EP0014426B1

EP0014426B1 - Rock anchor

Info

Publication number: EP0014426B1
Application number: EP80100454A
Authority: EP
Inventors: Friedrich Peter Dr. Brandstetter
Original assignee: Gebirgssicherung Gesmbh
Current assignee: Gebirgssicherung Gesmbh
Priority date: 1979-01-31
Filing date: 1980-01-29
Publication date: 1984-08-01
Also published as: EP0014426A1; ES488377A1; BR8000563A; JPS55105098A; ZA80209B; AT8809T; US4369003A; ZA8000209B; DE2903694A1; AR222520A1

Description

The invention relates to a rock bolt, comprising a tension element that can be inserted into a borehole and clamped therein, the outer end of which protrudes from the borehole by means of a tension device, consisting of tension nut, tension sleeve with a conical bore at least over part of its length and an external thread, tension wedge means and Anchor plate can be tensioned against the mountains.
In a known rock anchor (DE-A-2624559), the tension element consists of a steel tube, on the outer end of which a thread is cut for screwing on a tension nut. Glass fiber synthetic resin rods are used as reinforcement elements in the steel tube. This rock bolt is fastened in a borehole using liquid synthetic resin; After the pressed-in synthetic resin has hardened, the entire anchor is stretched over the anchor plate by means of the tension nut against the mountains.
Such rock anchors have already proven themselves in practice because they can be relatively easily fixed in a borehole by means of the hardenable synthetic resin and can also be placed under tension by means of the tension nut and the anchor plate, so that the mountains above are held securely.
Another form of anchoring the tension element in the deepest hole in the form of an expansion sleeve has proven to be particularly simple. Such anchoring is e.g. in the pocketbook for tunnel construction 1978, Verlag Glück-auf GmbH, Essen, page 380. However, it does not appear from this document how to actually design a rock bolt of the type mentioned at the beginning with such an expansion sleeve.
From German Patent 1,014,471, a rock anchor of the type mentioned in the form of a cable anchor is known, which has a pull rope that can be inserted into a borehole and tightened therein. The outer end of this traction cable protruding from the borehole is tensioned against the mountains with a traction device consisting of traction nut, traction sleeve with conical bore, traction wedge means and anchor plate, the traction sleeve having an external thread. However, the wedging of the part used in the interior of the borehole is extremely imperfect, since the means proposed there can only be inserted with difficulty into the borehole without slipping, and secondly, the device proposed in the aforementioned document can only absorb low tensile forces. On the other hand, the connection between the pulling sleeve and the pulling rope in the known device is designed in such a way that the pulling rope must be cut to length before the pulling sleeve can be attached to it.
Based on this prior art, it is an object of the present invention to design a rock bolt according to the preamble of the main claim so that, on the one hand, the connection deep in the borehole between the tensile element and the borehole wall is durable, and the rock bolt is nevertheless easy to use, and on the other hand, the connection between the tension sleeve and to design the tension element in such a way that a simple, firm connection can be established without having to cut the tension element to length beforehand.
In a rock bolt comprising a pulling element that can be inserted into a borehole and clamped therein, its outer end, which protrudes out of the borehole, is allocated by means of a pulling device consisting of a pulling nut, a pulling sleeve with a bore that is conical at least over part of its length and an external thread and the anchor plate can be tensioned against the mountains, in that an expansion sleeve which is clawed into the borehole is placed on the inner end of the tension element inserted into the borehole and which can be tensioned with the inner end of the tension element via a spline wedge when the tension nut is rotated, and that the tension sleeve and the expanding wedge are fastened either by wedge shells placed on the ends of the tension element, or by cross wedges inserted into cruciform slots of the tension element ends, or by wedges which are inserted into conically expandable ends of the tension element.
Further preferred embodiments result from the subclaims.
Such a rock anchor has the great advantage that, depending on the respective conditions at the place of use, a smooth, tubular tension element, which does not have to have a thread for screwing on the tension nut, is cut to length, after which the expansion device consisting of expansion sleeve and expansion wedge is placed on the inner end and on the outside End the pulling device composed of the pulling sleeve, the pulling means, for example a pulling wedge, as well as pulling nut and anchor plate, are pushed on. Despite this simple design of the rock anchor, which can be assembled extremely quickly and economically, it has an excellent hold in the mountains because the expansion sleeve, which has barbs or the like on its outer circumference, firmly grips in the borehole.
In a further embodiment of the invention, the traction element is tubular, and both ends of the traction element are conically expandable and each receive a cross wedge provided with an axially extending injection hole for filling material.
In this embodiment of the rock bolt, in those cases in which the anchoring by means of the expansion sleeve in the borehole is not sufficient, a curable synthetic resin can be injected through the cross wedge attached to the outer end, which can further improve the anchoring in the borehole.
In a further development of the invention, crosswise slots are worked into the conically expandable ends of the tension element, the cross wedges being star-shaped and engaging with their arms in the slots.
This design of the cross wedges has the advantage that the material of the tension element cannot escape into the slots when there is a strong tensile load, which would impair the safe functioning of the rock bolt.
Instead of a traction wedge arranged between the conically tapered inner end of the traction sleeve and the substantially cylindrical end of the traction element, the traction means can consist of the conically widened end of the traction element and a paired bore of the traction sleeve that is conical at least over part of its length. This alternative has the advantage that the outside is cylindrical over its entire length and can therefore accommodate a very long thread. In addition, the injection hole of the cross wedge arranged directly at the head of the rock anchor is exposed, so that easier operation is possible.
According to a further feature of the invention, the tension element is a smooth GRP tube (glass fiber synthetic resin). This has the advantage that a very light and easy to transport material is available for the tension element, which can be easily cut to the required length at the place of use without reducing the tensile strength of the entire rock anchor. Instead of the smooth GRP pipe, a roughened GRP pipe can also be used.
According to an alternative, advantageous embodiment of the invention, the tension element is designed as a rod. This embodiment of the invention is particularly useful when the rock bolt is to be subjected to particularly heavy loads. If the tension element has the shape of a rod, wedge shells are expediently placed on both ends of the tension element. However, it is also possible to design the rod-shaped tension element in such a way that crosswise slots are provided at both ends, into which correspondingly shaped cross wedges are inserted.
Further details and advantages of the invention result from the following description of two exemplary embodiments, which are shown in the drawing.
Show it:

1 shows a longitudinal section, interrupted in the central region, of a tie rod designed according to the invention,
2 is a frontal view of the outer end of the tie rod, omitting the tie nut and the anchor plate,
3 is a frontal view of the inner end of the rock anchor,
4 a representation corresponding to FIG. 1 of a second exemplary embodiment,
5 shows a cross section along the line VV of FIG. 4,
6 shows a cross section along the line VI-VI of FIG. 4,
7 is a side view of a tension element in rod form with wedge shells placed thereon and two associated cross sections through the tension element and the wedge shells attached,
Fig. 8 is a top, side and bottom view of a cross wedge, and
9 is a side view of a tension element in the form of a rod with a cross wedge inserted into corresponding crosswise slots and two corresponding cross sections.

The rock bolt shown in FIGS. 1 to 3 consists of a tubular tensile element 10 made of GRP, on the outer end 12 of which a pulling device, generally designated 14, is placed, while the inner end 16 carries a spreading device, designated 18. With the help of the expansion device 18, the rock bolt is anchored in a borehole, while the outer end 12 with the pulling device 14 partially protrudes outwards from the borehole.
The expansion device 18 consists of an expansion sleeve 20 with a conical inner bore and an expansion wedge 22 with a conical outer surface. The expansion wedge 22, which is preferably made of GRP, has at its end of smaller diameter a radially outwardly projecting flange 24 against which the expansion sleeve 20 can be supported axially. The expansion sleeve 20 is provided on its outside with barbs 26 which can wedge in a borehole.
The pulling device 14 has a pulling sleeve 28 made of metal or GRP, the end 30 of which projects into the borehole and tapers conically. In the conical end 30, an existing wedge 32 made of GRP is inserted. A thread for receiving a tension nut 34 is rolled onto the cylindrical part of the tension sleeve 32, with the aid of which an anchor plate 36 can be pressed against the mountains.
Both the inner end 16 and the outer end 12 of the tension element 10 are slotted crosswise (slots 38), so that an expansion wedge 40 made of GRP can be pressed into each end, which has an axially extending injection bore 42.
When using the rock bolt designed according to the invention, the tubular tension element 10 is first cut to the required length, the slots 38 being subsequently made at both ends 12 and 16. A wedge 40 is inserted into each of the ends 12 and 16 thus prepared, after the expansion device 18 has been placed on the inner end 16 and the pulling device 14 has been placed on the outer end 12. Now the tie rod is inserted into a borehole and then braced. For this purpose, the tension nut 34 is rotated so that the anchor plate 36 is pressed against the mountain. The expansion sleeve 20, the barbs 26 of which find a hold in the borehole, shifts in the axial direction relative to the expansion wedge 22 and widens - for this purpose the inner end of the expansion sleeve 20 is slotted (slots 44) - until it completely claws into the borehole has and no more relative movement can take place. With further rotation of the tension nut 34, the Anchor plate 36 pressed firmly against the mountains, with the tension sleeve 28 being firmly and immovably seated on the tubular tension element 10 by the tension wedge 32.
If required, hardenable synthetic resin can then be injected through the injection hole 42 of the outer expansion wedge 40 up to a sealing ring 46; after hardening, the plastic additionally secures the rock bolt in the borehole.
It is possible to manufacture all parts of the mountain anchor from GRP, which has the advantage that the anchor is corrosion-resistant and resistant to all mountain waters.
In the variant shown in FIGS. 4 to 6, the two expansion wedges 40 are star-shaped, the arms 48 formed thereby engaging in the slot 38 of the conically widened ends 12 to 16 of the tension element 10 and closing them. As a result, the glass fiber of the tension element cannot escape into the slots 38 even in the event of greater tensile loads.
As can further be seen from FIG. 4, here the pull sleeve 28 made of GRP has a cylindrical outer shape, while its bore is flared outwards; against the conical inner wall of the bore there is pressed conically widened, slotted end of the tension element 10 with the help of the cross wedge 40. In this embodiment of the traction device 14, the cross wedge 40 with its injection hole 42 is easily accessible at the head of the rock anchor and is therefore more convenient to use.
Finally, as shown in FIGS. 4 and 5, an injection groove 50 is worked into the outside of the tension sleeve 28 and into the inside of the tension nut 34, which, when paired with one another, form a longitudinal bore. If this is necessary due to poor rock properties, hardenable synthetic resin can be injected through this longitudinal bore to fill the borehole. This injection hole is particularly favorable when the rock is anchored upwards because the synthetic resin can also easily get under the tension nut 34.
It is also envisaged to accommodate this injection hole in the reinforced wall of the draw sleeve in order to avoid weakening the same by said injection groove.
A rod-shaped tension element 10 is shown in a shortened form in FIG. On the tension element 10, two wedge shells 52 and 54 are placed, the outer diameter of which tapers somewhat from top to bottom in the drawing. Fig. 7 also shows corresponding cross sections through this embodiment of the invention at the respective upper and lower ends of the wedge shells.
FIG. 8 shows a cross wedge 40 which is provided for insertion into a tension element 10 in the form of a solid rod with corresponding slots arranged in a crosswise manner.
FIG. 9 shows a traction element 10 in the form of a solid rod with crosswise arranged slots, in which a cross wedge according to the embodiment of FIG. 8 is inserted.
In addition to the advantages already mentioned, the rock anchor designed according to the invention has the advantage that it can be set directly during propulsion and can be mechanically tensioned, wherein a backfilling with synthetic resin can be carried out subsequently if required.
Furthermore, this rock bolt can be inserted into a so-called adhesive cartridge with the end of the tension element widened by the cross wedge, even without a mechanical expansion device, which cartridge was inserted into the borehole beforehand. After the adhesive cartridge pierced by the tension element has hardened, the anchor can be prestressed in this way and subsequently filled with synthetic resin.

Claims

1. Rock anchor, comprising a tension member (10) which can be inserted in a borehole and fixed therein, the outer end thereof, projecting out of the borehole, being capable of being tensioned against the rock by means of a tensioning device (14) consisting of a tensioning nut (34), a tensioning sleeve (28) with a bore which is conical over at least part of its length and an external thread, tensioning wedge means and an anchor plate (36), characterised in that, mounted on the inner end (16) of the tension member (10) which is inserted in the borehole, there is an expander sleeve (20) which engages firmly in the borehole and which can be clamped to the inner end (16) .of the tension member (10) via an expander wedge (22) on rotation of the tensioning nut (34), and in that the tensioning sleeve (28) and the expander wedge (22) are secured either by wedge shells (52, 54) mounted on the ends (12, 16) of the tensioning member (10), or by cross-shaped wedges (40) inserted in cruciform slots in the ends (12, 16) of the tension member, or by wedges (40a) which are inserted in conically expandable ends (12, 16) of the tension member (10).

2. Rock anchor according to claim 1, characterised in that the tension member (10) is tubular and receives a wedge (40a) or cross-shaped wedge (40) provided with an axially extending injection bore (42) for a filling material.

3. Rock anchor according to claim 1 or 2, characterised in that the tension member (10) is a smooth or roughened fibreglass plastics tube.

4. Rock anchor according to claim 1, characterised in that the tension member (10) is in the form of a rod.

5. Rock anchor according to one claims 1 to 4, characterised in that the wedge tensioning means consist of a tensioning wedge (32) arranged between the conically tapering inner end (30) of the tensioning sleeve (28) and the substantially cylindrical end (12) of the tension member (10).

6. Rock anchor according to claim 1, characterised in that the tensioning sleeve (28) and the expander wedge (22) are fixed to the associated ends (12,16) of the tension member (10) by means of dissimilar means (52, 54; 40; 40a).

7. Rock anchor according to one of the preceding claims, characterised in that an injection groove (50) is incorporated in the outside of the tensioning sleeve (28) and/or in the inside of the tensioning nut (34).