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diaphragm

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City tunnel. Steel diaphragm at tunnel end of drainage drift showing 8-foot opening to drift. ...  Contract 67. September 17, 1914.

City tunnel. Steel diaphragm at tunnel end of drainage drift showing 8...

Picryl description: Public domain image of an arch stone structure, bridge, or tunnel, free to use, no copyright restrictions.

City tunnel. View of drainage drift showing section of steel interlining riveted to diaphragm. ...  Contract 65. June 24, 1914.

City tunnel. View of drainage drift showing section of steel interlini...

Public domain scan of artwork related to technological or industrial history, free to use, no copyright restrictions image - Picryl description