• May 29 project update: New parts for Bertha arrive at Terminal 46

    The SR 99 tunneling machine’s new inner seals arrived from Japan as scheduled this week. The pieces, which are integral to Seattle Tunnel Partners’ effort to repair the machine, were offloaded at Terminal 46 and trucked a short distance north to the repair area. The piece shown below is the new inner seal ring, which houses the rubber seals that will protect the new main bearing. Additional photos of crews transporting the piece are available on Flickr.

    The SR 99 tunneling machine's inner seal ring

    STP and manufacturer Hitachi Zosen chose to redesign the machine’s seal system as part of their repair plan. Manufactured by Hitachi in Japan, the new seal system will be easier to access should the need arise. It will be installed in the coming weeks, along with other essential components designed to equip the machine for the remainder of its journey beneath Seattle. Other important elements of the repair plan include:
    • A new main bearing
    • Enhanced monitoring systems
    • Added steel to strengthen the machine and accommodate the new seal system 
    • Widened openings at the center of the cutterhead
    • Extended arms to mix excavated soil in the chamber behind the cutterhead
    Simulation showing additional steel to be installed in the SR 99 tunneling machine.      Crews installing additional steel in the SR 99 tunneling machine
    These images show the steel crews are adding to strengthen the tunneling machine.
    As owner of the tunneling machine, STP and Hitachi are responsible for all aspects of the repair effort, including the schedule. STP provides an updated schedule  to WSDOT each month, but the state cannot verify the schedule until work to resume tunneling is further along. We will continue to provide updates as we receive them.
    Digging into STP’s repair plan
    You can continue to track STP’s work on our time-lapse cameras and follow @BerthaDigsSR99 on Twitter for updates. Don't forget to check out the other resources we've created to give you a fuller understanding of Bertha's story:


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  • May 18 project update: Tunneling machine repairs and the release of new reports

    Seattle Tunnel Partners has confirmed that disassembly of the SR 99 tunneling machine is complete, and assessment of the damage is ongoing. They will not provide a revised schedule for resuming mining until they fully understand the scope of repairs.
    STP has indicated that they will replace the main bearing and outer seals of the machine as expected. They have also decided to replace the inner seals to make them more compatible with the new outer seals and easier to access should the need arise. The new inner seals were designed and manufactured in Japan and are scheduled to arrive in late May.
    Damage to the machine was more extensive in some areas than anticipated and some minor damage occurred during disassembly. For example, the outer seals and the steel retainers that hold them in place were destroyed. There was also damage to the cutter drive motor pinions and the main bearing bull gear.
    As owner of the tunneling machine, STP and Hitachi are responsible for all aspects of the repair effort. We will continue to provide updates as we receive them.
    Reports say natural influences, dewatering caused ground settlement near tunnel access pit
    Settlement levels remain steady six months after initial detection
    After months of study, experts agree: there are no simple answers regarding what caused the ground near the SR 99 tunnel access pit to settle approximately an inch last November. 
    Settlement near the pit and in the surrounding neighborhood was caused by a combination of historic and ongoing natural ground movement in the region, dewatering related to tunneling machine repair work and dewatering related to other construction in the area, according to two reports released Monday by the Washington State Department of Transportation. 
    One report, conducted by geotechnical firm Shannon & Wilson, Inc. and commissioned by WSDOT, concluded that dewatering related to tunneling machine repairs was the primary cause of the settlement. A second report , conducted by Brierley Associates and commissioned by tunnel contractor Seattle Tunnel Partners, concluded that natural settlement and other dewatering activities are the primary reasons for the settlement, and tunnel-related dewatering only contributed in areas immediately surrounding the pit. Both reports relied on the same data points.
    The issue began late last year, when the tunnel project’s monitoring system detected settlement in the vicinity of the 120-foot-deep pit STP built to access and repair the tunneling machine. In response to the settlement, WSDOT and STP increased the frequency of monitoring – which includes hundreds of instruments near the access pit – and assessed the viaduct and nearby buildings.
    Both reports demonstrate that settlement related to dewatering has since stabilized; they also agree the ground movement was minor and caused no structural damage. The Shannon & Wilson report, utilizing in part information from satellites, also identifies settlement in areas surrounding the project – in some cases, outside the ongoing monitoring area. Though satellite imagery is helpful to indicate trends, ground monitoring is the most reliable gauge of ground activity, which is why WSDOT’s monitoring program relies mostly on ground sensors throughout the project area.
    WSDOT and STP are continually evaluating ground conditions and taking proactive steps when needed to prevent further project-related settlement. That includes reviewing existing procedures for reducing dewatering should it become necessary. WSDOT has asked STP and city officials to work with project staff to further analyze the data and conclusions in the two reports to find consensus. The agency is also increasing monitoring in some areas and expanding the overall monitoring program in keeping with the analysis provided in the reports.
    Alaskan Way Viaduct Replacement Program Administrator Todd Trepanier made the following statement regarding the reports:
    “We all agree that public safety and protecting infrastructure are our top priorities. This is an incredibly complex issue, but all of us – the state, our contractor, the city – have a shared interest in reaching consensus and acting in the interest of public safety. Having reliable information is essential to any decision-making process. These studies will help inform future decisions about construction as we work to replace the viaduct.”
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Program Spotlight

  • Paving the way to the SR 99 tunnel

    Crews working for Seattle Tunnel Partners have reached a concrete milestone at the SR 99 tunnel’s south portal.

    As shown in the aerial photo below, crews are building the cut-and-cover section of the tunnel in SODO, just west of Seattle’s stadiums. Earlier this month, they successfully poured the final sections of northbound mainline roadway concrete for this 1,500-foot-long stretch of the future highway. 

    Sections of cut-and-cover tunnel at both portals will … more