WO1991006713A1

WO1991006713A1 - Inflatable ground anchor

Info

Publication number: WO1991006713A1
Application number: PCT/AU1990/000503
Authority: WO
Inventors: Norman Frederick Howell; Neil Edward Costello
Original assignee: Groutco (Aust.) Pty. Ltd.
Priority date: 1989-10-24
Filing date: 1990-10-23
Publication date: 1991-05-16

Abstract

An inflatable ground anchor for anchoring a structural element to the earth. The anchor comprises an elongate hollow drilling member (11) having a drill bit (14) connected to its leading end, and an inflatable member (15) for securing the anchor in ground. The inflatable member is in fluid communication with hollow drilling member and is inflated by pressurized fluid pumped into the drilling member when the desired anchoring depth has been attained.

Description

INFLATABLE GROUND ANCHOR

Technical Field of the Invention

THIS INVENTION relates to an inflatable ground anchor for anchoring a structural element to the earth, and to a method of using the inflatable ground anchor. This invention is particularly useful for temporarily or permanently securing embankments on the side walls of an excavation, for use in preparing foundations such as in the construction of buildings, bridges, dams and so forth, and for use as a piling system.

Background Art

Various inflatable ground anchors have been proposed in the past to overcome problems associated with the installation and use of conventional ground anchors, such as multi-strand ground anchors, conventional piles, or even large scale tent pegs. However, these known inflatable ground anchors still present problems in installation and/or use.

United States Patent No 3,141,534, for example, discloses a reusable, inflatable ground anchor which is effectively an enlarged tent peg incorporating an inflatable sleeve at its lower end. In use, the ground anchor is partially driven into the ground by hammering an anvil located in the top end of the anchor. The anvil is then removed and the sleeve inflated with a suitable pressurised fluid, such as water or air. The holding power of this anchor is limited, and in any case, is totally dependent on the sleeve remaining inflated. This is not always possible since the sleeve is formed from an elastomeric-type material, which is easily damaged during the driving operation, particularly when driven into rocky ground. Also, this anchor is a passive anchor, in that it only exerts forces on the ground in response to loads applied to the anchor; and the holding power of this type of anchor may be greatly reduced when a cyclic load is applied to the anchor.

United States Patent No 3,270,469 describes a more conventional ground anchor or pile, as compared to the tent peg described in U.S. Patent No. 3,141,534 above. However, an inherent disadvantage of the ground anchor of U.S. Patent No. 3,270,469 is the requirement that a bore hole be drilled into the earth prior to inserting the inflatable ground anchor. Such predrilling is necessary to ensure that the inflatable member or sleeve is not damaged during installation, as can happen with the anchor of United States Patent No 3,141,534. The necessity for a pre-drilled hole means that an extra operation is required to instal the ground anchor, and that extra time is taken, since the drilling apparatus must be removed from the bore hole before the ground anchor can be inserted. Where a large number of ground anchors are required, this extra operation will significantly increase the overall installation time and hence installation cost. A further inherent disadvantage of both the ground anchors of United States Patents 3,141,534 and 3,270,469 is that their inflatable sleeve is made from an elastomeric-type material, since both ground anchors are intended to be reusable. Such an elastomeric sleeve will continue to expand in response to an increase in inflation pressure until it finally ruptures, and renders the ground anchor inoperative. Hence, the inflation pressures for these anchors must be carefully monitored to avoid rupturing, particularly if the ground anchor is being installed in cohesive soils; such as clays; or in non-cohesive soils; such as sands or muds.

Further, care must be taken when installing these anchors in rock since any sharp edges of rock in the vicinity of the inflatable sleeve can rupture the sleeve when it is inflated and pressed against them.

An alternative solution to the problems of conventional ground anchors is proposed in United States Patent No 4,487,528. This patent provides a ground anchor having an inflatable body made from sheet metal folded in a zigzag pattern, and attached to the lower end of a hollow rod. The ground anchor of this patent is intended to be installed either in a pre-drilled hole, or by directly hammering it into the ground with a conventional pile driver. In practice however, this inflatable ground anchor normally requires a pre-drilled hole, since the slightest amount of buckling of the folded inflatable body caused by the hammering operation will prevent it from inflating correctly, and hence the load carrying capacity of the anchor is reduced. Only in non-cohesive ground can it be safely driven into the earth, and even then, a localised "hard" spot can cause buckling of the inflatable body.

It is an object of the present invention to provide an improved inflatable ground anchor which overcomes or substantially alleviates at least some of the abovementioned problems of the prior art ground anchors.

Disclosure of Invention

According to a first aspect of the invention, there is provided an inflatable ground anchor comprising an elongate drilling member having a longitudinal passage therethrough; a drill bit located at a leading end of the drilling member; an inflatable member attached to the drilling member adjacent to or spaced from the drill bit and in communication with the longitudinal passage, wherein the inflatable member is inflatable to dimensions greater than the diameter of the hole which the drill bit produces; and means for inflating the inflatable member in the longitudinal passage to secure the ground anchor within the hole.

The elongate drilling member may be adapted to couple to a drill chuck of a rotary or rotary-percussive drilling machine. Suitably, the elongate drilling member comprises a plurality of hollow drilling rods joined together to form a drill string. Preferably each hollow drilling rod is made from high tensile steel.

The drill bit used in the present invention may be formed integrally with the leading end of the lowermost drilling rod or alternatively, may be a separate component which is attached by any suitable method.

The drill bit may include one or more passages which are in fluid communication with the longitudinal passage of the drilling member whereby in use, the operative portion of the drill bit may be flushed clean by a fluid circulated through the drilling member. In one embodiment of the invention, the drill bit is adapted to drill rock or other "hard" materials. In an alternative embodiment, the drill bit is adapted to drill cohesive or non-cohesive soils.

The inflatable member is attached to the drilling member at a location behind the drill bit, typically immediately behind the drill bit. Preferably the inflatable member includes a collar at each end thereof with at least one of the collars attached to the drilling member.

Advantageously the collar closest the drill bit is attached to the drilling member.

The inflatable member is suitably formed from an abrasion resistant material, such as deformable sheet metal. Preferably the sheet metal material is no more than 6mm thick, typically being approximately 1mm thick. Alternatively, the inflatable member can be formed from an abrasion resistant plastics material which can be woven or non-woven, and is preferably fibre-reinforced.

In one embodiment of the invention, particularly suitable for use in rock or other "hard" earth material, the inflatable member comprises a tubular sheet metal bladder folded partially around the outer surface of the drilling member and adapted to wedge between the drilling member and the bore hole when inflated.

In another embodiment of the invention, particularly suitable for use in cohesive or non-cohesive soils, the inflatable member comprises a tubular sheet metal casing surrounding the drilling member. The inflatable member is pleated or folded to fit within the confines of the bore hole when uninflated. Preferably the pleats or folds extend longitudinally along substantially the entire length of the inflatable member. When uninflated, the inflatable member is folded in a stylised star-like manner when viewed in a transverse cross-section, but when inflated it is generally circular when viewed in a transverse cross-section.

The means for inflating the inflatable member can include means for diverting fluid from the longitudinal passage in the drilling member to the interior of the inflatable member. In use, the diverting means seals the distal end of the longitudinal passage so that any fluid pumped into the longitudinal passage is diverted to inflate the inflatable member. The diverting means comprises a fluid passageway joining the longitudinal passage to the interior of the inflatable member, and a sealing means for sealing the fluid passage below its junction with the longitudinal passageway. The sealing means can be a sphere or ball which is pumped into the drilling member when the inflatable member is to be inflated, and locates in a seat thereby sealing the fluid passage below the passageway to the inflatable member.

Alternatively, the sealing means can comprise a valve mechanism which is pressure actuated such that the valve is normally open to allow fluid to pass therethrough to the drill bit during drilling, but closes in response to a change in fluid pressure so as to divert fluid to the inflatable member. The valve means can alternatively be actuated by any other suitable method, such as by a reverse rotation of the drilling member.

The inflatable ground anchor of this invention can further include a tubular casing surrounding at least part of the elongate drilling member. This casing may be required to maintain the maximum free length of the drilling member, and hence, the drilling member can always be tensioned to the designed load. The casing prevents the wall of the bore hole collapsing during drilling and/or prevents any settable fluid accumulating around the drilling member. Preferably, the casing member comprises a plurality of tubes joined together. Each tube can be formed from a suitable plastics material, such as polyvinylchloride (PVC) or polypropylene.

According to a second aspect of the invention, there is provided a method for anchoring a structural element to the earth comprising the following steps:

(i) drilling a bore hole in the earth using the inflatable ground anchor described above;

(ii) inflating the inflatable member of the ground anchor to a predetermined size using a pressurized fluid; and (iii) stressing the ground anchor by applying a force to the drilling member so as to anchor the structural element to the earth.

The fluid used to inflate the inflatable member may comprise water, drilling mud or a grouting material. Preferably, the grouting material comprises a cementitious fluid or slurry. Alternatively, the grouting material may comprise a suitable synthetic product, such as epoxy resin.

Preferably, the ground anchor is stressed by applying a tensile force to the drilling member, for example by using a jacking mechanism. Alternatively, the ground anchor may be stressed by applying a compressive force to the drilling member.

Brief Description of Drawings

Preferred embodiments of the invention will now be described by way of example, with reference to the accompanying drawings wherein:

FIG 1 shows a part cross-sectional view of an inflatable ground anchor according to a first embodiment of the invention for securing a structural element to rock or other "hard" earth material;

FIG 2 shows a part cross-sectional view of an inflatable ground anchor according to a second embodiment of the invention for securing a structural element to cohesive or non-cohesive soils;

FIG 3 shows a cross-sectional perspective view of the lower end of the ground anchor of FIG 1 when uninflated;

FIG 4 shows a part cross-sectional perspective view of the ground anchor of FIG 1 when inflated;

FIG 5 shows two cross-sectional views of the ground anchor of FIG 1 before and after inflation of the inflatable member;

FIG 6 shows a cross-sectional view along line B-B of the ground anchor of FIG 5;

FIG 7 shows two cross-sectional views of the ground anchor of FIG 2 before and after inflation of the inflatable member;

FIG 8 shows a part cross-sectional perspective view of the ground anchor of FIG 2 before inflation of the inflatable member; and

FIG 9 shows a part cross-sectional perspective view of the ground anchor of FIG 2 after inflation of the inflatable member.

Best Mode for Carrying out the Invention Referring to FIG 1 , there is shown an inflatable ground anchor 10 comprising an elongate drilling member 11 having a drill bit 14 connected to its leading end, and having an inflatable member or jacket 15 for securing the anchor 10 in ground 17. Drilling member.11 is enclosed with a tubular casing member 23 which comprises a plurality of tubes 24 joined together to prevent the wall of bore hole 16 collapsing during drilling. This particular embodiment is particularly suited for use in ground 17 comprising rock or other similar "hard" materials such as concrete. Hence, casing 23 may not be necessary.

Drilling member 11 comprises a plurality of conventional drilling rods 12 that have been secured together, e.g. by coupling 13, to form a drill string. Each drilling rod 12 is nominally 3m long and has been formed from a high tensile steel to give a nominal ultimate tensile strength of approximately 1900 MPa.

Leading end drilling rod 12a is coupled or secured to drilling member 11 at one end, and to drill bit 14 at the other end. Drilling member 11 includes a longitudinal fluid passage 25 therethrough, as shown in more detail in FIG 3-6, which aligns with fluid passage 26 in drill bit 14. Passages

25, 26 allow the circulation of a fluid, such as air, water or drilling mud, through drilling member 11 and drill bit 14 during drilling, so that bit 14 can be cooled and cuttings

(not shown) can be flushed away from the cutting edges or inserts 27 set into the leading end 28 of bit 14.

Inflatable jacket 15 is secured to the lower end of drilling rod 12a adjacent drill bit 14 by a collar 30 which has a similar diameter to shank portion 29 of bit 14. Collar 30 comprises an outer ferrule 31 spaced from an inner ferrule 32 by a suitable distance so as to locate the end of jacket 15, with ferrules 31, 32 joined together by a suitable weld 33. Jacket 15 is welded to collar 30 by weld 34. A second collar 30 may be used to secure the upper end of jacket 15 to the drilling rod 12a. Jacket 15 comprises a tubular member made from a metal sheet of nominally 3mm thickness which has been folded or wrapped at least partially around drilling rod 12a and has uninflated dimensions which allow it to fit within the confines of bore hole 16.

A fluid passageway comprising radial bore 36 through the wall of rod 12a and radial bore 38 through inner ferrule 32 and inner wall 15a, allows the interior space 39 of jacket 15 to be in fluid communication with fluid passage 25. A pair of O-ring seals 35 are provided between collar 30 and drilling rod 12a to seal the space 37 formed between drilling rod 12a and inner ferrule 32. This permits collar 30 to be fitted to rod 12a in any rotational position and still maintain the fluid passageway described above (i.e. holes 36 and 38 do not have to be aligned as is shown in FIGS 3 and 5).

Referring now to FIG 5, when the bore hole 16 drilled by drill bit 34 has reached the desired depth, the drilling machine (not shown) is disconnected from drilling member 11, and a grouting machine (not shown) is connected so that jacket 15 can be inflated. To inflate jacket 15, a ball or sphere 42 is first pumped down passage 25 until it sealingly locates on seat 43 within drill bit 14. This causes the flow of fluid or grouting material 40 (indicated generally by arrow 41) to be diverted from passage 25 through holes 36, 38 and into interior space 39. The grouting is then pressurised to a pressure of approximately 28.0 MPa (4000 psi) so as to expand the outer wall 15b of jacket 15 into compressive and frictional engagement with rock 17 forming the wall of bore hole 16 as shown on the right side of FIG 5. The inflation of jacket 15 also tends to cause rod 12a to be displaced from its drilling position in the centre of bore hole 16, to a position nearer the wall of bore hole 16, as is shown in FIG 4.

Once jacket 15 has been inflated, drilling member 11 can then be stressed or tenεioned using a suitable jacking machine (not shown). The maximum tension or working load which can be applied to drilling member 11 depends on the diameter of the drilling rod 12 and its effective cross- sectional area. Table 1 shows typical working load values which can be achieved for various sizes of drilling rod. The tension or working load is distributed to/from structural element 21 from/to drilling member 11 via nut 18, washer 19 and a steel anchor plate 20.

FIGS 2 and 7-9 illustrate a second embodiment of the invention for use as a soil anchor, each component common to the first embodiment described above retaining the same reference number.

In this second embodiment, the inflatable ground anchor 50 comprises a drilling member 11 having a conical drill bit 51, and an inflatable member or sleeve 52 for securing the anchor 50 in soil 55. As can be seen in this embodiment, sleeve 52 inflates to a much larger diameter than that achieved by jacket 15 described above, with the outer periphery 51 of sleeve 54 extending well beyond bore hole 53 into the surrounding soil.

Sleeve 52 surrounds or encapsulates drilling rod 12a and is formed from thin sheet metal material nominally lmm thick, which has been folded or pleated in a star-like manner to produce a series of longitudinal pleats 57 (FIGS 7-

9). End portions 58 of sleeve 52 are welded to annular flange 60. Annular flange 60 is provided with radial slots 59 to prevent buckling during expansion. Flange 60 is welded to collar 61 which is attached to drilling rod 12a via a pair of O-ring seals 35. Collar 61 is provided with a radial bore

62 to form a fluid passageway between fluid passage 25 and the interior chamber 63 of sleeve 52 in a manner similar to that described previously. A frangible sheath 64 is also provided to protect sleeve 52 from damage during the drilling operation. Sheath 64 may be made from a suitable plastics material, such as PVC.

Conical drill bit 51 is provided with a fluid passage 56 and a seat 43 which sealingly locates sphere 42 when sleeve 52 is to be inflated.

The drilling and inflating steps of installing inflatable ground anchor 50 are similar to those already described for ground anchor 10, with the exception that the grouting material 40 is pressurised to a pressure of approximately 3.5 MPa (500 psi).

The above described invention possesses several advantages over the prior art inflatable ground anchors. First, it is a single pass system. That is, the ground anchor is used to drill its own bore hole, and hence, requires much less installation time than those anchors which require a predrilled hole. Time savings may be up to 50% for rock installations, and up to 90% for sand installations. Secondly, the inflatable member is protected from damage during installation, since the ground-anchor is installed by drilling and not hammering; and the drilling member passes through, or next to, the inflatable member to carry all the installation loads. Hence the inflatable member does not distort or buckle as would be the case in prior art hammered ground anchors.

The above description describes only some embodiments of the invention, and modifications obvious those person skilled in the art may be made thereto without departing from the scope of the invention. The ground anchor, for example, may include two or more inflatable members at any convenient spacing, since the drilling member is assembled during the drilling process and a drilling rod, similar to rod 12a may be inserted at any suitable location in the drill string.

Claims

CLAIMS :

1. An inflatable ground anchor comprising an elongate drilling member having a longitudinal passage therethrough; a drill bit located at a leading end of the drilling member; an inflatable member attached to the drilling member adjacent to or spaced from the drill bit and in communication with the longitudinal passage, wherein the inflatable member is inflatable to dimensions greater than the diameter of the hole which the drill bit produces; and means for inflating the inflatable member in the longitudinal passage to secure the ground anchor within the hole.

2. An inflatable ground anchor as claimed in claim 1, wherein the elongate drilling member comprises a plurality of hollow drilling rods joined together to form a drill string.

3. An inflatable ground anchor as claimed in claim 1 or claim 2, wherein the drill bit has one or more passages which are in fluid communication with the longitudinal passage of the drilling member.

4. An inflatable ground anchor as claimed in claim 1, wherein the inflatable member is attached to the drilling member immediately behind the drill bit.

5. An inflatable ground anchor as claimed in claim 4, wherein the inflatable member is formed from deformable sheet metal.

6. An inflatable ground anchor as claimed in claim 4, wherein the inflatable member comprises a tubular sheet metal bladder folded partially around the outer surface of the drilling member.

7. An inflatable ground anchor as claimed in claim 1, wherein the inflatable member comprises a tubular sheet metal casing surrounding the drilling member, said casing being of pleated form with the pleats extending longitudinally along substantially the entire length of the inflatable member.

8. An inflatable ground anchor as claimed in claim 1, wherein the means for inflating the inflatable member include means for diverting fluid from the longitudinal passage in the drilling member to the interior of the inflatable member.

9. An inflatable ground anchor as claimed in claim 8, wherein the diverting means comprises a fluid passageway joining the longitudinal passage to _.the interior of the inflatable member and a sealing means for sealing the longitudinal passage below its junction with the fluid passageway.

10. An inflatable ground anchor as claimed in claim 9, wherein the sealing means is a sphere, which is pumped into the drilling member when the inflatable member is to be inflated, which locates in a seat below the passageway to the inflatable member.

11. An inflatable ground anchor as claimed in claim 9, wherein the sealing means is a valve mechanism, which is pressure actuated such that the valve is normally open to allow fluid to pass therethrough to the drill bit during drilling, but closes in response to a change in fluid pressure so as to divert fluid to the inflatable member.

12. An inflatable ground anchor as claimed in claim 1 and including a tubular casing surrounding at least part of the elongate drilling member.

13. A method for anchoring a structural element to the earth comprising the following steps:

(i) drilling a bore hole in the earth with an inflatable ground anchor as defined in any one of the preceding claims;

(ii) inflating the inflatable member of the ground anchor to a predetermined size using a pressurized fluid; and

(iii) stressing the ground anchor by applying a force to the drilling member so as to anchor the structural element to the earth.

14. A method as claimed in claim 13 wherein the fluid is water, drilling mud or grouting material.

15. A method as claimed in claim 13 wherein the ground anchor is stressed by applying a tensile force to the drilling member.

16. An inflatable ground anchor substantially as herein described with reference to the accompanying drawings.

17. A method for anchoring a structural element to the earth substantially as herein described with reference to the accompanying drawings.