Concrete Pipe Resiliency Acknowledged for Vital Sanitary Sewer Interceptor
Concrete pipe has long been acknowledged as the premier product of choice for countless sanitary sewer projects, providing resilient infrastructure through engineered strength and durability. County Materials Corporation is supplying over 29,000 feet of 24 to 48-inch diam- eter precast concrete sanitary sewer and jacking pipe for a major interceptor in the Milwaukee Metropolitan Sewerage District.
Sewage was projected to be present in the interceptor for long transient times. To keep the interceptor in service for 75 to 100 years, the designation of interceptor materials was very important to eliminate corrosion as much as possible. It was decided that the interceptor pipe materials be limited to those that would resist corrosion by sulfuric acid formed by hydrogen sulfide buildup, while providing a sewer system capable of maintaining structural integrity at the required depths of 30-45 feet. For these reasons, PVC-lined reinforced concrete pipe and fiberglass reinforced polymer mortar pipe were selected. In addition, precast concrete manholes with field applied epoxy-coated interiors were specified.
Strength, service life, corrosion resistance and joint performance were the major considerations in the design of the interceptor. With depths reaching up to 45 feet, and portions of the project requiring tunneling under wetlands, Ruekert & Mielke, civil engineers for the project, selected precast concrete pipe as the clear material of choice. From the vertical overburden depth to the axial load of jacked-pipe tunneling, concrete pipe provides the flexibility of design to meet specific load requirements.
The interceptor project runs approximately 6 miles from Muskego to the Milwaukee Metropolitan Sewerage District (MMSD) interceptor at 60th street in Milwaukee.
Ruekert & Mielke awarded contracts to three local contractors who chose County Materials Corporation to supply T-Lock lined concrete pipe. The T-Lock lined concrete pipe incorporates a PVC inner liner during the manufacturing process. Fully anchored into the concrete prior to curing, the liner and pipe perform as a single product to resist both load and corrosion. Project-specific strength designs were individually engineered to support the variety of loads on the various sections of the sewer. To assure that the interceptor would be able to serve the entire service area by gravity, it was necessary to complete the preliminary design of more than 81,000 feet of local sewers (12 inch and greater in diameter) to determine the required invert elevations of the interceptor sewer.
Crews utilized open cut, jacking with tunnel boring machine, jacking with hand mining, hand mining with timber sets, auger boring and microtunneling to install the sewer system. These different methods were necessary given the varying conditions and topography found in the project corridor. In addition to the placement of 29,000 feet of gravity sewer, the project included 2,000 feet of microtunneling, four stream crossings, numerous wetland crossings, wetland mitigation, acquisition of forty-five easements, public participation with multiple communities, local, state, county and federal permitting, four extensive intermunicipal agreements and a Clean Water Fund financing plan.