Relaunch of the Seattle mega-TBM for the SR99 Alaskan Way viaduct replacement tunnel is pushed back yet another month: to December 23 (2015).
The latest schedule released by Seattle Tunnel Partners (STP) – the contractor JV of Dragados and Tutor Perini – now projects final breakthrough as occurring in January 2017, two months later than last month’s projection of November 23, 2016. The tunnel opening date is moved back by a month to April 13, 2018, with final project-wide completion – which follows work to tie in the SR99 highway – also moving back from November 4, 2018, to December 9, 2018.
A year ago, when STP was excavating the recovery shaft ahead of repairs to the TBM’s compromised sealing system and planning for full replacement of the main bearing, the contractor JV presented WSDOT with a recovery schedule that forecast the resumption of tunnelling in April this year (2015), final breakthrough by April 2016, and a tunnel opening date of August 2017. This means that a further eight months of project slippage has occurred over the last 12 months.
When TBM Bertha launched in August 2013 the original schedule projected that the tunnel would open in December this year (2015), with final completion in the first quarter of 2016.
“STP has told us the latest changes in the schedule reflect the current emphasis on giving crews the time they need to complete the tunneling machine repairs successfully,” said Laura Newborn for project owner WSDOT. “Like all large construction projects, the schedule for this project changes frequently.”
STP is currently carrying out a program of jet grouting just north of the recovery shaft. This work is intended to stabilize the ground above the tunnel as the TBM exits the shaft.
Crews are using a high-pressure pump to inject grout into the ground adjacent to the shaft’s north wall, creating a set of interlocking columns approximately 5ft in diameter. The top of the columns will begin approximately 20ft below the surface, and will extend down approximately 40ft, ending just above the tunnel crown. STP expects this work to take six weeks.
Meanwhile, STP and manufacturer Hitachi Zosen are continuing to reconnect machine parts in preparation for mining. That work includes welding pieces together, and reconnecting hoses and wires.