AU2008201006B2

AU2008201006B2 - Earth Anchoring System

Info

Publication number: AU2008201006B2
Application number: AU2008201006A
Authority: AU
Inventors: Ian Macdonald
Original assignee: Tristanagh Pty Ltd
Current assignee: Tristanagh Pty Ltd
Priority date: 2000-08-08
Filing date: 2008-03-03
Publication date: 2010-12-23
Anticipated expiration: 2021-08-08
Also published as: AU2006252264A1; AU2006101083A5; AU2007100712A4; AU2007100712B4; AU2006252264B2; AU2008201006A1

Description

1a TITLE EARTH ANCHORING SYSTEM This invention relates to improvements in earth anchoring systems, improved earth anchors and improved methods of installation 5 of earth anchors. The invention is particularly although not exclusively concerned with earth anchoring systems used in conjunction with sheet piling systems. Earth or "ground" anchors are well known and come in a wide 10 variety of configurations suitable for differing earth formations, installation systems and/or anchor loads. Many prior art earth anchors include either pivoted flukes or arms which engage with the wall of a borehole to resist withdrawal. Others may include a helical flight to assist in locating the anchor in 15 the earth formation and then acting as the anchoring means. Typical anchors of the type having pivotable flukes are described in United States patents 1 850 147, 1 636 617 and 4 593 500, United Kingdom patent application 2100314A, United Kingdom patent 656663 and Russian patents 676-685 and 1071-706. 20 United States patents 1636617, 4593500 and United Kingdom patent 656 663 require a borehole to be formed to enable insertion of the anchor into the ground. United States patent 1850147, United Kingdom patent 2 2100314 and Russian patent 1071706 require an anchor with retracted blades to be driven into an earth formation by a percussive force acting on the anchor head while Russian patent 676685 describes an anchor head with a helical screw flight to enable the 5 anchor head to be screwed into the earth formation. Our International Patent Application PCT/AU97/00365 published as W097/47824 described an anchor system having a pointed cutting head, pivotal flukes and a tubular driving tool extending over the anchor rod to rotate the anchor head to cut az 10 pathway through the earth formation. Rotatable engagement between a threaded nut and a socket on the driving tool causes the pivotal flukes on the anchor head to expand outwardly. The tubular driving tool also acts as a grouting conduit to grout the anchor rod as the driving tool is withdrawn from the earth formation. 15 While generally effective for their respective intended purposes, prior art earth anchors and their methods of installation suffer from a variety of disadvantages. Where an earth anchor requires a predrilled borehole, this is time consuming and weakens the earth formation along the length of the 20 borehole which later must be filled in. Percussively driven earth anchors require a driving tool which extends between the pointed anchor body and the power source for the driver. Such anchors generally are limited to soft earth formations 3 and shallow penetrations. Accordingly, with prior art earth anchors, the choice is largely governed by the geological nature (hardness) of the earth formation and the depth to which the anchors are required to be located. 5 A particular disadvantage of prior art earth anchors when used with sheet piling retention systems in an excavation is that the large aperture which must be cut in the sheet piling to accommodate an anchor head and/or driving tool causes a substantial localised weakness in the sheet piling. 10 Accordingly it is an aim of the present invention to overcome or ameliorate at least some of the disadvantages associated with prior art earth anchors and methods of installing same. According to one aspect of the invention there is provided an earth anchor including: 15 a hollow body member having a screw threaded aperture adjacent one end thereof to receivably locate a screw threaded anchor bar; a shaped cutting head located at an end of said body opposite said one end; and, 20 a helical flight located intermediate the ends of said body. Suitably said anchor is adapted to be driven rotatably into an earth formation. If required said anchor may include one or more drive engagers, 4 in use, engageable with a rotatable driving tool. The one or more drive engagers may comprise a socket and spigot engagement associated with said body. Suitably, the one or more drive engagers comprises a pair of rib 5 like projections diametically opposed on an outer surface of said body, said rib like projections being engageable, in use, with complementary recesses in a driving tool. The driving tool may be a tubular member, in use, forming a casing for a borehole formed by anchor, an inner surface of said 10 tubular member and an anchor bar attached to said body member forming an annular cavity therebetween. Alternatively the driving tool may comprise the screw threaded anchor bar. If required a grouting tube may be removably secured over said 15 anchor bar. Suitably said grouting tube is removably secured by a screw threaded nut engaging said anchor bar adjacent an end thereof remote from said body member. According to another aspect of the invention there is provided 20 an earth anchoring system including an earth anchor as described above wherein the anchor bar is encased in a cementitious grout over all or part of a buried length of the anchor bar. Suitably the earth anchoring system is used in conjunction with 5 a sheet piling system utilising lightweight contoured sheet steel piles. According to yet another aspect of the invention there is provided a method of installation of earth anchors of the type described above, said method including the steps of: 5 rotatably driving into an earth formation the anchor with a threaded anchor bar screw threadably attached thereto, said shaped cutting head forming a first region of fractured and/or loosened earth through which an inner portion of a helical flight on said body member rotates, said helical flight in use serving to draw said earth anchor into 10 the earth formation during rotation and, thereafter, providing an anchoring abutment resistant to withdrawal by a load applied to said anchor bar. If required said anchor is rotatably driven by a tubular driving tool removably engagable over said body member. 15 Alternatively, said anchor member is rotatably driven by a rotational force applied to said anchor bar. The earth anchor may be installed with a grouting tube removably located over said anchor bar, said grouting tube in use permitting encapsulation in a cementitious grout of all or part of a 20 buried length of said anchor bar. In order that the invention may be more readily understood and put into practical effect, reference will now be made to preferred embodiments described in the accompanying drawings in which:- 6 FIG 1 shows an anchor according to one aspect of the invention; FIG 2 shows a method of installing the anchor of FIG 1 into an earth formation through a contoured sheet piling wall; 5 FIG 3 shows one method of installing the anchor according to the invention; FIG 4 shows another method of installing the anchor according to the invention. In the drawings like reference numerals are employed for like 10 features for the sake of simplicity. FIG 1 shows a cross-sectional view of an earth anchor 1 and a sheet piling bearing plate 20 for the purpose of relative size comparison. Anchor 1 comprises a tubular steel body 2 having a steel 15 cutting head 3 welded therein. Cutting head 3 is simply a section of mild steel plate although if required it could include hardened and sharpened cutting edges on points 4. A helical flight 5 is welded onto body 2 and may included a shaped or sharpened leading edge (not shown). The shape and 20 configuration of helical flights for rotary excavators and tubular foundation members is well known and forms no part of this invention. On the outer surface of body 2 towards a trailing end thereof are a pair of diametrically opposed rib-like projections or "dogs" 6 7 which engage in corresponding slots of a driving tool described later. Within body 2 is located an annular steel washer 7 to which is welded an elongate coarse threaded nut 8 of the type utilised with thread rolled bar employed as tension members in the construction 5 industry. As shown a portion of a thread rolled anchor bar 9 extends through nut 8 and the free end 9a thereof rests against the rear edge 3a of cutting head 3. FIG 2 shows the exposed end of anchor bar 9 when installed in an earth formation supported by a contoured sheet piling member 10. 10 After a sheet piling member 10 is driven into an earth formation and the front face 10 a thereof exposed by excavation of earth, it is often necessary to anchor the sheet piling to the earth structure therebehind. Initially a generally "snail"-like aperture 11 (as shown in 15 phantom) is cut into the sheet piling at the radius of the trough 12 between adjacent ridges 13. The generally circular portion 11 a has a diameter slightly greater than the body portion 2 of the anchor and the elongate extension 11 b to the aperture 11 has a length slightly greater than the leading edge of flight 5. 20 It thus can be seen from FIG 1 that as the plane of the sheet piling face 14 in which the elongate extension 11 b lies is angled relative to the rotational axis of flight 5, the leading portion of anchor 1 comprising cutting head 3 and tubular member 2 extends through 8 the aperture 11a. Anchor 1 may then be rotated whereby the leading edge of flight 5 enters aperture portion 11 b and the anchor continues to rotate, the flight 5 follows through the aperture 11 a/11 b as the anchor 1 moves forward into the earth behind the sheet piling. 5 After the anchor 2 and associated anchor rod 9 is driven into the earth formation to a desired depth, the driving tool (not shown) is disengaged leaving a portion of anchor bar extending from aperture 11, which portion can then be cut to a desired protruding length 9a as required. 10 A bearing plate 20 having a cross sectional contour complementary to and nestable with that of the sheet piling member 10, having an aperture 15 slightly larger than anchor bar 9 is placed over the protruding end 9a and is pushed into contact with sheet piling member 10. Bearing plate 20 is then tack welded as required to 15 secure it to sheet piling member 10. A shaped bearing washer 16 is then placed over the end of anchor bar 9 and an elongate nut 17 is secured on anchor bar 9 and then is tensioned to a required degree. It can be seen from FIGS 1 and 2 that the use of a helical flight 20 associated with the anchor 1 permits an anchor head of relatively large diameter to be inserted through a minimally sized aperture in the contoured sheet piling without a substantial compromise to the structural integrity of the sheet piling.

9 FIGS 3 and 4 show alternative methods of installing earth anchors according to the invention. In FIG 3 there is shown an installation method suitable for anchor bars having a diameter of, say 25mm or less. 5 Initially, anchor 1 is assembled with a 25mm thread rolled bar 9 secured thereto. Over bar 9 is secured a grouting tube 21 having a quick release hydraulic coupling 22 at least on the end remote from anchor 1. A spacer 23 is then positioned over bar 9 and a threaded nut 24 compressively secures tube 21 over the bar. 10 A driving tool 25 comprising a steel tube having opposed slots 26 in one end 25a is secured over the tubular body 2 of anchor 1 to engage drivingly with dogs 6 and otherwise to enclose bar 9 and grouting tube 21. By means of a driving adaptor 27 attached to the drive shaft 28 of a rotary boring machine or the like (not shown), the 15 entire assembly as shown is inserted through the sheet piling 10 and driven to a required depth into the earth formation. For deep anchor installations, each of bar 9, grouting tube 21 and driving tool 25 are adapted by end couplings to be connected to further lengths respectively as required. 20 As can be seen, the driving tool tube 25 forms a borehole casing which serves to compact the earth therearound. When driving tool tube 25 is withdrawn from the borehole, the wall of the borehole maintains a considerable degree of integrity depending upon the earth 10 formation. If the borehole is unduly wet or clogged with loose material, grouting tube 21 may be coupled, after removal of spacer 22 and unit 23, initially to a source of compressed air to blow out loose material and/or dry the borehole. 5 Grouting tube 21 thereafter is coupled to a source of flowable cementitious grout under pressure and, as tube 21 is gradually withdrawn from the borehole, cementitious grout is introduced to encapsulate anchor bar 9 and otherwise fill the borehole to greatly enhance the frictional engagement of the earth anchor assembly with 10 the earth formation. FIG 4 shows an alternative embodiment of the assembly of FIG 3. This embodiment is particularly suited to anchor systems having an anchor bar of, say, 30mm or greater as it has been found in 15 practice that the torsional strength of the anchor bar material is sufficient to enable the bar itself to be employed as the driving tool. As shown, the anchor body 2 does not require the driving dogs 6 of the arrangement of FIG 3 and thus a grouting tube 21 having a diameter up to that of tubular body 2 is possible. 20 Like the arrangement of FIG 3 grouting tube 21 is secured over anchor bar 9 by means of a spacer 23 and a threaded nut 24 compressively engaged against spacer 23 and tube 21. A simple threaded adaptor boss 30 provides a drive coupling with the drive 11 shaft of a rotary boring machine (not shown). The boss has a blind aperture 31 whereby the threaded rod 9 locks against the end of blind aperture 31 during insertion of the ground anchor and it permits ready disengagement of the adapter 30 simply by reversing the direction of 5 rotation. Again, like the embodiment of FIG 3, the grouting tube 21 may be coupled to a source of compressed air to blow out loose earth and/or to dry the borehole. Thereafter, flowable cementitious introduced to fill the borehole and encapsulate the anchor rod as the 10 grouting tube 21 is gradually withdrawn. As described with reference to FIG 2, a bearing plate is then placed over the free end of the anchor rod together with a bearing washer and the anchor system is tensioned to a desired tension by a threaded nut as previously described. 15 It readily will be apparent to a skilled addressee that many modifications and variations may be made to the invention without departing from the spirit and scope thereof.

Claims

1. An earth anchor including : a hollow body member having a screw threaded aperture adjacent one end thereof to receivably locate a screw threaded anchor bar; 5 a shaped cutting head located at an end of said body opposite said one end; and; a helical flight located intermediate the ends of said body; wherein an attachment plate is provided, the attachment plate extending transversely across the hollow body member above the screw threaded 10 aperture to facilitate the attachment of the anchor bar relative to the hollow body member and to maintain the bar co-axially with the body member during use.

2. An earth anchor as claimed in claim 1 wherein the attachment plate is permanently attached to an interior surface of the hollow body member. is

3. An earth anchor as claimed in claim 1 or claim 2 wherein said anchor is adapted to be driven rotatably into an earth formation.

4. An earth anchor as claimed in any one of the preceding claims wherein said anchor includes one or more drive engagers, in use, engageable with a rotatable driving tool. 20

5. An earth anchor as claimed in claim 4 wherein said one or more drive. engagers comprise a socket and spigot engagement associated with said body. 13

6. An earth anchor as claimed in claim 4 or claim 5 wherein the one or more drive engagers comprises a pair of rib-like projections diametically opposed on an outer surface of said body, said rib like projections being engageable, in use, with complementary recesses in a driving tool. 5

7. An earth anchor as claimed in any one of claims 4 to 6 wherein the driving tool is a tubular member, in use, forming a casing for a borehole formed by anchor, an inner surface of said tubular member and an anchor bar attached to said body member forming an annular cavity therebetween.

8. An earth anchor as claimed in any one of claims 1 to 4 wherein the 1o driving tool comprises the screw threaded anchor bar.

9. An earth anchor as claimed in any one of claims 1 to 8 wherein a grouting tube is removably secured over said anchor bar.

10. An earth anchor as claimed in claim 9 wherein said grouting tube is removably secured by a screw threaded nut engaging said anchor bar 15 adjacent an end thereof remote from said body member.

11. An earth anchoring system including an earth anchor as claimed in any preceding claim wherein the anchor bar is encased in a cementitious grout over all or part of a buried length of said anchor bar.

12. An earth anchoring system as claimed in claim 11 whenever used in 20 conjunction with a sheet piling system utilising lightweight contoured sheet steel piles.

13. A method of installation of earth anchors as claimed in any one of claims 1 to 10, said method including the steps of:- 14 rotatably driving into an earth formation said anchor with a threaded anchor bar screw threadably attached thereto, said shaped cutting head forming a first region of fractured and/or loosened earth through which an inner portion of a helical flight on said body member rotates, said helical flight 5 in use serving to draw said earth anchor into the earth formation during rotation and, thereafter, providing an anchoring abutment resistant to withdrawal by a load applied to said anchor bar.

14. A method as claimed in claim 13 wherein said anchor is rotatably driven by a tubular driving tool removably engagable over said body member. 10

15. A method as claimed in claim 13 wherein said anchor member is rotatably driven by a rotational force applied to said anchor bar.

16. A method as claimed in any one of claims 13 to 15 wherein the earth anchor is installed with a grouting tube removably located over said anchor bar, said grouting tube in use permitting encapsulation in a cementitious grout is of all or part of a buried length of said anchor bar.

17. A method as claimed in any one of claims 13 to 16 wherein said anchor is inserted into an earth formation via an aperture in contoured sheet piling.

18. A method as claimed in claim 17 wherein said anchor is inserted by 20 rotation via an aperture having a cross sectional area smaller than a cross sectional area represented by a diameter of said helical flight.