The Northeast Interceptor project in Lake County, IL, included the first extensive sewer microtunnel installation in the Chicago area. The job used 8,000 feet of Hobas centrifugally cast fiberglass reinforced polymer mortar pipe in diameters of 42 in. and 48 in., and 16 Hobas tee base manholes.
Initially, the lines were used to receive flows from an abandoned wastewater treatment plant, but their primary purpose is to accommodate future development of the surrounding community. Low initial flows and long retention times made corrosion resistance critical. Hydraulics also were important to achieve the desired flow capacity. Specifications dictated a choice of PVC-encased reinforced concrete pipe, polyurethane-lined prestressed concrete cylinder pipe or Hobas centrifugally cast fiberglass reinforced polymer mortar pipe.
Hobas pipe was selected because the pipes OD and roundness tolerance range of less then 0.1 percent results in the lowest jacking loads of any sewer pipe. Lathe cut square ends and natural wall resiliency transfer jacking loads more uniformly. The pipes price was another winning attribute, the subcontractor said.
The project design consultants were Resek, Henry, Meisenheimer &: Gende of Libertyville, Ill. Jacking subcontractor was Westcon-Dillingham Microtunneling.
The new sewer lines were routed through sensitive farmland at depths up to 50 feet. Installation was completed with 16 drives averaging about 500 feet each. No intermediate jacking stations were needed even on the longest push of 794 feet. As expected, jacking loads were low with an average maximum force of less than 100 tons and a startup peak of no more than 175 tons. At the completion of the installation, testing showed the pipes and joints to be 100 percent leak-free.
