Post tensionable grouted anchor assembly

A post tensionable rock and mine roof anchor and nut assembly of the grouted or resin anchored type to be installed in a bore hole in a mine roof rock formation or the like and tensioned after mixing and setting of the grouting or resin for strengthening the same, comprising an elongated anchor including a generally cylindrical portion at its upper end having a shorter length than the depth of the bore hole in which it is to be fitted and having an elongated externally threaded rod portion at its lower end adapted to project a predetermined short distance externally of the bore hole when the anchor is normally positioned in substantially fully inserted condition in the bore hole, an internally threaded nut member to threadably receive the threaded rod portion therein providing companion thread surfaces forming a screw thread coupling assembling said nut member and anchor together and said nut member having an end surface to exert bearing force against the face of the rock formation, the anchor being adapted to be introduced into the bore hole in assembled relation with the nut member after insertion of a destructible cartridge containing quick-setting adhesive resin or grouting material therein to crush the cartridge and mix and distribute the resin or grouting material throughout the space outwardly surrounding most of the anchor and fixing the anchor in the bore hole upon hardening of such material thereabout, the nut member having a bore therethrough including a first smaller diameter bore portion extending from said end surface through a major portion of the axial depth of the nut member threaded to mate with the threads of the external threaded rod portion and having a second enlarged diameter bore portion forming the exit end of the bore communicating with the first bore portion, a disc seated in the second bore portion, and inwardly crimped lip formations integral with the nut surrounding the exit end of the bore and inwardly lapping the periphery of the disc in said second bore portion to retain the disc therein in position to bar penetration of the anchor rod portion through the nut until a predetermined torque force level is exceeded, the nut member being initially assembled in threaded relation with the threaded rod portion of the anchor to occupy an initial assembled position wherein the disc restrains relative rotation of the nut member with respect to the anchor until said predetermined torque force level is exceeded, and said crimped lip formations releasing the disc and accommodating further threaded insertion of the rod portion through the bore of the nut when the anchor is restrained against rotation by setting of the adhesive resin or grouting material and torque force in excess of the predetermined torque force level is applied to the nut member.