A colossal machine is digging a huge tunnel under Washington.
Self-study activity:
Watch the video and complete the blanks in the transcript with the missing words.
Going down.
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 (1) ... into the Anacostia River, about a third of it goes into the Potomac River. Our programme 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.
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 (2) ... the machine is advancing forward and ingesting material.
Then it stops, and the (3) ... 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 (4) ... and water and solution, and then getting (5) ... ... 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 (6) ... 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.
When we have sewage (7) ... into the Anacostia River, Potomac and Rock Creek,that causes water (8) ... ... . We're going to reduce the overflow volume by 96%.
Key:
1 overflows 2 spinning 3 crew 4 soil 5 pulled up 6 dumped 7 overflows 8 quality problems
