BACKGROUND OF INVENTION

[0001] The invention relates to a friction bolt assembly with an improved friction sleeve configuration for easier insertion into a rock hole. [0002] The applicant’s patent application WO2017/015677 (hereinafter referred to as the“prior application”) describes a friction bolt assembly which includes a radially expansible sleeve; a rod which extends through the sleeve; an expansion element mounted on the rod to engage the sleeve at a top end; and a stop formation on the rod which abuts the sleeve at a lower end such that, when the rod is actuated by turning a nut, the expansion element is drawn into the sleeve to expand the sleeve into frictional engagement with the rock hole.

[0003] The stop formation at the lower end of the sleeve prevents the sleeve from moving relatively to the rod, when the expansion element is drawn into the sleeve, to facilitate this radial expansion of the sleeve [0004] The sleeve is circumferentially larger than the hole in which it is to be inserted.

The reason for this is that the sleeve will compressively deform when forced into a hole to compressively load against the rock hole. However, a large insertion force is required to overcome the resilent forces of the sleeve. This force is reactively transferred to the stop formation by the sleeve. [0005] The problem with having the stop formation at the back of the sleeve is that the threaded rod along which the insertion force is applied to the stop formation is subjected to large compressive loads and bending moments which may result in the rod buckling or bending ahead of the stop formation. Also, when the friction bolt assembly is inserted into a hole, the sleeve tends to compress against the stop formation, as the trailing stop formation pushes the sleeve into the hole. This radially expansive reaction works counter to the compressive deformation of the sleeve, requiring a larger insertion force. As the insertion force increases, so does the risk of the friction bolt assembly buckling. [0006] The invention at least partially solves the aforementioned problems.

SUMMARY OF INVENTION

[0007] The invention provides a friction bolt assembly which includes: an expansible tubular sleeve longitudinally extending between a leading end and a trailing end, having a longitudinally extending formation, about which the sleeve resiliently deforms; a rod which longitudinally extends through the sleeve between a first end and a second end and which has a projecting portion which extends from the trailing end of the sleeve to the second end; an expansion element mounted on or integrally formed with the rod at or towards the first end; a wedge formation on an inside surface of the sleeve positioned to engage the expansion element; a load applicator engaged with the projecting portion between a load bearing washer and the second end of the rod; and a stop formation engaged with the rod, within the sleeve, in a position which abuts the wedge formation, when an axially directed force is applied to the second end of the rod, to transfer the force to the sleeve to pull the sleeve along with the rod; and which holds the sleeve in position, relatively to the rod, when the load applicator is actuated to draw the expansion element into the sleeve to radially expand the sleeve. [0008] The longitudinally extending formation may be a channel formed in a wall of the body or a slit which extends from the leading end along at least part of the sleeve.

[0009] The projecting part of the rod may be at least partially threaded.

[0010] The expansion element may be frusto-conical in shape.

[0011] The expansion element may have a sloping engagement surface. [0012] The wedge formation may have a tapered surface, adapted to engage the sloping engagement surface of the expansion element, and an abutment surface which faces the trailing end of the sleeve.

[0013] The wedge formation may be integral with the sleeve. Alternatively, the wedge formation may be an insert which is fixed to the inside surface of the leading end of the sleeve by, for example, welding. [0014] The wedge formation may include at least one retaining formation, for example a slot or indentation.

[0015] The rod may have a threaded section or sections.

[0016] The stop formation may have at least one projection which is adapted to engage the at least one retaining formation of the wedge formation to prevent the rod from rotating when the stop formation is affixed to the rod.

[0017] Preferably, the stop formation is a castle nut which is threadedly engaged to a threaded section of the rod.

[0018] The friction bolt assembly may include a load bearing washer mounted over the projecting portion of the rod between the trailing end of the sleeve and the second end of the rod.

[0019] The load applicator may be unitary, having a body adapted with a drive head surface and a washer abutting spherical seat. The drive head surface may be a hex- drive surface. Alternatively, the load applicator, separately, may include a nut and a barrel a spherical seat.

[0020] The barrel may have a central bore, through which the rod is received in engagement, and at least one grout conduit between an exterior surface of the barrel and the bore.

[0021] The friction bolt assembly may include a grout tube which encloses a length of the rod and which extends, at least partially within the sleeve, between a distal end and a proximal end with the proximal end engaging the barrel to provide a grout passage which communicates the exterior surface of the barrel with an interior of the grout tube.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention is described with reference to the following drawings in which: Figure 1 is a view in elevation of a friction bolt assembly in accordance with the invention;

Figure 2 is a view in longitudinal section of the friction bolt assembly;

Figure 3 is an isometric view from one end of the friction bolt assembly;

Figure 4 is a view in longitudinal section of one end of the friction bolt assembly; and Figure 5 is an isometic view of a castle nut of the friction bolt assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0023] A friction bolt assembly 10 according to the invention is depicted in the accompanying drawings.

[0024] The friction bolt assembly 10 has an expansible tubular sleeve 12 which longitudinally extends between a leading end 14 and a trailing end 16.

[0025] Within the sleeve a cavity 18 is defined. The sleeve 12 has a slit 20 longitudinally extending between the ends (14,16). The slit 20 allows for compressive deformation of the sleeve when inserted in a rock hole. This feature will be more fully described below. The feature of the slit 20 is a non-limiting example. [0026] The sleeve 12 has a slightly tapered leading portion 22 which tapers toward the leading end 14 to enable the sleeve to be driven into the rock hole having a smaller diameter than the body 12.

[0027] The friction bolt assembly 10 further includes an elongate rod 24 which longitudinally extends between a first end 26 and a second end 28. The rod extends through sleeve 12, projecting from each end (14, 16) of the sleeve. The rod extends to a significant extent beyond the trailing end 16 of the sleeve body as a proximal projecting part 30. The projecting part is at least partially threaded with a first threaded section 32. The rod also has a second threaded section 34. [0028] An expansion element 36 is threadedly engaged to the second threaded section 34 of the rod 24, initially flush with the rod’s first end 26. The expansion element 34 takes on a generally frusto-conical shape, with an engagement surface 38 which tapers generally towards the trailing end 16 of the sleeve 12. The maximum diameter of the expansion element is greater than the internal diameter of the sleeve. [0029] A pair of semi-cylindrical inserts 40 are fitted within the sleeve 12, from the leading end 14, each to present, within the cavity 18, a tapered surface 42 and an undercut abutment surface 44 which faces the trailing end 16 of the sleeve. A top edge of each wedge insert is welded to the leading end 14 of the sleeve. A pair of slots 45 is defined between the inserts. [0030] The assembly 10 further includes a load applicator 46 which comprises a barrel 48 and a hex-nut 50 which trails the barrel, threaded on the first threaded section 32 of the rod 24. In this example, a load indicating washer 52 is interposed between the nut and the barrel to indicate when load on the barrel has reached a predetermined level.

[0031] The barrel 48 has a domed end 54, a trailing end and a central bore 58 which extends between the ends. It is through the bore that the rod 24 passes in engagement of the barrel to the rod. In a sidewall of the barrel, a plurality of grout conduits 60 are formed to communicate an exterior of the barrel with the bore 46.

[0032] A domed faceplate (not illustrated) can be mounted on the rod 24 to seat on the spherical seat provided by the domed end 54 of the barrel 48. [0033] In addition, the assembly 10 includes a grout tube 62 which encloses a length of the rod 24 and which extends between a forward end 64 and a back end 66. A forward end portion 68 of the grout tube is positioned within the sleeve so that the forward end opens into the cavity 18 of the sleeve 12 (this deep insertion of the made possible by the position of a stop formation 72). The back end is fitted within bore 58 of the barrel 48, abutting a seat 70 in the bore, positioned to receive a grout input from the grout conduits 60.

[0034] Holding the sleeve 12 in position on the rod 24 is the stop formation 72 which is positioned high-up within the sleeve. In this example the stop formation is a castle nut (also designated 72), which is threaded on the second threaded section 34 of the rod. [0035] The castle nut 72 has a cylindrical internally threaded body 74 and a single or a pair of diametrically opposed prongs 76 which extend from the body in an axial direction. Each prong is received in a respective slot 45, between the inserts 40, with the body of the nut abutting the abutment surface 44 of each insert. In this position, the nut holds an initial positioning of the sleeve 12 relatively to the rod 24, with the expansion element 36 partially received in the sleeve at the leading end, with its engagement surface 38 engaging the abutment surfaces 44 of the inserts.

[0036] In use, the assembly 10 is installed by insertion in a rock hole (not shown) which is predrilled into a rock face (not shown) on which adjacent rock strata requires stabilisation. The rock hole will be of a diameter that is slightly smaller than the diameter of the sleeve 12.

[0037] The assembly 10 is inserted by application of a force, by a drill rig, to the second end 28 of the rod 24 and the nut 50 in a percussive or hammering manner. This force, by direct action, will drive the rod incrementally into the hole. The sleeve 12 will“follow” by being pulled along by reaction of the body 74 of the nut 72 abutting the abutment surface 44 of each insert 40. The sleeve elongates slightly, due to the tensile forces acting on the sleeve as it is pulled into the hole, decreasing in diameter and complementing the compressive deformation of the sleeve, about the slit 20. In this manner, the sleeve is eased into the hole with less force than would be ordinarily required. [0038] Furthermore, the risk of the rod buckling under load is reduced due to a reduction in the length of the rod between a leading end and the point at which an insertion force is applied to the rod i.e. at the castle nut 72 position.

[0039] With the assembly 10 fully installed and with the faceplate held against the rock face, the frictional forces retain the assembly in the hole and allow for the transfer of partial load from the rock strata to the sleeve body 12.

[0040] The rod 24 can now be pretensioned between the expansion element and the faceplate. This is achieved by tightening the nut 50, forcing the interposed barrel 48 against the facepate in progressive load supportive contact with the rock face. Reactively, the rod is drawn outwardly with further torque applied to the nut, pulling the expansion element 36 into the sleeve and wedging apart the inserts 40. This radial outward deformation of the sleeve anchors the assembly at this point within the rock hole.

[0041] As torque is applied to the nut, the propensity is for the rod to rotate in unison. To prevent this, thus allowing the rod to move axially relatively to the nut, the castle nut 74 is affixed to the threaded rod, either through deformation of the thread or by swaging the castle nut onto the rod. With the castle nut prevented from rotation relatively to the sleeve by engagement of the prongs 76 with the slots 45, the rod is thereby prevented from rotating. Eventually the prongs will move from the slots, as the rod is drawn outwardly, however this occurrence will coincide with full engagement of the expansion element 36 with the wedge inserts 40.