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Yonkers pressure tunnel. Steel ribs for concrete forms, made up of 5-inch I-beams spaced 3 feet apart. Lagging plates placed as concrete is built up from the invert. Contract 54. May 1, 1912.

Yonkers pressure tunnel. Steel ribs for concrete forms, made up of 5-i...

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