After putting the top jacket on, then came the problem of how exactly I was going to A) undercut it and B) actually flip it over. Normally, a trench is cut and then the pedestal is undercut from all sides leaving a pillar of rock underneath, which you can subsequently eliminate and then flip the jacket over. However, this jacket was far too large to do conventionally. And I couldn't really fit tools in all the way around the jacket to really undercut it from all sides.
So, in cases like this, go tunneling! I started two holes and dug and dug until they connected, and then widened them into a larve cavern underneath, and then added a hole on the other side. Problem was, this jacket was so large, I eventually couldn't reach the back wall with my rock hammer, and had to use my large estwing pick to scrape away underneath. Tunneling, by the way, is a good recipe for bloody knuckles.
Here you can see more of the tunnel. Aside from these two small columns, the back part remained as a large pedestal in back; the jacket stuck out from this like a surfboard with two pillars. Once I cut the pillars, I figured it would break the pedestal, and tilt forward.
The moment of truth! This was on the heavy side. Well, nothing happened - the left pillar remained still, but I figured it would fail if given this much weight. Apparently not, however - it just hung like this for several minutes.
When I cut through the other pillar, it shifted almost imperceptibly forward, but I knew at that instant that I had been successful. Then, I found one of the construction workers to help me flip it over and complete the jacket.
Here's what it looked like - you can see the overhanging plaster; that's where the crack formed, leaving a little bit of the pedestal back in the hole, which I'll excavate in a separate jacket.
Voila! Here's the completed plaster jacket. It's pretty heavy.
Well done!
ReplyDeleteWe have to similar techniques a lot on the east coast, when you're digging into a cliff face; when you have 150 feet of overburden, there's only so much you can remove (of course, the whale always seems to be oriented perpendicular to the cliff face). We use it a Carmel Church to get around problems associated with weathering rates on exposed bones. In principle, we could clear off large areas in the quarry, but the weathering rates are so high that it's impractical to do so, so we have to excavate as if we're digging into a cliff.
The first time I did this on a dinosaur bone in Wyoming, my volunteers (who were experienced with dinosaurs, but not whales) grumbled that I was going to destroy the bone. It came out fine.
Personally, the less amount of bone exposed during an excavation... the better. The other problem that faces us is that on the coasts, a lot of people will freak out if you have to dig a really big hole into the cliff. Most folks who work on dinosaur excavations do so in places where no one really cares about opening up a large quarry.
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