Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND DEVICE FOR ROCK BOLTING
Field of the invention
This invention concerns a method and a device for rock bolting.
Description of background art
Pre-stressed wire bolts for rock enforcement are installed by
grouting the wire bolt in a bore hole in the rock to be
reinforced. Hereby cement concrete or any other binding agent
is used as cement.
After injection of the binding agent this must be allowed to
set, whereby the bolt has to be left unloaded during the
setting period. After setting, a surface plate is mounted
against the rock face, whereupon the bolt is pre-stressed
through screw means or the like.
Because of the nature of the installation, the pre-tension
will occur only along the part of the wire which is pulled
free from the set binding agent. The length of the part being
pulled free from binding agent is undefined which is a problem
regarding the security of the fastener.
Altogether, the known method of installation of cable bolts is
a lengthy and not an entirely impeachable procedure since the
installation must be made in plural steps with intermediate
waiting period.
Also the fact that the bolt can not be used prior to the
setting of the binding agent is a considerable drawback in
many cases. According to the above the strength of the
completed installed bolt can also be questioned.
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Aim and most important features of the invention
It is an aim of this invention to provide a method and a
device wherein the problems of the background art are avoided.
In particular it is provided a method and a device which leads
to fast, rational, economic and safe installation.
Hereby it is achieved that pre-tension can be applied to the
bolt before grouting thereof with a settable agent, which
result in that the pre-tension will be well defined along a
complete length of an element of the bolt and that the
security of the installation is increased.
Further it is allowed that a rock bolt installed through a
method according to the invention can be loaded immediately
already after the tubular bolt has been expanded so as to be
anchored in the bore hole. Hereby the unwanted waiting periods
that are necessary in the method according to the background
art are avoided and altogether is achieved a less lengthy and
more economic rock bolting method.
By the channel for transmitting the said settable agent
provides means which open for communication with the outside
of the tension element through pressurizing to a certain
pressure level, the same channel may be used for transmitting
expansion medium and settable medium. When the same channel is
used for transmitting medium for expanding the tubular bolt as
well as for the settable medium, the said pressure level is
set such that the channel opens at a pressure increase with a
certain L\-pressure above the expansion pressure.
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It is preferred that the tension element is used for
transmission of medium for expanding the tubular bolt,
wherefore the tension element comprises a through channel for
transmission of pressure water or the like. Hereby also the
settable medium is transmitted through a channel in the
tension element, wherein in particular it is preferred that it
is this channel which can be opened through pressurizing to a
certain pressure level which exceeds a certain predetermined
threshold value.
By providing the tension element with a bursting plate, which
breaks at a predetermined pressure level, this function is
achieved in a simple way.
In particular the bursting plate can be an integral part of
the material in the tension element, for example a drilled-out
or milled-out portion having a certain remaining material
thickness, which allows shearing of the material when said
pressure level is reached.
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According to one aspect of the present invention, there is provided
method for rock bolting, wherein a tubular bolt with closed cross-section is
inserted
and expanded for anchoring inside a bore hole, which has an inner and an outer
portion as well as an inlet opening, and wherein the tubular bolt is expanded
to
contact in the inner portion of the bore hole, characterized in that a tension
element
which is arranged in the outer portion of the bore hole with an inner part
attached to
the tubular bolt is pre-stressed, that a settable medium is injected into the
outer
portion of the bore hole between the tension element and the wall of the bore
hole
and is allowed to set, and that a channel for transmitting said settable
medium is
opened for communication to the outside of the tension element through
pressurizing
to a certain pressure level.
According to another aspect of the present invention, there is provided
device for rock bolting, including a tubular bolt having a closed cross-
section for
insertion into and expansion for anchoring inside a bore hole which has an
inner and
an outer portion and an insertion opening, characterized in a tension element
to be
arranged at the outer portion of the bore hole having an inner part for
attachment to
the tubular bolt, means to pre-stress the tension element in a length
direction
between the tubular bolt and the insertion opening, means for transmitting a
settable
medium to the outer portion of the bore hole between the tension element and
the
wall of the bore hole, and that a channel for transmitting said settable
medium
provides means which are opened for communication to the outside of the
tension
element through pressurizing to a certain pressure level.
Brief description of drawings
The invention will now be described closer at the background of
embodiments and with reference to the annexed drawings, wherein:
Fig 1 shows a disassembled perspective view of a device for rock
bolting according to the invention,
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Fig 2 shows, partly in section, the device in Fig 1, assembled
and inserted into a bore hole,
Fig 3 shows a detail of the device in Fig 1 and 2 with a
bursting plate,
Fig 4 shows diagrammatically a block diagram of steps included
in a method according to the invention,
Figs 5 and 6 show diagrammatically alternative devices
according to the invention.
Description of embodiments
In Fig 1 numeral 1 generally denotes a device for rock bolting
including pre-stressing a rock bolt and with a tubular
expandable rock bolt, essentially of the kind which is
described in US-A-4459067 (Atlas Copco AB).
The tubular bolt includes in general an expandable portion 5
and a fastening portion 6, into which is attachable a tubular
tension element 3 including an inner portion 7 having a thread
for cooperation with the fastening portion 6 and a female
thread for cooperation with a tension section 8, which in turn
over a joining element 9 is arranged to be threaded to one
further tension section 8.
Preferably the parts included in the tension element 3 are
standard components, which can be combined as desired, for
example for adjustment to the depth of a bore hole wherein the
device 1 is intended to be inserted.
An abutment element 4 includes an abutment plate 10 and a
tension nut 11, which cooperates with an outside tension
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section 8, is arranged outside an insertion opening of said
bore hole.
Fig 2 shows the device in Fig 1 in an assembled state and
5 inserted into a bore hole 12, which is drilled in a rock
structure 20. The bore hole 12 provides an insertion opening
13, an outer portion 14 and an inner portion 15.
The installation of a device for rock bolting is such that all
the parts shown in Fig 1 are tightly screwed together such
that a sealed channel is established between the expandable
portion 5 of the tubular bolt and the outside end 29 of the
outermost tension section 8. Sealing may be achieved in a per
se known manner through not further described sealing
elements.
The outside end 29 of the outermost tension section 8 is after
insertion of the device into the bore hole 12 connected to a
pressure water source or the like for transmitting a pressure
of as an example 300 bar to the expandable portion 5.
This expandable portion 5 will thereby be brought to firm
anchoring against the inside of the inner portion 15 of the
bore hole 12 so that already in this step a considerable
anchoring of the complete rock bolt will occur.
After completed expansion, the tension element consisting of
the parts 7, 8 and 9 may now be pre-stressed, which is made in
such a way that the abutment plate 10 is pressed against the
rock face 20 around the insertion opening 13 with the aid of
the tension nut 11, which is tightened to a predetermined
torque value.
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After pre-stressing the device is now grouted-in in order to
reinforce the anchoring as well as for assistance against
corrosion, by injecting a settable medium into the space 27
between the tension element and the wall of the bore hole 12.
According to the preferred embodiment shown in Fig 2, this is
achieved in such a way that the channel inside the tension
element is pressurized with a pressure which exceeds the
pressure for expanding the expandable portion 5 and which is
chosen to such a level that a bursting plate 6, which is
positioned in the inner part 7 of the tension element, bursts
so that an open channel is formed between this channel 19 and
said space 27.
Thereupon the device is connected at its end portion 29 to a
cement pump or any other source of a suitable settable medium.
Fig 3 shows a detail of an inner portion 7 of a tension
element with a bursting plate 16, which in this case is
integrated in the material of the portion 7 in such a way that
a milling operation 17 has been made so that the surrounding
portion 18 of the bursting plate 6 provides a material
thickness that can be sheared off at a certain pressurizing
level.
The method of rock bolting according to the invention can be
summarized with reference to Fig 4, wherein:
Position 21 denotes the start of the sequence,
Position 22 concerns assembling a device for rock bolting and
inserting thereof into a bore hole,
Position 23 concerns expansion of a tubular bolt,
Position 24 concerns pre-stressing of a tension element,
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Position 25 grouting of settable material, and
Position 26 end of the sequence.
The invention can be modified within the scope of the
following claims, and as an example a device for rock bolting
can be used, wherein medium for expanding the tubular bolt as
well as settable medium is transmitted otherwise than through
the tension element, for example through separate inserted and
removable element (28 in Fig 5), wherein in that case the
tension element can be made homogenous.
The bursting plate can be a separate element inserted inside
the tension element and also other means for establishing a
channel for transmitting the settable medium can be used, for
example an element having a valve function may be used. A
further example is the use of a break-pin which is sheared off
at a certain pressure and fixes a potentially movable valve
element.
As a further alternative the tension element as an example can
be anchored in a way that is shown in Fig 6, through clamping
of a tension element 29 between an expandable bolt 2 and the
wall of the bore hole, wherein the tension element in that
case can be formed of a wire, which then can be pre-tensioned
and anchored and be secured against corrosion through
injection of cement or any other binding agent according to
the above.
