Potential BDCP Problems....???

[Darian]

A recent article appeared in a local and across the country newspapers reporting on problems encountered by the contractors and city of Seattle in digging a highway tunnel beneath/near the waterfront. The tunnel-boring machine quit unexpectedly and has remained that way for a year. Since this machine can't reverse itself, digging down to it must be done to either repair in place or raise the machine to complete repairs. Check out the article at:

http://www.bostonglobe.com/business/2015/01/01/delayed-seattle-tunnel-project-draws-comparisons-boston-big-dig/UZVmOOuRmEAi39EBkfx0rL/story.html

I don't recall seeing anything in the way of a contingency plan in the BDCP EIR/EIS covering the occurance of such an event in the construction of "the tunnels" here. Also, potential for this was not discussed in any of the BDCP meetings I attended. Might be worth mentioning to DWR, et al.

[SeanO]

Interesting, I wonder what it ran into.

Big Bertha's tunnel in Seattle must be much bigger than the ones proposed here, I imagine?

If so, extraction of a disabled machine would probably be easier for the twin tunnel project.

Best,

[Darian]

The article says that the drill just stopped for some unknown reason and the project team was unable to re-start it.

The Seattle tunnel-borer was the largest of it's type built to date. The length of it is over 100 yards (measurement of the width not provided). The borer looks to be circular but the traffic tunnel(s) will undoubtedly have to be rectangular with a flat road surface. Not sure how many lanes would be involved but the bore hole must be very large in diameter to accommodate the objective. The soils involved where drilling would occur in each project appear to be similar (muddy, for lack of a better term). The Seattle tunnel(s) are short in length and (from the photo of the borer) are closer to the surface than the proposed BDCP tunnel(s) maybe making extraction of the borer more doable. Also, the city of Seattle (the driver/owner of their project) has the infrastructure to support the heavy crane/machinery required for extraction/repair already in place.

The proposed tunnel(s) for BDCP run through relatively unpopulated areas, several city/county jurisdictions and private property without roads or other infrastructure that would have to be constructed to enable repairs. All of which would complicate/limit access in the event of the need to repair tunnel-borer(s). The BDCP tunnel(s) are to be 40' in diameter and planned to be approximately 35 miles long. If I recall correctly, they will be dug at a depth of 150' and 90' apart. Is extraction realistic or possible??? Suppose the approved design includes multiple tunnels and a breakdown occurs during boring of the second tunnel. Would digging down to the borer cause some type of damage to the first tunnel due to proximity???

All of this is just speculation on my part but I believe that some sort of breakdown requiring repair(s) occurring somewhere between the planned holes for tunnel maintenance is likely. In that event, lengthy delays in making repairs may be a big problem for the project and cause a substantial increase in overall costs of same. Given the potential for environmental impacts and increased costs from repair activities, seems like contingency planning should be a part of the EIR/EIS.

[SeanO]

Good points.

Looks like the Seattle tunnel is about 57 feet in diameter, which isn't too much larger than the BDCP ones!

[Darian]

That's a very big hole!! But, how do they make that into a tunnel for traffic?? Doesn't it have to be a rectangular shape and wide enough to accommodate two way traffic (it's supposed to replace an overhead freeway)?? More excavation needed?? Actually, it's interesting when these things work correctly and go as planned....