Thor wrote: Does anyone have any facts or opinion as to whether or not this should be considered over time when using glued-in bolts? Of course, all bolts should be checked before using.
Bolts used for climbing/rappelling/caving should all be placed where the shear force is going to be on the bolt and the rock and not in such a way that the bolt can be pulled straight out. The hangers are put perpendicular to the rock face and the pull is at a right angle to the rock/bolt. Never straight out. The epoxy helps keep the bolt in the hole drilled and acts as an additional bond to the rock along with the expansion collar.
I've seen bolts drilled into mines and seen the ones placed in ceilings and such. Of course over time they're going to fail, mines are never supposed to be permanent fixtures anyway and if they're for the long term usually the bolts are inspected on a regular basis and replaced where needed. Abandoned mines are dangerous for this lack of inspection/replacement. So of course over time (even as short as 10-15 years) an epoxied bolt placed straight up into the ceiling or at such an angle where the forces of the rock are pushing against it ... yeah they're going to fail.