Field of the Invention
[0001] The present invention relates to tunnelling through rock subject to squeezing, and
to a two-stage rock bolt suitable for use in such tunnelling.
Background Art
[0002] In some localities such as the Alps in Europe, the rock formations are not static.
Instead, in the event that a tunnel is driven through the rock, then the rock is subject
to "squeezing". What this means is that the rock is to some extent plastic and moves
under the force or pressure applied to the rock by the overlying strata in such a
way as to squeeze or reduce the cross-sectional area of the tunnel. Naturally, such
rock strata is fraught with difficulty for tunnellers and is normally avoided. As
a consequence, either tunnels for transport purposes, or tunnels for mining purposes,
have generally hitherto not being built in such rock strata.
DE 30 08 727 A1,
DE 38 20 700 A1,
DE 26 44 329 A1,
DE 32 36 569 A1 disclose each a method for pathly lining a tunnel which is subject to sqeezing
Genesis of the Invention
[0003] The genesis of the present invention is a desire to provide a method whereby such
tunnelling can be carried out.
Summary of the Invention
[0004] In accordance with the present invention there is disclosed a method of preparing
for concrete lining a tunnel through rock subject to squeezing according to claim
1, said method comprising the steps of:
- (i) placing a plurality of spaced apart plates over the interior of said tunnel, each
of said plates being secured by a two-stage rock bolt,
- (ii) allowing said squeezing rock to initially deform said rock bolts and drive said
plates into edge abutment,
- (iii) placing said rock bolts into a final tensioned condition, and
- (iv) using said edge abutting plates to comprise, or support, formwork for said concrete
lining.
[0005] Further preferred aspects of the method are claimed in the subclaims. A two-stage
rock bolt suitable for this method can comprise a tendon, a first anchor means adapted
to be anchored in a hole in said rock, and having associated therewith a pinch means
through which said tendon can pass by deforming, a second anchor means including a
trigger means and carried by said tendon adjacent said first anchor means, and an
elongate release extending alongside said tendon from said trigger means beyond said
rock, said release being operable to activate said trigger means to thereby actuate
said second anchor means.
[0006] A two-stage rock bolt suitable for this method can further comprise one or more of
the following features:
the first anchor may include grout located between said hole and said tendon. Said
first anchor may comprise a mechanical or point anchor. Said pinch means may comprise
a longitudinally split tube having a constricted interior. Said constricted interior
may have a generally S-shaped configuration. Said pinch means may be located between
the tip of said rock bolt and said first anchor. Said pinch means may be located immediately
adjacent, and abutting, said first anchor. Said elongate release may comprise a pull
chord. Said trigger means may comprise a transversely split ring, two portions of
said ring overlapping and including two pairs of aligned orifices, and a pin retained
in each said pair of aligned orifices by a friction fit whereby removal of said pin
activates said trigger means. A resilient means may urge said split ring portions
apart. Said resilient means may comprise an O-ring in compression. Said trigger means
may be located between first and second co-operating portions of said second anchor.
Said trigger means when triggered may permit said first and second co-operating portions
to commence their co-operation. Said first portion may be a barrel having a tapered
interior and said second portion may be a frusto-conical wedge which mates with said
tapered interior. Said first anchor may permit a loading of said tendon of approximately
50 kN and said second anchor may permit a loading of said tendon of approximately
330 kN. Said tendon may be a cable. Said tendon may be solid.
[0007] For the tensioning of such a two-stage rock bolt one can make use of the steps of:
(i) installing said rock bolt in a blind hole drilled in rock subject to squeezing,
(ii) activating a first anchor carried adjacent the tip of said rock bolt,
(iii) allowing tension to a first extent to be created in said rock bolt,
(iv) activating a second anchor carried adjacent said first anchor, and
(v) allowing tension in excess of said first extent to be created in said rock bolt.
[0008] With view to the tensioning of such a two-stage rock bolt, said tension to said first
extent may be created by rock squeezing and deformation of the tendon of said rock
bolt. Said tension beyond said first extent may be created by rock squeezing. Said
tension beyond said first extent may be created by applying a mechanical force to
the tendon of said rock bolt.
[0009] In connection with the present invention one may use a method of grouting a rock
bolt in a blind hole where a hollow breather tube is located alongside the rock bolt
and extends between opposite ends of the hole to allow escape of air from the closed
end of hole as grout is inserted into the open end of the hole, said method comprising
the step of:
- (i) inserting an electric circuit into said breather tube and extending beyond the
end thereof,
- (ii) said electric circuit including an indicator means at said open end of said hole
and a sensor means at said closed end of said hole, said sensor means being activated
by said grout reaching same to thereby indicate that said grout insertion should close.
[0010] Thereby, said sensor means may comprise a pair of electrical contacts and said grout
may be electrically conductive. Said indicator may comprise light. Further, said light
may incorporate at least one light emitting diode (LED).
Brief Description of the Drawings
[0011] The present invention will now be described with reference to the accompanying drawings
in which:
Fig. 1 is a transverse cross-sectional view through a tunnel showing the position
of steel plates prior to squeezing having taken effect,
Fig. 2 is a view similar to Fig. 1 but showing the position of the steel plates after
squeezing has taken effect,
Fig. 3 is a longitudinal cross-sectional view through the tip of a first two-stage
cable tendon rock bolt,
Fig. 4 is a longitudinal cross sectional view of the trailing end of the rock bolt
of Fig. 3,
Fig. 5 is a view similar to Fig. 3 but of a second rock bolt, and
Fig. 6 is a truncated longitudinal cross-section through a third one having a preferred
grout breather tube.
Detailed Description
[0012] As seen in Fig. 1, a tunnel 1 is excavated from rock 2 which is the subject of squeezing
forces indicated by arrows A. In order to prevent the tunnel 1 collapsing, in accordance
with the preferred embodiment of the present invention steel plates 4 are located
over the interior surface of the tunnel, each of the plates 4 being held in position
by means of a two-stage rock bolt 5. Each rock bolt 5 is positioned in a blind hole
6 which is drilled radially into the rock 2.
[0013] In the situation illustrated in Fig. 1, prior to squeezing having taken place, there
is a small gap 8 between each of the steel plates 4. However, in the situation illustrated
in Fig. 2 where squeezing has both commenced and progressed to a certain degree, the
movement of the rock 2 effectively eliminates the gaps 8 so, that the steel plates
4 edge abut. The rock bolts 5 are two-stage rock bolts in that the first stage which
arises immediately after installation of the rock bolts 5 permits the intended small
movement of the rock 2 so as to carry out the squeezing to the requisite extent. Thereafter,
once the gaps 8 have been eliminated, the rock bolt is tensioned to its final tension
which is intended to ensure that no further squeezing of the rock 2 takes place. In
the condition illustrated in Fig. 2, the steel plates 4 are edge abutted one against
the other and thus form a suitable boundary which can be used for formwork for a concrete
lining 9 indicated by broken lines in Fig. 2 and which is intended to provide the
final support for the walls of the tunnel 1. Alternatively, the steel plates 4 can
support formwork which is used in the construction of the concrete lining 9.
[0014] It will be appreciated that depending upon the nature of the rock 2, the steel plates
4 and rock bolts 5 may also be required on the floor of the tunnel, however, this
is not illustrated in Figs. 1 and 2 in order not to overburden the diagrams,
[0015] Each of the rock bolts 5 in Figs. 1 and 2 has a leading end 11 and a trailing end
12. In Fig. 3 a longitudinal cross-section through the leading end 11 of the first
rock bolt 15 is illustrated. The rock bolt 15 has a tendon 16 formed from a cable
fabricated from steel wires. A portion of the tendon 16 intermediate two annular washers
17, 18 is provided with a tube 19, for example made from plastics material such as
irrigation pipe extruded in high density polyethylene (HDPE). The tendon 16 is able
to slide through the tube 19.
[0016] A grout tube 21 passes through the trailing washer 17. In addition, a secondary tube
22 also passes through both washers 17 and 18 and a pull cord 23 passes through the
secondary tube 22.
[0017] The leading washer 18 is mounted on a pinch tube 25 (of the general type illustrated
in Fig. 3 of
US Patent No. 7,037, 046) which has a constricted interior passage 26 which is substantially S-shaped. The
pinch tube 25 is longitudinally split so as to be formed from two portions which are
clamped together about the tendon 16 and held in position by means of two keeper rings
27, 28.
[0018] Abutting the pinched tube 25 is a barrel 30 which has a tapered interior 31 which
matches the taper on a frusto-conical wedge 40 which surrounds the tendon 16. The
leading end of the barrel 30 is machined with an annular groove 33. A transversely
split annular keeper 34 has a re-entrant annular flange 35 which is retained in the
groove 33. The two parts of the annular keeper 34 overlap and are provided with two
pairs of aligned orifices through each pair of which a corresponding pin 36A (Fig.
3 or 36B Fig. 5) is retained by means of a friction fit. Within the keeper 34 an O-ring
37 is retained in compression. In addition, the annular keeper 34 clamps on the wedge
40 and retains same in position with the internal diameter of the passage through
the wedge 40 being sufficient to permit the tendon 16 to slide relative to the wedge
40. An important function of the intact keeper 34 is to maintain separation between
the locking taper of the wedge 40 and the barrel 30.
[0019] The pull cord 23 is bifurcated (Fig.6) and one portion thereof 23A is connected to
the pin 36A illustrated in Fig. 3. On the other side of the apparatus illustrated
in Fig. 3, and therefore not visible in Fig. 3, is another pin 36B (illustrated in
Fig. 5) which is connected to the other portion 23B of the bifurcated pull cord 23.
[0020] Turning now to Fig. 4, the trailing end 12 of the rock bolt 15 is illustrated. The
trailing end of the tendon 16 passes through a central aperture 42 in the steel plate
4. Abutting against the steel plate 4 is a conventional locking mechanism in the form
of an internally tapered barrel 130 and a frusto-conical wedge 140 which are capable
of clamping the tendon 16 so as to place same in tension. The grout tube 21 passes
through a corresponding opening in the plate 4 and a similar opening is provided for
the pull cord 23.
[0021] After the blind hole 6 has been drilled, the leading end 11 of the first rock bolt
15 is passed into the hole 6 to the maximum extent permitted by the length of the
tendon 16. The two annular washers 17 and 18 ensure that the tendon 16 is approximately
centred in the blind hole 6 and also define an interior space into which grout is
pumped in the direction of arrows B in Fig. 4 and C in Fig. 3. The grout fills the
volume between the two washers 17 and 18 and thus provides a first anchor which retains
the pinch tube 25 in position. Thereafter the tendon 16 can be lightly tensioned and
locked by means of the barrel 130 and wedge 140, thereby completing the installation
process.
[0022] As the rock 22 commences its squeezing action, the steel plate 4 is moved to the
left as seen in Fig. 4 thereby increasing the tension within the tendon 16 and forcing
the tendon 16 through the interior passage 26 of the pinch tube 25. This requires
the tendon 16 to be deformed, and preferably elastically deformed, and typically increases
the tension within the tendon 16 to approximately 50kN.
[0023] Once the plates 4 are edge abutting as illustrated in Fig. 2, then the pull cord
23 can be manually tugged so as to dislodge both pins 36A and 36B which retain the
annular keeper 34. As a consequence, the annular keeper 34 which now consists of two
separate parts radially expands under the urging of the resilient O-ring 37 thereby
permitting the wedge 40 to enter into the barrel 30 under the influence of the tension
within the tendon 16. That is to say, the wedge 40 and barrel 30 are permitted by
the rupturing of the keeper 34 to come closer together to form a second anchor which
securely grasps the tendon 16 and is capable of withstanding significant tension,
for example up to 300kN. As a consequence, further squeezing movement of the rock
2 is prohibited and the steel plates 4 remain in their abutting configuration illustrated
in Fig. 2 but do not move inwardly any further.
[0024] If desired, the significant tension in the tendon 16 can be created using a substantially
conventional cable jack.
[0025] A second rock bolt 5 is illustrated in Fig. 5 and takes the form of a rock bolt 115,
only the leading end 111 being illustrated. The tendon 16, pull cord 23, pinch tube
25, barrel 30, annular keeper 34 and wedge 40 are as before.
[0026] Instead of the first anchor being formed from grout as in Fig. 3, in the arrangement
of Fig. 5 a mechanical or point anchor 50 is provided. The anchor 50 consists of an
outer shell 51 which is preferably longitudinally split into three portions and which
has a serrated exterior surface 52. Located within the shell 51 is a tapered collet
53 which is urged to the left as seen in Fig. 5 by means of a spring 54 retained between
a washer 55 and a nut 56. The collet 53 is shaped to mate with the pinch tube 25.
The initial tension created within the tendon 16 following installation of the rock
bolt 115 expands the shell 51 thereby anchoring the anchor 50 relative to the blind
hole 6. As a consequence, the pinch tube 25 is fixed relative to the hole 6 in the
same way that the grout of Fig. 3 fixes the pinch tube 25 relative to the hole 6 in
the embodiment of Fig. 3.
[0027] At the trailing end of the rock bolt 115 the arrangement is the same as illustrated
in Fig. 4 save that the grout tube 21 is absent. In all other respects the operation
of the rock bolt 115 is the same as operation of the rock bolt 15.
[0028] In the third rock bolt 215 as illustrated in Fig. 6 the tendon 16, plate 4, barrel
130 and wedge 140 are as in Fig.4. Similarly, the washers 17 and 18 and pinch tube
25 are also as in Fig. 3. The grout tube 21 and the secondary tube 22 with its pull
cord 23 are also as in Fig. 3.
[0029] In Fig. 6 a breather tube 91 is provided which extends through the plate 4 and through
the washer 18. That is, the leading end of the breather tube 91 terminates in the
space between the two washers 17, 18 which is to be filled with grout (not illustrated).
In addition, the breather tube 91 has a pair of insulated wires 92 which run the length
of the breather tube 91 and terminate at its leading end in a pair of electrical contacts
93. At the trailing end of the rock bolt 215, the wires 92 terminate in a battery
98 and a light 99 preferably in the form of a light emitting diode (LED).
[0030] In operation the apparatus of Fig. 6 functions as follows: Grout is pumped into the
grout tube 21 as indicated by arrow B and exits from the grout tube 21 between the
washers 17, 18 as indicated by arrow C. As a consequence air is expelled from between
the washers 17, 18 entering the breather tube 91 as indicated by arrow D and exiting
the breather tube to the rear of the plate 4 as indicated by arrow E.
[0031] If the overall length of the bolt 215 was short, say 1-5 metres, when the space between
the washers 17,18 was full of grout, the grout would exit from the breather tube 92
(as indicated by arrow E) thereby signalling that no more grout should be pumped into
the grout tube 21. However, where the overall length of the rock bolt 215 is larger
(typically 30 metres or so) the resistance of the breather tube 92 to grout passing
through it prevents this simple system from working satisfactorily. Instead, grout
makes its way past one or both of the washers 17, 18 into places where it is not wanted
and grout continues to be pumped into the grout tube 21 for want of a stop signal.
[0032] Such a stop signal is provided by the wires 92. When the grout reaches the spaced
apart contacts 93, the grout (which is preferably water based) conducts sufficient
electric current to activate the LED 99. This signals that the pumping of the grout
should stop because the space between the washers 17, 18 is now full of grout. It
is to be understood in this connection that the grout tube 21, pull cord 23 and breather
tube 91 are preferably not located in the one vertical plate as indicated in Fig.
6 but are preferably radially spaced with approximately 120° spacing relative to the
longitudinal axis of the tendon 16.
[0033] In addition, the contacts 93 preferably are placed in the upper most portion of the
space between the washers 17, 18 to ensure that the grout which enters into this portion
of the space reaches the contacts 93 last.
[0034] The foregoing describes only some ways of the method of the present invention and
modifications, obvious to those skilled in the art, can be made thereto without departing
from the scope of the present invention. For example, although the tendon 16 is provided
by means of a cable, the tendon 16 could equally be a solid rod or a tube.
[0035] The term "comprising" (and its grammatical variations) as used herein is used in
the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting
only of".
1. A method of preparing for concrete lining a tunnel through rock subject to squeezing,
said method comprising the steps of:
(i) placing a plurality of spaced apart support members (4) over the interior of said
tunnel, each of said members being secured by a rock bolt (15, 115, 215),
said method being characterised by further comprising the steps of:
(ii) allowing said squeezing rock to initially deform said rock bolts and drive said
members (4) into edge abutment,
(iii) placing said rock bolts into a final tensioned condition, said rock bolts being
two stage rock bolts, and
(iv) using said edge abutting members to comprise, or support, formwork for said concrete
lining (9), said support members being plates (4).
2. The method as claimed in claim 1,
characterised by further comprising the step of
(v) forming said tunnel (1).
3. The method as claimed in claim 1 or 2,
characterised by the further step of:
(vi) allowing said final tensioned condition to arise through further squeezing of
said rock.
4. The method as claimed in claim 1 or 2,
characterised by the further step of:
(vii) creating said final tensioned condition by tensioning said rock bolt.
5. The method as claimed in any one of claims 1 - 4
characterised by the further step of :
(viii) forcing concrete into said formwork to create said concrete lining.
1. Verfahren zum Präparieren eines Tunnels durch Fels, welcher Felsdruck ausgesetzt ist,
für eine Betonauskleidung, wobei das Verfahren die Schritte umfasst:
(i) Anordnen einer Mehrzahl beabstandeter Stützelemente (4) über der Innenseite des
Tunnels, wobei jedes der Elemente durch einen Felsanker (15, 115, 215) gesichert wird,
wobei das Verfahren dadurch gekennzeichnet ist, dass es weiterhin die Schritte umfasst:
(ii) Zulassen, dass der druckhafte Fels die Felsanker anfänglich verformt und die
Elemente (4) dazu treibt, kantenmäßig aneinanderzustoßen,
(iii) Versetzen der Felsanker in einen endgültigen gespannten Zustand, wobei die Felsanker
Zwei-Stufen-Felsanker sind, und
(iv) Verwenden der kantenmäßig aneinanderstoßenden Elemente so, dass sie eine Schalung
für die Betonauskleidung (9) umfassen, oder stützen, wobei die Stützelemente Platten
(4) sind.
2. Verfahren nach Anspruch 1,
dadurch gekennzeichnet, dass es weiterhin den Schritt umfasst:
(v) Bilden des Tunnels (1).
3. Verfahren nach Anspruch 1 oder 2,
gekennzeichnet durch den weiteren Schritt:
(vi) Zulassen, dass der endgültige gespannte Zustand durch weiteren Felsdruck des Felsens entsteht.
4. Verfahren nach Anspruch 1 oder 2,
gekennzeichnet durch den weiteren Schritt:
(vii) Erzeugen des endgültigen gespannten Zustands durch Spannen des Felsankers.
5. Verfahren nach einem der Ansprüche 1 - 4,
gekennzeichnet durch den weiteren Schritt:
(viii) Drücken von Beton in die Schalung, um die Betonauskleidung zu erzeugen.
1. Procédé de préparation au revêtement par du béton d'un tunnel percé dans de la roche
sujette à compression, ledit procédé comprenant les étapes consistant à :
(i) placer une pluralité d'éléments de support (4) espacés les uns des autres sur
l'intérieur dudit tunnel, chacun desdits éléments étant fixé au moyen d'un boulon
à roche (15, 115, 215), ledit procédé étant caractérisé par le fait qu'il comprend en outre les étapes consistant à :
(ii) tout d'abord laisser ladite roche sujette à compression déformer lesdits boulons
à roche et amener lesdits éléments (4) à venir en aboutement latéral,
(iii) amener lesdits boulons à roche à un état final de tensionnement, lesdits boulons
à roche étant des boulons à roche à deux étages, et
(iv) utiliser lesdits éléments en aboutement latéral pour constituer, ou supporter,
un coffrage destiné audit revêtement de béton (9), lesdits éléments de support étant
des plaques (4).
2. Procédé selon la revendication 1,
caractérisé en ce qu'il comprend en outre l'étape consistant à :
(v) former ledit tunnel (1).
3. Procédé selon la revendication 1 ou 2,
caractérisé par l'étape supplémentaire consistant à :
(vi) amener ledit état de tensionnement final à se produire sous l'effet d'une compression
supplémentaire de ladite roche.
4. Procédé selon la revendication 1 ou 2,
caractérisé par l'étape supplémentaire consistant à :
(vii) produire ledit état de tensionnement final en tensionnant ledit boulon à roche.
5. Procédé selon l'une quelconque des revendications 1 à 4,
caractérisé par l'étape supplémentaire consistant à :
(viii) introduire du ciment à force dans ledit coffrage pour former ledit revêtement
de béton.