McCook 33 ft Diameter Main Line Tunnel Liner for the Chicago TARP: Fid-Bau Portal

McCook 33 ft Diameter Main Line Tunnel Liner for the Chicago TARP

Williams, B. Nash

The Chicago Tunnel and Reservoir Plan (TARP) is a combined sewer overflow system devised in the 1970s to control flooding in the metropolitan Chicago area. The system diverts storm water and sewage through 109 miles (175 km) of large tunnels 9 ft-33 ft (2.7 m-10.1 m) in diameter into holding reservoirs for later treatment and averts sewer overflows causing harmful effects to Lake Michigan. When completed, the TARP system will have a capacity of 17.5 billion gal (66.2 billion L) of storage and will complete one of the largest civil engineering mega projects in the United States. The McCook Reservoir Main Tunnel is a central component to the TARP system as it connects the McCook Reservoir to Chicago's Deep Tunnel system. The finished tunnel comprises a 33 ft (10.1 m) diameter steel liner that bifurcates into two rectangular cross-sectional legs that control the flow of the system through six high-head wheel gates. The tunnel and gates are located at the bottom of a 90 ft (27.4 m) diameter shaft that is 300 ft (91 m) below the surface. This tunnel pipe is one of the largest diameter steel tunnel liners in the country. This paper provides an overview of the project, plus details of the assembly and erection of the steel pipe sections. As these sizable sections could not be fabricated in shippable sized rings, the components to the pipe sections and bifurcations were required to be fabricated in more manageable piece sizes. An initial task for the construction team was to maximize the sizes that would minimize the onsite assembly requirements. In addition, the weight of some subassembled pieces was in excess of 180 tons, and most pieces required rotational manipulation during installation. An added challenge was to perform this subassembly, fitting and welding of high-strength steel in Chicago during winter conditions.