Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
ThiS invention relates to d roof bolt for use in resisting
strata separation in mines and tunnels and more
particularly to a bolt which is to be full-column grouted
with resin or cementitious material into the hole into
which it is to be located in use.
In this specification the term Ugrout'' is not limited to
cementitious materials only and may include resins and any
other settable material which is suitable for bolt
anchoring.
SUMMARY OF THE INVENTION :
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A roof bolt according to the invention includes an anchor .
arrangement which includes two wedge shaped elements which
when moved towards each other from opposite directions
cause the anchor arrangement to expand in a direction .
transverse to the direction of movement, an elongated :
support member which passes over the anchor arrangement to
be located on opposite sides of the anchor arrangement
which are normal to the expansion direction of the .
arrangement ~ith the opposite portions of the support
member parallel to the direction of movement of the wedge :~
shaped elements, and a tensioning arrangement at the free
ends of the support member for engaging the surround to
the mouth of the hole in which the bolt is located in use .
and against which the support member is tensioned when the
wedge shaped elements in the hole are forced towards each
other in the direction of movement, by à suitable tool
from the mouth of the hole, against the bight of the
support member to cause the anchor arrangement to expand
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lnto gripping contact with the wall of the hole.
In one form of the invention the support member is a flat
strip of ductile metal.
However, in a preferred form of the invention the support
member is a strip of ductile metal with the opposed
portions of the length of the strip between the anchor and -
tensioning arrangements being arcuate in cross section and
out of contact with each other to define between them a
substantially circular passage.
The tensioning arrangement conveniently includes a
formation which proiects transversely from and adjacent
the free ends of the support member with a passage through
the formation which is in register with the passage
between the opposite portions of the support member and a
roof washer which is located on the support member and on
which the formation bears in use to hold the support
member in tension. A portion of the support member
adjacent each of its ends is bulged radially outwardly in
opposite directions to provide the transverse tensioning
arrangement formation. Preferably a reinforcing ring is
engaged in the bulges between the free end portions of the
support member with the internal diameter of the ring -
being at least equal to the diameter of the passage
between the opposite portions of the support member.
Further according to the invention the wedge angle of one
wedge shaped element is greater than that of the other by
between 1 and 5. Preferably the wedge angle of one of
the wedge shaped elements is 10 and that of the other is
. ~.
Still further according to the invention the opposite
portions of the support member which embrace the anchor
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arrangement are spaced further apart b~ the anchor
arrangement than the spacing between the anchor and the
tensioning arrangement, to define a head on the bolt in
which the anchor arrangement is located.
A ethod of tensioning a roof bolt of the above type
includes, according to the invention, the steps of
locating the support member in a hole with the anchor --
arrangement towards the blind end of the hole, locating a ~ -
rod in the hole between the opposite portions of the
support member, feeding the rod into the hole to abut a
wedge shaped member of the anchor arrangement in the hole,
and hammering the rod from the outside of the hole to
cause the wedge shaped ele~ents to move towards each other
against the bight of the support member to tension the
support member against the tensioning arrangement at the
mouth of the hole and to expand the anchor arrangement
into gripping contact with the wall of the hole to anchor
the anchor arrangement in the hole and hold the support ;
member in tension between it and the tensioning
arrangement.
A e thod of grouting a roof bolt of the above type in a
pre-drilled hole according to the invention includes the
steps of locating the support member in the hole with the
anchor arrange~ent towards the blind end of the hole,
anchoring the anchor arrangement in the hole to tension
the support member in the hole between the anchor
arrangement and the tensioning arrangement at the mouth of
the hole, and pumping grout into the passage of the
support member to escape under pressure from between the
opposite port~ons of the support member through the space
between them into the hole surrounding the elongated
- ele~ent. Preferably the grouting method includes the
steps of feeding a tube into the passage between the
opposite portions of the support member until its end in
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the passage is adjacent the anchor arrangement, and
pumping grout under pressure through the tube
progressively to fill the support member passage and the
hole surrounding the element as the tube is moved along
the support member towards the tensioning arrangement.
BRIEF DESCRIPTION OF THE DRAWINGS
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The invention is now described by way of example only with
reference to the drawings in which:
FIGURE 1 is a partially sectioned side elevation of one
emb~diment of the roof bolt of the invention,
FIGURE 2 is a sectioned end elevation of the anchor head
portion of the Figure 1 bolt shown sectioned on the lines
2 - 2 in Figure 1,
fIGURE 3 is an enlarged plan view of the anchor head
portion of the Figure 1 bolt shown sectioned on the line 3
- 3 in Figure 1, and
FI W RE 4 is a sectioned side elevation of the anchor head
portion of a second embodiment of the roof bolt of the
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
The roof bolt of the invention is shown in Figure 1 of the
drawings to include an anchor arrangement 10, a support
member 12 and a tensioning arrangement 14.
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rhe anchor arrangement 10, in this embodiment of the
invention, consists of two wedge-shaped elements 16 and 18 ~ :
which are more clearly seen in Figure 2. Both ~.
wedge-shaped elements of the anchor arrangement are
S rectangular in plan as seen in Figure 3. The wedge-shaped
ele ent 16 has a smooth vertical gripping face 20 and a
wedge face 22 which, in this embodiment of the anchor
arrangement, has a wedge angle a of 10.
The wedge-shaped element 18 has a serrated vertical
gripping face 24 and a tapered wedge face 26 with the : .
wedge angle b of the face 26 being slightly 1ess than the
wedge angle of the element 16 and in this case in the . :
order of 9.
... :
The wedge-shaped elements 16 and 18 are made from a
substantially non-deformable iron such as SABS 936 SG42. : :~
. ~ ,
The support member 12 is made from a ductile metal such as
mild steel and is folded centrally over a rounded upper
end 28 of the wedge-shaped element 16 of the anchor
arrangement 10 to form a bight or a bridge 30 over the
upper end of the anchor arrangement 10 and two legs 32 and
34 which extend from the bridge 30 to the tensioning
arrangement 14.
As seen in Figure 3, the opposite leg portions of the
support member are arcuate in cross-section and have a
combined cross sectional area for any given strength of
material to provide the support member with a tensile
strength to withstand whatever the desired load capability
of the roof bolt is to be.
,:.
- The arcuate configuration of the legs 32 and 34 provides a
substantially circular passage 36 which extends from the
underside of the anchor arrangement 10 to the tensioning --
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2029742
arrangement 14 of the roof bolt. It is important that the
side edges of the legs 32 and 34 do not contact one
another so that the spaces between them provide slots 38
which extend over the length of the roof bolt.
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The legs 32 and 34 of the support member are outwardly
stepped at 40 to provide an anchor head 42 in which the -
anchor arrangement 10 is located. The wedge-shaped
elements of the anchor arrangement 10 could be held in the
head in the configuration shown in Figure 2 by suitable
strapping or wire ties 43 which are bound around the outer
surfaces of the support member legs and the exposed
gripping faces of the wedge shaped elements.
Additionally, the support member could be lightly tack
welded or temporarily fixed in any other suitable manner
to the bridge portion 30 of the support member 12.
The lower end portions of the legs of the support member
are outwardly bulged, as shown in Figure 1, to provide
formations 44 which project radially from the support -~
member 12. rhe tensioning arrangement includes a cast
iron or steel ring 46 which is located between the
oub~ardly bulged portions 44 of the legs of the support
member. The ring includes a hole through it which is held
in register with the passage 36 in the support member 12.
A suitable washer or the like surrounds and is fixed to
the support member 12 below the tensioning arrangement 14
to prevent outward splaying of the free ends of the legs
under load in use.
In use, a domed roof washer 48 is slid over the roof bolt
fro~ its headed end until it rests on the outwardly bulged
portions 44 of the tensioning arrangement 14. The bolt is
then slid head first into a pre-drilled hole which has a
slightly larger diameter than the dimension between the
gripping faces 20 and 24 of the wedge-shaped elements of
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20237~2
the anchor arrangement until the upper surface of the , ~-
~asher 48 bears on the rock surrounding the mouth of the
hole. The rounded upper surfaces of the bulged portions ~ -~
44 of the support member 12 enable the bolt to be slightly
S skewed relatively to the upper face of the washer 48 to
cater for any non-perpendicularity of the hole relatively
to the face in which it is drilled or irregularities in
the ~aterial of the face at the mouth of the hole. An
elongated striker rod is then fed into the passage 36 of
the bolt until its upper end abuts the flat underside of --
the wedge-shaped element 18. ~he striker rod is connected
tO a jack hammer or the like and the jack hammer is
activated to drive the wedge shaped element 18 upwardly
fro~ the position shown in Figure 2 against the ~ -
wedge-shaped element 16 which is held restrained from
movement in an upward direction by the bridge 30 of the
support member which passes over i~s upper end.
Initially, the impact force acting on the wedge shaped
element 18 will drive the wedge up against the wedge face
22 of the element 16 and expand the anchor arrangement 10
in a direction transverse to the axis of the bolt until
the gripping surfaces 20 and 24 of the wedge shaped
elements come directly into frictional contact with the
wall of the hole. Continued operation of the ~ack hammer
no~ drives the wedge 18 further up the face 22 of the
~edge 16 with the principal energy component which is, at
this stage, imposed on the anchor arrangement 10, being a
driving energy which tensions the bolt against the
friction between the gripping faces of the wedge-shaped ;, ~
elements and the wall of the hole and the tensioning -; -
arrangement 14 at the mouth of the hole. ~hen the wedges
become locked all of the energy imposed on the wedge
system is transmitted laterally through the wedges
directly to the wall of the hole to anchor the tensioned
bolt in the hole. The forces acting on the wedge system
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of the anchor arrangement are now balanced by the lateral
forces in the anchoring system and the bolt ~s now firmly
anchored in its hole.
S An important feature of the invention is that with the
anchor arrangement firmly anchored in a hole there is no
gripping force applied to the support member in the zone
of the anchor head 42. The reason for this will become
apparent from what is said below in connection with
emergency slip of the bolt.
Should the rock strata which is being held by the roof
bolt of the invention now be separated by seismic activit~
or any other cause the tension on the bolt will increase
markedly and so particularly the force acting on the
bridge 30 of the support member which bears on the anchor ^
head. The force on the bridge 30 will tend to move the
wedge shaped element 16 downwardly on the wedge element 18
and because the co-efficient of frict~on between the
gripping face 24 of the wedge shaped element 18 and the
rock with it is in direct contact is far greater than the
co-efficient of friction between the wedge faces 22 and 26
of the anchor arrangement 10, the wedge-shaped element
will be moved downwardly by the excessive load on it and
the anchor head will tend to become more firmly anchored
in the hole to resist any possibility of the anchor head
of the bolt being released from the side walls of the hole
and so causing the bolt to slip. To encourage emergency
slip of the wedge element 16 its gripping face 20 is
s~oothed as opposed to serrated and the face could include
a thin skin of a metal which will encourage slip of the
ele0ent. Should the tensile load on the bolt increase to a
level beyond the elastic limit of the material from which
the support member is made one or both of the legs 32 or
34 of the support member will fail. In practise, however,
in testing the roof bolt of the invention to destruction
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202974~
g
it has been found that it iS very rare that both legs fail
simultaneously and that when one only fails the bolt
yields in length while still maintaining a load by the no~
free broken l-eg of the support member being drawn in the
S hole over the upper end 28 of the anchor arrangement 10. ;~
The ener3y which is required progressi wly to * form the
support member over the upper end of the anchor
arrangement enables the bolt to support sufficient load to -
prevent the rock which it is supporting from merely
crashing onto the footwall. To encourage single leg
failure of the support member, beyond the design limits of
the bolt performance, one of the legs 32 or 34 could
include a deliberate line of weaknèss immediately above
the tensioning arrangement 14.
In the second embodiment of the roof bolt illustrated in
Figure 4, the legs 32 and 34 of the support member 12 are
separate elements ~hich are each folded over the anchor
arrangement 10 as shown in the drawing. ~ith this
embodiment of the invention, when a pre-determined tensile
load on the bolt is exceeded, both legs will be drawn over
the head of the anchor arrangement in the manner described
above to permit the bolt to yield in length in a
controlled fashion while holding a pre-determined load.
,.
To grout the bolt ~nto its hole, should this be desired, a
hose wh k h is m~ade from a flexible plastics material is
fed through the tensioning arrangement ring 46 into the
passage 36 of the bolt until its free end abuts the
underside of the wedge shaped element 18 of the anchor
arrangement 10. 6rout is now pumped under pressure through
the hose to leave the bolt passage 36 through the slots 38
between the legs of the support member to enter the hole
surrounding the bolt and into whatever fissures there may
be leading from that area of the hole into the surrounding
rock. Continued pu~ping of the grout under pressure will
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slowly force the tube down the bolt passage and
progressively fill the surrounding hole through the slots -
38 as the tube is slowly expelled by the back pressure of
the grout acting on it. When the tube is eventually
pressed from the bolt there can be little doubt that the
bolt is fully surrounded by the settable material over its
entire length in the hole.
'
In another method of grouting, using the roof bolt of the
invention, conventional grout capsules which have been
wetted are shot through the tensioning arrangement ring
and into the support member passage 36. The sleeve of the
first capsule which is fired into the passage 36 is
destroyed on impact with the anchor arrangement 10 with
the subsequent capsules being destroyed on impact with the
remnants of the capsule which was fired into the passage
before it. The grout which is released from the capsules
is released under the impact pressure of the capsule to be
ejected from the bolt passage under pressure into the hole
surrounding the bolt. This method of grouting works
particularly we11 using the bolt of the invention as the
support member passage provides the high velocity capsules ;
with a relatively smooth barrel in which to travel as
opposed to the rough walled holes into which they are
usually fired and in which more often than not they are
destroyed by rough edges before reaching the end of the
hole.
The invention is not limited to the precise details as
herein described. For example the gripping face 20 of the
wedge-shaped element 16 could be serrated as is the face
24 of the element 18 but this would, however, minimise the
tension locking aspect described above where it may be
necessary for the wedge shaped element 16 to slip
relati wly to the element 18 for emergency locking of the
bolt. A Mitionally the support member 12 need not
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necessarily have the arcuate shape described above and
could in fact be in the form a flat strap, such as that
illustrated in Figure 4, or even a ~ exible cable w~th the
tensioning arrangement in this embodiment being a
S conventional holed roof washer to which the free ends of
the cable are attached in any suitable manner.
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