CLOSURE OF AN UNDERGROUND TUNNEL WITH LONG-DISTANCE GROUTING

Christopher R. Ryan
Donald W. McLeod
Steven R. Day

A former water intake tunnel extending under the Niagara River was contaminated with DNAPLs and was closed at the request of regulatory authorities. The six-foot tunnel is nearly a mile long and accessible from just two vertical shafts, one of which is in the river. Closure of the tunnel presented a unique remediation challenge because of the limited access, considerable volume of the tunnel, and because the tunnel was full of potentially contaminated water. A plan was developed and implemented that closed the tunnel by filling it with cementitious grout while simultaneously removing and treating the displaced water. The grout used to fill the tunnel had to meet demanding requirements for both regulatory acceptance and workability. An extensive laboratory testing program was implemented to design the grout for compatibility with DNAPLs, low permeability, strength, flow, and set properties. In the fall of 2000, the tunnel was filled with over 7500 cy of grout in five days, using multiple and redundant grouting pipes while pumping from a stationary grout plant on the shore of the river. The primary filling operation was followed by secondary pressure grouting. Closure of the tunnel required underwater divers, remote-operated robots, and barge operations, as well as a state-of-the-art grout mixing and pumping plant. Field observations, sample testing, and continued monitoring indicate that the closure was successful. This paper presents a brief overview of the laboratory testing and construction phase of the project. A future paper is planned to present a more complete discussion of the project including monitoring results.