialized into lasting structural achievement. And within a few short years, more quickly than expected even by its creators, Boulder Dam amply demonstrated its economic and social value to the Southwest and the country as a whole. Its benefits were great and many. Soundly conceived, soundly constructed, Boulder Dam brought almost immediate returns.

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Last Updated: 01-Feb-2008