Patent Number: 055315453
Section: description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 mine roof strata 10 has a vertical borehole 11 which passes through mine roof surface 12. Disposed in the borehole is tubular member 13, the same having a plurality of external threads 14 as indicated. The interior bore 15 of the threaded tubular member has an interior chamfered shoulder area 16 which is conically shaped and which joins an enlarged counter bore area 17. Positioned within bore 15 is a cable length 18 comprised of a king wire 19 and a series of strands 20 helically wound thereabout. Of importance in the invention is the inclusion of one or more cylindrical members 21 and 22 which are pressed end-to-end over the king wire and about which the strands 20 are rewound. More will be said about this later. At this juncture it is important to note that the cable length 18 has an upper end 23 that is anchored by epoxy 23A (see FIG. 6) or otherwise into the upper reaches of borehole 11. The end of extremity 23 may include any one several types of structures, e.g. as common to the art, for aiding in the epoxy securement and anchoring of the cable length within the bore hole. Cable bolt 24 may be thought of as including the cable length 18 and the cylindrical members 21 and 22, while the cable bolt structure 25 may be considered as including cable bolt 24, plus tubular member 13 and torquing nut 26. Torquing nut 26 will include, of course, an interiorly threaded nut body 27 and a forward hemispherical, self-centering head portion 28. This allows for self-centering of the nut and associated structure relative to aperture 29 in the bearing plate or reaction plate 30, positioned about the bore hole and abutting the mine roof surface at 31. In FIG. 3A it is seen that cable length 18 is about to receive cylindrical member 22. The latter may take the form of a hardened roll pin having a surface hardness of the order of not less than that of the strands 20, minus 15%, of the cable length. In FIG. 3A cylindrical member 22 takes the form of a roll pin having a sidewall slot 33 and a long tapered end portion at 32. In FIG. 3B the makeup of the cable bolt comprehends temporarily unwinding the strands 20 so that the cylindrical elements 21 and 22 can be pressed on to the king wire 19. The leading, conically tapered edge 32 of member 22 aids in reducing the likelihood of cable failure. In any event, once the tubular cylindrical members are in place, being installed end-to-end, then the cable strands 20 are rewound so that the cable bolt achieves the structural integrity as seen in FIG. 3C. The greater the pressure bubble effect desired, the greater the over-all length to be selected, whether unitary or segmented, of the the cylindrical element(s) 21, 22. In installation the borehole is first generated and the cable bolt is thrust therein and spun by means of a tool gripping the lower end of cable length 18. An epoxy or other agent 23A (see FIG. 6) is employed for securing the upper end 23 within the upper reaches of the bore hole. The bearing plate 30, having aperture 29 is inserted over cable bolt 24 and externally threaded tubular member 13 freely passes through aperture 29, with torquing nut 26 being threaded thereon. For most installations it will be preferred that tubular member 13 will be pre-installed over the cable bolt 24. The interior counter bore area 17 is preferably dimensioned to receive the cable bolt 24, with the included cylindrical members 21 and 22 in a friction fit, for temporary holding purposes. In any event, and once the upper end of the cable bolt at 23 is securely anchored within the borehole, through upward thrusting and spinning of the cable bolt in a conventional manner, a tool will be employed to tighten nut 26 so as to supply to the cable length a tension preload of perhaps from 1 to 2 tons. In operation, the settling of the mine roof strata 10 above mine roof surface 31 will produce a dilation of such surface a downward direction, thereby causing the bearing plate 30 and also the nut 26 and tubular member 13 assembly likewise to move incrementally downwardly. This causes the enlargement portion 34, see FIG. 3C, as produced by the inclusion of cylindrical members 21 and 22, to advance from the press-fit area within the counterbore of the threaded tubular member upwardly into the primarily bore area. This operation acts to expand radially the metal tubular member 13 proximate the area of members 21 and 22. Such radial expansion is at least primarily within the elastic range of the material of the tubular member so that such action generates, by the tubular member 13, a radial, inward, elastic compression force, serving to enhance the frictional, elastically compressive holding power of the tubular member relative to the cable bolt. Further dilation of the mine roof surface will produce a further riding up, relatively speaking, of the enlargement portion of the cable bolt with respect to tubular member 13. Accordingly the pressure bubble that is produced advances upwardly, relatively speaking, as to cable bolt 24. Again, pressure bubble is defined as the frictional resistance generated through the coaction by and between the cable bolt, with it enlarged portion as previously described, and the elastically expanded material of tubular member 13. Such a friction generating bubble travels upwardly, relatively speaking, in accordance with the downward settling of mine roof strata. At this juncture it is important to note that cylindrical members 21 and 22, preferable comprising roll pins, will generally be case hardened and approach the surface hardness characteristics of tool steel. What is not wanted is any significant plastic deformation of members 21 and 22. Rather, these should preserve the outward integrity of the strands such that the strands 20, such that the latter are useful to urge outwardly the sidewall of the tubular member 13 to produce the elastic compressive forces as previously mentioned. Therefore, the surface hardness of the members should be not less than 15 percent the surface hardness of the strands 20. The structure in FIG. 2 is similar to that seen in FIG. 1 with the exception that this time, in lieu of the inclusions of the cylindrical members 21 and 22 one the king wire, a new cylindrical member 35 is employed which is pressed over the cable length in the manner seen in FIG. 2. Cylindrical member 35 is preferably case hardened and includes a sidewall slot 36 and also a tapered forward leading edge 37. For ease of installation, the cylindrical member 35, gripping the cable length, is lightly frictionally seated within counterbore area 17 such that the forward tapered edge or end 37 engages frusto-conically formed section 16 of the bore area of tubular member 13. Nut 26 is disposed in place as indicated and torqued for desired pre-load. The settling of mine roof strata will produce a downward movement of tubular member 13 relative to the cable bolt so that, relatively speaking, cylindrical member 35 as clamped on the cable travels upwardly into the bore area of tubular member 13. This advance passed the area 16 produces, again, a pressure bubble or elastic expansion of the tubular member 13 at that region which is proximate to cylindrical member 35. Whether the structure in FIG. 1 or FIG. 2 be used, it has been observed that resistant pressures of the order of 28 to 40 tons can be generated, thus producing a controlled settling of mine roof strata through tensioned integrity of the cable bolt installation prior to approaching the ultimate failure point of the cable. FIGS. 4A and 4B amplify upon the assembly of cylindrical member 35 and cable length 18. For fabricating cylindrical member 35, a threaded nipple can be supplied to provide gripping serrations 38. The nipple us turned down to proper, interference-fit size, and wall slot 36 is produced as well as forward tapered portion 38. The unit is then case hardened to a point approaching the characteristics of tool steel, i.e. by heating with a rosebut acetylene torch to 900 degrees F. and then quenching in a bath of oil, and made ready for installation on a selected cable length. The threads 38 serve as serrations to grip against the strands of the cable length, providing a non-slip junction, and which gripping action is enhanced through the pressure bubble effect above recited. For pre-load and adjustment purposes, it is very much desired that a threaded tubular member be used in conjunction with the torquing nut 26 as seen in FIGS. 1 and 2. It is possible, however, for the installation to be used as seen in FIG. 5, wherein tubular member 13A is now secured to bearing plate 30A by welding or otherwise, with the enlargement, see 35, being used with cable length 18 in the manner as previously described. Of course, a nut or other attachment means can be employed to secure the bearing plate 30A with respect to tubular member 13A. FIG. 6 illustrates the generation of the pressure bubble 34A relative to the enlargement 34 of the cable bolt. FIG. 7 illustrates the generation of a similar pressure bubble 34A relative to the cable bolt enlargement as occasioned by the inclusion of member 35, see FIG. 5. Inherent in the invention as shown and described is a method for controlling the dilation of a mine roof, as produced through settling of strata thereabove, comprising the steps of: (1) providing a borehole; PA1 (2) anchoring a cable bolt at its remote end within said bore hole; PA1 (3) providing an elongated, cylindrical enlargement of said cable bolt at its proximate end; PA1 (4) providing an elongated, exteriorly threaded metal tubular member of radially elastic expansion characteristics, said metal tubular member receiving said cable bolt at said cylindrical enlargement in a tube-expansion interference fit; PA1 (5) providing for said tubular member a reaction plate and also a torquing nut, threaded upon said tubular member and backing said reaction plate, PA1 (6) preloading said cable bolt through tightening said torquing nut against said reaction plate, and PA1 (7) creating a controlled, travel resistant pressure bubble as between said cable bolt and said tubular member, whereby to retard in a controlled resistive manner the descent of said tubular member relative to said cable bolt in response to dilation of said mine roof as occasioned through strata settling. While particular embodiments of the present invention have been shown and described it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the essential aspects of the invention and, therefore, the aim in the appended claims is to cover such changes and modifications as fall within the true spirit and scope of the invention.