Seattle Tunnel Parters, the contractor JV of Dragados and Tutor Perini, has successfully mined a total of 2,971ft (905m) of the 9,300ft-long (2,800m) SR99 Alaskan Way Viaduct Replacement Tunnel.
In the next few days TBM Bertha, which is currently located approximately 120ft (36.5m) below Post Avenue, between Madison and Spring Streets (Fig 1), will be stopped for a period of several weeks for planned maintenance.
Crews have mined nearly 1,500ft (457m) in the six weeks since the previous planned maintenance stop near Yesler Way, just beyond the Alaskan way Viaduct. STP plans to stop again in the coming days because the soils in Zone 4 of the drive alignment are dense and stable, providing more suitable conditions for maintenance. The stop is expected to last several weeks, depending on the extent of maintenance needs. STP’s previous maintenance stop lasted six weeks.
Over the course of the first week, STP will perform a thorough inspection of various systems throughout the machine. This inspection will help the contractor verify how much work is needed. Crews will then prepare to inspect the cutting tools, under hyperbaric conditions, replacing them as necessary.
TunnelTalk will update readers with more in-depth information about the latest maintenance stop in the coming weeks. In the meantime, Table 1 below outlines the major milestones on the project so far.
|Table 1. Bertha stoppage and milestone chronology|
|20 June 2016||Bertha reaches 2,971ft (449 rings, 905m, 32% complete), at a depth of 120ft (36.5m). A maintenance period of several weeks is due to take place in the next few days because dense and stable ground conditions favor this as a suitable location to stop|
|13 June 2016||Bertha reaches 2,724ft (411 rings, 830m), at a depth of 115ft (35m)|
|31 May 2016||Bertha reaches 2,314ft (705m), a landmark 25% of the tunnel is now complete|
|18 May 2016||300 rings (2,000ft, 610m) now completed|
|11 May 2016||After several days of critical 24/7 operations Bertha fully and safely clears the viaduct and takes a short break for crew rest and routine maintenance|
|29 April 2016||SR99 highway viaduct closed for up to 2 weeks to facilitate TBM undercrossing – Bertha restarts drive by mining through 10ft concrete wall at the end of Safe Haven 3|
|14 March 2016||Bertha reaches Safe Haven 3 for six weeks of scheduled maintenance after completing 300ft (91m) of tunnelling since restarting under supervision. Eleven of the machine’s 700 cutting tools are replaced during more than 100 shifts of hyperbaric inspections. Total distance travelled is now 1,560ft (475m)|
|23 Feb 2016||Drive resumes after WSDOT satisfied that STP management additions and additional operational protocols will prevent a repeat of the sinkhole incident||40 days|
|14 Jan 2016||WSDOT issues a forced stop order, pending an independent safety and operational review, and further discussions with STP|
|12 Jan 2016||Sinkhole appears above a section of the 100ft advance made by the TBM since breaking out of the recovery shaft previous week|
|22 Dec 2015||Drive resumes, with TBM breaking out of the recovery shaft – progress of 12 rings (73 ft) is made||270 days|
|14 Dec 2015||STP begins backfilling the recovery shaft|
|12 Nov 2015||TBM testing program begins – on Nov 24 the cutterhead is subjected to sustained rotation|
|TBM lowered in pieces back into recovery shaft|
|05 Jun 2015||Newly designed outer and inner seal systems installation begins; repairs include a new main bearing plus other major modifications|
|30 Mar 2015||TBM lifted out of recovery shaft over a 2-day period using specialist hoisting equipment|
|02 Mar 2015||TBM shut down after being driven through 57ft (9 rings) into recovery shaft|
|18 Feb 2015||Drive restarts||158 days|
|02 Sep 2014||TBM advanced 3ft to rest against the outside of the piles of the recovery shaft||216 days|
|May 2014||Excavation of 120ft x 80ft recovery shaft begins|
|29 Jan 2014||TBM advances 2ft before same heat readings prompt shutdown – a damaged bearing seal, allegedly caused by contractor’s failure to account for a steel well casing along the drive path, is blamed. Main bearing seal damage is diagnosed, plus possible damage to main bearing itself|
|28 Jan 2014||Drive restarts||75 days|
|06 Dec 2013||High temperature readings prompt precautionary machine shutdown and 158 hours worth of hyperbaric inspections are carried out between Jan 17–28|
|05 Dec 2013||TBM reaches 1,000ft milestone|
|14 Nov 2013||Drive restarts||14 days|
|31 Oct 2013||Stoppage for machine adjustments and fitting new cutting tools|
|23 Sep 2013||Drive restarts||34 days|
|20 Aug 2013||Breakout of labor dispute with Longshoremen’s union over muck handling at the wharf|
|20 July 2013||TBM Launch|
|TOTAL days lost||817 days|