Bertha’s Rescue Shaft

The Blue Begins Drilling

Malcolm has been awarded the support of excavation contract to drill the rescue shaft for Bertha, the world’s largest Tunnel Boring Machine (TBM). Bertha has stopped all forward progress after just 1,000-ft of mining the new SR99 transportation tunnel currently being built below downtown Seattle, Washington. The stalled TBM is currently 80-ft below the surface.

After vetting all possible repair/rescue methods, Seattle Tunnel Partners decided that accessing Bertha with a vertical shaft provides the best approach to gain access to the cutter-head and facilitate repairs. Due to the limited surface area above the tunnel alignment and physical constraints bound by existing infrastructure, the dimensions of the otherwise symmetrical shaft are heavily impacted requiring special considerations for design, layout, and water control processes. The final design for the rescue shaft requires the drilling a series of secant piles with a varying diameters ranging from 3-ft to 10-ft. The secant piles will overlap two 1,000-ft long walls constructed out of 5-ft dia. non-accessible shafts that Malcolm originally installed to support the initial TBM launch. The existing shafts, with depths ranging from 75 to 138-ft were installed to protect the existing sea-wall and control the below sea-level ground conditions. Jet grouting and dewatering wells will also be constructed to control water.

“Rescuing a one-of-a-kind TBM requires a one-of-a-kind access shaft.” said Clint McFarlane, project superintendent, Malcolm. “We’re happy to be working with STP and WSDOT to help get Bertha back on track and moving forward.” Malcolm’s crews and equipment have mobilized from their regional office in Kent, WA and will work around the clock to expedite completion of this time critical project.

The rescue operation is scheduled to be completed by March 2015 allowing Bertha to continue her journey.

For more information please contact Malcolm’s Project Superintendent at