Tunnel Visit: Tunnel and Shaft Excavation with SEM in Bellevue, WA

Our field trip to Bellevue, WA was worth the long roundtrip drive. The group departed Corvallis on Friday, June 1^st at approximately 5:40am. We were greeted by Archie Kollmorgen and his colleagues from Atkinson Construction and were kindly provided with pizza for lunch. During lunch, we listened to a brief overview of the Sound Transit tunnel project. The Sound Transit East Link Extension project shall connect Seattle with Redmond via light rail. The connection in downtown Bellevue will be made possible with a 2,000 feet long tunnel. The excavated dimensions are about 27 ft high and 34 ft wide. 

How do they dig the Bellevue tunnel?

The method used is called SEM – sequential excavation method. Imagine you are sitting in a large excavator. You’ve exchanged the front shovel for a digging tool with some teeth on it. You push it into the glacial till and sand to take it down: not all at once, just bit by bit. You drive backwards to give some space to the front loader, so the soil can be removed, and your fellow laborers place some steel sets and spray concrete on the walls. The complete tunnel cross section can be excavated in several steps – first the top part (top heading), then the middle part (bench), and lastly the bottom part (invert). With this piece-by-piece excavation it is possible to excavate a tunnel in urban areas with high-rises and very little soil between the road surface and the tunnel structure. 

Figure 2. From left to right: Atkinson Construction Employee, Sean Iiams,
Maggie Exton, Nathan Jones, Stephie Lange, Nick Carter, Tucker Jones,
Clinton Lindgren, Yingqing Qiu, Aleyna Donaldson, Amalesh Jana,
and Christopher Roach

How does a tunnel function in an emergency, such as during a fire?

There is a shaft that goes from the ground surface to the tunnel at the half-way point along the tunnels length. The shaft has emergency fans to remove deadly fumes from the construction site and also serves as an access path for rescue parties. This shaft construction is done with partial downward excavation, which is similar to the tunnel excavation method. A part of the shaft hole is excavated, steel is placed around the hole, a shotcrete layer is applied over the steel, and the cycle is repeated. See figure 8 below.

How does it look, sound, and smell?

The air quality is surprisingly great. The exhaust air and dust is vented through large ventilation ducts and fresh air is automatically sucked in from the entrance of the tunnel excavation from figure 3 by the pressure difference. It is loud with all the machinery operating. It smells like dirt and concrete mixed with some truck exhaust, but the air on the surface above smells worse due to all the cars and vehicles driving their daily commute in the sun. Luckily, the tunnel excavation hasn’t encountered ground water so far. Ground water makes excavation much more difficult.

I’d like to thank GIGSO (Geo-Institute Graduate Student Organization) of Oregon State University (OSU) for their financial support. The group would like to thank Atkinson Construction with Archie and his colleagues for their time, knowledge, and warm welcome. 

Stephie


Impressions from the tunnel construction visit:

How to Teach a Tunnel Course?

Being a student sitting in front of a black- or whiteboard is well known for many of us. The teaching-learning environment is diverse and can take on multiple facets, such as taking in information as a passive observer, working towards a learning outcome in group work, like discussions or smaller questions to be answered in pairs, or as a student-led lecture by learning-doing-teaching. 

Creating the content for any subject to teach, in the contrary, is not so much known by most of us. And thanks to the department of civil and construction engineering at Oregon State University (OSU), I am able to learn how much work teaching really is and how gratifying it feels once the “comprehension spark” happened - at the student level, as well as at the instructor level.

Currently, I am instructing a specialty topic course on tunnel design and construction. Asking myself what the students should get out of the course and how to accomplish this was difficult, especially for my first course. 

Tunnel Uetliberg, Zurich, Switzerland (image: Amberg)

I remember my first tunnel visit vividly. I had been on a week-long workshop about tunnel construction, ventilation, and muck transport and was able to visit the Uetliberg tunnel in Zurich, Switzerland. I hadn’t had much knowledge about tunneling, but being down there in the dark, carrying this large fanny pack with something very heavy in it, with those super large steel-toed rubber boots, and feeling so small and invisible compared to the diggers and machines, partial spot lights and loud sounds... I knew back then that it this is a fascinating world to me. Well, I did my Masters on the dynamic behavior of a pedestrian bridge, but jumped right into the opportunity of tunnel engineering during my first job and studied some more tunneling at the ETH Zurich while working full time. So, what is it I want my students to get out of this tunnel course? I hope for an interest in underground work in general - yes, with some background knowledge - but what I really wish for is a spark in their eyes. If the interest is not there, no learning will happen. If a subject is exciting, learning will happen with seemingly no effort.

For the preparation of the course itself, I’ve learned that talking to experienced teachers and professors who’s teaching style I liked was immensely helpful. Further, I asked myself what details from my own student experience I remember and which of them I remember because I liked them. I am trying to implement those positive details into my weekly lectures. Also, I took an Engineering Education class two years back at OSU and reflected a lot over my notes, even used the basis of the then created syllabus and my “mini-student-led-lecture” on tunnel boring machines (TBMs) in the actual tunnel course. I was reading the books "The Courage to Teach" by Parker J. Palmer and "Making Learning Whole" by David Perkins which helped me, too. 

For writing and grammar, I think it is unavoidable to get some help, especially for a non-native English speaker. So came "The Elements of Style" by W. Strunk Jr. and E.B. White and "Keys to Great Writing" by Stephen Wilbers into play.

I can say it now: I was not prepared for the large amount of work I had to put in to obtain a for me satisfying class environment and lecture outcome. One hour of lecture takes me about 8 hours of preparation and post-work, including creating course content, worksheets for during the course time, home work assignments and their rubrics with an example solution to stay objective, obtaining visuals from books or videos, or to give written feedback on the assignments for each student. 

All in all, “Hut ab!” (Hat down) to all teachers, instructors, and professors, as we say it in German to someone who is or was doing intense and ingenious labor with a surprisingly great and elegant outcome. The teaching profession deserves much more applauding, especially for extraordinary work.

In addition, I am extremely thankful to industry connections and partners to support tunnel classes at universities with guest lecturers and support for field trips. It is very exciting that two handful of students are able to go to Bellevue, WA to visit an ongoing tunnel excavation and construction for the East Link Light Rail metro connection between Seattle and Redmond. The excavation is scheduled to be completed very soon. (I will report on the site visit with many pictures and interesting views in my next entry —> so hold your eyes open!)

Until next time.

Yours,

Stephie