The 6.4m-diameter cutterhead for TBM Mary was lowered yesterday and the middle shield is expected to follow on Friday.
The TBM is one of two Herrenknecht machines commissioned for the project. TBM Mary will excavate the northern section of the tunnel, while TBM Emily will dig south to connect to the Anacostia River Tunnel system.
Once assembled, Marywill start her 3.87km journey from West Potomac Park to the Georgetown University entrance site. This week crews begin mobilising for construction at the Georgetown University construction site, staging equipment and resources to build a drop shaft and diversion facility that will connect to the tunnel.
Mary is scheduled to begin digging northward in the spring and Emily will be launched in the summer.
“Lowering Mary’s cutterhead is more than just a construction milestone – it marks progress toward a cleaner, healthier Potomac River for everyone,” said DC Water CEO and general manager, David L Gadis. “Soon, Marywill be fully assembled underground and ready to start her journey to help protect the river for generations.”
The Potomac River Tunnel is a key part of DC Water’s Clean Rivers Project, a long-term programme to improve water quality. The tunnel system will store combined stormwater and wastewater overflows during heavy rains, preventing millions of gallons of untreated sewage from reaching the Potomac. Once operational in 2030, it will reduce the volume of sewage and stormwater overflows into the river by 93% and lower the number of times this occurs from 74 to just four times in a typical year.
