US3521454A - Bearing pad and method of preparing - Google Patents

Description

July 21, 1970 v D. J. DODDS BEARING AND METHOD OF PREPARING Filed Oct. 17, 1968 INVENTOR. Donald J. Dodds Kolisch 0nd Hartwell ATTORNEYS United States Patent 3,521,454 BEARING PAD AND METHOD OF PREPARING Donald J. Dodds, Portland, 0reg., assiguor to Foundation Sciences, Inc., Portland, 0reg., a corporation of Oregon Filed Oct. 17, 1968, Ser. No. 768,307 Int. Cl. E21d 21 /00 US. Cl. 61-45 3 Claims ABSTRACT OF THE DISCLOSURE A rock bolt bearing pad encircling the rock bolt at the surface of a rock formation reinforced by the rock bolt. A method of preparing the bearing pad wherein the components of a hardenable plastic composition contained within a pliant envelope are mixed by working the exterior of the envelope while maintaining the integrity of the exterior of the envelope. The envelope may be shaped as an annulus circumscribing a central void region and be divided into separate compartments following one another circumferentially about the annulus with separate components of the hardenable plastic composition lodged within separate compartments prior to mixing. The envelope and its contents form a package which is transformed into the bearing pad on hardening of the material within the envelope. In a rock reinforcement, the pad encircles the rock bolt at the surface of the rock be ing reinforced, with one side of the pad following the contour of the rock surface.

This invention relates to the reinforcing or stabilizing of a rock formation, and more particularly to a bearing pad such as might be used in mounting the head of a rock bolt employed in reinforcing a rock formation. The invention also embraces a novel method of preparing the bearing pad, and a novel packaging of the components of the bearing pad prior to the preparation of the pad.

In mining, underground tunneling, and other types of excavation, frequently it is necessary to strengthen a rock structure which is inherently weak, or perhaps, weakened by the act of excavation. A practice followed in strengthening such a rock formation is to prepare a bore which extends into the rock formation, and by means of an elongated tension-transmitting member, such as a rock bolt or bar anchored within this bore, pull a retaining or anchoring plate against the surface of the rock formation, thus to shore it up. With such an anchoring or retaining plate, Whether used in the manner just specifically described or whether employed in other types of systems wherein it is made to bear upon the rock, it is important that the plate be firmly mounted on a solid formation if it is to perform its function properly.

Further explaining, when such an anchoring plate is employed to anchor the exposed outer end of a rock bolt, frequently the rock bolt is highly tensed to effect a compressive stressing of the rock. If the anchoring plate used in anchoring the exposed end of a rock bolt deflects or slips over a period of time, to the extent of a small fraction of an inch, all or substantially all of the tension in the rock bolt may be lost, with loss of loading of the plate. Deflection of the anchoring plate can result from bending of the plate between sharp protuberances in the rock formation supporting the plate, and slippage of the plate can result from the crushing of the sharp protuberances. Also, side slippage is a problem if the plate does not rest in a position extending normal to the axis of the rock bolt. Tension can be reestablished in the rock bolt by tightening the bolt at intervals, but this requires periodic checking and does not ensure optimum tension con ditions at all times.

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SUMMARY OF THE INVENTION An object of the invention is to provide a method of preparing a bearing pad such as might be used in the reinforcing or stabilizing of a rock formation with such functioning as an intermediary between a bearing plate which is brought against the formation by tightening of a nut on a rock bolt and the surface of the rock formation. A pliant envelope which circumscribes a central void region and is filled with a plastic filler composition is placed between and compressed between the surface of the rock formation and the bearing plate which is drawn against the pad. The rock bolt which has the bearing plate mounted on it passes through the central void region. With compressing of the envelope to the side of the pad which faces the rock formation is formed whereby it follows the contour of the formation and the side of the pad which faces the dying plate is formed to follow the contour of the bearing plate. On hardening the pad becomes a rigid unit providing support for the bearing plate.

Another object of the invention is to provide a novel type of rock formation reinforcement.

Yet a further object of the invention is to provide a novel form of package comprising a pliable envelope containing components of a hardenable plastic composition. Such package, in a preferred embodiment, is divided internally into multiple compartments separated from one another in a novel manner.

While certain aspects of the invention pertain to the production of pads of an annular shape, it is realized that other features of the invention apply to pads of other configurations, Where such are prepared utilizing a pliable envelope as the means for forming a hardenable plastic material contained within the envelope.

These and other objects and advantages are attained by the invention, and the same is described hereinbelow in conjunction with the accompanying drawings, where- 1n:

FIG. 1 is a section 1 view of a rock formation, showing a rock bolt passing through a bore in such rock formation, and an external anchoring plate and pad supporting the plate, as contemplated by one form of the invention;

FIG. 2 is a plan view illustrating a package utilized in preparing the pad of the invention; and

FIG. 3 is a cross-sectional view, taken generally along the line 33 in FIG. 2.

Describing initially a particular application of the bearing pad of the invention, illustrated in FIG. 1, in cross section, is a portion of a rock formation indicated at 8. Typically, an irregular surface, such as that shown at 10, forms the exterior of the rock formation. Depending upon the type of excavation work involved, the surface 10 may be substantially upright, as shown, or horizontal, or at substantially any angle between an upright and a horizontal position.

In reinforcing the rock formation, a bore 12 is prepared which extends inwardly into the rock formation from an entrance 13 adjacent surface 10. Such a bore may have any of widely differing lengths and diameters, depending upon the particular type of reinforcement be ing performed. Extending along the length of the bore, and with its inner end anchored in place as with a cementitious deposit 16, is an elongated rock bolt 14.

The rock bolt is tensed to produce a compressive stress ing of the rock formation through advancing a nut 20 by turning it on the fitted end 18 of the rock bolt. The nut bears against a washer also referred to as a retainer or anchoring plate 22 which has the rock bolt extending through the center thereof. interposed between the an choring plate and surface of the rock formation is a bearing pad, designated generally at 30 in FIG. 1.

Typically, the surface 10 of the rock formation has an irregular contour, with the region of the surface direct- 1y adjacent the entrance of the bore sometimes inclined from a plane extending normal to the axis of the rock bolt. As a consequence, a bearing pad 29 is provided which enables the anchoring plate to be seated in a position substantially normal to the axis of the rock bolt and against a solid member which will remain without deflecting in a region directly adjacent the bores entrance. The pad after final installation of the rock bolt, and as shown in FIG. 1, comprises a hard solid core 28 surrounded by a pliable envelope 30. In the form of the invention shown in FIG. 1, the pad has an annular shape, i.e., the bady of the pad circumscribes a central void or opening, and the rock bolt extends through this opening to the inner anchoring connection provided by cementitious mass 16.

As will be described in fuller detail, the mass within the pad prior to installation of the rock bolt anchoring plate comprises a hardenable plastic composition, which hardens during final installation to form the hard solid core described. During installation between surface 10 and the anchoring plate, with the plate drawn toward surface 10 and the contents of the envelope still plastic, the filled envelope may be made to assume a shape wherein the side that faces surface 10 conforms to this surface, as illustrated in FIG. 1, and the opposite side defines a fiat plane which is substantially normal to the axis of the rock bolt.

The package which is utilized in the preparation of the bearing pad is illustrated in more detail in FIGS. 2 and 3. Referring to these figures, in the form of the assembly shown it comprises expanses of a pliable film, shown at 30a and 30b, joined along inner and outer circumferential margins to form what might be thought of as a doughnut-shaped envelope. A seal is formed at 31a, 31b uniting the expanses at inner and outer margins. Ordinarily a plastic material is employed for the expanses mentioned, such plastic sheets being pliable and permitting working of the package after assembly. Exemplary of plastic films that might be employed are polyester, polyethylene or polypropylene films, or a laminated sheet comprising, for instance, a polyester film laminated to a polyethylene film.

The annular envelope described is filled with the components of a multiple component hardenable plastic composition. In this respect, the envelope may be divided into multiple internal compartments, each separate from another, preferably with the compartments following one another in a circumferential direction about the envelope. Separate ones of the components. are lodged within separate compartments. The components, when separate from each other, are stable and stay in a form which permits kneading or working of the package, i.e., stay in a plastic or moldable form. The envelope is constructed so that the compartments may be joined internally, without destroying the integrity of the envelope, the components then being mixable by kneading of the package. With mixing, a plastic composition is formed which cures or hardens with the passage of a short period of time.

In particular envelope shown, the compartments described are formed by pinch lines which extend radially in the envelope. Such pinch lines are formed by external, removable clips, such as those shown at 36. These clips 'each include a pair of opposed legs joined by a spring loop at one set of ends which functions to bias the legs tion, using filling ports 32 constructed to permit closing after filling of a compartment. Alternative procedures of filling the envelope may be employed, however. For instance, the package may be built up with final sealing of one or both margins of the envelope delayed until after placement of the components within the envelope.

As used herein, a plastic composition refers to any composition which is flowable to a degree when packaged within the pliable envelope, to enable working or kneading of the contents of the envelope through manipulation of the envelopes exterior. The components of the plastic composition by themselves are plastic in this sense, to permit mixing of the components on removal of the clips and joining of the internal compartments. Coming within this definition, therefore, are pastes, liquids and flowable masses of solid particles.

Illustrative of a plastic composition that might be employed are those disclosed in Bollmeier et al., US. 3,087,606, and McLean, US. 3,324,663. These patents disclose two component resin compositions which are mixable to produce a hardening composition. In McLean, a so-called resin paste is described as one component, and a so-called catalyst paste is described as the other component. The pastes when separate from each other are each storage stable, and when compounding by mixing, form a hardenable plastic composition that hardens at approximately room temperature over a period of a few hours to form a solid body. In this respect, it is preferred that plastic compositions be used as the filler for the envelope which product a hard core without the need of special environmental conditions, such as special temperature or pressure conditions, as this greatly simplifies the use of the package in the production of the pad as contemplated herein.

Describing now how the reinforcement of a rock formation might proceed, a package may be prepared as illustrated in FIGS. 2 and 3, comprised of an envelope divided by clips into two compartments, with one compartment having approximately three times the volume of the other compartment. The larger of the compartments may be filled with a resin paste of the type disclosed in the above-mentioned McLean patent, and the smaller compartment is filled with a catalyst paste as also described in such patent. The components when maintained sepa rate from each other are stable, i.e., they retain their plastic nature.

In anchoring the exposed end of a rock bolt, the clips described are removed by pulling them olf from the package. This removes the pinch lines in the package, to join the internal compartments whereby one enlarged compartment is formed. With working or kneading of the pliant walls of the package, a mixture of the components is produced, which mixture is pliable hardenable plastic composition, also referred to herein as a filler composition. The doughnut shape of the package promotes the mixing process by providing a continuous flow path extending in a circumferential direction.

Such envelope with the hardenable composition contained inside is then placed about rock bolt 14 with one side against the surface of the rock formation and with the washer or anchoring plate against the opposite side. Nut 20 is then tightened, slightly to tension the rock bolt, and to bring the washer up against one side of the package whereby the envelope and its contents is pressed against the surface of the rock formation. The surface of the rock formation forms a supporting surface for one side of the envelope, and the envelope wall along this one side follows the contour of this rock surface with slight pressure applied. The opposite wall of the envelope flattens to follow the contour of the inner face of the anchoring plate. With slight pressure applied, and to produce a balanced pressure condition, the anchoring plate will tend to assume a position normal to the axis of the rock bolt.

The hardenable plastic composition, which might be though of as a form of grout, is then allowed to harden.

Depending upon the specific temperature condition, this occurs in a period of from one to two hours. After such setting or harening, the nut is advanced on the threaded end of the rock bolt, to bring the bolt to its finally tensed condition. In the final reinforced state, the pad produced from the package forms a proper seat for the anchoring plate, which by being fitted to the surface of the rock formation adjacent the entrance of the bore is held from slipping sidewise at such bore entrance. Further, because of the conforming fit, there are minimal high and low pressure regions between the face of the rock and the pad, which prevents breaking off of portions of the rock formation after a lapse of time, and displacement of the anchoring plate.

With the invention, special preparation of the rock surface, as by chipping away rough regions, or attempts to adjust the plane of the surface to one of perpendicularity to the rock bolt axis, may be eliminated. The envelope functions as a form for the material hardening with it, eliminating the need to build up a form about the rock bolt. Wedges, etc., sometimes used to properly level the anchoring plate, may be dispensed with. The final reinforced condition produced is a stable one, eliminating the need to tighten the rock bolt to retense it after a period of time to take care of deflections in the anchoring plate.

Several modifications of the invention have been described, and it should be apparent that addition modifications are possible incorporating one or more of the novel procedural or structural aspects of the invention disclosed. Such modifications as would best conform the invention to any specific application would be apparent to one skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. A method of preparing a bearing pad functioning as an intermediary in the support of a bearing plate upon a supporting surface, the method comprising providing a pliant envelope which circumscribes a central void region and which contains within the envelope a filler composition which is plastic and hardena'ble after the lapse of time, placing the envelope between the supporting surface and the bearing plate, compressing the envelope between the bearing plate and supporting surface by forcing the bearing plate toward the supporting surface, such compressing of the envelope through forcing of the bearing plate being performed by tensing a member anchored to the bearing plate and passed through said central void region so as to draw the bearing plate against the supporting surface, and with compressing of the envelope and while maintaining the integrity of the exterior of the envelope forming the wall of the envelope which faces the supporting surface whereby it follows the contour of the supporting surface and also forming the Wall of the envelope which faces the bearing plate whereby it follows the contour of the bearing plate, the filler composition on hardening forming a rigid unit surrounded by the envelope.

2. The method of claim 1, wherein the envelope is annular in shape and the filler composition within the envelope is prepared by mixing components of the composition stored in separate compartments within such envelope through working of the exterior of the envelope and while maintaining the integrity of the exterior of the envelope.

3. The method of claim 2, wherein the separate compartments storing the components of the composition are distributed circumferentially about the annular envelope and are formed by external clips which squeeze the envelope, and mixing of the composition is performed after removing such clips to join the various compartments within the envelope.

References Cited UNITED STATES PATENTS 2,478,508 8/ 1949 Simpson -63 X 2,829,502 4/1958 Dempsey 61-45 2,666,354 1/1954 Din et al 81-1 2,682,152 6/1954 Bierer 61-45 3,108,442 lO/l963 Miller 61-63 X 3,222,076 12/ 1965 Hollingsworth 285-97 X 3,234,742 2/ 1966 Williams 61-45 3,257,072 6/1966 Reynolds 206-47 X 3,419,134 12/1968 Fitts 206-47 3,430,449 3/1969 Novotny et al. 85-63 X FOREIGN PATENTS 1,054,170 10/ 1953 France.

DENNIS L. TAYLOR, Primary Examiner US. Cl. X.R.

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