Northeast Boundary Tunnel Design-Build

DC Water

In order to reduce flooding caused by an undersized sewer system, DC Water is undertaking the $2.7 billion Clean Rivers Project. This ambitious program comprises 18 miles of new sewer tunnels, which will greatly increase the capacity of Washington’s sewer system and reduce combined sewer overflow (CSO) discharges into the Potomac River, Anacostia River, and Rock Creek. A central component of the program is the Northeast Boundary Tunnel (NEBT), a new 5.1-mile, 23-foot-diameter reinforced concrete sewer tunnel in central and eastern Washington. 

EnTech, as a member of the design-build team, led the geotechnical instrumentation and monitoring program, which entailed installing, monitoring, and reporting the results of more than 2,500 instruments and sensors to measure displacement at ground level and in the tunnel. The tunnel was excavated at depths ranging from 50 to 160 feet, using a 650-ton tunnel boring machine (TBM), which simultaneously dug the tunnel and constructed its concrete walls. The geotechnical monitoring program was essential to maintaining the safety of existing aboveground structures in the dense urban area and protecting workers underground.

In addition to monitoring the excavation of the tunnel itself, EnTech monitored the construction of seven deep shafts, ventilation control facilities, and diversion facilities to capture flow from the existing sewer system, and green infrastructure installations. EnTech further supported the design-build team by installing, monitoring, and automating over 60 observation wells and piezometers for the dewatering program during both tunnel and shaft construction.