Alright, for those of you searching the collapsed part, let me be more kind than Gygax wants me to be and give you a crude map.
It's approximately 200 feet long, and about 20 feet high. That black part is the corridor you guys found that collapsed in. It was located about ten feet up the collapsed debris, and took about two hours worth of work from three of you to open up. As you can see, totally clearing all of that out would take the lot of you some weeks.
What I am going to need is for people who are clearing or searching is to tell me where they are searching, how high up they are searching, and how they are doing it. You got lucky finding a kinda trick to the rubble with the first one, don't necessarily think that you'll find such a thing again. So be clever!