Patent GB-1323033-A (GB)
Title: Rock bolt assembly
IPC: E21D20/00
Filed: 1971-04-19
Abstract: 1323033 Rock bolt assembly C I WILLIAMS 19 April 1971 [3 Feb 1970] 32430/72 Divided out of 1323031 Heading F2H A rock bolt assembly includes at least one bolt rod section 34 and an expansible anchoring device 33, a surface plate 35 having a bolt rod hole and adjacent passage for a conduit 39, a nut 37, and an imperforate conduit extending throughout the length of the assembly wherein a longitudinal grout passage is formed through at least one side of the anchoring device in all conditions of expansion thereof. As shown in Fig. 3, relative rotation between the rod 34 and a conical member 44 has drawn the latter into a surrounding C-shaped shell 46 separating it along a weak region into two wedges fixing the device 33 in the hole 31 in a rock formation 30. The nut 37 is tightened to produce a prestress in the bolt 34 within its elastic limit. A thrust ring 45 holds the shell against longitudinal movement and a keying ridge on the conical member 44, located in the discontinuity of the shell 46, holds them against relative rotation. The discontinuity being wider than the ridge allows the passage of grout. The angle of the wedge is less than fifteen degrees and is preferably less than ten as in an alternative anchoring device, Fig. 20, wherein a solid bolt 89 has a forged flat 90 supplementing a thrust ring 88, a conical member 86 has a shoulder 91 formed by a cylindrical enlargement with a gap 92 wider than a keying ridge 93 which ends in a slope 94 down to the base of the gap, thus facilitating the flow of grout. To prevent stripping of the thread in the thrust ring 45 a shoulder is provided on the rod 34 against which the ring can advance. The threaded length of the ring is made at least as great as its diameter to enable the diameter to be kept lower than that of the unexpanded shell 46 and so facilitate insertion in the hole 31 and eliminate interference with the flow of grout in either direction through the unclosed area of the shell and over hardened slip rings 50, 51, which may be oiled or greased to minimize the transfer of torque between the shell and thrust ring. After sealing the hole 31 with mastic 38, grout is pumped through the conduit 39 or, if the rod is not solid, through an internal conduit through the rod 34 according to whether the hole 31 is directed upwards or downwards from its open end, the other conduit serving as an air vent until grout appears therethrough after a full circuit. The conduits are then plugged until the grout sets. If the bolt rod is solid, an external conduit is strapped thereto along the full length of the bolt rod and anchoring device. Fig. 6 shows a bolt rod 83 with anchoring device including an expansible shell 80 round a conical member 81 adapted for use in an oversize hole by mounting a shim sleeve 78 on the shell 80, locating it thereon by inwardly turned tabs 85, 86 and providing holes 84 to facilitate the gripping action against the rock formation. Where a threaded coupling sleeve 66, Fig. 18, is used to join two sections 64, 65 of a bolt rod, the rod may be back-rotated to release the anchoring device from rock which appears to be too soft without causing uncoupling by ensuring that the torque required to unlock the coupling is greater than that required to release the anchoring device. This may be done by means of a locking washer 67 or by jamming threads on the coupling against unthreaded parts of the sections Fig. 17 (not shown) or vice versa Fig. 19 (not shown). The grip of the anchoring device may be improved by suitable annular formations on the peripheral surface of the expansible shell, keeping the longitudinal slopes thereof in the region of ten degrees to provide a high degree of pressure normal to the perpheral surface, Figs. 8, 9 (not shown). The rock formation reinforced by the rock bolt assembly may form the walls of a tunnel Figs. 5, 10 (not shown) requiring various angle plates and conduit guides Figs. 12 to 16 (not shown).