To address inflow and infiltration (I/I) issues in portions of the Crabtree Basin interceptors, the City of Raleigh initiated the Crabtree Basin Wastewater System Conveyance Improvements project. This was the highest priority project identified in the City’s Sanitary Sewer Capacity Study.
The City of Raleigh selected McKim & Creed, in partnership with Hazen and Sawyer, to provide design and construction services in connection with seven miles of 54- through 72-inch diameter gravity interceptor, a 24-mgd expansion to the pre-existing 80-mgd Crabtree Valley raw wastewater lift station, and two miles of 42-inch diameter raw sewage forcemain.
The project included design and construction of parallel gravity sewer along an existing interceptor corridor on City park property, within road right-of-ways and on private commercial and residential properties. Furthermore, the project included 10 individual tunnels under NCDOT and City of Raleigh roads including I-440, one CSX railroad crossing, and one Norfolk Southern railroad bridge. The tunnel designs primarily consisted of microtunnels with single- and two-pass installations through various subsurface conditions with submerged groundwater conditions. The single-pass microtunnels were successfully installed, including one under two 60-inch gravity interceptors at an NCDOT interchange ramp of I-440, one under Capital Boulevard, a divided highway, and a third under Raleigh Boulevard.
The project also included replacement and rehabilitation of 24- through 42-inch gravity sewer..