Hoosac Tunnel - Construction Technology

Construction Technology

The tunnel construction project required excavation of 2 million tons (1,800,000 metric tons) of rock. On March 16, 1853, "Wilson's Patented Stone-Cutting Machine" (a tunnel boring machine) was used; it failed after excavating 10 feet (3 m) of rock. Tunnel builders resorted to hand digging, and later used the Burleigh Rock Drill, one of the first pneumatic drills. Construction also featured the first large-scale commercial use of nitroglycerine and electric blasting caps.

Digging the Central Shaft also allowed workers to open 2 additional faces to excavate: once the shaft was complete in 1870 workers dug outwards from the center to meet the tunnels being dug from the east and west portals. Engineers built a 1,000-foot (305 m) elevator to hoist the excavated rock from the Central Shaft.

One of the many engineering challenges posed by the project was getting the proper alignment between the four tunnel segments that were being dug: the east and west portal tunnels, and the two tunnels dug outward from the central shaft. Engineers cleared a path through the forest over the mountain, and strung a straight line from the east to west portals, through "sighting posts" on the east and west peaks of Hoosac Mountain. Repeated surveys verified the line ran true between the posts, and steel bolts were installed at fixed intervals along the line.

On December 12, 1872 workers opened the east portal tunnel to the Central Shaft-dug tunnel, which were aligned within nine sixteenths of an inch (1.4 cm), a tremendous engineering achievement at that time. On November 27, 1873 the remainder of the tunnel was opened to the west portal tunnel.

Lewis Cuyler of the Hoosac Tunnel Museum Society described the project as the 'fountain-head of modern tunnel technology.'

The American Society of Civil Engineers made the tunnel a Historic Civil Engineering Landmark in 1975.