New to List. Granite Problem

[Jeff Spencer <jeffespencer@zzzzzzzzz>]

I recently came to this list because I had nearly an identical problem. (See
the thread previously mentioned). But in my case, the boulder was smaller
and turned out to be weaker than granite.  First I'll tell you what I did to
remove the top 24". Then give my thoughts.

First I attacked it with a Bosch roto-hammer, 1/2 carbide bit and 8 sets of
1/2" plugs and feathers (wedges and shims). This easily popped the first 12"
off the top because I found an existing crack there. Then I trenched around
the entire boulder and I tried to remove another 14" off the top by drilling
and wedging a horizontal line at the height I wanted. Unfortunately the
boulder decided that rather than splitting horizontally through the rock it
was simpler to split at a 45 degree angle to the surface of the rock. In
hind sight makes complete sense, of course the rock split through 20" of
rock rather than the 48" I was hoping for. Since rock splitting requires
that the stress you induce in the rock take the path of least resistance.

After that I was in a hurry to get the remainder of the rock removed for
other reasons. So then I rented a diesel air compressor and 60 pound jack
hammer. But that was only able to take of 1/2" flakes of rock. So I
exchanged it for a 90lb jack hammer. The 90lb hammer took 3 hours of back
breaking work to remove about 6 cubic feet of rock.

I also used the 90lb hammer to break some concrete from which I can tell you
that rock is much much tougher than concrete.

If I was to do it again, I I'd rent a large cutoff saw and buy a diamond
blade appropriate for the rock I was dealing with. Then cut kerfs into the
boulder and knock the kerfs off with a sledge hammer. From talking with
people here and at the rental shop the diamond blades designed for concrete
will barely scratch rock, hence why I'd buy a diamond blade of my own.

The other option would be to rent a large piece of equipment with a heavy
rock breaking hammer. But I've heard these aren't that effective with truly
tough rock like granite.

If you want to e-mail me specific questions directly, I wouldn't mind. While
I've only worked on one rock, I did spend days on it.