Bertha completes a third of SR99 tunnel 22 Jun 2016

TunnelTalk reporting

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.

Fig 1. Bertha’s current location, nearly one third of excavation complete
Fig 1. Bertha’s current location, nearly one third of excavation complete

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
Date Event Delay length
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  
25 Aug–8
Sept 2015
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

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