Bertha (tunnel boring machine)

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.[23][24][25] Over 5,000 members of the public, along with Governor Jay Inslee, were present for the machine's dedication a week prior to the beginning of excavation.[26][27]

Route map of the Alaskan Way Viaduct replacement tunnel showing location where the tunnel boring machine became stuck on December 6, 2013

By December 6, 2013, Bertha had tunneled 1,019 ft (311 m), or 11%, of the total 9,270 ft (2,830 m) length of the tunnel,[28] stopping about 60 ft (18 m) below ground between South Jackson Street and South Main Street.[29] The machine's progress was halted on that day by an unexpected impediment.[30] 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. Because the machine cannot cut through metal, the pipe damaged several of Bertha's cutting blades, necessitating blade replacement before the machine could proceed. The pipes' locations were known to WSDOT and the agency thought they had been removed, while STP admitted in a 2019 lawsuit that they had knowledge of the pipe prior to excavation.[31][32][33][34]

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. Multiple options were discussed to fix the problem, but Bertha was expected to be out of commission until March 2015.[35] In December 2014, workers began digging a 120-foot-deep (37 m) pit in order to lift Bertha's front end up to street level for repairs,[36] but were delayed when groundwater pumping caused visible damage to nearby South King Street and some of its neighboring buildings.[37] The front end of the machine, including the damaged cutter head, was successfully lifted onto the surface on the morning of March 31, 2015.[38] STP estimated that fixing Bertha would delay the opening of the new tunnel by an additional nine months to August 2017,[39] which was later extended to March 2018 after additional damage was discovered in June 2015.[40][41]

On May 18, 2015, WSDOT reported to the Seattle City Council that the damage to the bearing and seals was worse than had been previously reported. Further inspection after the cutting head was removed and disassembled showed damage to the cutter head drive gears, so a new estimate of the repair time and cost was prepared.[42]

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.[43][44][45]

In June 2015, STP sued to force insurers to payout on the $85 million insurance policy to cover repairs needed after Bertha's cutting teeth were damaged in a collision with a steel pipe in December 2013. 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. The insurers claimed that the tunnel-boring machine's capabilities were inadequate for the project and should be excluded.[46]

It is unclear what triggered the damage to Bertha's main bearing. Problems with the seal system appear to date back to the machine's initial testing in Japan, when the seal assembly was damaged and required repairs.[47] 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. WSDOT disputed this, and stated that the well casing was not responsible.[48]

View of retrieval site for repairs of Bertha's cutter head. The red gantry crane, center, was used to lift the cutter head from a shaft dug in front of the stuck boring machine. The white shed, right, was built to house the head during repairs and upgrades, and then the head was lowered back down the shaft and reinstalled.

Rear of tunnel boring machine with completed tunnel walls behind it in 2017

On December 22, 2015 at 12:30 a.m., the machine resumed digging 1.5 feet (0.46 m) through sand poured into the recovery pit. By January 4, Bertha had traveled 1,098 feet (335 m) of its planned 9,270-foot-long (2,830 m) route from SoDo to South Lake Union.[5] On January 6, 2016, Bertha broke through the concrete access vault and began digging through normal soil.[49][50] 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.[51] The same day, a sinkhole formed within the tunnel's work zone approximately 35 feet (11 m) north of the access pit; the hole was filled with 250 cubic yards (190 m³) of concrete by contractors the following day and was not expected by WSDOT to delay the resumption of digging later in the week.[52][53]

On January 14, 2016, Governor Jay Inslee ordered drilling on the tunnel to stop, invoking a contract clause in the tunnel agreement that allowed the state to suspend work based on unsafe conditions for project personnel or the general public.[54] Before excavation of the tunnel could resume, WSDOT requested that STP complete and deliver an analysis of what caused the January 12 sinkhole and what modifications to tunneling operations could be made to prevent further ground-level problems.[55][56]

Digging resumed on February 23, after a WSDOT review determined that new soil monitoring practices were sufficient, allowing the machine conditional permission to bore through 160 feet (49 m) of material and finish the initial testing phase of the machine.[57] By March 14, Bertha had finished its 300-foot (91 m) bore to a "safe haven" located ahead of the Alaskan Way Viaduct;[58] allowing WSDOT and STP to prepare for a two-week closure of the viaduct in late April as the machine passed under the vulnerable structure while closely monitored.[59] Following a month of maintenance and inspections, Bertha resumed tunneling on Friday, April 29, 2016,[3] and crossed 15 feet (4.6 m) under the closed viaduct in an 11-day closure in early May that ended earlier than scheduled.[60]

In June 2016, the tunnel reached its lowest point, 115 feet (35 m) under Madison Street in downtown.[61] A maintenance stop from June 23 to July 18 was conducted under Spring Street, replacing 33 of the cutterhead's teeth.[62]

By September 30, 2016, Bertha had tunneled 4,635 feet (1,413 m), surpassing the halfway mark of the planned 9,270-foot (2,830 m) distance.[63] As of December 15, 2016, the tunnel length reached 70% completion.[64]

Tunnel boring was completed on April 4, 2017,[4] and the finished tunnel opened to traffic on February 4, 2019.[65] Practically none of Bertha's components were reusable, and most of its steel was melted and recycled.[4] The final, disassembled pieces of Bertha were removed from the tunnel portal in August 2017.[66]

Bertha's digging route was divided into 10 zones, representing different types of soil or progress under city landmarks.[67]