/ modern bolts and staples
Could be as little as 50mm in hard rock. In softer rock like sandstone 100mm might be more appropriate.
I would have thought nearly all bolts were longer than 50mm? At least all the glue-ins I've encountered have been, possibly expansions are shorter?
An expansion bolt in good rock (hard, compact) would be 50mm into the rock pretty commonly.
The requirements for EN959 (the European standard for rock anchors) are embedded length for mechanical bolts must be at least 5X the diameter and for glue-ins 70mm.
The usual size of bolt-ins is 10mm x 80mm which give a length in the rock of around 45 to 50mm and for glue-ins the industry standard length is 80mm. For some rock types they go longer, we make them up to 200mm on occasion for the paranoic climbing on rubble!
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