Friction rock stabilizer and sheathing means, in combination, and method of securing a friction rock stabilizer in an earth bore

Broadly, the structures of the invention comprises a friction rock stabilizer and a sheath therefor to isolate the stabilizer from the surface of an earth structure bore and its associated corrosion environment, and bonding between the engaging surfaces of the stabilizer and sheath. The sheath, of low-friction polyethylene (although other suitable material could be used), facilitates stabilizer insertion into the bore. Additionally, the polyethylene sheath is heat and pressure sensitive. Insertion of the stabilizer generates considerable frictional heat and pressure and, as a consequence, upon the stabilizer being fully inserted, the sheath fuses onto the exterior, interfacing surface of the stabilizer. Further, the sheath material extrudes from prominences and flows into crevices (a) in the surface of the bore against which it is forceably pressed, and (b) plastically deforms to insinuate itself into, around, and onto discontinuities in the interfacing surface of the stabilizer, lockingly to engage with the latter surface. Such fusing, extrusion and flow, and the aforesaid locking engagement inhibit disengagement of the stabilizer from the sheath, and the sheath from the bore, following insertion of the stabilizer into a sheath-lined bore. The method of the invention comprises preparing one of the aforesaid engaging surfaces with adhesive, or grit, etc., to secure the stabilizer, in the bore, firmly bonded to the sheath.

The invention pertains, generally, to friction rock stabilizers, such as 
are disclosed in U.S. Pat. No. Re 30,256, issued on Apr. 8, 1980, to James 
J. Scott (for "Friction Rock Stabilizers"). More particularly, it pertains 
to methods of securing friction rock stabilizers in earth bores, and to a 
combination friction rock stabilizer and corrosion isolating sheath 
therefor with means to inhibit separation of said stabilizer and sheath, 
or to means for bonding said stabilizer and sheath together. 
The invention comprises improvements for the "Friction Rock Stabilizer and 
a Method of Isolating the Same from a Bore Surface", of U.S. patent 
application Ser. No. 159,184, filed on June 13, 1980, by myself and 
co-inventor John A. Larson. As noted in the aforesaid patent application, 
there are many applications where it is necessary to protect the surface 
of a friction rock stabilizer from water, chemicals, and the like, which 
obtain in many mine environments, and which would cause the general 
degradation of the stabilizer in a relatively short period of time. Also, 
typically the surface of an earth structure bore is irregular and coarse 
and, as a consequence, frictionally resists entry therein by the 
stabilizer. By shielding or isolating the stabilizer from the bore 
surface, and presenting a smooth, low friction surface to the stabilizer, 
the aforesaid frictional resistance can be markedly reduced. 
Research and development efforts are being pursued to provide a 
corrosion-resistant friction rock stabilizer in which the stabilizer is 
inserted into a plastic sleeve which has been previously inserted in an 
earth structure bore. This practice has the benefit of accommodating a low 
thrust insertion. However, there is a need to bond the sleeve plastic to 
the metal stabilizer after insertion thus bringing the stabilizer 
anchorage up to acceptable levels. 
The aforesaid research and development efforts proceed from the teachings 
set out in the cited, co-pending patent application Ser. No. 159,184; 
6/13/1980). The instant invention concerns methods and structures 
inventively designed to meet the sleeve-to-stabilizer bonding. 
It is an object of this invention, then, to set forth, in combination, a 
friction rock stabilizer, for stabilizing an earth structure, and 
sheathing means therefor, wherein said stabilizer comprises an elongate 
element for resisting movement of an earth structure from within a bore 
formed, to receive said element therewithin, in the earth structure, and 
includes first means for exerting an outwardly-directed, radial, 
earth-stabilizing force against the surface of such an earth structure 
bore; said sheathing means has given surfacing, on opposite sides thereof, 
of given surface conformations; and said exterior surface of said element 
comprises second means for cooperating with said first means for altering 
at least one of said surface conformations, of said sheathing means, to 
cause said sheathing means lockingly to engage at least one of said bore 
and element surfaces. 
It is also an object of this invention to teach a method of securing a 
friction rock stabilizer in a closed-end earth structure bore, comprising 
the steps of providing plastic, sheath-material sheathing which has given 
surfacing, on opposite sides thereof, of given surface conformations; 
interposing a lining of such sheathing between the surface of at least a 
portion of the bore and the exterior surface of the stabilizer; treating 
the exterior surface of the stabilizer to cause such exterior surface to 
alter at least one of said surface conformations, to cause the sheathing 
means lockingly to engage at least one of the bore and stabilizer 
surfaces, upon the exterior surface of the stabilizer exerting an 
outwardly-directed, radial force against the lining and the bore; and 
manipulating the stabilizer to cause it to exert an outwardly-directed, 
radial force against the lining and the bore.

First embodiments of the invention comprise the use of adhesive systems to 
bond the friction rock stabilizer and its sheath together. Now, to be 
convenient for underground operations, an adhesive system must be 
factory-installed and the parts brought together some several months later 
at the mine site where the stabilizer boreholes are located. My invention 
provides a means of applying the adhesive in the factory and retaining it 
in position during shipping and handling as well as providing for 
spreading (and mixing) of the adhesive during stabilizer insertion. 
The basic concept of the novel adhesive system is to retain the adhesive in 
a position on the plastic sleeve or sheath (or alternatively on the metal 
stabilizer) in a containing system so that it is in the proper position at 
the time of insertion of the stabilizer into the earth bore. Insertion 
spreads (and mixes, if necessary) the adhesive by: (1) forcing rupture of 
the containers, (2) squeezing adhesive out of a wicking type retainer, or 
(3) cutting the containers with a specially designed cutting edge on the 
stabilizer. 
The containing system must be compatible with the storage requirements for 
the particular adhesives to be used. For instance, solvent-type adhesives 
must be in impervious containment, anaerobic adhesives must have access to 
oxygen, and two-component systems must be kept separated. Also, 
two-component systems require some degree of mixing during activation of 
the adhesive. 
FIG. 1 shows an impervious capsule system 10 suitable for retaining 
one-component adhesives. The capsules 12, for example, are made of a thin 
plastic film which is heat sealed. The capsules 12 are of short length but 
are shown as a continuous tape 14 which is glued to the plastic sheath 16. 
The system 10 is activated by the pressure of the inserted stabilizer 
which bursts the capsules. If an anaerobic is stored in the capsule, the 
later is partially filled with air, and is made of a material, such as 
polyethelene, which breathes oxygen to assist in preventing premature 
cure. 
FIG. 2 shows a similar capsule system 10a which employs a wicking type 
material 18 made into a continuous tape 14a which is glued to the plastic 
sheath (not shown). This system is tailored for single-component 
anaerobic-type adhesives and the capsules 12a are partially filled with 
air as well as being made of polyethelene to have access to oxygen. The 
system 10a is activated by the pressure of the inserted stabilizer which 
bursts the capsules. The glue bond of the stabilizer and sheath is made 
through the wicking material 18 as well as beyond it with excess adhesive. 
FIG. 3 is another system 10b configured for single-component anaerobic-type 
adhesives. It consists of a wicking material 18a comprising a thick porous 
paper. Open cell, sponge or other cloth-type materials, for example, could 
also be used. This is made into a tape-configuration and glued to the 
plastic sheath. The wicking material 18a is capable of absorbing more 
adhesive than it can retain under the pressure of stabilizer insertion. 
When the stabilizer is inserted it squeezes adhesive out of the wicking 
material which bonds the stabilizer to the plastic sheath. The two are 
also bonded through the wick material. This system also requires that the 
sheath be maintained as a closed container until ruptured during insertion 
of the stabilizer to prevent loss of the adhesive monomer. 
FIG. 4a shows an impervious capsule system 10d similar to that of FIG. 1 
but with two compartments 20 and 22 in each capsule 12b so that it handles 
a two-component adhesive. FIG. 4b shows an alternative construction. The 
capsules 12c are made up in a continuous tape system 10c which is glued to 
the plastic sheath. The construction is made of thin plastic film which is 
heat sealed. The system is activated by the pressure of the inserted 
stabilizer. This causes both compartments 20a and 22a (and 20 and 22) of 
the capsules 12c (and 12b) to burst. This, together with the sweeping 
motion of inserting the stabilizer both mixes and spreads the adhesive. 
FIG. 5 shows an alternate means of opening the capsules 12 . . . 12c. A 
specially-shaped cutting edge 24 is formed on the stabilizer 26 at the end 
of the taper 28 thereof. The cutting edge 24 is radially oriented and is 
configured so that it cuts the capsules 12 . . . 12c open but does not cut 
into the plastic sheath. In this manner, the adhesive is exposed and 
spread during insertion of the stabilizer 26. 
FIG. 6 depicts an alternative adhesive system 10e which also allows it to 
be factory-installed and the parts brought together some several months 
later in the mine. This concept consists of applying a solvent-activated 
adhesive to the surface of the stabilizer and sheath (if desired) in the 
factory, and letting it cure fully. The adhesive is then reactivated by 
solvent, at the mine, so that the parts can be slid together; the solvent 
quickly migrates into the cured adhesive and a bond is achieved. My 
invention comprises a means of achieving this reactivation of the adhesive 
using a device that avoids handling the solvent in the mine and permitting 
preparation of all components in the factory. 
The concept, as shown in FIG. 6, consists of an anular reservoir 30 filled 
with solvent and glued to the plastic sheath 16, and a wick 18b glued 
below the reservoir 30. A weakened diaphragm 32 exists in the reservoir 30 
on the face that attaches to the wick such that, when pressure is applied, 
the reservoir ruptures and fills the wick. The wick than acts as a wiper 
to reactive adhesive 34 which has been applied to the outside surface of 
the stabilizer 26a. The reservoir 30 is made of a thin plastic material 
and the wick 18b of cotton (although other suitable wicking could be 
used). 
FIGS. 7 through 9 depict alternative practices of the invention which 
provide mechanical means of enhancing the grip or anchorage of the 
stabilizer in the borehole, after insertion, by bonding thereof to the 
plastic sheath. 
The basic approach is to take advantage of the facts that: (1) plastic will 
flow under pressure loading, and (2) there is a time delay in the effect. 
When a plastic sheet is pressed against a rough surface, the plastic will 
be deformed or dispersed and will be extruded from prominences and flow 
into the crevices in the rough surface. This will greatly enhance the 
friction coefficient between the surfaces by providing a mechanical 
interlock. During testing of my instant invention another bonding 
mechanism, arising from the practice of my disclosure, came to light. The 
same pertains to the fusing of the sheath 16 to the stabilizer 26 due to 
the heat of friction. 
Inserting the stabilizer 26 into the plastic sheath 16, in rock, requires a 
considerable force. This force is applied through a given distance, 
typically 5 or 6 feet (i.e., the common length of a stabilizer). A force 
moved through a distance equates to work done. For example, if the force 
averages 3,500 lbs. times a distance of 5 feet, 17,500 ft-lbs of work will 
have been done. If this is done in 5 seconds (a typical installation time 
for a five-foot friction rock stabilizer), power is being expended at a 
rate of 6.4 HP or 4.7 KW. This power results in heat at the area of 
friction; i.e., at the interface of the sheath 16 and stabilizer 26. Since 
the heat cannot be dissipated fast enough, the temperature at this 
interface rises and the immediate surface of the plastic sheath 16 melts. 
(This probably results in some reduction in friction thereby easing 
insertion loads). When insertion of the stabilizer 26 has been completed, 
the heat rapidly dissipates and the plastic surface of the sheath 16 
solidifies again, but now it accomplishes a heat bond or fusing to the 
stabilizer 26. The net effect is an eased insertion and much higher loads 
to cause slip after insertion; i.e., easy in, hard out. In the test 
program, it was demonstrated that a common roof bolter, capable of 
exerting no more than 5,000 to 6,000 lbs. of thrust was able to insert 
stabilizers (such as stabilizer 26) into plastic sheaths in boreholes 
(without impact) that required up to 17,000 lbs. of pull-out force to 
cause slippage of the stabilizer after insertion. This is deemed to 
establish that the frictionally-induced fusing, and extrusion and flow of 
the plastic sheath, from prominences and into reliefs in the wall of the 
bore and the surface of the stabilizer, cause the anchorage force to be 
thrice the insertion force. 
FIG. 7 shows a roughened-surfaced stabilizer 36 which is to be inserted, 
with a high interference fit, into a plastic sheath 16 previously inserted 
in an earth borehole (not shown). Any means could be used to roughen the 
surface, such as grit blasting. Since a low-friction plastic 
(polyethylene) sheath 16 is used, the insertion loads are modest. However, 
the high compressive pressure on the plastic causes it to flow with time 
into the roughness in the surface of the stabilizer. Too, the heat of 
friction, occurring during stabilizer insertion, together with the 
aforesaid pressure, causes the plastic to fuse onto the stabilizer and the 
wall of the borehole. This greatly enhances the friction coefficient, and 
provides an adequate bond between the stabilizer 36 and sheath 16. 
FIG. 8 shows a similar concept in which the stabilizer 36a is coated with a 
powder plastics (frit) coating 38. This coating is applied in the factory 
where heat, good adhesives, cleanliness, etc. can affect a good bond. The 
coating can be made impervious to the passage or attack of mine waters. 
The stabilizer 36a is then inserted into the previously inserted plastic 
sheath, with a high interference fit. As low friction plastic 
(polyethelene) is used, the insertion loads should be modest, and the frit 
coating is not scraped off. After insertion of the stabilizer 36a, the 
high compressive pressure on, and the residual heat of friction, generated 
during stabilizer insertion, obtaining in the plastic forces a fusion of 
the plastic (polyethylene) surfaces and a flow into the surface roughness 
of the stabilizer 36a. Thus grip is enhanced by both mechanical interlock 
and an intermolecular fusion effect. 
The mechanical bonding practice of my invention can also be carried out by 
simply forming a knurled surface 40 on the stabilizer 36b, as shown in 
FIG. 9. Additionally, the surfacing of the stabilizers can be 
directionally-oriented to facilitate insertion thereof into the sheaths, 
and to inhibit withdrawal. FIGS. 10 and 11 illustrate embodiments thereof. 
The stabilizer 36c in FIG. 10 has a plurality of recesses 42 formed 
therein. Each of the recesses has a wall 44, which lies substantially 
normal to the exterior surface 46 of the stabilizer, and an inclined 
surface 48. The surfaces 48 rise and blend in, smoothly, with the surface 
46 of the stabilizer. Hence, the recesses 42 define something akin to 
saw-teeth which are ineffective in the insertion direction (shown by the 
arrow), but are mechanically effective in the opposite direction. The 
inner surface of the plastic sheath 16 insinuates itself into the recesses 
42 and "flows" onto the surfaces thereof to lock the sheath 16 and 
stabilizer 36c together. 
The stabilizer 36d, in FIG. 11, has an epoxy coating 50 which beds ends of 
a great multiplicity of filaments 52. The filaments 52 are short metal 
strands, and the pendant ends thereof and lie at an acute angle relative 
to the exterior surface of stabilizer 36d. Again, in the insertion/arrow 
direction of travel, the filaments 52 simply brush along the sheath 16. In 
the opposite direction of travel they penetrate into the sheath and lock 
the latter and stabilizer 36d together. 
While I have described my invention in connection with specific embodiments 
thereof, it is to be clearly understood that this is done only by way of 
example, and not as a limitation to the scope of my invention as set forth 
in the objects thereof and in the appended claims.