Abstract: A multipartite rock bolt includes a plurality of individual discrete elems which are connected to each other at their respective end portions to constitute the rock bolt which is anchored, especially cemented, in a hole of the rock to be consolidated by the rock bolt. The end portions of the elements have complementary recesses therein at which the respective assembled elements overlap each other and the connecting arrangement for connecting the respective end portions includes a projection, particularly a pin which extends transversely of the elongation of the element into the recess and is received in a complementary aperture, particularly a hole, provided at the recess of the other element. The recess is partially bounded by a detaining surface extending substantially longitudinally of the element, and the detaining surface may be inclined relative to the elongation of the element.

Abstract: A rod extensometer which can be inserted into a hole drilled into the roof or floor of an underground excavation to monitor the shifting of material surrounding the excavation. The extensometer has a head which is anchored in the inner end portion of the hole by a hardened synthetic plastic substance, an annular section which is inserted into the outer end portion of the hole and is bonded to surrounding material, and a set of interconnected coaxial cylindrical rods one of which is rigid with the head and another of which extends through the annular section. Changes in distance between the outer end of the other rod and the annular section are indicative of movement of material surrounding the inner end portion of the hole relative to material surrounding the outer end portion of the hole and/or vice versa.