To divert the Colorado River"s flow about the Hoover Dam building and construction site, four 56-foot-diameter tunnels were driven through the walls of black Canyon, 2 on the Nevada side and also two on the Arizona side. Their linked length was virtually 16,000 feet (more than 3 miles).

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Tunneling began at the reduced portals that the Nevada tunnels in might 1931. Quickly after, work began on two similar tunnels in the Arizona canyon wall.

The work presented an excellent difficulties. Initially, there to be no roads into the canyon, so every the workers and equipment had to be brought in by boat. In time, roads were constructed into the canyon, and also catwalks to be strung throughout the river, for this reason the workmen might ride to occupational in trucks.

During the summer that 1931 the temperature in the workings got to 140° F (60° C). Once winter arrived, icy winds whipped through the canyon as temperatures dropped come freezing.

At one point in September 1932, work had to be abandoned and the website evacuated as flood waters swept through the canyon.

Holes because that explosives to be bored into the rock making use of pneumatic drills. 5 hundred pneumatic drills, hoses and compressors were purchased indigenous Ingersoll Rand. Compressor tree were set up just below the outlet portals, close to the Arizona adit, and upstream through the inlet portals. Compressed wait was taken to the work sites through a network of pipes 2 to 6 inches in diameter.

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To rate the job-related of drilling the holes, a "drilling jumbo" was constructed on the back of a ten-ton truck. The jumbo was backed as much as the functioning face and 24 to 30 drills visited work, drilling powder holes into the rock. A jumbo allowed half of the tunnel face to be operated on, through all the holes gift drilled in ~ once. As soon as the holes in that ar were finished, the jumbo relocated to the other side that the face and began drilling, when the perfect holes to be packed v powder and wired. As soon as both sides to be drilled, the jumbo was removed. Eight of this jumbos were constructed allowing the drilling to be achieved in document time.

When the drilling was complete, the holes to be filled v dynamite, and the rock damaged up through the explosions. A ton of dynamite was supplied for every 14 feet of tunnel dug.

Once a shot had been fired, professional miners inspected the tunnel because that safety, climate crews relocated in and also mucked out the broken rock through power shovels and hand tools. Numerous conveyor belt kind mucking machines were provided to rate the work. The damaged rock to be loaded into dump trucks and also hauled down-river where it was dumped into great spoil dumps in the side canyons. To remove the should turn trucks roughly in the minimal space available, the trucks were backed right into the canyon. Ultimately, much more than 1,500,000 cubic yards of spoil were removed from the tunnels.

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In in march 1932, work began on lining the tunnels through concrete. First the basic or invert was poured. Gantry cranes, to run on rails v the entire tunnels, were used to place the concrete. The sidewalls to be poured next. Moveable sections of steel form were offered for the sidewalls. Finally, making use of pneumatic guns, the overheads to be filled in. The concrete lining is 3 feet thick, to reduce the finished tunnel diameter come 50 ft.

In November 1932, the tunnels to be complete, and a barrier throughout the inlets of the Arizona tunnels to be breached through explosives. Earth and also rock were dumped from a trestle leg to block the flow channel, forcing the whole flow of water into the tunnels.

For nearly two years, the Colorado flow flowed unchecked v the diversion tunnels. In the fall of 1934, this every changed. Cofferdams were developed at the gateways to tunnels 2 and 3, those closest come the river. Concrete plugs 405 feet thick were dovetailed right into the tunnels, closing the bores forever.

As winter short water approached, an additional cofferdam closed turn off tunnel 1. When this tunnel to be plugged, 4 six-foot diameter holes were left in the plug, every fitted with a door valve.

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On February 1, 1935, a steel door weighing more than 1000 loads was lowered over the enntrance gate to tunnel 4. By opened the valves in plug 1, adequate water to accomplish downstream demands was released while the waters the the Colorado River began to back up behind Hoover Dam to type Lake Mead. Because that the very first time in history, the Colorado river was under man"s control.