The project involves inspection and repair of three of the existing underwater tunnel systems which supply raw water from the Detroit River to three different potable water treatment plants in the Detroit/Dearborn, Michigan area.
Scope of Work
The three work zones under investigation and repair are the Pennsylvania, Springwells and Northeast Tunnels. The tunnels are in plant easements and city/roadway street Right-of-Ways (ROW) at various locations. The Pennsylvania Tunnel system is a fourteen-foot diameter tunnel with subsurface depths of eighty to one hundred feet of overburden, above the top of the tunnel with an area of concern of 225 LF for repair. The Springwells Tunnel system is a twelve-foot diameter tunnel with subsurface depths of eighty to one hundred feet of overburden above the top of the tunnel with an area of concern of 800 LF for repair. The Northeast Tunnel system is a ten-foot diameter tunnel with subsurface depths of eight to one hundred of overburden above the top of the tunnel with an area of concern of 400 LF for repair. Both the Pennsylvania and Springwells tunnels are pour-in-place concrete hand mined tunnels with the Northeast Tunnel constructed with an outer liner of O’Rourke Block, and then an inner poured-in-place concrete liner which was also hand mined. The project includes the underwater inspection and evaluation of the damaged tunnels section to assist with the design-build repair options. All three tunnel sections required access into the system through existing vertical down shafts with diameters ranging from eight to twenty feet.
Due to the limited access shaft locations, the inspection portions of the project required long distance diver penetrations to the work zones with tunnel horizontal penetration depth varying from 1,400 feet up to 3,000 feet. To assist the deployment of the long-distance penetration umbilical’s, Ballard’s crewing utilized specialized power sheave systems and rotation point sheaves for diver and tooling umbilical management. The crewing was also challenged by limited bottom time due to water depths. To maximize diver time, a custom mix breathing medium of NITROX was utilized which greatly extended the divers available underwater time, as well as increased safety and productivity.
The repair options included nonstructural and structural repairs inside the tunnel system while the plants stayed in operation, requiring divers to work in light-to moderate-flow.
Client: Great Lakes Water Authority
Location: Detroit and Dearborn, MI
Diver Depth: 50-80 ft