Overtightening bolts to failure

[mick]

I'm looking for advice on how to pull and/or chop some old bolts. To be clear, the developer was consulted and is in favor of their removal for safety reasons. In question are 3" x 3/8" stainless steel Hilti threaded mechanical expansion sleeve bolts, purchased from MEC. Usually I would just pound them in flush and cover with bondo and rock dust, but these bolts were not drilled deep enough.

I've heard that a long breaker bar can be used to overtighten such a bolt until it snaps cleanly off where it meets the rock face. This seems easier than a hacksaw, and less likely to damage surrounding rock. Some people have recommended that I just whack the bolts with a hammer until they break off, but this also seems like it would be a lot of work and rather imprecise.

tl;dr - What happens if I intentionally overtighten a hilti expansion bolt to failure? Where will it break?

[Greg]

The textbook method would be to pull them. http://www.safeclimbing.org/education/howtorebolt.htm

When I need to remove a bolt I just beat it back and forth with a hammer until it breaks. New or old they have always broken off just below the surface. Then just fill the hole with rock dust and glue. If they are bolted to a very shallow depth you could end up fracturing the rock by beating on it with a hammer though. That wouldn't be pretty.

An old rusty bolt will usually break off by over tightening it without too much trouble but it is very difficult to break a new bolt this way. I tried with a box end wrench and then a ratchet driver and could not do it. Might work with a long power bar.

[chossmonkey]

SS tends to seize up and start spinning if you try to over tighten.

If the bolts have not already been pounded to the back of the hole, just cut them off close to the rock and then pound in the remaining bit. If they have been pounded in already you might be able to draw them out some by tightening them.