Seeking to reduce pollution in Fort Wayne’s rivers and lessen storm-related street flooding, the city launched the Tunnel Works Program, a tunnel system that collects combined sewer overflows (CSOs) and transports them to the wastewater treatment plant. The premier project – the Three Rivers protection and overflow reduction tunnel (3RPORT) – is under construction, and Schnabel’s analyses helped secure the contract.

Our tunnel engineering service group is providing construction phase engineering services to the contractor, a joint venture of Salini Impregilo and Lane Construction. We contributed to the project win by preparing a pre-bid geotechnical and hydrological analysis of the bid documents, evaluating geotechnical parameters, specifying ground support systems, and advising on construction aspects of drilling in water-bearing, highly porous bedrock.

During construction, our design tasks involve initial rock support for the shafts, starter and tail tunnels, and adits; fiber-reinforced precast tunnel segments; and temporary construction works such as the tunnel boring machine launch frame, support of excavation systems, and crane slabs. We are also responsible for reviewing designs by specialty contractors and providing construction support services such as field verification and quality control procedures.

The tunnel, which runs roughly parallel to the St. Mary’s and Maumee Rivers, will be 5 miles long, 230 feet deep, and have a 16-foot finished inside diameter. It runs between several large shafts ranging from 25–64 feet in diameter. There are also seven drop shafts, up to 8 feet in diameter, that connect surface overflows to the tunnel through adits.

When operational, 3RPORT will reduce CSOs to Fort Wayne’s rivers by 90% and relieve street flooding during major rainstorms. The Tunnel Works Program is a major part of the city’s 2008 Long-Term Control Plan and associated consent decree with the Environmental Protection Agency.