Note: Descriptions are shown in the official language in which they were submitted.
1;286603
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METHOD OF STABLIZING A ROCK STRUCTURE AND STABLIZER THEREFOR
_ .
This invention relates to a method of stablizing a rock
structure and a stablizer adapted for performing the method.
In US patent 4,423,986 a rock stablizer is shown which
comprises a closed longitudinally fo:Lded tube which is
pressurized to expand to anchor in the borehole. This bolt pro-
vides an outstanding anchoring and the accepted diameter range of
the holes is extremely wide. However, the bolt is comparatively
expensive.
In the Swedish patent specification 8502981-7 a tubular
rock stablizer is shown which is expanded past the size of the
drillhole by means of an expansible body inserted into the
stablizer. Thereby the stablizer is anchored in the drillhole
by elastic compression of the rock surrounding the stablizer.
This allows the use of cheap stablizers but the expansible body
has a limited operational life due to the necessary high
pressure.
In US patent 3,3~9,567, a rock stablizer is shown which
comprises a tube to be inserted in the borehole and then expanded
at discrete points by pulsed magnetic fields induced by high
voltage pulses in a coil on a probe that is temporarily inserted
in the stablizer. The stablizer is cheap but the necessary
equipment very expensive and there are considerable safety
hazards due to the high voltage.
It is a feature of the invention to provide an efficient
method of stablizing a rock structure enabling the use of simple
stablizers which together with the method provide a low total
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cost for stablizers as anchored in the rock.
The present invention relates to a method of stabil-
izing a rock structure comprising providing an elongated ex-
pansible closed tubular stablizer of mild steel and a perimeter
equal to ~ D, drilling a hole in the rock of a diameter somewhat
larger than D to permit the tubular stablizer to be freely in-
serted in the drillhole, inserting the stablizer in the drillhole
with one of its ends, the bottom end first, coupling the outer
end of said stablizer to an external source of hydraulic high
pressure fluid, pressurizing the stablizer by a controlled supply
of hydraulic high pressure fluid to such an extent that the
stablizer is widened past the amount D by radial expansion
thereby filling the irregularities of the drillhole and widening
the rock elastically therearound, whereafter the stablizer is
relieved of pressure, emptied and left anchored in the drillhole
by the shrikage fit between the rock and the stablizer.
The present invention also relates to a tubular rock
stabilizer to be anchored by the method according to claim 1 in
a drillhole drilled in a rock ~tructure, comprising a closed
elongated tubular body of mild expansible steel having a peri-
meter equal to ~ D dimensioned to be freely insertable into a
drillhole of a diameter somewhat larger than D, the stablizer
being closed at one end which is the bottom end thereof, an
open inlet at the outer end portion of said stablizer opposite
said bottom, and means removably connectable to said inlet for
controllably supplying hydraulic high pressure fluid via said
inlet to the interior of said stablizer sufficiently to widen
said stablizer by radial expansion substantially past the
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perimeter value ~ D.
The invention will be described with reference to the
drawings. Figure 1 is a longitudinal section of a bolt inserted
in a drill hole prior to expansion.
Figure 2 is a section on the line 2-2 in Figure 1.
Figure 3 shows the bolt in Figure 1 after anchoring
by radial expansion.
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Fig 4 shows an alternative outer end portion for the stabili2er in
Fig 1.
Fig 5 shows an expansible stabilizer section intended for an
extension build-up of stabilizers provided by one or more
interconnected such sections, and outwardly terminated by the
end portion of Fig 4.
Fig 6 is a closure plug for the bottom end portion of such an
e~tens ion build-up.
Fig 7 is a non-expansible stabilizer section providing an
alternative for one or more extension section according to Fig
5.
The rock stabilizer 10 or roof bolt shown in Fig 1 comprises a
closed elongated straight cylindrical tube ll of steel of a property
providing uniform elongation under expansive load. ~ suitable steel
given as an example is the deep drawing quality steel Swedish
standard SS 141147. If the outer diameter of the tube 11 is
designated D cm, its perimeter would te ~ D cm. Unchanged in
perimeter the tube may have a slightly welled or somewhat irregular
cross-section for increased stiffness. The bottom end of the tube 11
is closed tightly by a circular plate 12 welded to the tube 11
preferably by friction welding. To the outer end i5 similarly
tightly connected a flange 13 with an outwardly protruding
cylindrical boss 14. ~n inlet 15 of a passage 16 to the interior of
tube 11 i5 provided on the bo~s 14.
The stabilizer 10 is freely inserted into a drillhole 20 drilled in
a rock structure 21 with a diameter somewhat larger than D cm. While
inserted, the stabilizer lO by its flange 13 keeps a supporting
plate 22 which surrounds the tube 11, resting against the rock 21.
Before or after insertion a diagrammatically indicated chuck Z5,
preferably of the type shown in US patent 4 423 986, Figs 1, 10, is
slipped and tightly set onto boss 14 and the opening 15 is supplied
under pressure control of a valve 26 by hydraulic high pressure
fluid under a pressure of up to 500 bar from a pump 27. This
pressurizes the interior of the stabilizer 10 causing a radial
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expansion thereof which fills the normal always present
irregularities of the drillhole and widens the surrounding rock
elastically as depicted in Fig 3. The pressure is then relieved and
the chuck 25 removed so that the stabilizer eventually is emptied of
fluid. ~Ithough some shrinking may take place at relief, the
stabilizer remains firmly anchored in the drillhole 20 due to the
significantly larger shrinkage fit of the rock 21 around the
expanded stabilizer 10. ~ suitable manometer or other instrument in
the hydraulic supply may be used for increased control during the
radial hydraulic expansion of the stabilizer 10.
~s an alternative the stabilizer 10 may be provided instead of the
boss 14 with a coupling nipple 28 of the type shown in Fig 4. In
such case a quick release coupling may be used for the hydraulic
high pressure fluid supply.
In order to match long drillholes by short lengths of expansible
stabilizers of the type in question, extensible expansible tubular
stabilizer sections 30 according to Fig 5 may be used, at will
combined with non-expansible ~narrow channel 36) sections 31 of the
type shown in Fig 7, both sections 30,31 having respectively male
and female coupling means 34,35 for tight interconnection of their
ends. ~ head 32 with a coupling means formed by a threaded hole 33,
Fig 4, provides the outer end of the extended stabilizer, to which
for example one or more non-expansible sections 31 can be tightly
connected as by threaded coupling means 34,35 and terminated within
the drillhole by one or more expansible sections 30 coupled thereto,
the last of them closed by a threaded plug 38, Fig 6.
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