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Video transcripts for website:
The SFMTA is also extending rail transit which began with the launch of the T Third light rail line in 2007. The next step, extension of the new line northward, to Moscone Convention Center, Market Street, Union Square and Chinatown, under one of the most congested corridors in the City.
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Station Visualization Video (1:24)
Music only
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[Video property of Herrenknecht. Permission was obtained to use this video.]
When the tunneling project is on its way, the EPB shield is the first choice in homogenous cohesive soil. An EPB shield consists of the widely closed cutting wheel with special tooled arrangement and a center free ring drive, a pressure wall with stators which form the excavation chamber, together with the cutting wheel, a screw conveyer and a conveyer belt to transport muck, thrust cylinders and articulation cylinders for inclining the tail skin when driving curves, a compressed air lock and the erector. In contrast to the bentonite shield in the case of the EPB shield, the excavated soil itself acts as a supporting medium. To be able to fulfill this function, it must first be turned into a plastified consistency. Depending on the local conditions, this is done by the controlled injection of conditioning agents, such as foam. This makes it possible to reduce the drive torque and cut down wear at the same time. The foam is injected into the soil ahead, via a nozzle installed on the cutting wheel. Once the soil has been prepared in this way, it is no problem to transport from the excavation chamber via a screw conveyer or onto a conveyer belt. From here, it will be further transported via rail or lorry [truck]. In the case of the EPB shield, the pressure for supporting the shield is controlled by the coordinated control of advancement speed and the screw speed. The excavation chamber will be filled to ensure adequate support of the face at all times, and to be able to react correspondingly to pressures from the earth or groundwater.
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