Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to an improved dowel device for g~outing in a
drillhole in hard material to provide reinforcement or anrhorage means.
ThP invention also includes a method oi reinforcing a hard ~edium> a method
of providing an anchosage in a hard medium, and a hard medium wherein the
said dowel devlce is grouted in a drillhole in said medium.
The praotlce of grouting dowels such as reinforcing dowels or anchor
bolts in hard medium such as, for example, hard rock is well establi~hed
and has been described in British Patent Specificatlons Nos. 953,056 and
1,408,366. In general the method consists in drilling into the medium a
hole oversize with respect to the dowel and inserting the dowel wlth a
surrounding layer of hardening grouting composition into the drillhDle so
tha~, on hardening of the grouting composition~ the dowel is bonded to the
drillhole wall. The dowel may terminate w~thin the drillhole or i~ nay
extend beyond the mouth of the drillhole and be provided with fixing means
for the attachment of other elemen~s or holding a compression plate agains~
the medium at the mouth of the drillhol~. The dowel is preferably fo~med
with a flared-out conical portion at its insertion end, which portion acts ;~
as a wedge on the grout material when the dowel is tensioned and thereby ` ;~
improves the holding power of the grout~ ;
- 20 It is an object of this inve~tion to provide an improved flared end
dowel device for grouting in a drillhole which can be quickly and simply
made from plain dowel stockD
In accordance with the invention a dowel device for grouting in a
drillhole comprises a dowel having a wedge member located in an opening -
formed in the ins~ertion end of the dowel whereby an end portion of the do~el
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is radially expanded and flared outwardly.
When the dowel is grouted into the drillhole with a set grouting
composition and is tensioned~ either by an end load applied to the dowel
end at the mouth of the drillhole or by deformation of the ad~acent r~c'~,
the grout adjacent to the flared~end portion of the dowel ls compressed
- and its holding power is thereby increased.
The dowel is conveniently split in one or more planes of cleavage
extending from the insertion end of the dowel and the wedge member is
inserted into the cleavage slit so as to spread the end ~egments. In the
preferred form of dowel the end portlon is split along a medial plane and a
; wedge member is placed in the cleavage slit to hold the end segments apart.
The wedge ~ember is preferably disposed in the cleavage slit so as to
engage the end segments at a position spaced from the dowel end~ leaving
a surface portion of at least one segment bet~een the said position of `
engagement and the dowel end free to fle~ inwardly under ex~ernal pressure `~
on the dowel. This disposition of the wedge member gives a most important
practical advantage when the dowel is grouted in rock which undergoes
plastic deformation after the grout has set7 With a conventional dowel
flared at its lnsertion end the tensile load will progressively increase
until the dowel breaks whereas wi~h dowels having the aforedescribed
flexible end seg~ent the tensile load wlll be partially released at a
characteristic yield pressure and ~he dowel continues to support the -
grouting material. Several successive cycles of lsad increase and partial ~- -
release can occur so that the reinforcing action of the dowel is maintained
' 25 throu hJuC substsDtial s~vessent of the surrounding rock strat~
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A convenient form of wedge member is a generally flat, rigid plate
with its two main faces parallel ~r convergent in the direction of i~sertion
into ehe dowel end. Advantageously the leading edge of th~ wedge element is
formed as a chisel edge whi~h facilitates its insertion into the dowel end
If the dowels are made of wood or plasti~s ~aterial) a metal chisel edged
wedge element, for example a steel element3 may àdvantageously be driven lnto
a plain dowel end eo split and flare the end, and locate the wedge element
iD one rapid operation.
The wedge member preferably extends outside the side surf~ce of the
dowel so that the projecting portion assists mixing of the grouting
composition when the dowel device is rotated in the drillhole. It is also
preferred that, the said projecting side portion of the wedge element is
provided with one or more outting ëdges whereby the capsules of encapsulated
grout components may be ruptured. The wed~e element may be disposed
symmetrically or eccentrically with respect to the longltudinal axis of ~he
dowel and~ when the dowel is used in a drillhole in soft material~ an
eccentric wedge element may advantageously be effective ~o score a groove
in the drillhole wall and thereby provide a key for the grout. The dowel
may be made from any constructional material which is sufficien~ly strong
to reinforce grouting material and is sufficiently flexible to permit its
end to b~ 1ared-out and held in the flared~out pOSitiOn by a wedgeO Thus
metals such as irsn, ccpper and aluminium and allDys such as steel, brass
and aluminium alloys are suitable. ~ood and hard plastics naterials are
also suitable. An especially useful dowel may be made from resin bonded
Z5 glasc fibre aDd preferably the glass Eibre Ls proYided as Ei1aments extending ~`
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parallel to the dowel axis whereby splitting of the dowel end along an axial
plane is facilitated.
Where the aforedescribed load release property is desirable the dowsl
preferably has a generally plain cylindrical surface bue otherwise the
cylindrical surface ~ay be uneven and be provided~ for example with
projections, grooves or threads to enlarge its surface area and improve
- the binding to the grout.
The invention also includes a method of reinforcing a hard medium such
as rock stra~a, or providing an anchorage in said medium, in which method a
dowel device as described above, having its insertion end expanded and
flared-out by means of a wedge member located in said end, is inserted into
an oversize drillhole in the said medium with said insertion end adjacent
to the blind end of the drillhole and a hardening grout material is disposed -
in ~he space between the dowel and the drillhole wall wherebyg when the
grout material h~rdens, the dowel is bonded to the drillhole wall7 me
grouting material may~ for example comprise portland cementJ calcium
sulphate hemihydrate plaster or a thermosetting resin. Two-component
encapsulated rapid h2rdening resins are especially conv2nient since the
components may be dispersed and mixed by a wedge element which pro~ects
beyond the side surface of the dowel.
In order to illustrate the $nvent$on further, a preferred dowel device
is hereinafter described, by way of example only, with referencè to the
- accompanying drawings wherein
Fig. 1 shows diagramatically in longitudinal Medial section a dowel
device ready or insertion into a drillhole in a rock mass; ~ -
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Fi8. 2 shows diagram~atically a longitudinal medial section of the
do~el device of Fig. 1 in a plane penpemdicular to the section of Fig. 1
after the device has been inserted in the drillholeO
me dowel device consists of a generally cylindrical dowel 10 which
is split along a medial plane eo provide a bifurcate portion 11 at the
insertion end having end segments 12 and 13. The segments 12 and 13 are
separated by a wedge element 14 which flexes the seg~ents outwardly so that
the end portion 11 flares out from the right cylindrical surface of the
remainder of the dowel lO.
me wedge element 14 is a rigid flat rectangular plate with generally
parallel transverse main faces 15 and 16 which are fined to converge at a
chisel edge 17. The end faces 18 and 19 converge with the main faces 15
and 16 at sharp rectangular cutting edges. The wedge element 14 engages
the segments 12 and 13 at positions ~0 and 21 respectively and the segment
portions intermediate these positions and the free segment ends are free to
flex inwardly.
To grout the dowel deviceg capsules of two-component resin are inserted
into a drillhole 22 drilled oversize with respect to the dowel device in
rock mass 230 Each capsule consists of an outer container 24 containing
hardenable resin 25 and an lnner container 26, located entirely within the
rontainer 24 and containing hardening catalyst 27 for the resin 25. BGth
contalners are made of thin easily rupturable thermoplastic material.
The dowel device is then simultaneously rotated and inserted into the
drillhole 22~ whereupon the capsule~ are engaged by the dowel segments 12
and 13 and the rectangular cutting edges of the wedge element 14. The
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thermoplastics containers are ruptured and thP contents are mixed and flow
into the space between the dowel lC and the wall of r~he drillhole 22 where
the resin subsequently hardens~
When a tensile load is placed on the dowel the resin between the
S flared-end portion 11 and the drillhole wall i5 compressed and its holding
power enhanced. ~hen the load is increased beyond a critical Yalue, the
tension i3 abruptly partially released probably due to inward flexing of the `
- ends of the segments 12 and 13. Ihe tension can then be increased again to
the critical value.
In a specific exam?le of dowel device the dowel was a rod 80 cm long x ~ ?
17 mm diameter made from axially oriented fibre glass filamenes bonded by
thermosettlng resin. me wet,~,~e element was a generaliy rectangular fibreglass
plate 32 mm x 15 mm x 4 mm th~ck located transversely in the split inse~tion
~`~ end of the dowel with its chisel edge 17 at a depth of 3.3 cm from the
dowel end, the dowel end se,gments being spread to an overall width of 32 mm,
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' 'The dowel was groueed in a 30 cm x 34 mm diameter drillhole in a roc~ mass
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with a polyester resin grout (which was initially encapsulated) and ~;
subjected to an axial pull. The load on the dowel was progressi~ely `~ ~-
increased up to 7 tons whereupon the flared dowel segments yielded and
released the load to about 2 tons. The load on the dowel then increased ;
again to the yield point at about 7 tons and was again released. me cycle
of load increase and release was repeated and the cycle continued
substantially in the same pattern whilst the dowel was withdr,a~n 10 cm
` along the drillhole. `
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