Ground settlement from TBM operations was minimzed to protect numerous nearby utilities, requiring 24-hour tunneling operations in critical locations.
Mining shafts were designed as dual-purpose structures that provided construction access for tunneling operations before becoming permanent system components.
The City of Allen Park's Sanitary Sewer Overflow (SSO) Tunnel and Relief Sewer project was honored by the American Public Works Association, Michigan Chapter, as Project of the Year (Environment $15 - $25 million). The award recognizes the collaborative effort of the project team to design and construct a large-diameter pipeline through a highly congested urban area while protecting existing utilities and infrastructure.
The project provides big relief for the City's overloaded sanitary system, reducing bypass pumping to Ecorse Creek and limiting Allen Park’s peak wet weather flows to the Detroit sewer system. It also reduces the future risk of basement flooding by providing storage during wet weather events and eliminating hydraulic bottlenecks in the system. The .86-mile tunnel can store 1.34 million gallons of wet weather flow that is lifted through a new 8.4-cfs submersible dry weather/wet weather pump station and force main, and ultimately to an existing trunkline sewer.
Rigid mining shafts, detailed specifications for tunneling materials, and a dynamic mix of trenchless construction and rehabilitation methods were used in conjunction with robust geotechnical instrumentation and monitoring to mitigate settlement risks and overcome historical challenges with tunneling in the area. Extensive coordination with federal, state, and local agencies; two railroads; three schools; and several residential neighborhoods was critical to completing this sewer transport and storage system that will protect public health and the environment for years to come.