Factory testing has been completed on DC Water’s first TBM to be used on the $819M design-build contract Potomac River Tunnel project being constructed by the CBNA-Halmar Clean Rivers JV, comprising CBNA, Halmar, COWI, and Hatch.
Named ‘Mary’ the 6.4m diameter Herrenknecht machine has been designed to bore through the alignment’s hard rock ground conditions. The factory acceptance testing was completed in April in Germany, with the TBM now set to head to DC to start work on the Potomac River Tunnel.
Mary passed all the necessary requirements and is one of two TBM’s to be used on the project. The tunnel is part of DC Water’s Clean Rivers Project, to reduce the amount of sewer and stormwater discharged into the Potomac during rain events.
“We are excited to mark this major milestone. These machines are truly a marvel of modern technology and must be custom built for the project,” said DC Water Chief Executive Officer and GM David L. Gadis. “We look forward to Mary’s arrival. She and her sister TBM, Emily, will have their work cut out for them to dig the 8.8km tunnel.”
Mary is due to arrive in the fall. In preparation for shipment, the machine must be carefully disassembled and the parts crated for shipment to the U.S.
Mary and Emily will tunnel in opposite directions slowly boring through bedrock and soil. Mary will work north 3.8km toward the tunnel’s endpoint near the entrance of Georgetown University. Emily will head south, tunnelling 4.9km to connect to the Anacostia River Tunnel system.
Manufacturing is already underway on Emily. Factory acceptance testing is expected to occur in October, after which it will be shipped to DC too.
The Potomac River Tunnel is designed to reduce the volume of sewer and stormwater released into the river by 93% in an average year of rainfall. That amounts to more than 600 million gallons of wastewater and stormwater which will be captured and sent to the Blue Plains Advanced Wastewater Treatment Facility for treatment. It’s expected to be completed in 2030.
Herrenknecht
Pioneering Underground Technologies - Herrenknecht AG is the technology and market leader in mechanized tunnelling. As the only company worldwide, Herrenknecht delivers cutting-edge tunnel boring machines for all ground conditions and in all diameters - ranging from 0.10 to 19 meters.
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