Lady Bird Digs Deep Tunnel Below DC

July 2014, Vol. 69 No. 7

Now partway through a 10-year, $4-billion capital program, the District of Columbia Water and Sewer Authority (DC Water) is experiencing the largest expansion in its history.

To manage the city’s combined sewer overflows (CSOs), DC Water’s Clean Rivers project comprises a system of tunnels and diversion sewers for the capture of CSOs to Rock Creek and the Anacostia and Potomac rivers for treatment at DC Water’s Blue Plains Advanced Wastewater Treatment Plant. The anticipated completion date is January 2018

To create the massive underground structures that form the Anacostia River solution to CSOs, giant tunnel boring machines are being used to bore metro-sized tunnels more than 100 feet underground. The Lady Bird tunnel boring machine (TBM) is being used to dig the first portion a $2.6 billion tunnel project, known as the Blue Plains Tunnel, a four-mile section of the 13-mile Anacostia River Tunnel. The tunnel is expected to reduce sewage overflow to DC’s bodies of water by 96 percent.

Manufactured in Germany specifically for the DC Water Authority and this project, the $30 million machine boasts a 26-foot diameter, is 443 feet long and weighs 1,323 tons. At full speed, the machine can tunnel 100 feet per day.

Each foot of progress requires three dump trucks to haul away the dirt tunneled and by the time the project is completed, Lady Bird will have removed approximately 13 million cubic feet of soil, or 205,820 truck-loads.

Since July 2013, the joint venture team of Traylor-Skanska-Jay Dee, supported by CHSM Hill-Halcrow, began tunneling more than 4,900 feet from the Blue Plains treatment plant. The $330-million tunnel will connect the 370-million-gallons-per-day treatment plant and the main southeast D.C. pumping station.