This special wooden form was assembled to construct the concrete lining where a 21-foot diameter sha
This special wooden form was assembled to construct the concrete lining where a 21-foot diameter shaft meets City Water Tunnel No. 2. It was built in the contractor’s yard and designed so it could be taken apart in sections for transportation. Here the ribs are covered with lagging of narrow wooden strips that were steamed and bent to the required curvature. March 25, 1932 From NYC water -- source link
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