Patent Number: 055315453
Section: summary

FIELD OF INVENTION The present invention relates to cable bolt structures, related components and method for use in underground mines, such being useful in achieving ground control as to mine roof strata disposed above a particular mine opening. DESCRIPTION OF PRIOR ART AND BRIEF HISTORY OF CABLE BOLT SUPPORTS Incorporated by way of reference herein is the inventors' prior filed patent application entitled: CABLE BOLT STRUCTURE AND RELATED COMPONENTS, application Ser. No. 08/332,266 filed 31 Oct. 1994. This application is presently on pending status. Also fully incorporated by way of reference are Seegmiller U.S. Pat. Nos. 5,015,125 and 5,215,411. Other patent literature which is tangentially related include Gillespie U.S. Pat. Nos. 5,230,589 and 5,259,703. All of the above patent literature, including additional literature recited in the inventors' pending patent application above referenced, include other references and teach in rather substantial detail the prior art, and problem situations addressed thereby. The patents of the co-inventor herein, Seegmiller U.S. Pat. Nos. 5,015,125 and 5,215,411, teach what the co-inventor describes as a pressure bubble technique. This is to say, a tubular member is positioned in a selected borehole of mine roof strata and is provided with a reaction plate or bearing plate that abuts the mine roof surface about the borehole. In both the prior and the present applications of the co-inventors herein, a take-up torquing nut is threaded upon the tubular member and directly abuts the bearing plate utilized. Cable bolt structure is disposed in the borehole and is anchored at its remote end within the upper reaches of the hole. In the present invention the cable bolt structure includes a cable length having a friction-bubble-producing enlargement at or near the proximate end thereof. The cable bolt of course is disposed through the tubular member and the enlargement is initially seated, preferably in a friction fit, for preinstallation purposes, in a counterbore area supplied the bore of the tubular member at its proximate end. In dynamic operation, such enlargement coacts in an interference fit with the primary bore of the tubular member so as to radially expand in its elastic range the tubular member at the section thereof directly contacting and/or proximate the enlargement. The takeup torquing nut is turned so as to provide an initial preload of perhaps one to two tons tension relative to the cable bolt. In active mode, as the mine strata settles and the mine roof surfaces dilates, the cross-sectional enlargement of the cable bolt, relatively speaking, progresses upwardly relative to the tubular member; or, looking at it from a reverse point of view, and what actually occurs, the descending tubular member experiences a relative movement, i. e. relative to the enlargement, so that a controlled resistance feature is present as between the cable bolt at its enlargement and the radially elastically expanded tubular member supplied. Particular attention is called to a primary feature in the present invention wherein the enlarged portion of the cable bolt finds its genesis in the provision of either a cylindrical gripping member disposed about and secured to the cable length of the cable bolt or, alternatively, one or more elongated cylindrical members such as roll pins which are situated on the king wire of the cable length interior of the cable strands. Whether roll pins or their equivalent are employed, or whether simply a circular gripping member is used, it is requisite that the surface hardness of these elements be at least of the order of the surface hardness of the cable strands. Thus, what is not wanted is any appreciable plastic deformation of the cylindrical members or roll pins. Any possible scarring by the cable strands of the roll pins or cylindrical member should be held to a minimum. Therefore, the surface hardness of the roll pins or their equivalence, or the cylindrical member, should be held to to a point not less than minus 15 percent of the surface hardness of the cable strands of the cable bolt. When such a condition exists, then the roll pins are fully functional in holding outwardly the cable strands so that these will frictionally engage and indeed radially elastically expand the tubular member proximate that portion thereof which the enlargement engages. It is this elastic expansion of the tubular member that produces the radial, elastic, contractive or compressive forces needed to generate heightened force normals for producing the resistance loading desired. Thus, in such an arrangement, a dynamic resistances offered by the invention achieves tensile loading of from perhaps 23 to even 40 tons. This is a substantial resistance, and one which is needed for appropriate mine roof ground control. Further, this resistance loading is dynamic in operation in that further dilation of the mine roof will maintain or perhaps even increase the resistance loading of the cable bolt. None of the prior art as known to the applicants teach the concept of producing a circumferential, essentially cylindrical sectional enlargement of a cable bolt wherein there is essentially no plastic deformation experienced as to elements of the cable bolt wherein the requisite radial elastic expansion of the tubular member is nullified. BRIEF DESCRIPTION OF THE PRESENT INVENTION In the present invention, a cable bolt installation is provided a selected mine roof borehole produced in mine roof strata. A cable bolt structure is provided a cable length having a proximate end and also a remote end constructed for anchoring within the essentially upper reaches of the borehole. Epoxy anchoring, point anchors, etc., provide the essential end-anchoring of the cable length. Proximate the proximate end of the cable length is structure providing a circumferential enlargement as contributed by one or more cylindrical elements. Such elements are disposed either over the king wire and interior of the cable strands, or over the cable length proper. An elongated tubular member is disposed over the cable and is provided with a reaction plate, either secured to or slipped over the end of the cable bolt. The tubular member is preferably exteriorly threaded, and a torquing nut is threaded thereon and abuts the reaction plate, the latter being designed to thrust against the mine roof surface surrounding the applicable borehole. A tension pre-load, of the cable bolt, of perhaps 1-2 tons is produced by torquing the nut against the reaction plate. The interior bore of the tubular member receives the cable bolt and reacts with its circumferential enlargement, operating in essentially the elastic range of the tubular member, in offering a controlled resistance to tubular member travel relative to said cable bolt. To facilitate assembly, it is desire that there be a proximate counterbore or bore enlargement, relative to the proximate end of the tubular member, and that its junction with the bore proper be a conically tapered portion. It is preferred that, initially, the enlarged portion of the cable bolt be in friction-fit relationship relative to the enlarged bore portion; subsequently, the nut is tightened for an initial desired preload. As the mine roof strata tends to settle, the mine roof surface dilates so as to urge the tubular member downwardly. The latter's coaction with the enlargement of the cable bolt produces a circumferential, at least partially elastic enlargement of the tubular member at that portion thereof which is transversely proximate such enlargement. This creates a moving pressure bubble, as between the tubular member and the enlargement, for increasing travel constraint of the enlargement area, thereby offering resistance to mine roof strata settling. As to the circumferential enlargement of the cable bolt, this is produced either through the inclusion of one or more cylindrical members, disposed on the king wire of the cable length, or an internally serrated cylindrical member position upon the cable length and constructed to grip the cable length in an increasing manner as the pressure bubble is produced. The method inherent in the invention, broadly stated, is to supply cable bolt anchoring structure in a mine roof, wherein dilation of the roof, as produced through settling of roof strata, is constrained through controlled descent as is regulated through the generation of a pressure bubble, i.e. by the radial elastic pressure, exerted circumferentially about a cylindrically enlarged portion of the cable bolt of the structure, by a tubular member expanded elastically thereabout and secured relative to a mine roof reaction plate, as by torquing nut structure or otherwise. OBJECTS Accordingly, the principal object of the present invention is to provide new and improved cable bolt structure and related components. A further object of the invention is to provide a cable bolt installation having a cable bolt constructed in such manner that the same has an enlargement capable of producing an elastic radial expansion within a tubular member employed, whereby to rely upon the radial compression of such tubular member against the periphery of the cable bolt enlargement to produce a dynamic-control resistance relative to relative motion between the cable bolt and the tubular member employed. A further object is to provide an improved cable bolt structure wherein the cable length constituting a principal portion of the structure includes a king wire, multiple strands wrapped about said king wire, and one or more hardened cylindrical elements disposed along said king wire for expanding outwardly the strands immediately adjacent the cylinders, thereby permitting said strands to coact in interference fit relationship with a tubular member so as to radially expand the tubular member in its elastic range, this for producing the compressive forces needed to supply the dynamic frictional resistance characteristic desired relative to the cable bolt and its tubular member. An additional object is to provide a cable bolt member having an enlargement taking the form of a cylindrical member that grips the peripheral strands of the bolt length, a side wall of the cylindrical member being slit to provide for structural circumferential compression without chancing plastic deformation of such cylindrical member. A further object is to provide a method for achieving ground control in mine roof strata, this by supplying a dynamic resistance characteristic which in effect is spring-loaded by virtue of the elastic expansion of a supplied tubular member relative to the enlargement of the cable bolt with which the later cooperates.