Severe flooding over the past 40 years led the city of Quincy, Mass., to construct a deep-rock flood tunnel beneath its downtown area. The 4,200-foot-long tunnel, part of a $35 million flood control project, would divert flood waters from an overflow area to an egress channel. The U.S. Army Corps of Engineers, acting as project manager, wanted a cast-in-place or precast concrete liner at least 12 inches thick and a 12-foot inside diameter.
Unforeseen problems arose as the more than 900 gallons of water per minute were flowing through the tunnel. The tunnel's diameter was too small to accommodate standard 12-inch-thick precast concrete pipe liners.
A 6-inch layer of pea stone and grout around the 8-inch-thick pipe was recommended. To assure sufficient structural integrity, prototype pipe was tested to simulate the maximum stress in the installed pipe and also stresses caused by the pipe carrier that would move sections into place within the tunnel.
To prevent damage, the pipe was stored and delivered on end. Onsite supports were needed to keep the pipe from deforming or cracking during installation. Sections of pipe were moved by a carrier. The 90-degree transition elbow from the outlet shaft to the precast tunnel, designed for slipformed, cast-in-place construction, ended up being precast pipe. The tunnel was pressed into service ahead of schedule due to heavy rains.
Keywords: tunnel, pipe