TUNNEL TOUR: Follow along on an 8-flight descent into what’s already been dug

(EDITOR’S NOTE: Even if you agree with the advocacy group that has declared the Highway 99 tunnel a “boondoggle,” nine months after its boring machine stalled, you might be interested in a look at what’s already been done and what’s continuing to progress even before the upcoming repairs. WSDOT invited media to tour the site Thursday, and photojournalist Christopher Boffoli went on behalf of WSB. Here are his photos and narrative of how it went.

Photos, video, and story by Christopher Boffoli
Reporting for West Seattle Blog

The meeting point for our tour was an entrance at the end of South King Street just under the Alaskan Way Viaduct. After being issued safety clothes (hard hat, safety glasses, gloves, and reflective vests) we were greeted by Chris Dixon, Project Manager for Seattle Tunnel Partners, who led our group of about 7 or 8 journalists over to one of the engineering and orientation trailers.

This was a small meeting room with a lot of colorful schematics and cross-section geologic diagrams on the walls:

Dixon explained that – while the Tunnel Boring Machine (TBM) is idle – work is advancing at both the north end of the site (where a cut and cover tunnel is being prepared in the area where the TBM will eventually emerge) and the south end of the site, near the stadiums, where the future roadways are being prepared.

There is also a great deal of activity inside the existing tunnel itself. On a whiteboard Dixon drew a cross-section of the tunnel and explained how crews are busy installing structures called corbels along the tunnel floor:

These concrete structures are essentially footings that will bear the weight of the straight interior tunnel walls and the concrete road decks (southbound traffic above and northbound traffic below) that vehicles will drive over.

He said that by the time the TBM resumes its digging, they expect to have 450 feet of the tunnel’s interior complete. Dixon said that this work was originally set to happen later but that they have reconfigured the schedule while work is underway to repair the TBM.

We were joined by Matt Preedy, Deputy Program Administrator, WSDOT (and a West Seattle resident).

All of the journalists were issued numbered brass tags which were recorded on a ledger and that we pinned to our vests. As we left the engineering trailer and entered the site, there were a number of large boards with numbered dots painted on them. Dixon and Preedy went to the boards and attached their own brass tags to them.

They didn’t take the time to explain, but those ‘pit tags’ (also called check tags) are a system employed for hundreds of years to keep track of who is working inside a mine, or in this case, a tunnel. One of the first things we saw (at ground level) were piles of curved, pre-cast concrete panels that are arranged in place behind the TBM.

Bolted together into rings, they form the very strong, outer tunnel walls. Their tight-fitting gaskets are designed to keep ground water at bay.

There are ten panels in each ring and there are to be 1,450 rings in the complete tunnel.

We walked out over a concrete gantry from which we could look down on the launch pit below. To the south were the almost completed roadways that someday would carry traffic in and out of the SR-99 tunnel:

Turning around, we could see the entirety of the launch pit and the tunnel entrance at the end of it.

We descended about eight flights of steep, metal stairs to the floor of the site.

Behind us (to the south) was a completed section of cut-and-cover tunnel, with its neat, square walls, unlike the circular structure of the bored tunnel that we were about to tour.

Construction material (mostly rebar) was everywhere:

Along the sides of the pit, workers were busy covering the walls with Spray-Crete, a light, liquid form of cement.

To our right we could see the below-ground part of what we were told would become the South Operation Building. Water also seemed to be ubiquitous, seeping in all over the walls of the site.

Dixon said that, though some of it might be from nearby Elliott Bay, most of it was fresh groundwater.

We descended a ladder to an even lower section of the launch pit, level with the bottom of the tunnel.

Walking inside the tunnel at last, we could see large red concrete forms and workers installing structural re-bar along the bottom sides of the tunnel.

This is the corbel work we were told about.

Beyond the equipment and activity near the entrance of the tunnel, it was only when you walked a bit further into the tunnel that could you appreciate the impressive size of the space.

It was here that you could also appreciate the intricate puzzle of curved concrete panels.

Overhead was a large yellow ventilation shaft that brings fresh air into the deepest part of the tunnel and that can be reversed in an emergency to pull smoke from a fire out of the tunnel. Also above was part of the long conveyor belt on which tailings and slurry are removed to awaiting barges. Dixon explained that, as the TBM advances, sections of conveyor belt are added.

By the end of the project, the belt will be as long as the tunnel itself.

Outside in the open pit we had seen piles of coiled belt sections waiting to be installed in the future.

The first part of the TBM you see is the white-painted, rear superstructure of the
300 foot long trailing section.

Massive wheels support the entire machine, which includes all of the systems of wires and pipes for power and to pump chemicals and grout towards the face of the TBM. As you move forward, you encounter the system that receives the curved panel sections, picks them up, orients them to the proper position and location for installation when they are needed.

Moving forward still, you approach the section of the TBM that is behind the cutting face.

Everything there seems covered with some form of water or mud. There are hazards to footing and low clearances, making it a challenge to decide if you should watch your head or where you step. Everything was lit with fluorescent tubes, giving it a bright – if slightly green – cast. As we arrived to the most recently-installed ring of curved concrete sections, at the very bottom, Dixon and Preedy showed us the enormous pistons that the TBM uses to push against the edge of the course of concrete rings to advance itself forward.

As politicized as the bored tunnel has been and continues to be in Seattle, I must say that standing in the bowels of the machine, it is difficult not to be in awe of the scale and size of the complex machinery, the intricate tapestry of conduits, hoses, pistons, motors, fittings and beams – the sheer audacity of the technology involved in pushing through the earth blindly at 100 feet below sea level.

It is a level of technological complexity that I have only before seen when watching a Ridley Scott film set inside of a spaceship. It did not seem like a place that a group of human beings should be standing. And it was even more incomprehensible that people had designed and built it.

We climbed narrow staircases through a maze of passageways to see where the muddy tailings from the cutting face begin their journey out of the tunnel.

On another level we visited the control room with the screens and consoles from which workers can manage and monitor all aspects of the TBM when it is in operation.

Dixon explained that the numbers we saw on the primary displays indicated just over two bars of pressure (regular atmospheric pressure is one bar; most commercial espresso makers operate at 10-15 bars of pressure). Even though the TBM was not running he said that the instruments generally don’t read much more than that. He added that – when in operation – the cutting face of the TBM isn’t even all that loud, though Preedy added that all of the motors that power the conveyor belts for the removal of tailings do make the back of the machine very noisy.

Though the TBM was idle, Dixon said that workers are kept busy “exercising” and maintaining many of the parts of the machine that might atrophy or otherwise fall into disrepair if left sitting for a long time. It wasn’t uncomfortably warm inside the heart of the machine, though Dixon said that when the TBM is in operation it does get quite hot down there as the heat of friction is transferred through the cutting face to the surrounding spaces. Heat played into what went wrong, and what’s being fixed, he explained:

Adjacent to the control room – still inside the heart of the TBM structure – was a break room that, with coffee maker, microwave oven, long lunch tables, etc. would look at home in any factory. It was hard to believe it was at the center of an incredibly complex machine deep underground.

Nearby we saw a collection of cutting heads, each weighing 1500 pounds, that could be attached to an overhead rail for transport to the front of the cutting face for replacement. Various cutting heads are used, depending on the soil conditions.

The “rippers” we saw are best suited for the type of loose glacial soils that are expected in this section of the project.

At the very front of the TBM we could see the large blue motors that individually power each of the cutting heads.

On the same level we could see the central drive shaft, painted light green. And to the sides were large pressure vessels through which men and equipment could safely transition to the pressurized area on the other side of the cutting face, if needed.

With our tour complete we walked back through the various stairways and passages, back down to the tunnel floor at the rear of the TBM’s trailing gear, and out the way we came.

The palms of my light-colored gloves – which had honestly seemed like overkill at the start of the tour – had somehow become darkened.

After we had climbed the fairly treacherous ladders and countless treads of metal stairways, we were led back to the engineering and orientation trailers where, one by one, we turned in our numbered brass tags and were signed out of the ledger.

What happens next in the repair process? Here’s the latest update on the project website. For more on the project’s status, here’s what our partners at The Seattle Times published post-tour.

35 Replies to "TUNNEL TOUR: Follow along on an 8-flight descent into what's already been dug"

  • rocky raccoon September 19, 2014 (3:04 am)

    Very impressive coverage. Haven’t seen this anywhere else.

  • WSobserver September 19, 2014 (4:52 am)

    Agreed! Emailed to those who are fascinated by the engineering of this project.


    Great report WSB.

  • mark47n September 19, 2014 (5:30 am)

    All of the rebar was made right here in W. Seattle.

  • wade September 19, 2014 (6:49 am)

    Excellent article, thank you very much for the depth of this coverage.

  • Rick September 19, 2014 (6:58 am)

    Brass tags! NOW I’m impressed!

  • Scott September 19, 2014 (7:00 am)

    Nice piece Christopher. Thanks.

  • John September 19, 2014 (7:08 am)

    I agree! I haven’t seen coverage like this. I’m amazed at how far along they’ve progressed at finishing what portion of the tunnel has been dug.
    I will admit I’m not thrilled about the tunnels two lanes each way, but I’m thrilled about removing the viaduct and opening up the waterfront.

  • John September 19, 2014 (7:33 am)

    Great photographs – I’ve wanted to see that for a while!

  • ocean September 19, 2014 (7:36 am)

    Very true, Rocky.
    Great work, Christopher Boffoli– thanks!

  • Chris W September 19, 2014 (8:07 am)

    I swear, WSB = most comprehensive local media in town!

  • JoB September 19, 2014 (8:14 am)

    very cool perk to your job

  • Jetcitygirl September 19, 2014 (8:29 am)

    Great story and photos- excellent work WSB!!!

  • CEA September 19, 2014 (8:41 am)

    Thank you for a fascinating story – as always, WSB leads the way. The photos are amazing and really help to explain exactly what is going on down there!

  • Deodara September 19, 2014 (8:52 am)

    Thank you Christopher for taking us along. Wonderful pics and detailed coverage. Merits an award!

  • miws September 19, 2014 (8:56 am)

    Thank you Christopher, and WSB, for such a thorough and descriptive report.


    The “Brass Tags” remind me of how cool it is that as impressive as modern technology and procedures are, that there are still some of each that are still employed after so many years, or in this case centuries.



  • Toni Reineke September 19, 2014 (9:11 am)

    Wow! Thank you!

    Looking at the scope of this coverage, it suddenly struck me that WSB has REINVENTED JOURNALISM. Thank you again and again!

  • heather September 19, 2014 (10:12 am)

    I am really impressed… the news coverage, the photos… but I also am so appreciative at being able to see the work being done. It’s absolutely fascinating.

  • chas Redmond September 19, 2014 (10:13 am)

    as always, superior photography Christopher, thanks for documenting this.

  • I. Ponder September 19, 2014 (10:21 am)

    Excellent coverage! The machine however, is a LEMON!

  • David September 19, 2014 (10:27 am)

    Great story. Nice to hear some calm sane engineering information and not just the hysterical “it’s all going to fail and we’re doomed” non-sense you hear about the tunnel.

    The tunnel machine broke, sucks, but things break. You repair it. This isn’t the “Boston big dig”. This is ONE barely over mile long tunnel. There’s no problems with the tunnel, the machine digging just broke. So it gets fixed. Yawn! Who cares? Highway 99 is STILL up and running, that’s WHY we did a tunnel (as opposed to cut & cover or such), so 99 could stay running during the tunnel project HOWEVER LONG it takes. So it’s delayed 2 months, 6 months or a year. We still have highway 99. The ONLY issue at all is the final “who pays for the delay and fixes” issue. Must be the private sector (this is private sector built machine, run by a private sector contractor…the only government involvement is that we “paid” them to do this…if they screw it up, it’s their fault).

    Tunneling isn’t magic, and works just fine. There’s tunnels under EVERY major city on earth (subway, car, utility). When was the last time you heard of a tunnel collapsing and killing people in San Francisco, New York, LA, London (been there since the 1850s)…heck between England and France even. We’ve tunneled through Beacon hill, under I-5, through Capital Hill and to Husky Stadium without a single issue. I remember all the hysterical ranting about how houses would fall in and everything would collapse. We’re tunneling NOW from Husky stadium to Northgate Mall and 95% of the people don’t even notice or are aware that machine is chugging along every day.

    There “was” a valid debate to be had (over now) over tunnel vs new viaduct vs cut & cover, but that’s moot now. The tunnel will get done, and people using it 25 years from now won’t remember it was 6 months delayed.

  • dsa September 19, 2014 (11:04 am)

    Excellent reporting, thank you.

    David the issue is the replacement tunnel will support less traffic capacity then what we had prior to construction.

    • WSB September 19, 2014 (11:49 am)

      Thanks to all for the kind words, and for taking the time to read/view this. We are so glad Christopher was able to go – he’s contributed so much to WSB in the past seven years. Though his own career has him astoundingly busy now, he carved out the hours for the tour and then the storytelling! – TR

  • miws September 19, 2014 (11:23 am)

    This History Link Article has perhaps been shared before, in Articles related to but the DBT, here is an approximately 110 year “Contrast and Compare” look, at tunnel digging technologies and procedures:




  • trickycoolj September 19, 2014 (11:25 am)

    Wow, I would love to pick the brain of the Project Manager! Maintaining the schedule for a project of this magnitude is impressive. It’s great they were able to pull other work to the left in the schedule while Bertha is being repaired. I can’t even wrap my head around the magnitude of scheduling work that has to be done to mitigate the delays as much as they have.

  • Jason September 19, 2014 (11:42 am)

    Last six photos appear to be duplicates of ones at the beginning of the story? Maybe it’s a phone browser issue?

  • metrognome September 19, 2014 (11:46 am)

    Christopher – kudos on the story and accompanying pictures; the technical challenges and solutions are truly amazing and you did a great job of illustrating the complexities of the project.
    wish I could say the same about the USPIRG report – sloppy, sloppy, sloppy! It seems pretty clear to me that they started with a conclusion and only included information that supports that conclusion. Interesting that the title blares ‘Boondoggles’ and ‘wasted money’, which are conclusions, the text switches to using the term ‘questionable highway projects.’ The term ‘boondoggle,’ which is not defined, appear nowhere except the title and the footer. As search engines will focus on they title, they’ve accomplished their goal of stirring up the public.
    They clearly didn’t research the history of the project in depth (i.e. they didn’t mention that the other alternatives would have resulted in massive traffic jams for 3-4 years between the viaduct being torn down and the new alternative being available) nor did they explore local topography that restricts adding capacity. The factors they didn’t mention are more important than the generic national statistics and template they attempted to apply to a specific situation to try to force social change that they feel is justified.
    And lastly, as has been mentioned by other ‘news reporting’ organizations, the report did not declare that tunnel is the biggest boondoogle; Seattle merely appears first on the list for no explained reason. The list is not numbered and no criteria are provided to explain a project’s position on the list.

  • Jtk September 19, 2014 (12:00 pm)

    Awesome Reporting and mesmerizing photos… wow

  • Thomas M. September 19, 2014 (3:30 pm)

    Truly awesome journalism. This is what a news story should look like.

  • Pibal September 19, 2014 (4:59 pm)

    Very interesting! I noticed that the Seattle Times approached its storyline from a much different perspective. WSB had very specific details of what’s going on in the tunnel today and stayed on that message. The Times reported on a far wider strategic overview of what is happening along with touching upon related storylines. I find the two coverages together very complementary of each other.
    Nice work Christopher & WSB!

    • WSB September 19, 2014 (5:11 pm)

      Thanks, Pibal. That’s why I included their link at the bottom of this story … the loose “partnership” we’ve had for several years now includes no obligation, only rare communication, but in particular, I follow Times transportation reporter Mike Lindblom’s work – he’s a West Seattleite, too – and also thought its overview/update nature was a good addition.

  • Sara September 19, 2014 (5:33 pm)

    Wow, wow, wow. Really wonderful reporting. Love you guys. What Thomas M. said: “This is what a news story should look like.”

    Mr. Boffoli, I feel proud (and a bit smug) to claim you as a fellow Seattleite. And likewise for WSB. In an era when original reporting seems to have been reduced to cleverly copied hashtags, WSB always delivers something REAL on a local and regional level. Thanks, guys.

  • pupsarebest September 19, 2014 (5:39 pm)

    Exceptional photo-documentary journalism.
    Exceptional, albeit apparently flawed, technology too.

    dsa succinctly states the major fly in the ointment with the project, whether perfectly executed or any degree of otherwise: reduced capacity (and no exits to downtown) is absurd, foolhardy and a recipe for exacerbated traffic woes for decades to come.

  • Mike September 20, 2014 (12:10 am)

    Nice, this is very interesting stuff. The photos really put into perspective the massive size of this project.

  • Michael Oxman September 21, 2014 (12:30 pm)

    Unsafe work practices by Seattle Tunnel Partners are shown in this video. A Seattle City Light electric wire is struck by a tree branch being cut and lowered by workers on Aurora Avenue.

    The site is across the street from where the King 5 news helicopter can be seen taking off from the roof of their building.

    After a while, violations of worker safety regulations may result in accidents. Until then, there is no publicity of infractions of safety policy.

    In fact, I was unable to obtain any written records of this incident, in spite of a verbal Stop Work Order being issued by Seattle City Light. All workers are required to maintain a 10′ clearance from electric wires, and a City Light inspector who witnessed this incident shut the contractor down for the day. The following day, after I left, the City Light crews cut all remaining branches that were in proximity to the wires, and the contractor finished removing the tree trunks.

    The trees are owned by Seattle Department of Transportation, and no permit authorizing removal of the trees was produced in response to my request.

    The policy of SDOT is to require personnel doing any tree work in the right of way be certified arborists, yet the general contractor does not have such credentials.


  • cookie September 23, 2014 (9:57 am)

    What a waste of money and time.

Sorry, comment time is over.