In reply to mikealexpayne:
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!