Jan. 14 Bertha Update: Going Hyperbaric – Source: WSDOT This press release by WSDOT is fascinating, you should definitely check it out. It describes the hyperbaric intervention that deep see divers performed to try and determine what has impeded the progress of the Bertha TBM on the Alaska Way Viaduct Tunnel project. They describe how a bentonite mud is injected in front of the cutterhead to create a "membrane" so they could pump air into the excavation chamber to create an air bubble that the hyperbaric divers could work in. The air pushes the bentonite membrane into the soil face and holds back the soil and water. They use the screw conveyor to remove sufficient material from the excavation chamber so that the divers can work in the top half of the excavation chamber.
Jan. 21 Bertha Update: Initial Results of Hyperbaric Inspections – Source: WSDOT In this press release, WSDOT reported that as of January 21, STP divers had spent more than 35 hours under hyperbaric conditions inspecting the TBM cutterhead from inside the excavation chamber. They removed a piece of bent well casing, pieces of PVC pipe, and found a large boulder or piece of concrete in a cutterhead opening.
Jan. 23 Bertha Update: More Hyperbaric Work, No New Findings – Source: WSDOT In this press release, WSDOT mainly just updated the total tally of hours worked by the deep see divers in the TBM intervention at the cutterhead. As of January 23, they were up to 68 hours of work performed during 17 sessions.
Jan. 31 Bertha Update: Further evaluation required before tunneling can resume – Source: WSDOT Bertha moved forward about 2 feet on January 28 to test the cutterhead and build the next tunnel liner ring. STP crews observed abnormally high temperatures in some components, similar to what was observed during the original stoppage on December 6. The made adjustments, moved forward another 2 feet but the temperatures persisted. The analysis will continue.
The Gotthard Base Tunnel will eventually be a 35-mile rail tunnel through the famed Alps in southern Switzerland. So what does it take to survey the world’s longest tunnel? How about setting some 7,000 points […]
The Seattle Times (hat tip to ASCE SmartBrief) has reported that seven voids have been discovered above the Beacon Hill Tunnel with one opening up at the ground surface. The tunnel is being constructed by Sound Transit, the area’s transportation agency as part of a roughly $2.6 billion (yep, billion) light-rail project connecting downtown Seattle with the University of Washington and SEA-TAC airport. The voids were a result of running sand pockets in the otherwise stable clay units that were encountered by the tunnel boring machine or TBM. These voids migrated up like a chimney with one reaching the surface, almost 160-ft above the tunnel. This void was apparently 21-ft deep and opened up in a resident’s front yard and could have easily swallowed her up as she noticed it while gardening. The other voids were discovered at a depth of 20- to 65-ft below the ground surface. More after the break. (Illustration from Seattle Times)
The August 2011 issue of Tunnel Boring Magazine contains a profile on Brierley Associates, an engineering firm specializing in tunnel design based in the Denver, Colorado area. The article provides some nice insight into the […]