Bertha, the world’s largest tunnel boring machine, today broke through a 20-foot wall of a repair pit, WSDOT reported. It will continue drilling two more feet before stopping to build another concrete tunnel ring.
The top of my cutterhead has broken through the wall. I'll dig 2 more ft. before stopping to build a ring. pic.twitter.com/SVcThsimnv
— Bertha (@BerthaDigsSR99) February 19, 2015
Bertha is digging a 1.7-mile underground tunnel in Seattle that will replace the Alaskan Way Viaduct. The $80 million drill began digging from the Sodo neighborhood in July 2013, but stopped five months later due to damages that required extensive repairs. It hadn’t moved until earlier this week.
Once Bertha reaches the repair pit, the plan is to lift the front of the machine to the surface in order to fix the damages. Here’s the latest from WSDOT:
This is just the beginning of the repair effort being led by Seattle Tunnel Partners and manufacturer Hitachi Zosen. The machine will continue to move forward in 6 ½ foot increments, stopping to build rings on its way into the pit. When the front end of the machine is fully exposed, crews will begin the disassembly process. STP has told us that taking the machine apart and lifting it to the surface will take significant time and effort.
Here’s WSDOT explaining the repair process: