Originally posted by zorgon
"Between 1971 and 1974 Lawrence Berkeley Laboratory performed
experiments with electron beams that indicated such beams could be
useful for excavating rock...."
So now I have a lot more homework to do... particle beams for drilling tunnels? In 1974?

An intense electron beam produces large amounts of heat in a very localized area. The attendant rapid expansion of the heated material results in
shock waves which produce cracksaround the area of impact. The beam is pulsed to achieve this effect. Two friends of mine were looking at this problem
from different perspectives (one was an experimentalist, the other was trying to model it).
This received a lot of attention in early to mid 80s when the military were concerned about the effect of intense heat wave produced by a nuclear
explosion, on tank armor (obviously, the tank was supposed to be in close vicinity and possibly targeted). It is possible for the armor to crack due
to aforementioned thermal effect. Since it's hard to achieve in the lab, it was sometimes emulated with an electron beam.
On the topic of this thread -- I was dating a girl in the 80s who lived about a mile away from the structures depicted on this page, and I could see
the remnants of the collapsed structure myself on a couple of occasions.