fact_tbm-4
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of the machine. The operator steers the machine using sophisticated positioning technology that is accurate to within an inch.
The machine was manufactured by Mitsubishi Heavy Industries in Kobe, Japan and arrived in Seattle by ship. It took 25 truck loads to deliver the boring machine in pieces to the construction site.
Lining the tunnel with concrete
Tunnel liner segments made out of pre-cast concrete are brought into the tunnel. The machine positions each segment into place using an arm or erector, creating a ring. Then cement grout is placed behind the ring, forming the tunnels permanent liner.
Sound Transit l Union Station l 401 S. Jackson St., Seattle WA 98104(800) 201-4900 l (888) 713-6030 TTY l [email protected] l www.soundtransit.org
FACT SHEET I JANUARY 2006
Tunnel Boring Machine
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About the equipment
The Tunnel Boring Machine at its full size is approximately the length of a football eld. The machine includes trailing gear such as supply tanks, electrical support, exhaust fans and a conveyor belt.
The weight of the TBM and trailing gear is approximately 642 tons.
A 21-foot in diameter cutterhead (the blue part) is positioned at the front of the machine. Equipped with various cutting tools, the cutterhead turns around at the rate of 0.1 to 2.5 revolutions per minute. Excavated material goes through openings in the face of the machine.
The spoils are brought into the machine by a corkscrew-like screw conveyor located behind the cutter head. The spoils are then taken out the back on a conveyor system to be temporarily stored on site and then loaded into dump trucks.
Foam is usually added to condition the soil cuttings into a paste in order for it to pass through the conveyor for removal. Water, bentonite or polymers may also be used, depending on the soil type, groundwater and other factors. The conditioning agents are bio-degradable.
The machine is propelled and steered with 16 hydraulic jacks that are located around the perimeter
The boring machine Obayashi is using to construct the light rail tunnel through Beacon Hill.
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The segments are manufactured in Tacoma by Technopref Industries/Concrete Technology Corporation. 10 inches thick, the segments include rubber gaskets and are water-tight.
The TBM then uses the surface of the liner ring to propel itself forward, by pushing against it.
The TBMs path
The TBM starts tunneling on the west side of the tunnel, under Interstate 5.
The tunnel is just under one mile from the west opening of the tunnel to the east end near McClellan Street and 25th Avenue South.
The machine tunnels through Beacon Hill twice: Once to construct the southbound tunnel, and then again to construct the northbound tunnel. After the rst tunnel is completed the machine will be disassembled and taken back to the west portal to start the second tunnel.
Beacon Hill Station is currently being constructed from the top of the hill downward. The TBM will enter the Beacon Hill Station and be pushed through the stations previously excavated cavity. While the TBM is in the station area, the contractor will perform maintenance on it.