Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~o-2892
PU~187
HOLLOW FIBER GLA5S ROOF BOLT
BACKGROUND OF THE INVENTION
Field of the Inven~ion
The present invention is directed to a hollow
5 roof bolt to be used in conjunction with pumpable
grouting resins to provide support in underground
constructions such as in the mining and tunneling
industry.
Descrip~ion of the Prior Art
In underground operations such as mining or
excavation, the unsupported rock formation is stabilized
and supported by various methods. In one method, a bore
hole is drilled into the rock formation and a me~al bolt
is inser~ed into the bore hole. The bolts are secured
15 into the bore hole by the engagement of an expansion
shell on the end of the bolt. A roof plate is retained
on the other end of the bolt that extends from the bore
hole such that the plate abuts the roo~. Rotating the
bolt expands the expansion shell to enga~e the rock wall
20 of the bore hole. The bolt is tensioned with the
resultant ef~ect o compressing the rock strata between
the expansion shell and roof plate, thereby reinforcing
the strata to resist ~orces that apply shear stresse~ to
the rock formation. Over a perlod of time in soft rock
25 strata, the expanded shell slips in the bore hole,
reducing tension and decrea~in~ the amount of roof
support provided by the bolt.
Another method of providing roo support i9 by
the use of grouted bolts. The bolts, which may be metal
30 or plastic are again inserted into bore holes; however,
instead of an expansion shell the bol~s are bonded into
the bore hoLe by the use of a two-component resin
composition, i.e., either a polyester resin and a
catalyst or a two-component polyurethane, which rnay be
contained in a cartridge. One or more of the cartridges
are positioned in the bore hole and are broken by the
insertion of a bolt into the bore hole. The bolt is
5 rotated to mix the components and provide a homog~neous
curable resin mixture. The cured resin firmly holds the
bolt in position in the bore hole and reinforces the
strata.
The quali~y of the cured resin can be reduced
10 by either under rotating the bolt in the bore hole
(which does not provide sufficient mixing and leads to a
heterogeneous as opposed to a homogeneous resin) or by
over rotating the bolt in the bore hole. In either
event, the holding strength of the bolt is reduced. In
15 addition, the bore hole could have an undetected void
into which the resin can penetrate leaving less resin in
the annulus between the bore hole and the bolt, also
reducing the holding strength of the bolt. Further, the
length of bolt which can be inserted into a bore hole
20 with resin cartridge adhesives is usually limited to
less than 10 feet. These difficulties may be overcome
by injecting the resin into the annular space between
the bore hole and the bolt or by the use of a hollow
bolt. Grouted bolts are disclosed in U.S. Patents
25 4,461,600; l~,289,427; 3 9 896,627; ~,526~l~92; 4,501,516;
4,4g7,595; 4,490,074; 4,430,025; ancl 3~797,254.
A third method or provLding roof support is
accomplished by combinin~ the use o an expans-Lon shell
with a grouted bolt as di.sclosed in U.S. Patents
30 4,140,429; 4,413,930; 4,419,805; and 4,000,623. ~ile
adequate roof support may be obtained by the use of such
bolts, these bolts are generally complicated in design
and thus too expensive for commercial use.
Mo-2892 - 2 -
~2~57
It is an object of the present lnven~lo~ to
provide an inexpensive, hollow roof bolt which may be
adhesively bonded to a bore hole by injecting a grouting
resin. In a preferred embodiment of the invention,
5 lightweight bolts made of plastic, preerably fiber-
glass, are used. Becau~e of their lightweight nature,
these bolts are easy to handle 9 ancl also pro~ide an
efficient means for reinforcing rock strata. It is also
an object of the present invention to provide an
10 efficient method of holding a roof plate against the
surface of the roof through the use of the hollow roof
bolt. These objects may be achieved by the hollow roof
bolt described in detail hereinafter and entails the use
of a collar which is fitted over one end oE said hollow
15 bolt and a hollow plug which is inserted in~o the end of
the bolt to expand the end against the inside of the
collar.
U.SO Patent 3,797,254 also discloses a method
of expanding a hollow tubular reinforcing member;
20 however, these bolts are generally made of metal and
rely upon resin cartridges to provide the adhe~ive.
East German Patent 146,362 and German Offenlegungs-
schrift 2,145,572 disclose methods o securing plastic
rods in ~ransformers either by expanding a hollow ~od or
25 by forming a rod with an expanded end.
SUMMARY OF TSE INVENTION
The pre~ent invention is directed to a hol.low
roof bolt based on
a) a hollow rod,
30 b) a collar which i~ internally tapered and fitted over
one end of the rod and
c) a hollow plug located in the end of the rod having
the collar, the plug being externally tapered such that
it forces the rod to expand and thereby conform to the
35 internal taper of the collar.
Mo-2892 ~ 3 -
r~?~
The present invention i9 additionally directed
to the rod in combination with a roof plate such that
the roof plate fits flush against the distant end o the
collar.
BRIEF DESCRIPTION OF THE DR~WINGS
Flgure 1 is a sectional view of a rock
formation representing an embodim~nt of the invention
showing the roof bolt in a bore ho].e.
Figure 2 is side view of the collar shown in
10 Figure 1.
Figure 3 is a bottom view of the collar shown
in Figure 1.
Figure 4 is a sectional view through line 4-4
of Figure 3.
DETAILED DESCR.IPTION OF THE INVENTION
In Figure 1 hollow fiberglass rod 2 ls shown
inserted into bore hole 1. An internally tapered collar
3 is positioned over the rod and held in place by an
externally tapered hollow plug 4. The collar holds a
20 roof plate 5 against the rock formation. Grout stop
bushing 6 i9 used to center the hollow rod in the bore
hole and to prevent grout from running out of the
annular space between the hollow rod and the sides of
the bore hole. A grout tube 7 extends through the roof
25 plate 5 and grout stop bushing 6 to provide a means o~
entry for the grout to fill the annular space between
the bore hole and the hollow fiberglass ro~. When grout
1~ injected throu~h the center portion of the hDllow
rod, air can escape through grout tube 7.
Figure 2 represents a side vi.ew of collar 3.
The distant end 8 of collar 3 preferably has a
hemispherical shape. Collar 3 also has ribs 9 to
provide support between the upper hemispherical end of
the collar and the bottom portion. The taper from ~he
Mo-2892 - 4 -
upper to the lower end of collar 3 could be ~olid;
however, the rib-type structure uses signiicantly less
material and still provides su~ficient strength and
support to the collar. Figure 3 represents a bottom
5 view of the collar 3 showing ribs 9 spaced equidistantly
around the collar and the hollow center portion 10.
Figure 4 represents a section view through line aa of
Figure 3. Figure 4 shows the internal taper o hollow
center position 10 of collar 3.
The components of the present invention include
a hollow rod of sufficient strength and length to
provide the desired support to the rock formation. The
hollow rod may be metal or plastic, preferably plastic
and most preferably fiberglass, and should have a
15 tensile strength of greater than 10,000, preferably
greater than 16,000 and most preferably greater than
30,000 lbs. Over one end of the hollow rod is fitted an
internally tapered collar. The collar is held in place
by a hollow externally tapered plug fi~ted into the end
20 of the rod. The hollow tapered plug forces the rod to
expand and conform to the internal taper of the collar.
The collar and hollow plug may also be made of either
metal or plastic, provided that it has sufficient
strength to hold the rock formation in place~ The
25 collar and hollow pLug are preferably made of plastic.
Though the hollow rod, collar and hollow plug may be
made of different materials and still be used ln
combination, it is preferred that if the rod is
nonmetallic~ then the colLar should also be nonmetallic.
The strength of the attached collar mag be
lncreased by using an adhesive on the internal taper.
To provide even more strength, it is preferred to insert
the hollow plug into the rod in order to expand the
hollow rod and then mold the collar directly onto the
35 expanded hollow rod.
Mo-2892 - 5 -
The roof plate may also be made o either metal
or plastic. Even though it i~ less critical for -the
roof plate to be made of the same material as the
collar, it is still preferred that the roof plate be
S made of the same material as the rod, plug and collar.
The shape and size of -the collar is designed to
hold a roof plate against the rock formation. The outer
surface of the distant end of the collar, i.e., the part
of the collar closest to the bore hole, may be of any
10 shape provided that it fits flush against the
corresponding part of the plate. The preferred convex
shape for the distant end of the collar and the
corresponding concave portion of ~he plate is hemi-
spherical. This shape allows the plate to rotat2 on the
15 collar so that it can fit firmly against the rock
formation. With other shapes for ~he collar and plate,
the plate cannot rotate on the collar and must remain at
a fixed angle, generally perpendicular, to the hollow
rod.
The plate has a grout tube passing through it
such that a pumpable grout can be injected into the
annular space between the 'bore hole and the hollow rod.
While it is possible to introduce the grout ei~her
through the hollow rod or through the grout tube and to
25 allow air to escape through the other opening, it is
preferred to introduce the grout into the a~mular space
between the hollow rod and bore hol.e rom t'he 'lowest
point. Accordingly, when the hollow rod is placed
upw~rdly and vertically lnto the bore hole as sho~n ln
30 Fl~ure 17 it ls preferred to introduce t'he grout through
the grout tube 50 that it enters the annular space from
the lowest point and not through the hollow tube where
the grout would enter the annu'lar space from the highest
point. To the contrary, when the hollow rod is inserted
Mo-2892 - 6 -
3~S7
lnto the bore hole vertical'ly and downwardly to provide
support, i.e., the opposite of Figure 1~ it is preferred
to introduce the grout through the hollow rod so that
the grout enters the annular spaee from the lowest
5 point.
The plate and grout tube may be made of any
material which has sufficient burst strength to
withstand the grout pumping pressure. However, high
strength thermoplastic materials are preferred,
10 especially when the hollow rod and collar are also made
of thermoplastic materials.
Grout stop bushing may be used on the hollow
rod for the purpose of preventing the pumpable grout
from running out the annular space between the bore hole
15 and the hollow rod. The grout stop bushing may be
located at any point along the length of the hollow rod,
but is generally located near the end of the rod which
is closest to the roof plate so that a sufficient
portion of the anntllar space is filled with grout to
20 provide consolidation of the rock strata. No particular
shape or material is required for the grout stop bushing
provided that it preforms its previously described
function. The grout stop bushin~ i5 afflxed firmly to
the hollow rod to prevent it from moving during instal
25 lation o~ the bolt into the bore hole and pump:lng of the
grout. The outsLde diameter of the bushing i'3 genera'Lly
larger than t'he diame~er of the hole in orcler to ass,ure
a good seal. For ex~mp'le, i~' the bore 'hole has a
diameter o 1-3/3 inches, t'he bushing diameter shouLd be
30 about 1-1/2 inches. A preferred bushing i~ made oE a
semi-hard rubber and has three (although more or less
may be present) 1/8 inch thick bore hole wipes spaced at
1/4 inch intervals. If grout stop bushing is used, it
is important that ~he grout tube extend through the
35 grout stop bushing.
Mo-2892 - 7 -
In order to install the hollow bolt, a bore
hole is initially drilled inko the rock formatlon to be
supported to the desired depth. The roof plat~ is then
pressed firmly against the formation surface and a hollow
bolt is inserted into the bore hole to such a depth that
the distant end of the collar contacts the plate. The
bolt and plate assembly is held in place by the grout
stop bushing. The pumpable grout is then introduced into
the annular space through the grout tube when the bolt is
lo inserted upwardly or through the hollow bol~ when the
bolt is inserted downwardly. Any air or other fluid is
forced from the bore hole through the remaining opening.
The grout is pumped in the bore hole until grout appears
from the other opening. There are several different
types of pumpable grouts including, but not limited to
cements and epoxies. The preferred grout is a low
viscosity, fast setting, high strength polyurethane
(StrataGee* grout available from Mobay~. It is known the
prior art to use hollow bolt lengths of greater than
about 1 foot, preferably about 1 to 20 ~eet and most
preferably about 5 to 15 feet in grouted installations.
As previously discussed, these rods must have sufficient
burst strength to withstand the grout pumping pressure.
The rods generally have an outside diameter o~ at leask
3/4 inch, preferably about 1 inch or greater and a hollow
cora (inside dlameter) o~ about 1/4 inch.
The prefexred use of thermoplastic, especially
fiberglass, hollow bolts offer several major advantages
over the use of hollow steel rods. The hollows bolts
weight about 1/4 as much as hollow steel bolts of
equivalent size, have a greater tensile strength and can
be fabricated at a substantially reduced cost. The
lighter weight of the hollow fiberglass bolt permits
Mo-2892 -8-
* Trademark
f 9-'~
d~ 7
easier handling and installation, results in reduced
transportation C08ts and allows for the use of ~ longer
bolt when required.
Although the invention has been described in
5 detail in the foregoing for the purpose o~ illustration,
it is to be understood that such detail is solely for
that purpose and that variations can be made therein by
those skilled in the art without departing rom the
spirit and scope of the invention except as it may be
10 limited by the claims.
Mo-2892 - 9 -
