Yieldable rock anchor

Abstract

The invention relates to a yieldable rock anchor comprising an anchor element extending along a longitudinal center axis and having a first end, a second end and an outer surface. An anchor plate is attached near the first end of the anchor element, and an anchor head is secured to the first end of the anchor element and adapted to clampingly engage the anchor plate. On its outer surface, the anchor element is provided along at least substantially its entire length with a plurality of ribs. A plurality of sleeves, each sleeve having two opposing ends, for covering some of the plurality of ribs is fixedly arranged on the outer surface of the anchor element such that each of the opposing ends at least substantially sealingly engages the outer surface of the anchor element.

Claims

1. A yieldable rock anchor, comprising: an anchor element extending along a longitudinal center axis and having a first end, a second end and an outer surface, an anchor plate attached near the first end of the anchor element, and an anchor head secured to the first end of the anchor element and adapted to clampingly engage the anchor plate, wherein the anchor element is provided, on its outer surface with a plurality of ribs, and wherein one or more sleeves for covering some of the plurality of ribs, with each sleeve having two opposing ends and being fixedly arranged on the outer surface of the anchor element such that each of the opposing ends at least substantially sealingly engages the outer surface of the anchor element, while an inner surface of each sleeve is spaced apart from the outer surface of the anchor element except at the opposing ends of each sleeve.

2. The yieldable rock anchor according to claim 1, wherein each sleeve is one of a single-piece member and a multi-piece member.

3. The yieldable rock anchor according to one of claim 1, wherein each sleeve is formed from a material selected from the group of materials having a same tensile strength or a lower tensile strength than a tensile strength of the anchor element.

4. The yieldable rock anchor according to claim 3, wherein the material forming each sleeve and the material forming the anchor element is the same material.

5. The yieldable rock anchor according to claim 1, wherein each sleeve covers a length interval of the outer surface of the anchor element, and wherein uncovered length intervals between adjacent sleeves are bigger than covered length intervals.

6. The yieldable rock anchor according to claim 1, wherein the sleeves cover between 10% and 50% total length of the anchor element.

7. The yieldable rock anchor according to claim 1, wherein a separate sealing element is disposed at each of the two opposing ends of each sleeve between the sleeve and the outer surface of the anchor element.

8. The yieldable rock anchor according to claim 7, wherein the separate sealing element is an elastomeric sealing element.

9. The yieldable rock anchor according to claim 1, wherein the anchor head is formed integrally with the anchor element.

10. The yieldable rock anchor according to claim 1, wherein the anchor head is a nut in mating engagement with a threaded portion on the anchor element, and wherein a shear pin extends through the threaded portion and the nut at right angle to the longitudinal center axis.

11. The yieldable rock anchor according to claim 1, wherein the plurality of ribs on the outer surface of the anchor element are one of continuous ribs, broken ribs and staggered ribs.

12. The yieldable rock anchor according to claim 1, wherein the anchor element is at least one of a solid rod, a hollow rod and a stranded wire.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Currently preferred embodiments of a yieldable rock anchor according to the present invention will now be described in more detail with reference to the accompanying schematic figures.

(2) FIG. 1 shows a side view of a first embodiment of a yieldable rock anchor according to the present invention.

(3) FIG. 2 shows a partially broken away side view of a second embodiment of a yieldable rock anchor according to the present invention.

(4) FIG. 3 is an enlarged portion of FIG. 2, showing a sleeve fixedly arranged on an outer surface of an anchor element in more detail.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a side view of a first embodiment of a yieldable rock anchor, or rock bolt, generally designated at 10. The rock bolt 10 includes an anchor element 12 having a first end 14, a second end 16 and an outer circumferential surface 18. The second end 16 may have an oblique cut, as shown, or may be a blunt end. In the embodiment of FIGS. 1 to 3, the anchor element 12 is in the form of a solid steel rod.

(6) An anchor plate 20, taking the form of a dished plate in the embodiment shown, is received on the anchor rod 12 near its first end 14. An anchor head 22 secured to the first end 14 of the anchor rod 12 is adapted to clampingly engage the anchor plate 20 and in the present embodiment takes the form of a domed anchor nut having a hexagonal portion at its free end. The rock bolt 10 shown in FIG. 1 is of the forged head type, which means that the anchor head 22 is formed integrally with the anchor rod 12 by forging.

(7) On its outer surface 18 the anchor rod 12 is provided along its entire length with a plurality of ribs 24 formed integrally with the anchor rod 12. A plurality of hollow cylindrical sleeves 26, two of which are shown in FIG. 1, cover certain portions or length intervals of the outer surface of the anchor rod 12. Each sleeve 26 has two opposing ends 28, 30 and is fixedly arranged on the outer surface of the anchor rod 12 by pressing the opposing ends 28, 30 against the outer surface 18 of the anchor rod 12, e.g. using a crimping process, whereby each of the opposing ends 28, 30 at least substantially sealingly engages the outer surface 18 of the anchor rod 12. At least substantially sealingly engages in the context of the present invention means that the opposing ends 28, 30 of each sleeve 26 need not form a waterproof sealing between the sleeve 26 and the outer surface 18 of the anchor rod 12, but will form a sealing which substantially prevents grout or resin to enter into a sleeve 26.

(8) In the embodiment as shown, the anchor rod 12, the anchor plate 20, the anchor head 22 and the sleeves 26 are all made of steel. Further as shown, the sleeves 26 have a smooth outer surface, but may have a non-smooth surface in alternative embodiments not shown.

(9) The hexagonal end portion of the anchor head 22 is able to cooperate with a mounting adapter (not shown) used to set the rock bolt 10 into a borehole (not shown).

(10) The anchor rod 12 may for example have a diameter in the range of 12 to 40 mm, and may have a length in the range of 1.5 to 10 m, with 3 to 4 m being a typical length. The sleeves 26 may for example be 10 to 100 cm long, and a rock bolt 10 having a typical length of 4 m may be provided with four sleeves 26 each having a length of 10 to 30 cm.

(11) Each sleeve 26 when mounted onto the anchor rod 12 serves to cover a length interval or zone of the outer surface 18 of the anchor rod 12 such that all ribs 24 on that length interval are masked or concealed. Therefore, by mounting the sleeves 26 onto the anchor rod 12, first zones or first length intervals 32 are defined which are not covered by the sleeves 26, and second zones or second length intervals 34 are defined, where the sleeves 26 mask the ribs 24.

(12) As is well-known to skilled persons in the field to which the present invention pertains, grout or resin is used to fasten a rock bolt in a borehole. The first zones 32 of the rock bolt 10 will bond to the borehole wall by means of the grout or resin present in the borehole and will thus form zones which provide a high static load bearing capability.

(13) In the second zones 34, however, only the sleeve 26 will bond to the borehole wall, whereas the outer surface 18 of the anchor rod 12, in each second zone 34, will be kept free or at least substantially free from grout or resin, thus retaining the capability to yield under e.g. dynamic loads. As shown (cf. FIG. 3), an inner surface of each sleeve 26 does not contact the outer surface 18 of the anchor rod 12 except for the opposing end portions 28, 30. The sleeves 26 as shown are single-piece members, but may consist of two or more parts in embodiments not shown.

(14) FIG. 2 shows a schematic side view of a second embodiment, which is similar to the first embodiment except for the anchor head 22. In the second embodiment, the anchor rod 12 is provided on its outer surface 18 with a thread 36 in an end portion including the first end 14. A domed anchor nut 38 matingly engages the thread 36 and is provided with a shear pin 40 extending transversally through a hexagonal portion of the anchor nut 38 and the anchor rod 12. Shear pin 40 blocks anchor nut 38 against rotation relative to anchor rod 12 when installing rock bolt 10 into a borehole. Once the grout or resin used for fastening the rock bolt 10 in the borehole has fully cured, a torque applied to the anchor nut 38 may be increased until the shear pin 40 breaks, thus allowing to tighten the anchor nut 38 and anchor plate 20 against a rock face.

(15) FIG. 3 shows an enlarged view of a sleeve 26 mounted onto the anchor rod 12. As shown, ring-shaped sealing elements 42 may be used to further enhance a sealing action between the opposing ends 28, 30 of sleeve 26 and the outer surface 18 of anchor rod 12. In the embodiment as shown, the sealing elements 42 are elastomeric O-ring seals.

(16) Typical embodiments of rock bolts 10 of the present invention will have more than just two sleeves 26. By suitably selecting the position and length of the sleeves 26, the rock bolt 10 can easily be tailored to provide yielding and non-yielding characteristics, as desired for a given application.