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<br />c., <br />c.! <br />00 <br />- <br /> <br />- <br />~. <br /> <br /> <br />First bucker of COllcrete fill' 11001'('1' Dam was <br />placed JUlle 6. 1933. <br /> <br />Tunnel excavation began in June 1931 <br />and was completed in November 1933. <br />The tunnels were constructed by tradi- <br />tional drill-unci-blast methods. After <br />batteries of compressed-air drills had bit- <br />ten 10 to 20 feet into solid rock, a ton <br />of dynamite was loaded into the holes. <br />The electrically fired blasts, which broke <br />1,000 cubic yards of rock and advanced <br />the heading 17 feet on average, shook the <br />canyon walls. The resulting rock and <br />debris were loaded into trucks and <br />dumped into side canyons. <br />During one 24-hour period, 256 feet <br />of tunnel were driven. and the highest <br />total for a single month was 6,848 feet. <br />It required 3,561,000 pounds of dyna- <br />mite, or 2.38 pounds per cubic yard, to <br />remove the 11/2 million yards of rock <br />from the four tunnels. <br />Each of the tunnels was holed out to a <br />56-foot diameter, then lined with con~ <br />crete 3-feet thick. The combined length <br />of the 4 tunnels is approximately 3 <br />miles. <br /> <br />The River Is Turned <br /> <br />When the two Arizona tunnels were <br />complete, steps were taken to divert the <br />river's flow. <br />A small earth and rock dam known as <br />a cofferdam was constructed in the river <br />just below the tunnel inlets. Twenty-four <br />hours after the dam was started, it was <br />high enough to block the channel and <br />force the river through the tunnels. <br />At the same time, another cofferdam <br />was built across the river channel below <br />the damsite but above the tunnel outlets. <br />This prevented the river from backing <br />into the construction area. <br />On November 14, 1932, the mighty <br />Colorado River had been diverted! <br />Now, excavation for the dam and <br />powelplant foundation proceeded swiftly. <br />Manning huge power shovels, draglines, <br />and other equipment, men labored 24 <br />hours a day digging through the mud <br />and silt of the river channel before <br />reaching solid bedrock. More than <br />500,000 cuhic yards of muck were <br />removed. <br /> <br />Removal of loose and projecting rock <br />from the canyon walls also continued. <br />To reach the desired spots, "high <br />scalers" either climbed up ropes or were <br />suspended from anchors sunk in the can- <br />yon walls. These men swung in safety <br />belts or "bosun" chairs, pendulum <br />fashion, hundreds of feet above the river <br />and gouged at weak spots or drilled <br />blasting holes. Nearly one million cubic <br />yards of rock were dislodged from the <br />walls of the canyon. <br /> <br />Building the Penstocks <br /> <br />When the time came to install the dam's <br />penstocks, the huge watclpipes that <br />would carry water from the reservoir to <br />the powerplant through the canyon walls, <br />the engineers were faced with a major <br />problem. <br />The penstocks were to be built of <br />nearly 3-inch-thick plate-steel pipe. Two <br />and three-quarter miles of this pipe, <br />weighing more than 44,000 tons, would <br />be needed. It was obvious that the pipe <br />sections could not be built and shipped <br />from eastern plants - standard railroad <br />cars couldn't handle the weight, and the <br />sections wouldn't fit through a nOffi1al <br />railroad tunnel. <br />To SUffi10unt this problem, a plate-steel <br />fabricating plant was built along the con- <br />struction railroad ll/z miles from the <br />damsite on the Nevada side of the <br />canyon. Flat steel plates were shipped to <br />the plant and made into the required <br />sections. <br />Special equipment was required for <br />fabricating and transporting the finished <br />pipe sections to the damsite. Planers, <br />rollers, presses, electrical equipment for <br />welding the plates, and x-ray equipment <br />for examining the welds were installed in <br />the plant. A 200-ton trailer, pulled and <br />controlled by two 60-horsepower crawler <br />tractors, transported the heavier pipe <br />sections from the plant to the canyon <br />rim. From here the pipe was lowered to <br />the portal of one of the construction <br />passages by a 150-ton cableway. A <br />specially constructed car received each <br /> <br />21 <br />