The Seattle Times (hat tip to ASCE SmartBrief) has reported that seven voids have been discovered above the Beacon Hill Tunnel with one opening up at the ground surface. The tunnel is being constructed by Sound Transit, the area’s transportation agency as part of a roughly $2.6 billion (yep, billion) light-rail project connecting downtown Seattle with the University of Washington and SEA-TAC airport. The voids were a result of running sand pockets in the otherwise stable clay units that were encountered by the tunnel boring machine or TBM. These voids migrated up like a chimney with one reaching the surface, almost 160-ft above the tunnel. This void was apparently 21-ft deep and opened up in a resident’s front yard and could have easily swallowed her up as she noticed it while gardening. The other voids were discovered at a depth of 20- to 65-ft below the ground surface. More after the break. (Illustration from Seattle Times)
More information on this project
CAn you send me more inifirmation on this project and also the companies and people involved in this project.
This is all I have…
I just came across the project through ENR (link at top of the article). I’m afraid I don’t have any other info. If you find anything else, by all means drop us a note or leave another comment here. — Rockman
I work on one of these projects where “they” are boring underground (using a Tunnel Boring machine – TBM) to feed water from one reservoir to another. I have no direct hand in the geotechnical applications of the project, as I mostly deal with the chemistry of the rock/muck that comes out behind the TBM. Our TBM has been slowed by incomplete knowledge of the rock (from drill core) and is becoming a costly (oh god you can’t imagine how costly a TBM is) project. I can’t even begin to imagine the bill at the end of this project. And maybe it doesn’t matter, water means life.
Gawd-i would love/go crazy/be so scared if I were to be underground in that tunnel
Sounds like interesting work. What is your background? Geology? Geochemistry? Or something else?
I can imagine it’s hard to get good geotechnical and geological data on the rock that the TBM will be drilling through, even if it isn’t 7,000 ft underground like this project. I imagine you drill for a couple hundred ft and at the bottom you get 30-ft of core that will be in the path of the TBM, then you move a few hundred/thousand ft away and do it again. Not a very complete picture of the material the TBM has to drill through. Thanks for the comment. — Rockman
I’m part of the Robbins Co. crew in the Olmos Project, There is just two companies, Odebrecht and The Robbins Co.
They used on site pre-drill exploration for quite a few cut tunnels ensures one does not chop a leak into the tunnel wall and also gives local data … just makes it a little difficult for forward drive into unknown which may your tunnel direction vulnerable … pilot drives have been common as in coal mines but there they have some bedding previous knowledge to follow through and a high return on the yield , it leads to better local pinning data and that has been used to some good result, if geophysics and general section improves maybe only uncertain stability and water ingress may need pre-plan research drills as increased drilling leaves dataset behind from projects over the years … our best source, research is usually too specific and chemical, then projects could forward with more specific data out of the tunnel drive as it goes as log as the pre-geo-structure and technology answers make it safe. Mike
it may … make … your tunnel direction vulnerable to change to drill laterally as you go, although it does reduce vertical drill cost and damage risk … sorry about preceding mistype
(1)I would be glad to know kind of geological-geotechnical problems being faced during tunnelling by TBM and solutions suggested to overcome in the project, kindly give the excavated dia of the tunnel.
(2) The present cost per meter of tunneling.
Site investigations for deep tunnels are problematic because as Rockman has said, drilling from the top produces a lot of hole length that is not relevant to the tunnel geology. You can whipstock holes and reach more than one location from a single setup but it wtill products a lot of drilled length. However, seldom is such a project undertaken with no knowledge of the tunnel geology. There should be at least a few holes, which can be tied together with inferences from geologic mapping and geophysics.
One way to tackle the subsurface exploration problem is to conduct drilling from the tunnel portal and once progress is made, from the face, but access behind the TBM cutterhead for this is a problem. It’s easier with drill-and-blast tunnels, although not often done.
The biggest fear in tunneling is the sudden inrush of water, which is one reason it is ideal to carry a pilot hole 50-300m in front of the face.
The second biggest fear is squeezing/caving ground. At these depths the rock stresses are significant, and if the sides sluff or are soft, you can be in trouble real fast. TBMs must be able to exert high radial pressures on the tunnel walls in order to develop enough thrust and control the direction of thrust. If the ground squeezes and the pads penetrate deeply, a TBM can become stuck. There have been instances of early TBMs that remain entombed because of unanticipated soft ground.
There are also concerns for rock stress conditions, particularly when passing through an active subduction zone like the Andes, at depth. The depth range mentioned is just within the envelope of possible rock burst conditions.
For this project I think the published TBM cost range would probably not be applicable.
Altogether a challenging project. I am ready to buy my plane ticket tomorrow…..
hi everybody ive seen this project on discovery and i wonder how far are they was it on discovery up to date or not cuz it was an awesome project and realy fasanating ( srry if thats not correct ).
it was good for the people on the west side so pls tell me when its finised 😀
I also just watched this on Discovery and was wondering if it is complete, and the rest of the story about it.
Its very disappointing when Discovery only do “half” the story and leave the viewers wondering if the project ever succeded >:(
According to [url=https://geoprac.net/s/l]this ENR article[/url], the TBM had made it approximately 70 percent of the 20-km when they suffered a serious setback last month. A rockburst damaged a hydraulic cylinder connected to one of the grippers and even injured two workers in the operator cabin. A nationwide search is on by the Robbins Company, makers of the TBM to find a replacement part. If one cannot be found, it will require 6-months to manufacture. From the article, it sounds as if there have been many rockburts and the going has been fairly tough. Projected earliest completion date is July 2011.
What is the status of this project?How far it is behind the schedule completion.