The soils vary quite significantly between the two projects with the soils up at Northlink being much more amenable to tunneling than those that plagued the SR 99 job at the start (and might at the finish).

I have close ties to both jobs.

Yeah, I've heard a bit about it, but I've not really heard enough to Know What I'm Talking About. My impression is the early phase of SR99 was running through infill from early Seattle and thus a significant amount of debris etc was involved in the problems getting Bertha going.

Do you know of any good resources on these projects for the transit / infrastructure geek who's willing to read technical information? Executive summaries and dog-and-pony documents only go so far. :)

You may be able to get the bid documents from the Owners (e.g. - WSDOT and SoundTransit) although I'm not sure. This would give you information on the soils and what the original consultants thought.

Anything past that probably hasn't come out yet since the jobs are aren't in a position where much has been published about them. If you want more information in general you can read conference proceedings (RETC, WTC, NATC).

Much of the deeper analysis and such isn't really accessible to the layman because it's really buried in the litigation.

SR 99 is likely your best bet between the two jobs because WSDOT has had an open book policy on the job. I think they've been too much of an open book, but that's neither here nor there.