[3] Over the next two years, a recovery pit was dug from the surface in order to access and lift the machine's cutterhead for repair and partial replacement in 2015.

Bertha resumed tunnel boring on December 22, 2015, but was stopped in early January 2016 after a tethered barge in Elliott Bay damaged nearby piers and a sinkhole opened near the project site.

Governor Jay Inslee halted all work on the tunnel on January 14, 2016, citing concern over public safety after the sinkhole incident.

[7] The final disassembled pieces of the boring machine were removed in August 2017, and the finished tunnel opened to traffic on February 4, 2019.

[12][13] Bertha was designed and manufactured by Hitachi Zosen Sakai Works of Osaka, Japan, and was the world's largest earth pressure balance tunnel boring machine,[14] at a cutterhead diameter of 57.5 feet (17.5 m) across.

[18] Test assembly and shakedown on Bertha in Japan indicated issues with the main-drive unit and tolerances that required repairs in February 2013.

[23] The machine began excavation of the 1.7-mile-long (2.7 km) route on July 30, 2013, with completion of the bore scheduled in 14 months' time and the tunnel opening to traffic in December 2015.

[31] After a month's investigation, WSDOT announced that the machine's cutting blades had encountered an 8-inch-diameter (20 cm), 119-foot-long (36 m) steel pipe, one of several well casings left over from a previous 2002 drilling project that had assessed groundwater conditions and soil stability in the area in case of another earthquake, such as the 2001 Nisqually earthquake, which led to a need for the replacing of the Alaskan Way Viaduct in the first place.

[32][33][34][35] In early February 2014, as Bertha was being prepared to resume operation, workers discovered it was overheating and that a damaged main bearings seal needed to be replaced.

[43] The front end of the machine was lowered back into the access pit for reassembly in a four-lift process beginning with the repaired cutter drive on August 24, 2015.

In August 2015, a consortium of eight insurers filed a lawsuit against STP in order to avoid a $143 million payout to cover the cost of repairs to the boring machine.

[48] However, Hitachi Zosen general manager Soichi Takaura later stated that "there was nothing wrong with the seals in the original machine", noting that Bertha appeared to function properly before striking the well casing.

[50][51] Digging was halted once again on January 12, 2016, after a barge carrying excavated dirt tipped over in Elliott Bay, spilling its load and damaging a dock at the Port of Seattle's Terminal 46.

[60] Following a month of maintenance and inspections, Bertha resumed tunneling on Friday, April 29, 2016,[4] and crossed 15 feet (4.6 m) under the closed viaduct in an 11-day closure in early May that ended earlier than scheduled.