CA2029742A1 - Roof bolt - Google Patents
Roof boltInfo
- Publication number
- CA2029742A1 CA2029742A1 CA002029742A CA2029742A CA2029742A1 CA 2029742 A1 CA2029742 A1 CA 2029742A1 CA 002029742 A CA002029742 A CA 002029742A CA 2029742 A CA2029742 A CA 2029742A CA 2029742 A1 CA2029742 A1 CA 2029742A1
- Authority
- CA
- Canada
- Prior art keywords
- support member
- hole
- arrangement
- anchor
- wedge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Abstract
ABSTRACT OF THE DISCLOSURE
A roof bolt 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 elongate support member is located with opposite portions parallel to the direction of movement of the wedge-shaped elements. The support member is tensioned when the wedge shaped elements in the hole are forced towards each other in the direction of movement, by a suitable tool from the mouth of the hole.
A roof bolt 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 elongate support member is located with opposite portions parallel to the direction of movement of the wedge-shaped elements. The support member is tensioned when the wedge shaped elements in the hole are forced towards each other in the direction of movement, by a suitable tool from the mouth of the hole.
Description
20297~2 ,. 1 .
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 :
.
~, . ..
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 .
i, . . .; ; - , ., . . - . ~." . - - ... . ... ., ... , .... ;. . ., "., .. .-.. .~ .~ ,. . . . . . .
20297~2 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 20297~2 ~ 3 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 ~, : '' 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
_ . _ ._ : , . , , .
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.
'' - . . ~ ' . .; ' ' '.,~;t~t~ ,X '-X -:' - -~ :. - . .
. ' ': " " ' ~ ' ' .' '" ' . ' ' :~ ' 20297~2 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 --:,.:, ...
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.
,.
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 . . ' ' . ' ! ' ' . . `, . , ' . . . : ' , ,, ' . . : . .
', ', ',: ', ' .": ' ' ~. ' ' . .
:, '- ' - .. , : '' 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 , .
' ' ' "" , " . . . ' ; ' ' `'"'' . '," , ' '",' ' ' ; ':
20297 ~
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 " ~ .
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 ' '', ' ' . ~i .
. . .
.. ' .
20297~
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 202~7~2 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.
' - ' ' , ' ' : :.
:
,: .
;r , . ., ~.'. . .: ' ' . ' ' ' . ;. . i . ' ' ' '
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 :
.
~, . ..
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 .
i, . . .; ; - , ., . . - . ~." . - - ... . ... ., ... , .... ;. . ., "., .. .-.. .~ .~ ,. . . . . . .
20297~2 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 20297~2 ~ 3 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 ~, : '' 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
_ . _ ._ : , . , , .
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.
'' - . . ~ ' . .; ' ' '.,~;t~t~ ,X '-X -:' - -~ :. - . .
. ' ': " " ' ~ ' ' .' '" ' . ' ' :~ ' 20297~2 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 --:,.:, ...
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.
,.
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 . . ' ' . ' ! ' ' . . `, . , ' . . . : ' , ,, ' . . : . .
', ', ',: ', ' .": ' ' ~. ' ' . .
:, '- ' - .. , : '' 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 , .
' ' ' "" , " . . . ' ; ' ' `'"'' . '," , ' '",' ' ' ; ':
20297 ~
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 " ~ .
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 ' '', ' ' . ~i .
. . .
.. ' .
20297~
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 202~7~2 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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Claims (14)
1. A roof bolt including 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 with 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 a suitable tool from the mouth of the hole, against the bight of the support member to cause the anchor arrangement to expand into gripping contact with the wall of the hole.
2. A roof bolt as claimed in claim 1 in which the support member is a flat strip of ductile metal.
3. A roof bolt as claimed in claim 1 in which 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.
4. A roof bolt as claimed in claim 3 in which the tensioning arrangement includes a formation which projects 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.
5. A roof bolt as claimed in claim 4 in which 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.
6. A roof bolt as claimed in claim 5 including a reinforcing ring which 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.
7. A roof bolt as claimed in claim 1 in which the wedge-shaped elements of the anchor arrangement are, in the direction of movement of the elements, substantially rectangular in plan.
8. A roof bolt as claimed in claim 1 in which the wedge angle of one wedge-shaped element is greater than that of the other by between 1° and 5°.
9. A roof bolt as claimed in claim 8 in which the wedge angle of one of the wedge shaped elements is 10° and that of the other is 9°.
10. A roof bolt as claimed in claim 1 in which the surfaces of at least one of the wedge shaped elements in the direction of expansion of the anchor arrangement is suitably profiled to provide rock gripping formations.
11. A roof bolt as claimed in claim 7 in which the opposite portions of the support member which embrace the anchor arrangement are spaced further apart by the anchor arrangement than the spacing between them. between the anchor and the tensioning arrangement, to define a head on the bolt in which the anchor arrangement is located.
12. A method of tensioning a roof bolt as claimed in claim 1 including 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 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 elements 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.
13. A method of grouting a roof bolt as claimed in claim 3 in a pre-drilled hole including the steps of locating the support member in the hole with the anchor arrangement 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 portions of the support member through the space between them into the hole surrounding the elongated element.
14. A method of grouting an anchor bolt as claimed in claim 13 including the steps of feeding a tube into the passage between the opposite portions of the support member until its end in 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.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA898798 | 1989-11-17 | ||
| ZA89/8798 | 1989-11-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2029742A1 true CA2029742A1 (en) | 1991-05-18 |
Family
ID=25579908
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002029742A Abandoned CA2029742A1 (en) | 1989-11-17 | 1990-11-13 | Roof bolt |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2029742A1 (en) |
-
1990
- 1990-11-13 CA CA002029742A patent/CA2029742A1/en not_active Abandoned
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| FZDE | Dead |