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| the drill head of Big Becky, tunnel boring machine. The drill head has disc cutters made of special tool steel that cut through the different types of rock in Niagara (shale, sandstone, limestone) |
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| Big Becky, tunnel boring machine used in Niagara Falls. |
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| The Niagara Escarpment is made up of different types of rock. The rock at the very top is dolomite and is very hard. Underneath it is shale which is very soft. Do you see how the rock underneath is wearing away faster? When they were digging the new tunnel, the tunnel boring machine had to deal with the different hardness levels of each type of rock. |
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