Bertha (tunnel boring machine)

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Front of a model of Bertha at Milepost 31, the tunnel project information center
Walls of tunnel in place in January 2017, about two years before the 2019 opening date

Bertha was a 57.5-foot-diameter (17.5 m) tunnel boring machine built specifically for the Washington State Department of Transportation's (WSDOT) Alaskan Way Viaduct replacement tunnel project in Seattle, Washington, United States.[1] It was made by Hitachi Zosen Sakai Works in Osaka, Japan, and the machine's assembly was completed in Seattle in June 2013. Tunnel boring began on July 30, 2013, with the machine originally scheduled to complete the tunnel in December 2015.

On December 6, 2013, work was halted approximately 1,083 feet (330 m) into the planned 9,270-foot-long (2,830 m) route because of an unexpected impediment. Initially, it was thought that the machine had damaged several of its cutting blades after encountering a steel pipe that was used to measure groundwater in 2002 around the Alaskan Way Viaduct. However, subsequent investigations revealed that portions of the main bearing seal system were damaged, which caused the bearing to overheat during operation.[2] 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. Digging briefly resumed on February 23, but was halted again for maintenance and inspections before resuming full operations on April 29.[3] Tunnel boring was completed on April 4, 2017, with Bertha's cutterhead breaking into a disassembly vault at the tunnel's north portal in South Lake Union.[4]

In December 2015, WSDOT estimated that the tunnel would be completed and open to traffic in early 2018.[5] The estimate was revised in July 2016 to open in early 2019; an estimated $223 million in cost overruns stem from the two-year delay of the machine.[6]


The name Bertha, after Seattle's first female mayor, Bertha Knight Landes, was chosen by a panel (that included the Governor and Transportation Secretary) from 150 submissions from kindergarten through 12th graders, who were asked to submit female names with Washington state heritage.[7] The winning entry, which was submitted by two elementary schools in Poulsbo and Hoquiam, was selected in December 2012.[8]

Some media have also referred to the machine as "Big Bertha".[9][10]

In March 2016, regional transit agency Sound Transit decided to drop names for its own tunnel boring machines, used for smaller light rail tunnels, citing unwanted association and confusion with Bertha, especially the machine "Brenda" used on the Northgate Link Extension and University Link Tunnel.[11][12]

Design and assembly[edit]

Freighter Fairpartner carrying the disassembled tunnel boring machine into the Port of Seattle in April 2013

Bertha was designed and manufactured by Hitachi Zosen Sakai Works of Osaka, Japan, and is the world's largest earth pressure balance tunnel boring machine,[13] at a cutterhead diameter of 57.5 feet (17.5 m) across. The machine was 326 feet (99 m) long and weighed 6,700 short tons (6,100 t).[14] The machine itself cost $80 million and is owned by Seattle Tunnel Partners, the project contractors.[15] Seattle Tunnel Partners is a joint venture of New York-based Dragados USA, a wholly owned subsidiary of Dragados, S.A., the construction division of ACS Group of Spain; and Tutor Perini Corporation, based in Sylmar, California.[16]

Hitachi Zosen held a completion ceremony for the machine, performed at the same time as the naming ceremony, in Osaka, Japan, on December 20, 2012.[17] Test assembly and shakedown on Bertha in Japan indicated issues with the main-drive unit and tolerances that required repairs in February 2013.[18] [19] Bertha was shipped to the Port of Seattle in 41 sections, arriving on April 2, 2013.[20][21]

Bertha had a special pre-programmed melody that played for workers inside the machine and those monitoring the tunnel-borer.[22]


Dedication and first section[edit]

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]

Damage to cutterhead and two-year delay[edit]

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] Seattle Tunnel Partners (STP), the contractors overseeing the project, 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, Seattle Tunnel Partners 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.

Resumption of digging and subsequent activities[edit]

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 the contractors, Seattle Tunnel Partners, 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] Most of Bertha's components are not reusable, with the exception of steel machinery on the cutterhead that can be melted and recycled.[4] The final, disassembled pieces of Bertha were removed from the tunnel portal in August 2017.[66]

Zone advancement[edit]

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

Zone Date reached Days since entering the previous zone
Zone 3 May 26, 2016[68] n/a
Zone 4 June 16, 2016[69] 21
Zone 5 August 1, 2016[70] 46
Zone 6 August 29, 2016[71] 28
Zone 7 November 3, 2016[72] 66
Zone 8 December 1, 2016[73] 28
Zone 9 January 27, 2017[74] 57
Zone 10 March 9, 2017[75] 41


The two-year stoppage of Bertha has been criticized as an example of a political boondoggle by opponents.[76][77]

In January 2015, two Republican state senators introduced a bill in the Washington State Legislature to kill the project, citing Bertha and its delay in particular. The bill was never heard in the state senate and failed to pass the Senate Transportation Committee.[78]

See also[edit]


  1. ^ "Tunneling toward a new SR 99". Washington State Department of Transportation. 2012. Retrieved May 19, 2015.
  2. ^ Newcomb, Tim (February 10, 2014). "Damaged Main Bearing Seals Cause of Bertha Overheating, Shutdown". Engineering News-Record. Retrieved April 4, 2017.
  3. ^ a b Demay, Daniel (April 29, 2016). "Bertha inches ahead, viaduct closure begins, traffic slows". Seattle Post-Intelligencer. Retrieved April 30, 2016.
  4. ^ a b c Lindblom, Mike (April 4, 2017). "Bertha's breakthrough just 'halftime' for tunnel project". The Seattle Times. Retrieved April 6, 2017.
  5. ^ a b Lindblom, Mike (January 4, 2016). "Tunnel machine Bertha expected to bust out of vault this week". The Seattle Times. Retrieved January 4, 2016.
  6. ^ Lindblom, Mike (July 21, 2016). "Bertha's woes grind on: more delay, higher cost for Highway 99 tunnel". The Seattle Times. Retrieved July 21, 2016.
  7. ^ Yerkan, KaDeena (December 10, 2012). "SR 99 tunneling machine tweets her name: Bertha" (Press release). Washington State Department of Transportation. Archived from the original on November 10, 2014. Retrieved May 19, 2015.
  8. ^ Cohen, Aubrey (December 10, 2012). "World's largest tunneling machine gets name, face, voice". Seattle Post-Intelligencer. Retrieved April 29, 2016.
  9. ^ Grayson, Wayne (April 4, 2013). "Big Bertha, world's largest tunnel-boring machine, arrives in Seattle". Equipment World. Retrieved January 15, 2016.
  10. ^ Dahl, Timothy (January 8, 2016). "Seattle's Big Bertha Tunneling Machine Is Finally Back on Track". Popular Mechanics. Retrieved January 15, 2016.
  11. ^ Bush, Evan (March 28, 2016). "Thanks to Bertha, Sound Transit nixes nicknames for its own tunnel machines". The Seattle Times. Retrieved April 18, 2016.
  12. ^ Sullivan, Chris (March 18, 2015). "Bad news Bertha overshadows successful sisters". MyNorthwest. Retrieved April 18, 2016.
  13. ^ "The World's Largest EPB Shield Tunneling Machine". Hitachi Zosen Corporation. Retrieved April 29, 2016.
  14. ^ "Big Bertha – world's largest tunnel boring machine – facing big Seattle challenge". CBS News. December 25, 2013. Retrieved April 29, 2016.
  15. ^ Wilhelm, Steve (April 2, 2013). "Bertha tunnel-boring machine arrives to make big splash in Seattle". Puget Sound Business Journal. Retrieved April 29, 2016.
  16. ^ "SR 99 Bored Tunnel Alternative Design-Build Project" (PDF). Washington State Department of Transportation. Archived from the original (PDF) on February 20, 2017. Retrieved June 12, 2017.
  17. ^ "Becoming Bertha: the journey begins for the world's largest tunneling machine". WSDOT Blog. Washington State Department of Transportation. December 21, 2012. Retrieved April 29, 2016.
  18. ^ "Testing of the SR 99 tunneling machine continues in Japan". WSDOT Blog. Washington State Department of Transportation. January 23, 2013. Retrieved February 16, 2019.
  19. ^ "SR 99 tunneling machine problem nearly fixed". WSDOT Blog. Washington State Department of Transportation. February 11, 2013. Retrieved February 16, 2019.
  20. ^ Lindblom, Mike (April 2, 2013). "Mammoth tunnel drilling machine arrives in Seattle". The Seattle Times. Retrieved April 29, 2016.
  21. ^ "World's largest tunneling machine arrives by ship in Seattle April 2" (Press release). Washington State Department of Transportation. April 1, 2013. Retrieved April 29, 2016.
  22. ^ Raftery, Jillian (April 29, 2016). "Did you know Bertha whistles while she works?". MyNorthwest. KIRO Radio. Retrieved April 29, 2016.
  23. ^ Yerkan, KaDeena (July 30, 2013). "Bertha starts digging: tunneling underway in Seattle" (Press release). Washington State Department of Transportation. Retrieved December 5, 2015.
  24. ^ Lindblom, Mike (July 30, 2013). "Bertha's excavation mission beginning under downtown". The Seattle Times. Retrieved December 5, 2015.
  25. ^ Aitchison, Sarah (July 17, 2015). "State officials skeptical Bertha contractor can deliver on new deadline". Puget Sound Business Journal. Retrieved December 27, 2015.
  26. ^ Yerkan, KaDeena (July 20, 2013). "Bon voyage party for Bertha draws 5,000 to SR 99 tunnel site" (Press release). Washington State Department of Transportation. Retrieved December 5, 2015.
  27. ^ Jarvis, Brooke (July 31, 2013). "Bon Voyage, Big Bertha! Seattle Digs a Cave For the Future". Gizmodo. Retrieved December 5, 2015.
  28. ^ Yerkan, KaDeena (December 10, 2013). "WSDOT Statement on SR 99 Tunneling Machine" (Press release). Washington State Department of Transportation. Retrieved May 19, 2015.
  29. ^ Newborn, Laura (December 13, 2013). "Tunnel crews lowering groundwater to get a closer look at what's blocking Bertha" (Press release). Washington State Department of Transportation. Retrieved May 19, 2015.
  30. ^ Johnson, Kirk (December 20, 2013). "'The object': Something deep and mysterious has blocked the world's biggest tunnel boring machine under Seattle". The National Post. Retrieved December 21, 2013.
  31. ^ Lindblom, Mike (January 3, 2014). "Bertha's nemesis: 119-foot steel pipe". The Seattle Times. Retrieved January 5, 2014.
  32. ^ Lindblom, Mike (December 13, 2019). "Contractor ordered to pay Washington state $57M over tunnel-boring machine Bertha;s big stall". The Seattle Times. Retrieved December 18, 2019.
  33. ^ Johnson, Kirk (January 3, 2014). "Prosaic Pipe Stymied Seattle's Big Bertha". The New York Times. Retrieved January 5, 2014.
  34. ^ Newborn, Laura (January 4, 2014). "Progress made on SR 99 tunnel blockage" (Press release). Washington State Department of Transportation. Retrieved May 19, 2015.
  35. ^ Newborn, Laura (April 21, 2014). "SR 99 tunneling machine to resume digging in March 2015" (Press release). Washington State Department of Transportation. Retrieved May 19, 2015.
  36. ^ Lindblom, Mike (December 9, 2014). "Actually, digging continued Tuesday at Bertha's repair pit". The Seattle Times. Retrieved May 19, 2015.
  37. ^ Lindblom, Mike (December 8, 2014). "New delay in Bertha rescue as engineers study sinking soil". The Seattle Times. Retrieved May 19, 2015.
  38. ^ Lindblom, Mike (March 31, 2015). "Bertha's mammoth cutter head emerges from tunnel vault". The Seattle Times. Retrieved May 19, 2015.
  39. ^ Lindblom, Mike (December 22, 2014). "New estimate of tunnel opening: August 2017". The Seattle Times. Retrieved May 19, 2015.
  40. ^ Newborn, Laura (July 17, 2015). "Seattle Tunnel Partners submits new schedule for completing SR 99 Tunnel Project" (Press release). Washington State Department of Transportation. Retrieved July 17, 2015.
  41. ^ Lindblom, Mike (July 17, 2015). "New Bertha start date to resume digging is Nov. 23". The Seattle Times. Retrieved July 17, 2015.
  42. ^ Lindblom, Mike (May 18, 2015). "Bertha repair will take longer – there are lots of broken parts". The Seattle Times. Retrieved May 19, 2015.
  43. ^ "Aug. 24 project update: Seattle Tunnel Partners planning to lower Bertha into the access pit today". Washington State Department of Transportation. August 24, 2015. Retrieved August 26, 2015.
  44. ^ DeMay, Daniel (August 24, 2015). "Bertha going back underground". Seattle Post-Intelligencer. Retrieved August 26, 2015.
  45. ^ Lindblom, Mike (August 24, 2015). "Crews start moving Bertha's rebuilt cutter drive back into pit". The Seattle Times. Retrieved August 26, 2015.
  46. ^ "Case information". August 30, 2015. Retrieved August 30, 2015.
  47. ^ Lindblom, Mike; Garber, Andrew (February 25, 2014). "Bertha's big troubles started in Japan". The Seattle Times. Retrieved May 3, 2017.
  48. ^ Lindblom, Mike (July 20, 2016). "Bertha's builders: Tunnel borer started out 'perfect'". The Seattle Times. Retrieved May 3, 2017.
  49. ^ "Jan. 7 project update: Bertha exits the access pit". Washington State Department of Transportation. January 7, 2016. Retrieved January 7, 2016.
  50. ^ Bush, Evan (January 7, 2016). "Bertha making progress, tunnels 73 feet since repairs". The Seattle Times. Retrieved January 7, 2016.
  51. ^ Lindblom, Mike (January 12, 2016). "Bertha stops digging again, but this time it's because of a barge". The Seattle Times. Retrieved January 12, 2016.
  52. ^ Lindblom, Mike (January 13, 2016). "Sinkhole adds to Bertha's problems, but drilling to resume". The Seattle Times. Retrieved January 13, 2016.
  53. ^ DeMay, Daniel (January 13, 2016). "While Bertha halts over barge issues, sinkhole opens near access pit". Seattle Post-Intelligencer. Retrieved January 13, 2016.
  54. ^ Lindblom, Mike (January 14, 2016). "Inslee orders tunnel dig halted as soil sinks above Bertha". The Seattle Times. Retrieved January 14, 2016.
  55. ^ "Jan. 14 project update: Tunneling on hold pending safety review". Washington State Department of Transportation. January 14, 2016. Retrieved January 14, 2016.
  56. ^ Stewart, Ashley (January 14, 2016). "Gov. Inslee halts Bertha work after sinkhole forms near project". Puget Sound Business Journal. Retrieved January 14, 2016.
  57. ^ Lindblom, Mike (February 23, 2016). "She's ba-ack! Yes, Bertha's on the move once again". The Seattle Times. Retrieved February 23, 2016.
  58. ^ Lindblom, Mike (March 14, 2016). "Tunnel machine Bertha moves 300 feet, reaches 'safe haven'". The Seattle Times. Retrieved April 18, 2016.
  59. ^ Lindblom, Mike (April 11, 2016). "Viaduct closure coming once Bertha's ready to dig". The Seattle Times. Retrieved April 18, 2016.
  60. ^ Demay, Daniel (May 11, 2016). "Viaduct closure ends, Bertha to make pit stop". Seattle Post-Intelligencer. Retrieved May 15, 2016.
  61. ^ "June 13 project update: Bertha passes the half-mile mark". Washington State Department of Transportation. June 13, 2016. Retrieved June 15, 2016.
  62. ^ Lindblom, Mike (July 19, 2016). "Bertha restarts early — with 33 new teeth (out of 750)". The Seattle Times. Retrieved July 20, 2016.
  63. ^ "Bertha Passes Halfway Point" (Press release). Washington State Department of Transportation. October 3, 2016. Retrieved October 3, 2016.
  64. ^ Oxley, Dyer (December 15, 2016). "'Finish line in sight' for Bertha under Seattle". MyNorthwest. Retrieved December 15, 2016.
  65. ^ "New tunnel? No problem? It was an easy, light-traffic day Monday on Highway 99". The Seattle Times. February 4, 2019. Retrieved March 6, 2019.
  66. ^ Lee, August 23, 2017. "From disassembly pit, crews haul away last bits of Bertha". The Seattle Times. Retrieved August 26, 2017.
  67. ^ "Follow Bertha". February 10, 2017. Retrieved February 10, 2017.
  68. ^ "Bertha is now tunneling under buildings in downtown Seattle". May 27, 2016. Retrieved February 26, 2017.
  69. ^ "Distance update: Bertha has traveled a total of 2,886 feet. She's now in Zone 4 of the tunnel drive". June 16, 2016. Retrieved February 10, 2017.
  70. ^ "Bertha is now in Zone 5 of the tunnel drive". June 16, 2016. Retrieved February 10, 2017.
  71. ^ "Monday tunneling update: Bertha has reached zone 6". August 29, 2016. Retrieved February 10, 2017.
  72. ^ "Bertha is past Stewart St. & the 1-mile mark". November 3, 2016. Retrieved February 10, 2017.
  73. ^ "#BalloonsOverBertha at 2nd/Lenora. Now past 6,000 ft., Bertha digs into Belltown and Zone 8 of the tunnel drive". December 1, 2016. Retrieved February 10, 2017.
  74. ^ "Yesterday's progress update: Bertha has reached Zone 9 of the tunnel drive!". January 27, 2017. Retrieved February 10, 2017.
  75. ^ "March 9 project update: New 360-degree video takes you inside the tunnel as Bertha enters Zone 10". Washington State Department of Transportation. March 9, 2017. Retrieved March 9, 2017.
  76. ^ Lindblom, Mike (September 18, 2014). "Seattle tunnel tops U.S. green group's 'boondoggle' list". The Seattle Times. Retrieved January 14, 2016.
  77. ^ Roberts, David (June 5, 2015). "Seattle's unbelievable transportation megaproject fustercluck". Grist. Retrieved January 14, 2016.
  78. ^ Connelly, Joel (January 27, 2015). "Bertha: Off the hook in the Legislature but not out of mind". Seattle Post-Intelligencer. Retrieved January 14, 2016.

External links[edit]