Holing Through At QMT 74 Years Ago
It was 74-years ago this month that Mayor Fiorello La Guardia pulled a switch to blast the last six feet of rock separating the Manhattan and Queens tubes at the Queens Midtown Tunnel.
One photograph from the Bridges and Tunnels Special Archive collection shows the mayor, aided by Peggy MacDonald, the daughter of the construction company’s Chief Engineer, John MacDonald, pulling the switch on Nov.8, 1939. Another shows the sandhogs tigthening a cast -iron tunnel lining bolt and a third photo shows Mayor La Guardia on the inspection tour.
Both tubes were excavated through the rock and earth under the riverbed using a combination of dynamite drills and four circular cutting devices that were slightly over 31-feet in diameter called shields.
The shields were lowered into construction shafts at each end of the tunnel and hydraulically shoved through the riverbed until they met under the middle of the river. As the shields were shoved forward, tunnel construction workers known as “sandhogs” assembled the 32-inch wide cast iron rings that line the tunnel. Each time a new tunnel lining ring was completed, 28 jacks on the back of the shield would hydraulically shove off the new ring by exerting 5,000 pounds of pressure per square inch.
In the areas where the shields had to move through rock, the path was cleared with dynamite. This was a slow process, proceeding at a rate of about 18 feet per week for each shield.
The dynamite charge that blasted away the last six feet of rock went off the morning of Nov. 8. Above ground, Mayor La Guardia, Chief Engineer Ole Singstad and 2,500 sandhogs gathered to celebrate. The sound of the blast was shared with gathered guests through the use of a public address system. The mayor then changed into sandhog clothes and led a small group to the blast site, followed by an inspection of the entire tunnel from Manhattan to Long Island City in Queens.
Engineers and surveyors had made careful calculations throughout the tunnels’ construction and when the two tunnels met they were only off by just over half an inch --- an amazing feat in the days before calculators and computers.
Construction on the 6,272-foot long Queens bound south tube and the 6,414-foot long Manhattan bound north tube began Oct. 2, 1936 and was completed four years later on Nov. 15, 1940. It took 54 million man-hours of labor to build (18 million at the tunnel and the rest to manufacture materials needed to build it.)
It cost $58.7 million to build and was, at the time, the largest non-federal public works project in the country.