U.S. patent number 3,877,235 [Application Number 05/419,644] was granted by the patent office on 1975-04-15 for anchor bolt assembly and utilization.
This patent grant is currently assigned to West Virginia Bolt Inc.. Invention is credited to David H. Hill.
United States Patent |
3,877,235 |
Hill |
April 15, 1975 |
Anchor bolt assembly and utilization
Abstract
A pull-up bolting assembly is constructed to be inserted endwise
and rotatably advanced as a unit within a bore hole of a rock-like
roof or other structure, with the forward end of the assembly being
employed to fracture an in-placed, adhesive resin material
containing capsule, and to mix the adhesive material and force it
about a hollow pipelike anchor member of the assembly and along the
spacing between it and the bore hole. After the adhesive material
has set or hardened about the hollow anchor member to non-rotatably
fix it in position within a back end portion of the bore hole, a
stop means is sheared by a bolt member of the assembly which is
then relatively rotatably advanced within a resin-clear, front
portion of the bore hole into and along the hollow anchor member
until a bearing plate of the assembly is tension-held by the bolt
against an outer face of the rock-like structure.
Inventors: |
Hill; David H. (Clarksburg,
WV) |
Assignee: |
West Virginia Bolt Inc.
(Clarksburg, WV)
|
Family
ID: |
23663116 |
Appl.
No.: |
05/419,644 |
Filed: |
November 28, 1973 |
Current U.S.
Class: |
405/259.6;
405/259.2; 52/698 |
Current CPC
Class: |
F16B
13/146 (20130101); E21D 20/025 (20130101); F16B
13/144 (20130101) |
Current International
Class: |
E21D
20/02 (20060101); E21D 20/00 (20060101); F16B
13/14 (20060101); F16B 13/00 (20060101); F21d
020/02 () |
Field of
Search: |
;61/63,45B ;52/698,704
;85/63,75 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,268,624 |
|
Jun 1961 |
|
FR |
|
955,678 |
|
Jan 1957 |
|
DT |
|
Primary Examiner: Taylor; Dennis L.
Attorney, Agent or Firm: Parmelee, Miller, Welsh &
Kratz
Claims
I claim:
1. A roof bolting assembly for mounting in position within a bore
hole of a mine roof that is to be strengthened which comprises, a
hollow pipe anchor member of a shorter length than the depth of the
bore hole, a destructible capsule that contains quick-setting
adhesive resin and catalyst-hardener resin materials for insertion
into a back end of the bore hole, a headed bolt having a threaded
stem and an associated wide-face bearing plate, front and back
closure walls at opposite ends of said anchor member, a threaded
nut secured to a front end of said anchor member to rotatably
receive a back end of said threaded stem therein, said bolt being
initially limited in its positioning within said nut by
endwise-abutment of the back end of said stem against said front
closure wall, said anchor member and said bolt as assembled in the
defined manner being adapted to be endwise-inserted and rotatably
advanced within the hole until said back closure wall engages and
fractures said capsule and mixes and distributes the resin material
content thereof within the bore hole from its back end and
forwardly along said anchor member, sealing means carried by said
anchor member for preventing the mixed resin material from
advancing along the bore hole beyond said front closure wall, said
mixed resin material being adapted to quickly set within the bore
hole and to thereby non-rotatably secure said anchor member
therein, and said stem of said bolt being thereafter adapted to be
turned within said nut to fracture and penetrate said front closure
wall and advance relative to and within said anchor member until
said bolt is drawn-up and tensioned to hold said bearing plate in
tight engagement with the front face of the roof about the bore
hole therein.
2. A roof bolting assembly as defined in claim 1 wherein said back
and front closure wall are separate pieces that are welded to the
front and back ends of said anchor member, and said sealing means
is a ring-like gasket positioned about said anchor member adjacent
to said front closure wall.
3. A roof bolting assembly as defined in claim 1 wherein, said
front closure wall is a relatively thin piece of metal that is
secured within the front end of said anchor pipe member and that is
easily fractured by a backward advance of said bolt within said nut
when said anchor member has been secured by the setting of the
resin material thereabout within the bore hole.
4. A mine roof bolting assembly as defined in claim 1 wherein said
back closure wall has at least one backwardly projecting portion
for facilitating fracturing said capsule and the mixing of its
resin material content.
5. A mine roof bolting assembly as defined in claim 4 wherein said
backwardly projecting portion is a chisel-like edge.
6. A mine roof bolting assembly as defined in claim 1 wherein said
back closure wall has a spaced-apart pair of upset projections
adjacent its outer periphery that substantially correspond in width
to the wall thickness of said anchor member.
7. A roof bolting assembly as defined in claim 1 wherein, said
front closure wall is a thin metal disc having a peripheral flange
portion projecting beyond the outer periphery of said anchor member
to provide a seating shoulder for said sealing means, and said
sealing means is a ring-like gasket encircling the outer wall of
said anchor member and resting in abutment with said flange
portion.
8. A bolting assembly for mounting in position within a bore hole
extending inwardly from the face of a rock-like structure such as a
mine roof and that is adapted to be secured in position within the
bore hole by an adhesive material that has been placed within the
bore hole which comprises, a cavity defining longitudinal extending
metal anchor member of shorter length than the depth of the bore
hole and adapted to be introduced into the bore hole and pressed
into the adhesive material and to be thereafter non-rotatably
secured in position therein by a hardening of the adhesive material
thereabout, a bolt having a threaded stem and an associated
washerlike bearing plate that is adapted to rest against the face
of front part of the structure to close-off the bore hole therein,
a threaded nut centrally secured over the cavity to the front end
of said anchor member and adapted to rotatably receive a back end
of the threaded stem of said bolt therein, stop means cooperating
with said nut for limiting the amount of insertion of the threaded
stem therewithin until said anchor member has been secured in
position within the bore hole by the adhesive material, said stop
means being adapted to be thereafter sheared by a rotational
advance of said bolt within said nut into the cavity, so that said
bolt can be fully advanced into tension-holding engagement with the
face of the structure through the agency of said bearing plate.
9. A bolting assembly as defined in claim 8 wherein said stop means
is an end closure disc secured in position between a front end of
said anchor member and a back end of said nut.
10. A bolting assembly as defined in claim 9 wherein, said closure
disc is a metal member of relatively thin wall construction, said
closure disc has a flange portion extending radially outwardly
beyond the diameter of said anchor member, and a gasket is
positioned on said pipe member against said flange portion for
engaging the bore hole and restricting outward flow of the adhesive
material to the length of said anchor member.
11. A roof bolting assembly as defined in claim 8 wherein, a
ring-like gasket is carried by a front end portion of said anchor
member for sealing-off the joint between the bore hole and said
member during setting of the adhesive material within the bore
hole, the outer surface of said anchor member is roughened to
facilitate adherence of the adhesive material thereto, and said
anchor member has a usual length from end to end of about 6 to 8
inches and has an outer diameter of about 1 to 13/8 inches.
12. A roof bolting assembly as defined in claim 8 wherein, said nut
is directly secured on a front end portion of said anchor member,
said stop means is a closure wall secured over a back end of said
nut, said nut has an outer periphery that extends radially beyond
the outer periphery of said anchor member, and a ring-like gasket
is carried on a front end portion of said anchor member in
forwardly limited abutment with the outer periphery of said
nut.
13. A method of reinforcing a mine roof having a rock-like
construction which comprises, boring an elongated hole into the
roof from an outer face thereof; providing a bolting assembly of a
pipe-like hollow anchor member having a cross-extending back end
wall and a fracturable closed-off front end wall portion, having a
nut secured to the front end wall portion and projecting forwardly
therefrom and having a headed bolt carrying a bearing plate and
with its threaded end mounted within the nut for endwise abutment
with the front end wall; first inserting a quick-setting resin
adhesive material contained within a thin skin resin capsule into
the inner end of the bore hole, inserting the bolting assembly
endwise as non-rotatably unit into the bore hole with the back end
wall of the pipe member in engagement with the capsule, rotating
the bolting assembly and employing the back end of the anchor
member to rupture the skin of the capsule and mix its resin
material content, flowing the mixed resin material about and
between the outer periphery of the anchor member and the inner
periphery of the bore hole and restricting its forward flow to
substantially the length of the anchor member during the rotative
advance of the bolting assembly, hardening the mixed resin material
about the anchor member to nonrotatably secure it within the bore
hole, rotatably advancing the bolt by turning it with respect to
the anchor member within the nut and fracturing the front end wall
portion, and then advancing the bolt within the anchor member and
drawing the bearing plate into tight abutment against the outer
face of the roof over the bore hole by tightening the bolt under
tension within the nut.
14. A method as defined in claim 13 wherein an annular width of
spacing within a range of about one-sixteenth to one/eighth of an
inch is maintained between the inner diameter of the bore hole and
the outer diameter of the anchor member within which the resin
material is hardened.
15. Am improved anchor bolting assembly for mounting in position
within a hole extending from a face of and into a support structure
and that is adapted to be secured in position within the hole by an
adhesive material placed therein which comprises, a longitudinally
extending anchor member adapted to be introduced into the hole and
having a back end portion for movement into the adhesive material
therein, said anchor member being adapted to be thereafter secured
in position by hardening of the adhesive material thereabout, a
headed bolt having a threaded stem and carrying a bearing plate
member thereon that is adapted to rest against a face of the front
part of the structure to close-off the hole therein, threaded
nut-like means secured on a front end of said anchor member and
adapted to receive a back end of said stem therein, means carried
by the front end of said anchor member to initially limit the
advance of said stem within said nut-like means when said anchor
member is being inserted into the hole and to thereafter fracture
under rotational advance of an end portion of said stem within said
nut-like means and with respect to said anchor member when said
anchor member has been secured in position within the hole by the
adhesive material, so that said bolt can be advanced into holding
engagement with the face of the support structure through the
agency of said bearing plate member.
16. An improved anchor bolting assembly as defined in claim 15
wherein flange means is positioned about a forward end portion of
said anchor member and extends radially outwardly beyond the outer
periphery of said anchor member.
17. An improved anchor bolting assembly as defined in claim 16
wherein a ring-like gasket is carried on the front end portion of
said anchor member in forwardly limited abutment with said
flange.
18. An improved anchor bolting assembly for mounting in position
within a hole extending from a front face of and into a support
structure and that is adapted to be secured within the hole by an
adhesive material carried within a destructible capsule that has
been placed therein which comprises, a longitudinally extending
pipe-like anchor member having means closing-off its back end, a
headed bolt having a threaded stem and carrying a bearing plate
thereon, threaded nut-like means carried on a front end portion of
said anchor member and adapted to rotatably receive a forward end
of said stem therein, stop means carried by the front end portion
of said anchor member to initially limit turning advance of said
stem within said nut-like means and with respect to said anchor
member when said anchor member is being inserted within the hole,
said closing-off means being adapted to move into pressure
engagement with the capsule to fracture it and force the adhesive
material along the outer side of the length of said anchor member
when said anchor member is introduced into the hole by said
threaded stem, said anchor member being adapted to be secured in
position within the hole by the adhesive material, and said stop
means being adapted to thereafter be displaced under relative
rotational backward advancement of said stem within said nut-like
means whereby said bearing plate may be moved into holding
engagement with the front face of the support structure.
19. An improved anchor bolting assembly as defined in claim 18
wherein means is carried by the front end portion of said anchor
member for confining flow of the adhesive material to substantially
the length of said anchor member.
20. An improved anchor bolting assembly as defined in claim 19
wherein said closing-off means has means for facilitating
penetration of the capsule.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to a new and improved pull-up bolting
assembly which is particularly designed for use in strengthening
mine roofs and also, to a bolting assembly that is adapted to
effectively utilize a minimized amount of quick setting adhesive,
grout or cement within a bore hole that extends from a face of a
rock-like structure. A phase of the invention deals with a bolting
assembly having means for enabling it to be rotatably endwise
introduced into a bore hole as a unit and, after a hollow anchor
member of the assembly has been secured therein by an adhesive
material, for thereafter utilizing a bolt element of the assembly
to finalize its installation as a tensioned unit.
2. Description of the Prior Art
Over the years, two approaches have been made in providing
so-called anchor bolts, such as may be used for strengthening roofs
in a coal mine, a subway tunnel, etc. An older type of construction
employs parts that can be expanded on insertion within a drill or
bore hole to provide a mechanical type of expansion gripping
action, to thus permit a bolt or screw to be tightened-down against
a face of the rock structure. It is important to provide a bolting
assembly that will enable a tension pull-up or tightening-down of a
bolt and bearing plate assembly under present day Bureau of Mines
standards. The Bureau of Mines requires that such a unit be capable
of assuring that the installed bolt tension be within a range of 6
to 8,000 pounds.
A second and more recent type of assembly makes use of adhesive or
grouting material within and substantially along a drill or bore
hole for securing a rod or bolt in place; if a pull-up tensioning
is desired, the outer end of the rod or bolt is threaded and
provided with a nut and face plate washer. The nut may be
tightened-down to, in effect, pull-up the plate against the front
face of the structure.
The mechanical type has not been too satisfactory in view of the
fact that it requires a relatively strong or more stable type of
stratum and many different types of formations are encountered,
such as (1) mudstone or siltstone, (2) limestone or massive
sandstone, and (3) laminated sandstone or shales. Where adhesive
materials have been used for bolt anchorage, bonding strengths have
ranged from 1,200 lbs/ linear inch (11/4 inch hole diameter) for
(1) above, to 4,000 lbs/inch for (2) and 2,000 lbs/inch for (3).
However, difficulty has been encountered in endeavoring to provide
a better type that will have a maximum tensile strength in its
utilization and without excessive cost. The second or adhesive type
has the advantage that the adhesive may be employed to strengthen
the particular rock formation as well as to secure the bolt in
position therein. However, an assembly of the latter type has been
rather expensive and requires considerable amount of adhesive in
that the idea has heretofore been to substantially fill the hole
about the full length of the rod or bolt member, as positioned to
extend substantially along the full length of the drill hole. The
drill hole, depending on the type of rock formation or stratum,
usually has a depth of about 2 to 5 feet, but in some cases has
gone to a depth of about 12 feet.
There has been a need for an improved type of bolting assembly
which will make possible a maximized amount of face compression and
draw-up tension strength in its installation, and, at the same
time, which will be relatively inexpensive from the standpoint of
time and materials. As to the cost of installation, it is important
to minimize the time required for the setting or hardening of the
adhesive material within the drill hole, in order that the bolt
tensioning portion of the operation may be quickly accomplished to
complete the installation. The present invention makes possible the
employment of an assembly of the second type that can be provided
and installed at a relatively low cost, with a maximized economy as
to the adhesive, and that will have an essential strength in
installation.
SUMMARY OF THE INVENTION
It has thus been an object of the present invention to devise a new
and improved type of pull-up bolting assembly that may be used for
mine roof and other installations wherein a strong and stable
structure may be attained.
Another object of the invention has been to evaluate the factors
involved and devise a new approach to the fixing of a bolting
assembly within a rock-like structure.
A further object has been to devise new procedure in roof
strengthening and in rock-like formation securing which will enable
a material saving of cost.
A still further object has been to devise a bolting assembly which
will minimize quantity requirements for an adhesive material, will
enable the use of the adhesive material in such a manner as to
minimize the time element in effecting its curing, setting or
hardening, and will enable an effective relative movement between
parts of the assembly when an inner part has been secured in
position by the adhesive and, at the same time, will enable a
forwardly advancing rotation of the assembly initially as a unit
during its insertion into the bore hole of a rock-like
structure.
These and other objects of the invention will appear to those
skilled in the art from the illustrated embodiments and the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 is a vertical section in elevation showing the construction
of a bolting hole assembly constructed in accordance with the
invention, and also showing an initial step in its utilization. In
this view, an enclosed sealed-off capsule containing a main body of
adhesive resin material and a segregated content of a catalyst,
hardening or curing resin material, both in liquid or somewhat
viscous form, has been fully inserted into a drill hole; a bolting
assembly of the invention has been thereafter inserted into the
hole and with its back end in engagement with a forward end of the
adhesive capsule, preliminarily to fracturing the capsule for
releasing and mixing the materials therein.
FIG. 2 is a view on the scale of and similar to FIG. 1, but showing
a second step in a utilization of the assembly of the invention in
which a hollow, pipe-like, anchor member has been rotatably
advanced within the hole by a unitized, rotative endwise advance of
the bolting assembly, with the hollow member being employed to not
only fracture the adhesive capsule but to mix its contents and
force them as in a mixed condition about and along the full extent
of such member.
FIG. 3 is a view similar to and on the scale of FIGS. 1 and 2,
illustrating a third step of the operation which is effected after
the adhesive material has set or hardened to secure the hollow
anchor member in a non-rotatable fixed position within the bore
hole, and a headed bolt is advanced relative to the fixed anchor
member by employing an end of its threaded stem to break-through or
penetrate a front end wall or closure disc of the hollow anchor
member. Thereafter, the bolt is screw-advanced until its bearing
plate has been pulled-up into tight abutment with the face of the
rock structure and into a covering relation with respect to the
hole therein.
FIG. 4 is a slightly enlarged fragmental side perspective view
showing details of the construction of a back end wall of the
hollow member of the construction which serves as a cutting and
mixing means for the adhesive material.
FIG. 5 is a similar view on the scale of FIG. 4, illustrating a
modified type of back end wall having a chisel edge and which may
be in the form of a plug-like element or a cap.
And, FIG. 6 is a fragmental side perspective view on the scale of
FIGS. 4 and 5 illustrating a preferred simplified construction of
the front end of the hollow member.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In carrying out the invention, an adhesive resin capsule, cartridge
or sausage 30 is shown, since a quick setting type of resin
material can be very effectively utilized. It has been discovered
that, contrary to previous ideas, it is not necessary to distribute
or provide an adhesive material of a quantity sufficient to
substantially fully fill the depth extent of the bore or drill hole
and about the bolt assembly employed therein. In accordance with
the present invention, the length of adhesive material is
proportioned to an amount sufficient to, as shown in FIG. 2, fill
in the spacing between the innermost end of the hole and a back end
of and fully along the extent of a hollow, pipe or shell anchor
member 16. The member 16 may be an inexpensive piece of hollow
material, such as a length of ordinary steel pipe and is preferably
provided with a roughened or cross-hatched outer surface that may
be rolled thereon to assure a maximum adherence between it and the
adhesive material employed. However, it has been determined that
the bond between the resin matrix and bore hole surface is more
important than the bond between the resin and the hollow anchoring
member.
In evaluating the factors involved in providing an installation
that will have sufficient strength, both from the standpoint of
tension and compression, it was determined that as little as a 5
inch length of an ordinary steel pipe member of about 1 inch in
outer diameter, utilized in the manner shown in FIG. 2, within a
bore hole 11 of about 11/4 inches in diameter, will provide a
holding strength of at least about 22,000 lbs. in a limestone or
massive sandstone structure. The amount of adhesive resin material
may be minimized for each type of stratum or strata structure, and
the time required in curing, setting or effecting a hardening of
the material may be minimized to effect a material saving in the
overall cost of each installation. For example, using a
quick-setting resin material 30, such as a polyester, and employing
the bolt construction 15 illustrated, it is now possible to make a
complete installation within 1 minute from the time of the initial
insertion of the bolting assembly as a unit within a bore or drill
hole 11. The mixing, setting or hardening of the mixed resin
material involves a matter of a few seconds.
Using a 11/4 to 13/8 inch bore or drill hole diameter and a 1 to
11/8 outer diameter of pipe member 16, successful use has been made
of pipe member lengths of about 6 to 8 inches. However, it has been
determined that about a 6 inch length of anchoring pipe or head
member 16 is a good average length that provides a full safety
margin where the unit or assembly is to be installed in ordinary
rock strata. However, the length may be increased for unstable,
soft rock as may be required. By utilizing a short length amount of
adhesive material, cartridge or capsule, a saving of about 25 cents
per foot of bolt length may be effected with the hardening or
setting being accomplished within a matter of about a minute, as
distinguished from about 2 minutes, utilizing a full hole-filling
length of old type or group of resin cartridges. The strength
attained will equal or exceed the strength of the bolt, with a
material saving in cost and a 50 percent reduction in installation
time.
For very soft shales, a greater length of about 18 to 24 inches may
be used, but it has been determined that lengths of 6 to 8 inches
are generally sufficient, utilizing an 80,000 psi high tension
steel bolt with a diameter of anchor shell of about 1 inch with a
11/4 or 13/8 inch bore hole. To maximize holding of the anchor pipe
member 16, it may be given a light side blow to form it into a
slightly oval or ellipsoid shape.
Referring to the drawings, 10 represents a rock-like wall or
support structure which is to be secured together or reinforced and
which is provided with a bore or drill hole 11 for receiving a
bolting assembly of the invention. The assembly has a forward,
somewhat cylindrical, pipe-like hollow member, shell or part 16
that constitutes an anchor for the construction. Opposite open ends
of the hollow member 16 are closed-off by back and front end walls
17 and 18, such as may be provided by small, stamped-out, disc-like
parts or pieces of a metal such as steel, that may be electrically
resistance or induction welded to the pipe member.
The back end wall 17, as shown in FIG. 4, is provided with a pair
of upset portions 17a along its outer edge that serve as breaking
and cutting edges as well as a mixing means for the adhesive resin
containing capsule 30. To save expense, the element or piece 17 may
be stamped-out at 17a and then secured by weld metal w to the back
end of the pipe member 16. The width of each portion 17a may
substantially conform to the wall thickness of the pipe member 16,
so that a full sealing-off may be easily accomplished by securing
the piece 17 in position by a weld w over the back end of the
associated pipe member. A front metal disc 18 may also be secured
by electric resistance or induction welding to the front end of the
member 16 to fully close it off.
As shown in FIGS. 1, 2 and 3, a standard nut 20, such as a
hexagonal nut element, is secured by weld metal w, directly on the
front face of the front disc or closure wall 18 to project
forwardly therefrom. A bolt, bar or rod 15, headed with a wrench
flat, is provided having a stem 23 which is of a length equal to
the distance between the front end wall 18 of the pipe member 16 in
its in-place secured position of FIG. 2 and the outer face of the
drill hole. The stem 23 is threaded at its backwardly extending end
portion to turnably or rotatably fit within the nut 20 and to later
shear the end wall 18 and advance past the nut into the hollow
anchor member 16 (see FIG. 3).
During an initial insertion of the bolting assembly into the drill
hole 11, the stem 23 of the bolt 15 has its back end portion 23a
(see FIG. 1) in tight abutment with the front face of the closure
wall or disc member 18. Thus, the entire assembly may be inserted
and rotatably advanced endwise as a unit within the drill hole 11,
and such rotative inward insertion continued until the bolt head
and its bearing plate 25 has made contact with the face of the rock
structure 10 thereby preventing further insertion of the assembly
as shown in FIG. 2. A pneumatic or other suitable form of power
tool may be applied to a head 24 of the bolt 15 for this
purpose.
At this time, a short wait of, for example, 60 seconds will enable
the material to cure, harden or set about the pipe member 16 to
anchor or secure it non-rotatably within the end of the drill hole
11. Thereafter, the bolt 15 is screw or turnably advanced by again
applying rotative force to the head 24 to thereby cause a backward
end portion 23a of the bolt 15 to displace, shear or fracture and
penetrate the relatively thin wall thickness of the front disc or
end wall member 18. The relative movement of the bolt 15 with
respect to the anchored pipe member 16 is continued until, as shown
in FIG. 3, the bolt 15 has advanced within the pipe member
sufficiently to bring its head 24 into tension to compression-hold
its associated bearing plate or enlarged washer 25 against the
front face of the rock formation and close-off the bore hole
11.
In FIG. 5, a modified form of back end wall 26 is illustrated which
is in the form of a plug that may be electrical induction or
resistance-welded at w to extend from within the back end of the
pipe member 16. The end wall 26 terminates in a central,
wedge-shaped edge portion 26a centrally to provide a chisel-like
cutting and mixing pair of surfaces for the adhesive resin
material.
With reference to FIG. 1, a typical adhesive capsule or cartridge
30 consists of a main body of resin material 31 and a segregated
supplemental body of a catalyst, curing or hardening resin 32. Both
resins are retained in the capsule or cartridge by means of a
relatively thin wall resin bag or sausage of any suitable type that
is easily ruptured or broken by the rotative advance of the forward
end wall 17 or 26 of the shell member 16 which becomes an anchoring
part or member when the mixed resin material has hardened or set.
The resin material 32 is used for polymerizing, curing and setting
the main body of the resin material 31 when they are mixed together
and displaced along the bore hole 11 and about the pipe member 16
up to a sealing gasket 19.
In order to conserve the adhesive material, avoid clogging threads
of the screw assembly and limit movement of the adhesive to the
full extent of the outer periphery of the hollow member 16, the
sealing gasket 19, shown of a rubberlike O-ring type, is mounted
about the outer periphery of the hollow member 16 adjacent its
front end and in seated, forward, position-limited abutment with a
radially outwardly extending flange portion of the front end wall
18. The gasket 19 will have a larger diameter than the drill or
bore hole 11 such that it is slightly compressed when inserted
within the hole.
The requisite length of anchoring shell, pipe or hollow head member
16 may be checked by pull tests to determine its anchorage
strength, which need not be more than the minimum breaking load for
the bolt 15. A standard mine roof bolt of five/eighths of an inch
in diameter will yield at a load between 9,700 to 14,700 lbs. and
fail between about 16,200 and 24,600 lbs. Celtite, Inc. of
Cleveland, Ohio and DuPont of Wilmington, Del. are two
representative companies that are in a position to supply the resin
cartridges or capsules, and which can be mixed and cured under
rotation of at least 120 r.p.m. within about 60 to 75 seconds where
the starting resin temperature is within a range of about
65.degree. to 75.degree. F or at usual mine temperature (of about
68.degree. F). The nut 20 may be a conventional hex nut for a bolt
15 of about five/eighths of an inch in diameter. The length of the
bolt-anchor assembly from back end wall 17 to bearing plate 25,
ideally, should be equal to or slightly less than the depth of the
bore hole. However, the bolt take-up during tensioning will
compensate for an under-depth bore hole.
In accordance with the present invention, it has been definitely
determined that full length resin encapsulation is not necessary,
and depending on the particular rock or roof formation, that, using
a sleeve or pipe member, a resin grouting length of about 6 to 8
inches is sufficient. For example, using an anchoring sleeve member
16 having an outer diameter of about 11/8 inches within a bore hole
of about 13/8 inches, provides a one/eighth of an inch spacing
width within which the resin material will provide a matrix layer
or encapsulation. Such spacing should preferably be within a range
of about one/sixteenth to three/sixteenths of an inch on the side
with an optimum of about one/eighth inch. The full strength of the
main resin body 31 requires a good or thorough mixing with the
catalyst or hardening resin 32. A rotational speed of at least 120
r.p.m. has been found to be satisfactory, although the extremely
fast setting resins to be used with this device should be mixed at
maximum speed (about 475 r.p.m.). The working face of the average
coal mine has been found to have a temperature of about 68.degree.
F which requires a total time of mixing-curing of about 60 to 75
seconds.
Although, as above pointed out, a device of the invention is
particularly suitable for mine roof usage, it also may be employed
in tunnels, and for tieing-together rock-like pieces, such as
foundation stone, etc. It enables obtaining the full tensile
strength of the bolt, with minimal loss of tension due to
subsequent weathering and deformation of the anchor rock, that is
competitive with a so-called mechanical expansion type of unit. It
eliminates the need for an easily damaged and loose nut on a
threaded rod or bolt such as used with a type in which the rod or
bolt is, itself, directly resin or grout anchored in place
substantially fully along its length extent within a bore hole.
FIG. 6 shows a simplified and optimum construction of the front end
of the hollow member 16 in which front metal disc 18' has a smaller
diameter such that it will fit therewithin, and the nut 20 has an
effective diameter such that its outer edge portion or at least its
corners serve as position-limiting abutment or shoulder means for
the gasket 19. This enables a direct welding of the nut 20 on the
front end of the hollow member 16. The disc 18' may be an integral
closed, thin end portion of the nut 20 or may be a separate piece
welded to the inner wall of the member 16 or to the back end of the
nut to serve as a temporary barrier for the end of the bolt 15
during the resin mixing and curing phases. The disc 18' is
penetrated and ruptured when the bolt 15 is later advanced for
tensioning.
* * * * *