ABSTRACT
The Northeast Boundary Tunnel (NEBT), the largest component of the Clean Rivers Project, is a deep, large sewer tunnel that will increase the capacity of the existing sewer system in the Washington DC area, significantly mitigating sewer flooding during large storm events and improving the water quality of the Anacostia River. The construction of this last portion of the project was awarded to Salini Impregilo Healy JV (Lane), already successfully leading the completion of the previous Anacostia River Tunnel (ART) project in 2018. The Salini Impregilo Healy JV is currently (Dec. 2018) excavating the new tunnel using the same ART machine after full refurbishment, recertification and size adjustment. This will operate in the same Potomac formation but under larger overburden and water head, thus introducing additional design and construction challenges. The NEBT project is benefiting from the lessons learned from ART in terms of fine tuning the TBM equipment, soil conditioning strategy, EPB pressure definition, segmental lining design and adits connections with shafts performed through soil improved areas.
