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Location: North Adams, Massachusetts, USA
Completion Date: 1873
Cost: $21 million
Length: 25,081 feet (4.75 miles)
Engineer(s): H. Haupt & Company, Thomas Doane, Walter Shanly
In March 1853, one of the earliest tunnel boring machines ground 10 feet into the Hoosac Mountain and died, never to run again. It remained stuck in its hole for many years as a grim symbol of engineering failure. In fact, it would take several failed attempts, 200 lives and 20 years to complete the Hoosac Tunnel.
When construction began in 1851, workers relied on gunpowder to blast through the mountain. Progress was slow as each blast produced only a few feet of shattered rock. In 1866, two tunnel blasting tools -- nitroglycerin and the compressed air drill -- were used in the Hoosac for the first time. Workers blasted faster than ever before, but not without risk. Nitroglycerine is an extremely unstable explosive. Hundreds of workers lost their lives in unexpected explosions.
The Hoosac Tunnel remains a landmark in hard-rock tunneling. Over the course of its construction, virtually every kind of tunnel digging device was used to bore through the Hoosac Mountain -- and virtually every kind of mistake was made. Thanks to these mistakes, engineers today can build longer tunnels in a fraction of the time.Here's how this tunnel stacks up against some of the longest tunnels in the world.
(total length, in feet)