EP0006703B1

EP0006703B1 - Ground anchor, method of making a ground anchor and corrosion-proof sleeve for use in said method

Info

Publication number: EP0006703B1
Application number: EP79301094A
Authority: EP
Inventors: John Vincent Brown
Original assignee: Fosroc International Ltd
Current assignee: Fosroc International Ltd
Priority date: 1978-06-17
Filing date: 1979-06-08
Publication date: 1982-09-15
Also published as: DE2963669D1; ZA792992B; BR7903733A; JPS557393A; ES481592A1; EP0006703A1; ATE1554T1

Abstract

A method of making on site, a ground anchor comprising an anchor element (9) having a corrosion proof sleeve (1) secured to an end portion of the element, comprises locating a number of lengths of the sleeve (1) about the end portion of the element (9), applying a cap (11) to the end of the sleeve, and supplying a self-setting composition via the cap into an annular clearance (15) between the sleeve (1) and the element (9). The cap (11) may be left in place to seal the end of the anchor and to protect the anchor during insertion into a borehole. The sleeve (1) preferably comprises an outer layer of plastics, an intermediante layer of set filler and an inner layer of metal. The invention includes the sleeved anchor element and the sleeve lengths themselves.

Description

The invention concerns ground anchors for use in the civil engineering, construction and mining industries for example. It also concerns a method of making the ground anchor and a corrosion-proof sleeve for use in the method.
There is a requirement for ground anchors to have at least a double corrosion protection about the central anchor element, such as that provided by a waterproof sleeve which is grouted on to the element. Such anchors are known, see for example United States Patent No. 3 641 772, which discloses an anchor assembly comprising an elongate sealing tube closed at one end and receiving a stressing cable with set material filling the space between the cable and the tube. Such an assembly is made in a workshop remote from the building site with the tube in the vertical position. The assembly is then transported to the site and placed in the bore. The tube is joined to the anchor element in a factory remote from the building site and each anchor must be purpose- built. It is also known from DE - A - 2511863 to make in a factory an anchor element having double corrosion protection. Such prior techniques make it expensive to manufacture and transport a small number of anchors for a specific application, and there is often a long delay before the anchors can be delivered to the site of use. There is therefore a need for a simple and cheap way of corrosion proofing anchor elements on site to specific requirements.
It is an object of the invention to provide a simple and cheap way of corrosion-proofing an anchor element on site to specific require- _, ments.
According to the invention there is provided a method of making a ground anchor to be received in a bore in the ground or like substrate, the ground anchor comprising an anchor element formed of a bar, tendon, or the like, the element being surrounded by a corrosion-proof sleeve made of plastics or the like, an annulus of set self-setting composition such as cement being present between the sheath and the element, characterised by

(i) locating about an end portion of the anchor element at a location adjacent the bore a plurality of lengths of corrosion-proof sleeve in end-to-end relation to cover the length of the element to be corrosion-proofed, each sleeve length being preformed and comprising at least two corrosion-proof layers,
(ii) applying a cap to the sleeve at the end of the anchor element, the cap having an inlet for self-setting composition, and
(iii) supplying a self-setting composition through the inlet, via the cap, into an annular clearance between the element and the sleeve there to set to secure the sleeve to the element.

Preferably the cap is secured to the anchor element by means of the self-setting composition to seal the end of the anchor against ingress of moisture and to protect the leading end of the anchor during insertion into a borehole.
The sleeve lengths will usually be connected together such that the sleeve is sealed against escape of self-setting composition during introduction of the composition into the sleeve.
Preferably the sleeved anchor element is upwardly inclined away from the cap for best escape of air whilst the self-setting composition is supplied into the sleeve.
The inlet is preferably located in the side of the cap. When the anchor is upwardly inclined for introduction of self-setting composition, the inlet is less liable to damage in this location, and the inlet is less likely to become blocked by dirt.
The sleeve preferably has at least two corrosion-proof layers. It is especially preferred for the sleeve to comprise three layers, the intermediate layer being of set filler such as a resinous or a cementitious grout and at least one of th_8"other two layers being of plastics. Most preferably the sleeve comprises an outer layer of plastics, an intermediate layer of set filler and an inner layer of metal. The metal inner layer serves to strengthen the sleeve for handling purposes.
The anchor element may be a bar having either a plain or a ribbed profile. Plain bars may be used with threaded nuts and plain washers, the nuts being screw-threaded on to a cooperatively threaded end portion of the bar.
Ribbed bars do not require the use of a nut and washer, but rely instead upon the ribs to transfer load from the tendon to the sleeve.
The method is particularly useful for corrosion proofing strand tendons. Known factory methods require "noding" of each strand to transfer the stress from the strands to- the sleeve. This noding involves removal of a polypropylene coating from the length of the tendon to be corrosion proofed, followed by untwisting of the strands and thorough cleaning off of any grease from the strands. A node is then applied to each strand whereupon the strands are re- twisted and secured inside the sleeve. The nodes serve to lock the strands to the sleeve.
When the method of the invention is used to corrosion proof a strand tendon on site, the ptastics sheathing is stripped off the tendon and the tendon surface is wiped free of grease without untwisting the strands. A metal ferrule is then compressed onto the end of the tendon for best transfer of tendon load to the sleeve. The sleeve is then secured to the end portion of the tendon by the method of the invention.
The sleeve should have longitudinally spaced apart external circumferential ribs and should be internally threaded to respectively provide a good key between the sleeve and the grout used to secure the element in the hole, and between the sleeve and the self-setting composition which is used to secure the sleeve to the anchor element.
The invention includes a ground anchor made by the method, and further includes the sleeve lengths themselves as new items of commerce.
The invention is described below by way of example with reference to the accompanying diagrammatic drawings in which:

Figure 1 is a side view, partly in section, of a length of sleeve for use in the method,
Figure 2 is a sectional view showing the sleeve being secured to an anchor element by the method of the invention, and
Figure 3 is a sectional view of an alternative method of securing together two sleeve lengths.

The sleeve 1 of Figure 1 comprises an outer tube 2 of plastics, the tube having spaced-apart castellations 3, an inner steel tube 4 having a thread 5, and an intermediate layer of set polyester resin 6. Both ends of the sleeve 1, only one end being shown for convenience in Figure 1, have two diametrically opposite recesses 7. Towards each end of the sleeve, an 0-ring 8 is located about the tube between the castellations 3.
In use, a ribbed steel bar 9, Figure 2, to be corrosion proofed for use as a ground anchor, is mounted on a trestle, not shown, at a construction site. A suitable number of sleeve lengths 1 are fitted over one end of the rod 9 in end-to-end relation. For convenience only two sleeve lengths are shown in Figure 2. A connecting tube 10 is fitted over the adjacent 0-rings 8 of adjacent sleeve lengths. An end cap 11 comprising a mouth portion 12 and a side inlet 13, is fitted over the end of the sleeve. The clearance between the mouth 12 of the end cap 11 and the sleeve 1 ts sealed by the adjacent 0- ring 8.
A polyester resin grout 14 is then pumped through the inlet 13 of the cap 11 into the annular clearance 15 between the sleeve and the rod. The anchor is upwardly inclined away from the end cap for best escape of air during introduction of the grout. The grout is forced into the clearance between adjacent ends of the sleeve lengths there to provide a moisture-proof seal. The recesses 7 facilitate passage of the grout between the sleeve ends and also act as keys more firmly to secure the sleeve lengths together by means of the grout within the recesses.
After sufficient time to allow the polyester grout to harden, the inlet 13 is sawn off and the anchor located in a hole in a substrate in known manner. The cap 11 serves as a guide for the anchor and protects the leading end of the anchor during insertion into a hole. The grout within the end cap 11 seals the end of the anchor against penetration of moisture.
A strand tendon may be used in place of the rod 9. In this case, the tendon is prepared by removing the protective sheath along the length of the tendon to be corrosion proofed. The bared tendon is then thoroughly degreased and a ferrule is compressed on to the end of the tendon. The tendon is then sleeved as described, the ferrule being located within the cap 11.
Figure 3 shows an alternative way of joining together adjacent sleeve lengths. The external plastics layer 2 of one sleeve length 1 a has a female extension 16, and the same layer of the adjacent sleeve length 1 b has a male extension 17. The extensions 16, 17 are screw-threaded one into the other.
The method of the invention allows corrosion-proof anchors to be made quickly and cheaply on site to meet individual requirements. The sleeve is capable of transferring the maximum load of the anchor element to the borehole grout, provided a sufficient length of sleeve is used. The minimum length of sleeve for full load transfer ranges from 4 m for a 110 mm external diameter sleeve, to 1.5 m for a 65 mm external diameter sleeve.

Claims

1. A method of making a ground anchor to be received in a bore in the ground or like substrate, the ground anchor comprising an anchor element (9) formed of a bar, tendon, or the like, the element being surrounded by a corrosion-proof sleeve (1) made of plastics or the like, an annulus of set self-setting composition (14) such as cement being present between the sheath and the element, characterised by

(i) locating about an end portion of the anchor element (9) at a location adjacent the bore a plurality of lengths of corrosion-proof sleeve (1) in end-to-end relation to cover the length of the element to be corrosion-proofed, each sleeve length being preformed and comprising at least two corrosion-proof layers (2, 6),

(ii) applying a cap (11) to the sleeve (1) at the end of the anchor element, the cap having an inlet (13) for self-setting composition, and

(iii) supplying a self-setting composition (14) through the inlet (13) via the cap (11) into an annular clearance (15) between the element (9) and the sleeve (1) there to set to secure the preformed lengths of sleeve (1) to the element (9).

2. A method according to Claim 1, characterised in that the cap (11) is secured to the anchor element (9) by means of the self-setting composition (14).

3. A method according to Claim 1 or Claim 2, characterised in that the anchor element is upwardly inclined away from the cap (11) when the self-setting composition (14) is being supplied into the sleeve (1).

4. A method according to any one of Claims 1 to 3, characterised in that the inlet (13) is located in the side of the cap (11).

5. A method according to any one of Claims 1 to 4, characterised in that the sleeve (1) comprises three layers (2, 6, 4), the intermediate layer (6) being of set filler and at least one of the other two layers (2, 4) being of plastics.

6. A method according to Claim 5, characterised in that the sleeve (1) comprises an outer layer (2) of plastics, an intermediate layer (6) of set filler and an inner layer (4) of metal.

7. A ground anchor comprising an anchor element (9) having a corrosion-proof sleeve (1) secured to an end portion of the element by means of a set self-setting composition (14), characterised in that the sleeve (1) comprises a plurality of preformed sleeve lengths lying in end-to-end relation around the anchor element (9), each length comprising at least two corrosion-proof layers (2, 6).

8. A ground anchor according to Claim 7, characterised in that the sleeve (1) comprises three layers (2, 6, 4), the intermediate layer (6) being of set filler and at least one of the two layers being of plastics.

9. A ground anchor according to Claim 8, characterised in that the sleeve comprises an outer layer (2) of plastics, an intermediate layer (6) of set filler and an inner layer (4) of metal.

10. A ground anchor according to any one of Claims 7 to 9, characterised in that a cap (11) is secured to an end of the anchor by means of the self=setting composition (14).

11. For use in a method according to any one of Claims 1 to 6, or in a ground anchor according to any of Claims 7 to 10, a sleeve length (1), characterised in that the sleeve comprises three layers, (2, 6, 4), the intermediate layer (6) being of set filler and at least one (2) of the other two layers being of plastics.

12. A sleeve according to Claim 11, characterised in that the outer layer (2) is of plastics and the inner layer (4) is of metal.

13. A sleeve according to either of Claims 11 and 12, in which the sleeve (1) is internally threaded (5).