Why a Giant Machine Is Digging a Tunnel Under D.C.
July 3, 2014
-- A colossal machine called the "Lady Bird" is boring a huge
tunnel
under Washington, D.C., to channel storm water for treatment, keeping
runoff out of the city's notoriously polluted rivers. The $30 million
machine is named for Lady Bird Johnson, who, as First Lady of the United
States, had advocated for cleaner rivers around the nation's capital.
To learn more about the "Lady Bird" and the tunnel it's digging,
click here.
Transcript
Man In Elevator
Going down.
Carlton Ray
Director
DC Clean Rivers Project
We had about 3 billion gallons of raw or combined sewage that would discharge on an annual basis from our combined sewer system. About two thirds overflows into the Anacostia River, about a third of it goes into the Potomac River. Our program is to capture that.
So we're about to go into the head of the tunnel here. We're about to go approximately a mile to the head of the machine. Overhead you can see the big air ventilation system bringing fresh air in.
Brett Zernich
Construction Manager
So it's a fairly simple process, the shield has a main barring unit that has drive motors that turn this cutter head and that cutter head is digging into the ground. Simultaneously, the machine is advancing into the ground, so as this is spinning the machine is advancing forward and ingesting material.
Then it stops, and the crew builds a ring inside of the tail shield, that tail shield has a seal that's not he backside of it, and that keeps the ground and water and grout and stuff from invading the tunnel. So as it advances it's pulling material out of the screw conveyor for that complete advance. That's getting mixed up into a mixture of soil and water and solution, and then getting pulled up all the way out to the conveyor belt. And then that conveyor belt then takes all that material out to the shaft where it's dumped into big boxes and hoisted up the shaft
Not it's ready to excavate again so it starts the cycle all over.
This machine does around a 100 millimeters a minute, so that's about 4 inches per minute. So it can theoretically do a six foot push in about 18 minutes.
Carlton Ray
When we have sewage overflows into the Anacostia River, Potomac and Rock Creek,that causes water quality problems. We're going to reduce the overflow volume by 96%.
