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Show Ticklish Bit of Tunneling. A very interesting bit of tunneling was recently done on the Fourteenth street tube under the East river, 'New York. The heading was being run in rock and at one point test holes showed a thickness of only eight Inches of sound dry rock above the line along which the top of the tunnel was to run. As the tunnel was being driven without the use of compressed air it was decided to drop the upper heading four feet until this thin cover of rock was passed. The cast iron lining was set in place at eacli side of this section and then the rock was removed very carefully by using a great many holes each loaded with about one-eighth of a stick of dynamite. dyna-mite. As eacli bit of rock was removed the arch of the tunnel lining was set in place. By this means the dangerous section was tunneled without breaking through the thin shell Scientific American. |