With the final repairs having been made earlier this summer and Big Bertha finally picked back together underground, Washington State Department of Transportation and Seattle Tunnel Partners crews are hopeful that their 18-month nightmare is nearing a close.
Now two years behind schedule, the world’s largest tunnel-boring machine is pegged for a return to digging in November. The machine went down in January 2014 one-tenth of the way through digging a 1.7-mile tunnel which will replace the Alaskan Way viaduct and carry a double-deck highway beneath Seattle.
In April we showed you the process of lifting the massive machine’s cutterhead through a 120-foot deep access tunnel and now, WSDOT has shared all the photos of the machine’s massive repair process.
Seven of the machine’s rubber seals meant to protect its main bearing became clogged by sand and water and steel casings around the seals “broke apart, sending fragments into the drive gears,” the Seattle Times reported back in May. Plus, some of the teeth in the machine’s bull gear, which rotates the drill face, were cracked as well as several pinion gears. Hitachi-Zosen, the machine’s manufacturer, resurfaced much of the front end to allow its circular parts to move smoothly and replaced the full set of 24 pinion gears and the outer seals of the main bearing.
The company also lengthened the mixing arms and equipped them with paddles, attached more steel blades to the cutting surface and ordered a replacement for the machine’s cracked center pipe. The full repairs are expected to be completed later this month.
In August the machine was lowered back into the pit and a resume digging date of November 23 was set. Between now and then, crews will be performing open-air testing on the machine.
Don’t miss the gallery detailing the extensive repairs, above.