[0001] The present invention concerns an arrangement for detecting the presence of one or
more cavities in a borehole
[0002] A large number of reinforcement systems are today available to stabilise and reinforce
a rock structure during the building of tunnels, mining operations, tunnelling, etc.
Such a reinforcement system involves the drilling of a large number of boreholes in
the wall or roof that is to be reinforced, the subsequent filling of these boreholes
with grout, and the subsequent introduction of bolts into the boreholes, to be cast
in place in the boreholes, by which means the wall or roof is reinforced. One example
of a bolt for casting into a reinforcement system is what is popularly called the
"kiruna bolt", which consists of a reinforcement bar with a slotted end with a wedge.
Another example is a cable bolt, which consists of a 7-stranded twisted steel thread.
These types of bolt have lengths of 3-7 metres.
[0003] The rock reinforcement is carried out through a portion of the grout being injected
into a borehole by a nozzle, normally a tube. The borehole is filled from the deepest
part of the borehole bottom, after which the tube is withdrawn, as filling continues.
Rock material may be constituted in different ways: cracks and natural cavities are
sometimes present that are filled by an injected portion of filler material. This
means that the portion of grout that has been injected may be insufficient to fix
the rock bolt, which may have as its consequence that the reinforcement system is
deficient and has an insufficient load-bearing capacity. When the rock bolt is introduced
into what appears to be a filled hole, there may, therefore, arise empty spaces or
cavities, along the bolt that are difficult to detect. These cavities, in particular,
usually arise at the extreme end, at the deepest part of the borehole. A serious problem
with these reinforcement systems, therefore, is that it is not possible to be certain
that any individual bolt is completely cast and well-anchored. The greatest problem
arises if the uppermost part of the bolt is not covered by hardening grout. If this
is the case, a part of the load-bearing capacity of the bolt is lost. Furthermore,
the risk for corrosion of the bolt increases, since the rock in itself may be wet.
[0004] One efficient method of detecting directly the presence of a cavity in a borehole
with cast bolts is revealed by the document SE 533769. This method makes it possible
to detect whether any cavities remain after a hardening grout and bolt have been introduced
into the borehole.
[0005] SE 533769 reveals a reinforcement means, a rock bolt, that has a passage for the
introduction of a medium into the borehole. The passage is provided with radially
directed holes, openings, through which the medium flows if there is a cavity at the
outer surface of the passage. This results in a change in pressure that can be measured,
and that indicates that a cavity is present in the immediate vicinity of the reinforcement
means. When using the method and the system according to the said document, the reinforcement
means is introduced into a borehole shortly after the borehole has been filled with
unhardened filler material that risks penetrating through the holes, the openings,
in the passage wall. This is solved by the holes, the openings, being provided with
a covering surface layer, a cover of a thin layer of a material, a rubber sheet, a
plastic film, or a thin membrane of paint or tape. During the supply of the pressurised
medium, the cover is pressed away from the holes, and penetrates out if a cavity is
present. The protective cover is normally destroyed, independently of whether there
is a cavity present or not. This means that if a cavity is not present, and the protective
cover has been destroyed by being put under pressure, the filler material can penetrate
into the opening. Thus the filler material risks clogging the passage, which cannot
then be used for the intended purpose. This risks influencing the measurement result.
[0006] There is thus a need to design the passage such that the problem with the penetration
of filler material through the holes, the openings, is avoided.
[0007] One purpose of the present invention, therefore, is to achieve an arrangement for
the detection of the presence of a cavity in a borehole, which arrangement solves
the problems with filler material that penetrates into the measurement passage.
[0008] This purpose of the invention is solved through an arrangement according to claim
1. Other distinctive features and advantages of the invention are made clear by the
non-independent claims.
[0009] Advantages and positive effects of the invention will be described below based on
embodiments of the invention and with reference to the drawings, which show:
Fig.1a shows schematically an arrangement according to the invention in a condition in which
supply of medium under pressure is not taking place;
Figure 1b shows the arrangement according to Figure 1 a in a condition in which supply of medium
under pressure is taking place.
[0010] Figure 1 shows schematically an arrangement 1 according to the invention. The arrangement
is intended to be used for the detection of the presence of a cavity 2 in a borehole
3 that has been made in a rock structure 4 during tunnel construction, mining, tunnelling
or similar according to the method revealed in SE 533769. The borehole 3 is intended
for the reception of a reinforcement means, a rock bolt 5.
[0011] The reinforcement means, the rock bolt 5, comprises a separate measurement tube 6.
The measurement tube has a passage 7 that is intended to introduce a pressurised medium
8 into a borehole that has been filled or partially filled by hardening grout 16.
The measurement tube 6 is constituted by a thin, hollow tube that is open in its longitudinal
direction, made from, for example, semi-rigid flexible plastic, or semi-rigid flexible
rubber that has a certain elasticity. The term "semi-rigid" is here used to describe
a flexible material that has the ability to regain essentially its original form after
the effect of a force on the material has ceased.
[0012] The measurement tube may, for example, be made from polyamide or polyurethane, or
a combination of these. Such materials are particularly suitable for this purpose,
but are not limiting for the invention. The semi-rigid aspect relates to the transverse
stability, when the measurement tube is bent or influenced in its transverse direction
it afterwards regains its original form. The measurement tube has a tube wall 9, the
thickness of which is selected such that an externally applied load from hardening
grout 16 or similar does not influence the function of the passage 7.
[0013] The measurement tube 6 with the passage 7 is provided with a passage opening at at
least one tube end, where the passage opening at the surface of the rock structure
is intended for the introduction of a medium into the borehole.
[0014] The diameter of the tube is considerably less that the diameter of the reinforcement
means, the rock bolt, but it has essentially the same length, or is longer than the
rock bolt. The length of the tube thus exceeds the depth of the borehole.
[0015] The measurement tube has an inner end 10 that is located in the vicinity of the bottom
end 11 of the rock bolt and the bottom 12 of the borehole, and it has a contact end
(not shown in the drawings) that extends out from the borehole. The measurement tube
is attached to the reinforcement means with one or several fastening arrangements
13. The fastening arrangements 13 are, for example, regularly distributed at points
along the length of the rock bolt and the tube. The fastening arrangements consist,
for example, of ties, tape, steel wire or similar.
[0016] The measurement tube 6 with the passage 7 may be attached to the rock bolt 5 during
manufacture of the bolt, in particular if the reinforcement means is an independent
rock bolt, for example a kiruna bolt. If the reinforcement member 5 is a twisted bolt,
the length of the bolt is adapted immediately before the rock reinforcement operation
is carried out. The bolt is manufactured from metal, for example steel. The measurement
tube 6 with the passage 7 is then attached to the rock bolt just before the rock bolt
with the measurement tube is introduced into, pressed into, the borehole filled with
hardening grout. After anchoring, the contact end of the measurement tube is available
for its connection to measuring equipment (not shown in the drawings) for the supply
of medium under pressure and the detection of a change in pressure in the medium in
the event of the presence of a cavity along the rock bolt, for example such equipment
as is shown in SE 533769.
[0017] The measurement tube 6 with the passage 7 is provided with at least one means 14
for the supply of a measurement medium 8 to the borehole 3, where the means 14 acts
as a valve and has a valve function that is activated by the application of pressure,
when measurement medium under pressure is supplied to the passage 7.
[0018] The means 14 is designed as a cut, a section,that penetrates the wall 9 of the tube,
through the side surface of the passage. The means 14, the cut, has two cut surfaces
15a, 15b that make contact with each other. In their uninfluenced condition, the cut
surfaces 15a, 15b are in contact with each other, and seal the cut. No material has
been removed from the tube in the cut surfaces. The measurement tube consists of a
plastic material of a semi-rigid type, and this has the effect that the means, the
cut, acts as a valve. The means 14 is in this way arranged to be opened when placed
under pressure from the inside of the passage 7.
[0019] When the measurement tube 6 with the passage 7 is supplied with a medium 8 under
pressure the means 14, the cut, opens and the cut surfaces 15a, 15b are pressed apart
such that an opening, a passage, arises between the cut surfaces, as is shown in Figure
1 b. The passage is united with the outer surface of the wall of the tube when the
pressurised medium is supplied. If a cavity is present at the outer surface of the
measurement tube, the medium 8 under pressure will be pressed out, and this results
in a change in pressure that can be measured, which indicates the presence of a cavity,
an empty space, along the rock bolt 5.
[0020] One advantage of the cut surfaces 15a, 15b being pressed apart is that, if there
is a thin membrane of solidified grout outside of the measurement tube 6, this membrane
can be burst by the pressure in the measurement medium 8 that has been supplied. The
force that influences the cut corresponds to the pressure multiplied by the area of
the passage. The cut has a considerably greater area of passage than, for example,
the holes or perforations that have been previously suggested. The force, and thus
the bursting ability, is for this reason greater.
[0021] When the passage 7 is not being supplied with medium under pressure, the means 14,
the cut, remains closed. The means is thus arranged to be closed in a condition in
which measurement medium under pressure is not supplied. This has the effect that
unhardened grout is essentially fully prevented from pressing in through the means
and sealing the passage 7. In contrast to previously suggested solutions, it is not
necessary to cover the opening with any cover, which saves a lot of time and will
be significantly more cost-efficient.
[0022] The means 14 has in this way a valve function that, furthermore, essentially allows
the transport of medium in only one direction. The means thus acts as a non-return
valve, and has an effect as that of a non-return valve that allows measurement medium
8 supplied under pressure to be transported out from the passage 7 through the open
means 14, but prevents unhardened grout from entering the passage 7 when the means
14 is closed and the passage 7 is not being supplied with a medium 8 under pressure.
[0023] By selecting material and adapting the number of means 14 and the length of the cuts,
it is achieved that the means opens only when the pressure in the pressurised medium
8 that is supplied exceeds a certain limiting value. The possibility of controlling
the means is in this way obtained.
[0024] It is preferable that the measurement tube be provided with several means 14, cuts,
distributed along its complete length and circumference. The measurement tube is provided
with several means along its length, in particular in the region close to its inner
end, since it is more common that cavities arise at the inner end, close to the bottom
of the borehole.
[0025] The contact end of the measurement tube is connected during measurement to measuring
equipment of the type that is described in SE 533769 (not shown in the drawings).
1. An arrangement (1) for the detection of the presence of a cavity (2) in a borehole
(3) intended for the reception of a reinforcement means comprising a measurement tube
(6) with a passage (7) whereby the measurement tube (6) comprises at least one means
(14) for the supply of a measurement medium (8) to the borehole (3), wherein the means
is characterised by comprising a cut arranged through a wall (9) of the tube, said cut having two cut
surfaces (15a, 15b) that make contact with each other, where the means (14) functions
as a valve that is activated by the application of pressure when measurement medium
(8) is supplied to the passage (7), and wherein the means (14) is opened only when
the pressure in the supplied medium exceeds a threshold value.
2. The arrangement according to claim 1 where the means (14) is arranged at the tube
wall (9) of the measurement tube and is opened on the supply of medium (8).
3. The arrangement according to claim 1 or 2, where the means (14) is arranged to be
closed when no measurement medium (8) is supplied.
4. The arrangement according to any one of claims 1-3 where the means acts as a non-return
valve where the means (14) is opened on the supply of measurement medium (8) under
pressure and allows the measurement medium under pressure to be transported out through
the open means from a passage (7) arranged in the measurement tube (6), and that the
means is closed when measurement medium under pressure is not supplied, whereby grout
is prevented from entering the passage (7).
5. The arrangement according to any one of claims 1-4, where the material of the measurement
tube (6) comprises a semi-rigid plastic material.
6. The arrangement according to any one of claims 1-5, where the measurement tube is
provided with a large number of means (14) distributed along the complete length of
the measurement tube (6).
1. Vorrichtung (1) zum Erkennen der Anwesenheit eines Hohlraums (2) in einem Bohrloch
(3), vorgesehen für die Aufnahme eines Verstärkungsmittels umfassend ein Messrohr
(6) mit einem Durchgang (7),
wobei das Messrohr (6) zumindest ein Mittel (14) zum Zuführen eines Messmediums (8)
zu dem Bohrloch (3) umfasst, wobei das Mittel dadurch gekennzeichnet ist, dass es einen durch eine Wand (9) des Rohrs angeordneten Schnitt umfasst, welcher Schnitt
zwei Schnittflächen (15a, 15b) aufweist, die Kontakt miteinander herstellen, wobei
das Mittel (14) als ein Ventil funktioniert, das durch das Aufbringen eines Drucks
betätigt wird, wenn das Messmedium (8) dem Durchgang (7) zugeführt wird, und wobei
das Mittel (14) nur geöffnet wird, wenn der Druck in dem zugeführten Medium einen
Schwellenwert überschreitet.
2. Vorrichtung nach Anspruch 1, wobei das Mittel (14) an der Rohrwand (9) des Messrohrs
angeordnet ist und bei der Zuführung des Mediums (8) geöffnet wird.
3. Vorrichtung nach Anspruch 1 oder 2, wobei das Mittel (14) so ausgelegt ist, dass es
geschlossen wird, wenn kein Messmedium (8) zugeführt wird.
4. Vorrichtung nach einem der Ansprüche 1 bis 3, wobei das Mittel als ein Rückschlagventil
funktioniert, wobei das Mittel (14) bei der Zuführung des unter Druck stehenden Messmediums
(8) geöffnet wird und ermöglicht, dass das unter Druck stehende Messmedium durch das
geöffnete Mittel aus einem in dem Messrohr (6) angeordneten Durchgang (7) herausgefördert
wird, und dass das Mittel geschlossen wird, wenn das unter Druck stehende Messmedium
nicht zugeführt wird, wobei das Eindringen von Injektionsgut in den Durchgang (7)
verhindert wird.
5. Vorrichtung nach einem der Ansprüche 1 bis 4, wobei das Material des Messrohrs (6)
ein halbsteifes Kunststoffmaterial umfasst.
6. Vorrichtung nach einem der Ansprüche 1 bis 5, wobei das Messrohr mit einer großen
Anzahl von entlang der Gesamtlänge des Messrohrs (6) verteilten Mitteln (14) versehen
ist.
1. Dispositif (1) de détection de la présence d'une cavité (2) dans un trou de forage
(3) destinée à recevoir un moyen de renforcement comprenant un tube de mesure (6)
avec un passage (7), le tube de mesure (6) comportant au moins un moyen (14) d'alimentation
d'un milieu de mesure (8) vers le trou de forage (3), dans lequel le moyen est caractérisé
en comprenant une coupe agencée à travers la paroi (9) du tube, ladite coupe ayant
deux surfaces de coupe (15a, 15b) qui entrent en contact l'une avec l'autre, dans
lequel ledit moyen (14) fonctionne comme une soupape qui est activée par l'application
de pression lorsque le milieu de mesure (8) est fourni au passage (7), et dans lequel
le moyen (14) n'est ouvert que lorsque la pression dans le milieu fourni dépasse une
certaine valeur de seuil.
2. Dispositif selon la revendication 1, dans lequel le moyen (14) est disposé au niveau
de la paroi de tube (9) du tube de mesure et est ouvert lors de l'alimentation du
milieu (8).
3. Dispositif selon la revendication 1 ou 2, dans lequel le moyen (14) est disposé de
manière à être fermé lorsqu'aucun milieu de mesure (8) n'est fourni.
4. Dispositif selon l'une quelconque des revendications 1 à 3, dans lequel le moyen agit
comme un clapet antiretour, le moyen (14) étant ouvert au moment de l'alimentation
du milieu de mesure (8) sous pression et permettant au milieu de mesure sous pression
d'être évacué à travers le moyen ouvert à partir d'un passage (7) disposé dans le
tube de mesure (6), et que le moyen est fermé lorsque le milieu de mesure sous pression
n'est pas alimenté, ce qui empêche le mortier d'entrer dans le passage (7).
5. Dispositif selon l'une quelconque des revendications 1 à 4, dans lequel le matériau
du tube de mesure (6) comprend une matière plastique semi-rigide.
6. Dispositif selon l'une quelconque des revendications 1 à 5, dans lequel le tube de
mesure est muni d'un grand nombre de moyens (14) répartis sur toute la longueur du
tube de mesure (6).