Friction Rock Stabilizer Set, and a Method of Fixing a Friction Rock Stabilizer in an Earth Structure Bore

This invention pertains to friction rock stabilizers, and to methods of fixing them in earth structure bores, and in particular to a novel method of inserting and fixing such stabilizers in earth structure bores with minimal thrust forces, albeit yielding high anchor loads therefore.

U.S. Pat. Nos. 3,922,867, issued on Dec. 2, 1975, and 4,012,913, issued on Mar. 22, 1977, both to James J. Scott, and both for "Friction Rock Stabilizers", are exemplary of the stabilizers to which the invention pertains. Such stabilizers comprise hollow bodies having substantially uniform inside diameters; additionally, they have means, such as an axially-extending slot, to facilitate contraction thereof.

Friction rock stabilizers are not readily susceptible of use in coal mines because state-of-the-art rotary roof bolters lack sufficient thrust force to push the stabilizers into the required anchor load. Impacting hammers, and various other modifications to rotary roof bolters, are being developed to enable insertion of stabilizers into mine bores, but market exploitation of the stabilizers would be greatly facilitated if existing, unmodified roof bolters could be used for their insertion. In general, the maximum thrust force which can be gotten from a roof bolter in poor condition is about 5,000 to 6,000 pounds. A friction rock stabilizer, however, requires an average of 10,000 pounds of thrust for full insertion.

It is an object of this invention to set forth a method of stabilizer insertion which will yield high anchor loads with only about half as much insertion force as is required in prior art insertion methods.

It is particularly an object of this invention to teach a method of fixing an elongate friction rock stabilizer in an earth structure bore of a given, transverse dimension, comprising the steps of inserting an elongate friction rock stabilizer in an earth structure bore; and expanding the inserted stabilizer, into fast frictional engagement with the bore surface, by forcing an insert internally and lengthwise of the stabilizer.

Further objects of this invention, as well as the novel features thereof, will become more apparent by reference to the following description, taken in conjunction with the accompanying figures, in which:

FIG. 1 is an elevational view, in cross-section, of a portion of a friction rock stabilizer in an earth structure bore prior to being expanded by inserts, according to an embodiment of the invention;

FIG. 2 is a cross-sectional view taken along Section 2--2 of FIG. 1;

FIG. 3 is another elevational view, in cross-section, of a portion of a friction rock stabilizer in an earth structure bore prior to be expanded by an insert, according to an alternative embodiment of the invention;

FIGS. 4, 5, 6 and 7 are similar to FIG. 3, but show still further embodiments of the invention;

FIG. 8 is a perspective view of the insert used in the embodiment of FIG. 7;

FIG. 9 is a perspective view of the working end of a tool used for installing the FIG. 8 insert;

FIG. 10 is an elevational view, similar to those of FIGS. 3-7, of a further embodiment of the invention;

FIG. 11 is a plan or top view of the insert of the FIG. 10 embodiment; and

FIGS. 12 and 13 are cross-sectional views taken along sections 12--12 and 13--13, respectively, of FIG. 11.

As shown in FIG. 1, the novel method, in a first embodiment 10, comprises the use of an inexpensive, expendable insert to expand the hollow friction rock stabilizer 12 tightly against the wall of a drilled hole 14 in the mine roof. The stabilizer 12 has a substantially uniform inside diameter. However, in the practice of this method of fixing a friction rock stabilizer 12 in a bore, first, the stabilizer is formed with one or more inner, substantially annular lands 16 and 16a. It is fixed in place in the predrilled hole 14 in the mine roof. Next, oversized inserts 18 and 18a are forced into the stabilizer 12, into engagement with the lands, expanding the stabilizer 12 against the wall of the drill hole 14. The forced engagement of the inserts 18 and 18a with the lands 16 and 16a results in an expansion which is sufficient to cause the stabilizer 12 to hold fast against the wall. A blade-ended and flanged or shouldered push rod (not shown), which forces the inserts through the stabilizer 12, is extracted; it has only a slidingfit engagement with a rod-receiving aperture 19 formed in the inserts 18 and 18a. The apertures 19, of course, are provided to allow the leading end blade or tongue of the push rod to engage therewith, with the flange or shoulder of the rod engaging the under surface of the inserts. The lands 16 and 16a are welded in place before the stabilizer 12 has been formed into its tubular shape. Typically, only one land 16 or 16a and only one insert 18 or 18a will be sufficient to expand the stabilizer into adequate, gripping engagement with the hole 14. Especially is this so where the stabilizer is not of significant length, and has a free, outside diameter larger than the dimension of hole 14 and, as a consequence, has been pressed into the hole with a force of two and a half tons or so. Then, with one land 16, and one oversized insert 18 forced into the stabilizer--again with two and a half tons of force--the combination will result in a five ton anchorage for the stabilizer.

If the stabilizer 12 is of considerable length then such stabilizer should have at least two lands 16 and 16a and two inserts 18 and 18a therefore. Too, the relative dimensions of the latter have to be different. As shown in FIG. 1, land 16 has a fair thickness, and insert 18 is of moderate diameters. Land 16a, however, is quite thin, and insert 18a is of greater diameters. Thus, insert 18 is freely passed through land 16a to come into forced engagement with land 16, and insert 18a is properly dimensioned to engage land 16a. Insert 18, then, is first pressed into place, and insert 18a is installed next.

Inserts 18 and 18a are of tapered configuration, and the lands 16 and 16a are straight-sided. Now, as shown in FIG. 3, this may be reversed. In this latter embodiment, the land 16b is tapered, and the insert 18b is straight-sided.

As illustrated and described thus far, the method contemplates bringing inserts to the borehole installation for insertion into the stabilizer 12. Alternatively the stabilizers can be shipped to the mine site with the expanding inserts captive therewithin. Such an arrangement is possible with the embodiments shown in FIGS. 4 and 5.

In FIGS. 4 and 5, lands 16c and 16d have tapering surfaces 20 and 22 for frictionally engaging the respective inserts 18c and 18d, and reduced-thickness portions 24 and 26 in which to nest the inserts. Below land 16c, however, is a split annulus 28, welded to the inside of the stabilizer 12, which serves as a keeper for the insert 18c. Before shipment of the stabilizer 12 from the manufacturer, the insert 18c is forced past the annulus 28, securely to be retained (until it is addressed with a push rod into engagement with surface 20). Land 16d (FIG. 5) comprises its own keeper 18a, the latter being a prominent, lower portion contiguous with surface 26.

Possibly, in some earth environments subject to significant ground movement, the embodiments of FIGS. 1-5, which employ the inventive method, may be inadequate. If the insert and land surfaces thereof are too smooth, and ground planes shift, the inserts may slip downwardly and allow the stabilizer 12 to contract. In such circumstances, the embodiment of FIG. 6, or that of FIGS. 7 and 8 shall have to be employed.

In FIG. 6, the land 16e is formed with a plurality of successive, stepped ridges 29, and the insert 18e also has complementary ridges 29a, one or more of which, on insertion, lock with one or more of the ridges 29.

FIGS. 7-9 disclose the principal elements used in an alternative and preferred practice of the invention. Here, no lands are required the stabilizer 12a is like those set forth in priorly-cited U.S. Pat. No. 3,922,867. It comprises a hollow body having a substantially uniform inside diameter. An oversized, split insert 18f is used to engage the inside surface of the stabilizer 12a. Insert 18f is of a generally frustoconical shape, having a circumferential bearing surface 30 for engagement thereof by an insertion tool 32.

Stabilizer 12a is forced into a one and a half inch bore, with approximately a two and a half ton force, and thereafter the insert 18f, by means of tool 32, is forced into the bore-installed stabilizer 12a with a same approximate two and a half ton force.

As shown in FIG. 8, a preferred embodiment of the insert 18f, for the standard, commercially distributed stabilizers, is of tapered or frusto-conical configuration, having free, outermost dimensions of one and a quarter inch and one and forty-five hundreds inch, and a length of two inches. When pressed into a bore-installed stabilizer 12a, the larger outside diameter of the insert 18f is reduced, and the smaller outside diameter expands, to the bore-installed i.d. of the stabilizer: one and thirty-five hundreds of an inch. As with the inserts of FIGS. 1-6, this practice with insert 18f results in an average fiveton anchorage for the stabilizer 12a.

The invention, according to our teachings, requires no complicated mandrel withdrawing techniques, does not disturb the stabilizer 12 or 12a once it is in place, and requires only expendable inserts 18 and 18a through 18f which can be made inexpensively.

We are aware of a somewhat similar, prior art practice, notably the U. S. Pat. No. 3,349,567, issued to J. E. Munn, on Oct. 31, 1967, for a "Mine Roof Support and Method of Providing Same". However, our novel method is clearly distinguished over these teachings.

Patentee Munn sets forth the use of a metal tube; the latter is "slidably fitted into the hole" and, by a process of "pulsed magnetic metal forming", creates one, two, or more localized, expanded bulges in the tube. Whatever the merits of this teaching, it has an inherent disadvantage. The bulge (or bulges) create localized stresses in the rock adjacent thereto--as does a top anchor in a conventional roof bolt--and the tube metal, between the bulges, has no frictional, stabilizing engagement with the rock. The remarkable benefit of the friction rock stabilizer is its fast engagement with the rock substantially fully along the whole length thereof, and its total lack of local stress points. Applicants' invention improves over the Munn teaching, while retaining the inherent simplicity of the basic friction rock stabilizer, by the use of inserts which cause the tubular stabilizer to expand, radially, along the length thereof. No localized stresses arise from Applicants' method.

Conventionally, friction rock stabilizers receive a roof plate at the lower, exposed end thereof, to engage the face of the bored roof. It is an ancillary teaching of our invention to employ the stabilizer inserts as anchors for the roof plates. FIGS. 10--13 illustrate this latter practice.

As shown in FIGS. 10--13, a stabilizer 12, having an inner land 16 therein, confines therewithin a loose-fitting insert 18g. According to the foregoing disclosure, it is intended that insert 18g shall be forced downwardly into land 16 to cause radial expansion of the stabilizer. In order to secure a roof plate 34 in place, however, the "tool" which is used to forceably position the insert 18g is retained and used to fix the plate 34 fast against the face 36.

Insert 18g has an aperture 38 formed therein which comprises a first, through-going passage 40 of a width "A" which is greater than the width "A.sup.1 " of the head 42 of a T-headed, threaded rod 44. Transverse to passage 40 is formed an "A"-width recess 46 in which to freely nest the head 42 of rod 44. Following installation of the stabilizer 12, the rod 44 is passed, head-end first, through the passage 40, rotated ninety degrees of arc, and allowed to nest in the recess 46. The plate 34 is emplaced, and a nut 48 is threaded onto the rod end. Next, the nut 48 is torqued up tightly against the plate 34 which, resultantly, forces the insert 18g into the land 16, to expand the stabilizer 12, and fixes the plate 34 firmly against the face 36.

As will be evident from the foregoing, a friction rock stabilizer set, according to the invention, comprises a stabilizer 12 or 12a, having a given inside diameter, and at least one insert 18, 18a . . . 18g, having an outside diameter which is greater than the given diameter, for forced movement of the insert internally and lengthwise of the stabilizer to cause radial expansion of the latter.

While we have described our invention in connection with specific embodiments and methods of practice therewith, it is to be clearly understood that this is done only by way of example and not as a limitation to the scope of our invention as set forth on the objects thereof and in the appended claims.