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Gunpowder, nitroglycerin, and dynamite allowed tunnel diggers to blast through mountains much faster than ever before.
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Gunpowder was first used in 1679, to build an underground section of the Canal du Midi, a canal connecting the Atlantic Ocean and the Mediterranean Sea. The tunnel was 157 meters long. Nitroglycerin was first used in 1867 to excavate the Hoosac Tunnel in North Adams, Massachusetts. That same year, Swedish physicist Alfred Nobel patented another blasting explosive called dynamite. Dynamite is based on nitroglycerin but is much safer to handle than nitroglycerin alone.
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One of the first tunnels to be excavated with gunpowder was the Harcastle Canal Tunnel in England in the 1700s -- and it was an absolute disaster. Gunpowder blasts struck springs, which flooded the tunnel and delayed construction. To save time and money, the chief engineer built a very small and narrow tunnel. The tunnel was so tiny (2.2 meters wide by 3.6 meters high), barges had to be "legged" from end to end. This meant that men lay on their backs on the barge deck and pushed the barge through by walking their feet along the tunnel roof!
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