Seattle’s tunnel: No boring way it’ll be done on time
Looking into the Highway 99 tunnel from the "launch pit." Credit: Bill Lucia
The restricted flow of data and information from the Washington State Department of Transportation (WSDOT) has hampered schedule analysis of Seattle's deep bore tunnel project. WSDOT said "it is too early to speculate on the schedule" earlier this month and is sticking to that talking point, with a spokesperson telling Crosscut today that "it’s too soon to say if the end date for tunneling will be revised."
But estimating project schedule impacts is vital when a megaproject with enormous financial and political implications faces a crisis.
Crosscut has obtained daily tunneling data from WSDOT and performed basic analyses that show that finishing tunnel boring within the original 14 month schedule, which called for digging to be done around September of 2014, is now nearly impossible.
In tunneling, two fundamental project measures are utilization and production. Utilization is a measure of a TBM's "uptime" versus "downtime." The machines are vast and complex and a large part of the challenge is to keep them running – and digging – as much as possible. The higher the utilization, the more effective the project is at getting digging done. A second fundamental measure is production, which is the rate that a tunnel machine can dig when it is running. High rates of production show that a project team has learned how to optimize machine, crews and techniques for the conditions being encountered.
Tunnel project managers track and calculate utilization and production rates with detailed, high resolution data logged by minute, hour, shift and many more slices. For this analysis, we used the coarser daily data at hand, which nonetheless reveal the schedule implications of the current situation.
Tunneling drives are usually slow at the start and increase as things get dialed in. But at a certain point, low utilization (machine uptime) can bite a schedule so hard that no realistic rate of production (digging) can catch up to the original schedule. At that point, the original schedule is blown and it's time to chart a new one.
WSDOT's original timeline for completion of the tunnel and waterfront park. Graphic: WSDOT
That is where Bertha is now, according to the data. Bertha's daily utilization since being launched has been a crushingly low 25 percent through January 27, 2014. That means 75 percent of the 182 project days since launch have been days where zero forward progress has been made. (These data do not distinguish any days where Bertha was operating, but may have made zero progress from any days where she wasn't operating at all — any day with zero progress was counted as a non-mining day.)
In terms of production, Bertha's rates have varied on the days she has been digging. On the whole, she has averaged just under 22 feet a day on days when forward progress occurred. There have been only four mining days where she made more than 50 feet of progress and there have been 16 mining days where she eked out ten feet or less of forward progress.
Over the entire time of the tunnel drive, from launch and including all machine downtime, Bertha's average progress is a meager six feet per day. That's a vivid demonstration of how a low utilization rate crushes a project's momentum and will ultimately impact the overall schedule.
WSDOT has cited a high tunneling rate of 37 feet per day, but that only was during the four days immediately prior to Bertha's shutdown, when the TBM was being run at fill tilt — so much so that WSDOT demanded data from the contractor out of concern that the machine was being pushed beyond operating limits.
To put the situation in big picture terms, a few weeks from now, Bertha will have used up half the original 14 month schedule, but only travelled about one-tenth of the planned distance. That is a schedule reality that will become increasingly difficult for WSDOT and Seattle Tunnel Partners to ignore before the press, the public and policy makers.
The data analyzed comes from a WSDOT spreadsheet that tallies tunnel distance in feet mined per day since the project's launch. The spreadsheet was used by WSDOT to prepare a chart for the agitated Washington State Senate Transportation Committee at a January 16 Olympia meeting. The data is "not widely available to the public" said WSDOT spokesperson Laura Newborn, but Crosscut obtained it through a public records request.
That chart is shown here in an (admittedly quite fuzzy) screenshot from television coverage of the hearing:
WSDOT's chart was selective in nature. It showed a classic upward climbing line of progress, but did not show the full project schedule or tunnel distance to provide perspective. Recasting WSDOT's data to reflect the full scope of the project paints a more accurate — and far more sobering — picture:
Bertha is clearly in a tough spot. She's submerged below the waterline in a crazy-quilt of geological conditions, about ready to head into areas of work where the pressures are several times greater than anything she's seen so far. She likely has more pipes, boulders and detritus in her path. She's unsure of what's holding her back and uncertain how fast she can go once she gets started again.
What does that mean for the schedule?
Even if Bertha were to restart tomorrow, continue to dig without stopping for a single day (meaning 100 percent utilization) and even dig a bit faster than before, say 25 feet a day, it would be impossible for her to finish on time.
Of course, utilization rates of 100 percent are not realistic. Downtime will be necessary for tool repair, maintenance and removing blockages. So altering the scenario to a still challenging, but more realistic utilization number, say 60 percent, means that Bertha would need to produce 56 feet of tunnel every single digging day in order to hit the schedule. And that's a rate that the TBM has only ever achieved one single day until now.
Put simply, the TBM can only dig so fast, there's too much distance to travel and there are too many surprises in the ground that could grind things to a halt again. And the project operators have not been able to keep Bertha running enough.
The schedule is blown. Now it's time to talk about it.