Slashdot Mirror
Seattle's Behemoth Boring Machine, Idle Since 2013, Makes Some Progress
After being blocked by an obstruction ("the object") which left it idle just over two years ago, repair work has continued on Bertha, Seattle's enormous tunnel-boring machine. Now, reports KOMO News and The Seattle Times, Bertha is once again ready to work. From The Times' coverage:
Tuesday morning's push of one and a half feet provided Seattle Tunnel Partners (STP) enough space behind Bertha’s drive motors to fasten the next concrete ring at the 1,085-foot mark of the planned 9,270-foot tube. Chris Dixon, STP project manager, is calling this a testing phase. The team is measuring how Bertha responds while rotating through heavy loads of compacted sand. Last week, a fixed steel arm in the front end broke and needed a one-day repair. ... This week’s two-day push would leave the nose of the drill just short of the north edge of the concrete vault, dug in 2014 so STP could reach and lift the 4million-pound front end for repairs. The winning bid from STP called for the tunnel to be completed this month.
Rock is more brittle than steel. Hit rock with a hard enough cutter blade, pushing with enough force, and you will chip away at it. Hit a malleable and tough steel pipe with the same cutter blade and the same amount of force, and the blade may dig in to the steel and get caught in it.
The operator doesn't exactly have visibility into the obstruction, so when progress stops, he may not recognize what's going wrong. He can add more force in an attempt to break through. Add enough force and something will eventually give, but there's no guarantee if it will be the obstruction that gives way, or the engine, or the power train, or the frame of his machine.
And what kinds of sensors do you think you can deploy on the face of a giant cutting disk that will survive the thousands of horsepower of force mashing it into the earth? (Trick question, the answer is none.) About all they can effectively monitor is from the back side of the cutting face. That means indirect measurements only, like the amount of power, rotational speed, rate of travel, temperature of the cutting face, sound of the cutting face, and the composition of the tailings. It's not exactly like looking out the windshield and seeing you're about to drive into a big steel pipe. The amount of power is regulated by the operator, but what are his options when it stops going forward? It's not like he can back up and turn left to go around it. He can pretty much decide "add power" or "stay stuck".
John
If anyone's in the area and wants to find out who did the work then I just might be able to get some sort of preview about real expectations (those expectations not given in the city council meetings or in press releases) and find out any scuttlebutt - though it might be a bit dated, I suspect the modeling company and/or traffic engineers have someone either on-call or on-site and they'll be capable of recommending, designing, and remodeling - or at least collecting the data and pushing it back to be done on big iron.
http://www.tunneltalk.com/Alaskan-Way-May10-RFP-released.php
With determination to maintain momentum, State officials met deadline this week and issued a request for proposals to build a bored tunnel replacement of the Alaskan Way Viaduct in Seattle. Three international pre-qualified teams now have until October to return proposals ahead of a planned award of contract in January.TBM tunnelling of the 54ft (15-16m) diameter bore could start in 2013 towards a targeted official opening on December 31st, 2015.
p1 Route of the double-deck highway viaduct that is to come down
Released on Wednesday (May 26th), the documents describe the scope of the estimated $1 billion and $1.2 billion project and set technical requirements to be met by the design-build contractors. Much of the strategic and detailed design elements however are left open to the contractors. These include the design, type and manufacture of the TBM; the method and destination of muck disposal; design and manufacture of the segmental lining; and the sequencing of tunnel excavation with construction of the interior road decks. The base design documents prepared by the client's designer Parsons Brinckerhoff and its PMAC (Program Management and Advisory Consultant) Hatch Mott MacDonald includes a geotechnical baseline report (GBR) and specifies pressurised EPB or slurry TBM excavation to cope with ground water pressures up to 5 bar, and control surface settlement above the 9,100ft (2.7km) long large diameter drive some 60ft to 200ft (18-60m) benearth the streets of the city. The RFP also sets out requirements for the highway tunnel's ventilation, fire/life safety, and electrical systems, and construction of its portals.
The three joint ventures prequalified to bid the contract are:
Seattle Tunneling Group (STG) comprising S A Healy; FCC Construccion, SA of Spain;
Parsons Transportation Group; and Halcrow
AWV Joint Venture (KBB) of Kiewit Pacific; Bilfinger Berger of Germany; and AECOM
Seattle Tunnel Partners (STP) comprising Dragados-USA of Spanish parent company; HNTB Corporation
Seattle Tunnel Partners is a joint venture of New York-based Dragados USA, a wholly owned subsidiary of Dragados, S.A., the construction division of ACS Group of Spain; and Tutor Perini Corporation, based in Sylmar, Calif.
They won the boring bid.