• Milepost 31 speaker series: Local geologist to discuss Seattle's changing landscape this Thursday

    Join us at 6 p.m. this Thursday at Milepost 31 as geologist David B. Williams gives a special guest presentation, The Protean City: Reshaping the Seattle Landscape. Since settlers first arrived in Seattle, the city’s citizens have altered the landscape with an unrivaled zeal. Seattleites have regraded hills, re-engineered tideflats, and replumbed lakes to provide better locations for businesses and easier ways to move through the city’s challenging topography. Williams’ presentation will focus specifically on the area around Pioneer Square, looking at how early Seattleites altered the land and how that still influences the modern city.
    Williams is a freelance writer focused on the intersection of people and the natural world. This talk is based on his recently published book, Too High and Too Steep: Reshaping Seattle’s Landscape (University of Washington Press). Previous books include Stories in Stone: Travels Through Urban Geology and The Seattle Street-Smart Naturalist: Field Notes from the City. Williams also works at the Burke Museum and maintains the website
    Williams' presentation this week is part of our monthly speaker series at Milepost 31. The event is held in conjunction with Pioneer Square's First Thursday Art Walk. After the talk, be sure to leave enough time to explore other happenings in the neighborhood. Milepost 31 is open Tuesdays through Saturdays from 11 a.m. to 5 p.m., and stays open until 8 p.m. on First Thursdays. Free parking is available for First Thursday art walk patrons in Pioneer Square. Please visit for more information about participating garages.
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  • Nov. 24 project update: Video of Seattle Tunnel Partners rotating Bertha's cutterhead

    Commissioning of the SR 99 tunneling machine continues as Seattle Tunnel Partners prepares to resume mining. STP began testing machine components earlier this month as crews continued welding pieces and reconnecting hoses and cables. Last week, STP began rotating the machine’s cutterhead a few degrees at a time, stopping periodically to take measurements before completing a full rotation.
    Tuesday, Nov. 24 marked the first sustained rotation of the cutterhead since the machine broke through the southern wall (links to YouTube) of the access pit on Feb. 19. STP indicated they will rotate the cutterhead in both directions for about one hour at a time. Watch a short video of the cutterhead rotating below.
    During the next phase of commissioning, STP will backfill the access pit with sand and gravel to prepare the machine for mining. STP's most recent schedule shows that the machine will be ready to resume mining on Dec. 23. The state cannot verify the contractor's schedule.
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  • Nov. 12 project update: Tunneling machine testing underway

    Seattle Tunnel Partners and manufacturer Hitachi Zosen have begun testing components of the SR 99 tunneling machine as they prepare to resume mining. A few initial tests were performed last week, and several others are slated to occur in the coming weeks.
    This week’s highlights include tests of various pumps inside the machine, as well as the screw conveyor system that carries excavated material from the cutterhead to the back of the machine and out of the tunnel. All of the tests are being conducted by STP and Hitachi Zosen, who are jointly responsible for ensuring the machine is ready to complete the remainder of the tunnel drive. Future tests will include rotation of the machine’s cutterhead, which, according to STP, will occur in late November.
    Some reassembly work is ongoing. Major components of the machine are in place, but crews continue to weld pieces together and reconnect wires and hoses. STP’s most recent schedule shows that the machine will be ready to resume mining on Dec. 23. WSDOT cannot verify the contractor’s schedule. The narrated video below explains STP’s repair effort in more detail.
    Other work
    STP crews have finished treating the ground north of the access pit. They began injecting grout into the soil there last month to stabilize the area where the machine will exit the access pit. Crews will soon place a thin layer of sand at the bottom of the pit; the rest of the pit will be filled after initial testing is complete. 
    STP crews are also preparing to install glass walls at the operations buildings located at each portal. The north building’s glass will be installed first. Read more about those efforts in this post.
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Program Spotlight

  • Milepost 31 marks four years, 50,000 visitors

    For being Seattle’s “most boring” exhibit, Milepost 31 sure is popular. December marks the four-year anniversary of the information center, which blends information about the SR 99 Tunnel Project with the history of Seattle’s Pioneer Square neighborhood. In addition to recently welcoming the center’s 50,000th visitor, Milepost 31 staff have led hundreds of tours to see SR 99 tunnel construction, and hosted educational programs for school groups and youth … more