AU2487501A - Ground and rock anchoring - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

0 *0 00 *00..

Name of Applicant: Actual Inventor(s): Address for Service: Invention Title: SCREW IN TECHNOLOGIES PTY. LTD.

DALE ANDERSON and PETER YTTRUP SANDERCOCK COWIE 69 Robinson Street, DANDENONG VIC 3175 GROUND AND ROCK ANCHORING Details of Associated Provisional Application Nos: Australian Provisional Application No. PQ6044 Filed: 6 th March, 2000 The following statement is a full description of this invention, including the best method of performing it known to us: -1- 2001-03-06,A:321scrcwin.compfilc.wpd, I la- TITLE: GROUND AND ROCK ANCHORING FIELD OF THE INVENTION This invention relates to screw-in ground anchors and to rock anchors.

200 I-03-05,A:\320screwin.couipletc2. vp I -2- BACKGROUND OF THE INVENTION Prior Art Screw-in ground anchors have been known for some time. These anchors generally comprise a shaft carrying one or more helical flights. Rotation of the shaft of such an anchor causes the anchor to screw into the ground. Typical descriptions of such anchors include the following patent documents:- United States Patents 3,011,597 and 3,011,598 to Samual R. Galloway and William H. Galloway, published 5 h December, 1961. This specification relates to a supporting post. It discloses an open-ended tube carrying one screw thread.

British Patent 1,098,555 to Trefileries Leon Bekaert P.V.B.A, published 10 th January, 1968. This specification relates to a post suitable for use as a fence-post.

It discloses an open-ended tube carrying one or more screw threads. When multiple screw threads are provided, they may form a multi-start screw thread.

Hereto, screw-in ground anchors have been used either as tension anchors or as foundation anchors.

For example, the A.B. Chance Company subsidiary of Emerson Electric Co. (Centralia, Missouri, USA) has for some years manufactured screw-in tension anchors for anchoring guy-wires of electrical reticulation poles and radio transmission towers.

In this specification the inclusion of a reference to a granted patent by a number is not an admission that the contents of that specification form part of the common general knowledge in this field. In this specification and claims the use of "comprising" is used in the sense of "including" and does not limit the definition to the integers which follow.

The A.B. Chance Company has also manufactured screw-in foundation anchors for some years. Forms of these anchors specifically designed for street lighting generally comprise a hollow steel pipe, carrying at least one helical flight or auger adjacent one end.

2001 -03-05.A:U20screvin.ncomple2.pd,2 -3- Rotation of the pipe screws the foundation into the ground. The leading end of the pipe may be open, or it may be closed off with a shaped blanking plate. The other end of the pipe generally carries a plate to which a street light may be bolted. Some other forms of screw-in foundation anchors produced by the A.B. Chance Company are illustrated in United States Patent 4,339,899 (issued 20 h July, 1982).

Our co-pending International Patent Application PCT/AU98/00606 discloses an alterative use of screw-in ground anchors in which the anchor element is normally neither in tension nor in compression. That application discloses the use of screw-in ground anchors as ground reinforcement or stabilisation. The anchors are installed in earth structures, and are not normally loaded unless ground slippage starts to occur. At the point of ground slippage, interaction between the ground and the anchor tends to stabilise the ground. The loading on the shaft of the anchor at that time is tension loading along the length of the shaft.

Deficiencies of the Prior Art *:.Presently known types of screw-in ground anchors are not ideal under all conditions.

The leading end of the anchor sometimes strikes rock during installation. This results in the anchor being "anchored" into a lesser depth of ground than is necessary for it to meet the design loading capacity. When such an anchor is being used as a tension anchor, it may not be able to develop adequate resistance to tension loads and it may be pulled out of the ground.

The problem of anchors striking rock faces is particularly serious when the anchors are being used for ground reinforcement or stabilisation. Often when ground slip failure occurs, it occurs at an interface between soil and rock. A ground anchor which does not stabilise the ground mass relative to the underlying rock will not prevent slip failure of the ground relative to the rock.

The present invention accordingly seeks to provide ground anchors for use in environments in which there is rock dispersed among or underlying the earth mass.

2001 -03-OS.A:\3Zscrwin.compl2.wpd3 The present invention also seeks to provide methods of installing ground anchors.

The present invention also seeks to provide methods of stabilising soil layers which are prone to slippage over underlying rock.

SUMMARY OF THE INVENTION This invention provides a ground anchor for anchoring a soil layer to an underlying rock layer, the anchor comprising a first portion adapted for anchoring within the soil layer and a second portion for anchoring within the rock layer.

PREFERRED ASPECTS OF THE INVENTION It is preferred that the first portion includes a shaft having a leading end and a trailing end.

It is further preferred that the shaft is hollow with an open leading end and an open trailing end.

It is preferred that the first portion includes at least one substantially helical flight.

It is preferred that the second portion includes a rod which is within the first portion and which extends out of an open leading end of the first portion.

It is preferred that the first portion and the second portion be fixed together by fixing means which includes grouting.

In this specification "grout" includes fluent hardenable mixes routinely used in this field, namely masonry type mixes such as concrete and their mineral analogues and organic polymeric mixes such as epoxy compounds with delayed release hardeners.

2001-03-OSAA:320sccwin.cvmpicte2.wpd4 BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS Figure 1 is a side elevational view illustrating a screw-in ground anchor according to the prior art.

Figure 2 is a vertical sectional view illustrating a ground reinforcement method and apparatus according to our co-pending International Patent Application PCT/AU98/00606.

Figures 3 and 4 are vertical sectional views illustrating failure of a road cutting by slip of soil over underlying rock.

Figures 5 and 6 illustrate a method and apparatus according to the present invention.

DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS Prior Art Figure 1 shows a screw-in ground anchor according to the prior art. The ground anchor 1 has a hollow tubular shaft 2, usually circular in section, with helical flights 3 and 4 welded to the shaft. Holes 7 pass through the tube for connection of a drive tool (which is not illustrated).

Figure 2 shows the use of ground anchors according to our co-pending International Patent Application PCT/AU98/00606. In this figure, an embankment 9 has an exposed, inclined earthen face 11. Geomechanical failure of a structure such as embankment 9 tends to take place by slippage of soil mass 12 along surface 13 as a coherent structure about point 14, which is the centre point of the circular arc which defines surface 13. In accordance with our co-pending patent application, ground anchors 16, 17, 18 and 19 have been placed into the embankment from the direction of exposed face 11. When the soil mass 12 is in equilibrium, there is not resultant stress applied by the soil in the direction of the length of the ground anchor. When the soil mass 12 begins to move, there is adhesion of soil to the surface of the nails, and friction between the soil and the 200 I 3-05.A:'20scrcwin.complctdwpcL -6surface of the nail. The consequent adhesive and frictional forces put the nails into tension along the direction of their length and provides some degree of restraint to prevent the soil mass 12 from moving. However, in addition to the forces of adhesion and friction, the movement of soil relative to the flights adjacent opposite ends of an anchor will tend to place the shaft of the anchor in tension, and the shaft of the anchor acting through the flights will tend to put the mass of the soil between the flights into compression, so generating additional forces which tend to prevent the soil mass 12 from moving.

However, if there happen to be boulders or bedrock at or near the incipient slip surface 13, then it will not be possible to install ground anchors such as 16, 17, 18 and 19 in this manner which stabilises the soil mass 12 relative to the underlying ground structure.

APPARATUS AND METHODS ACCORDING TO THE PRESENT INVENTION Figure 3 illustrates a hillside or like slope which includes an overlaying soil strata 22 on eooo a layer of bedrock 23. Any tendency to down-hill slipping by soil layer 22 generates shear resistance to that slippage in the region of the interface 24 between the soil layer 22 and the rock 23.

Figure 4 illustrates the hillside of Figure 3 after a cutting 26 has been constructed. The cutting 26 includes an exposed soil face 27 as a region where the mass of soil 28 which is up-hill from the cutting lacks any support against down-hill slippage. Depending on the nature of the soil-mass 28 and the magnitude of shear resistance generated in the vicinity of region 24, the soil mass 28 may tend to slip down-hill into cutting 26. One early indicator of incipient slip may be the development of tension cracks such as 29 uphill from the cutting.

Figure 5 illustrates a hillside or slope which has been stabilised according to the method and apparatus of the present invention.

As illustrated in Figures 3 and 4, a ground anchor 30 according to one embodiment of the present invention includes a tube 31 (preferably of steel) carrying at least one helical 2001-03 0SA:\320screwin.conplctc2.wpd,6 -7flight 32. It is preferred that the tube 31 carry a plurality of helical flights 32.

Before construction of a cutting, one or more ground anchors such as 30 are driven into the soil mass up the slope from the location of the proposed cutting. Each tube 31 is driven into the soil mass until the substantially open leading end of the tube 31 strikes the underlying rock. When this happens, it is preferred that the interior of the tube 31 be cleared of soil or other debris. Methods suitable for doing this are disclosed in United States Patents 4,637,758 (Tamaki et al) and 4,793,740 (Schelhom).

A bore hole 36 is then drilled into the underlying rock 23, substantially co-axially with the tube 31.

A reinforcing rod 33 (preferably of steel) is then inserted into the full length of the tube 31 and bore hole 36. Preferably, the trailing end of the rod 33 is threaded at 37 for reception of a screw-threaded nut.

Suitable grouting 34 is then pumped into the interior of the tube 31 and the bore hole 36.

When this grouting has set, it serves to anchor the reinforcing rod 33 within the tube 31, and to anchor the reinforcing rod 33 within the bore hole 36. When an adequate number oooo• of such anchors have been installed above the site of a proposed cutting, the overall effect will be to secure a soil mass such as 28 from slipping into the cutting.

0A. When the grouting on each anchor has set, an end cap 39 is placed over the trailing end 00 of reinforcing rod 33, and a screw threaded nut 38 screwed onto the rod 33. The end cap 39 serves to transmit forces from the reinforcing rod 33 to the tube 31, without such an end cap the grouting 34 would provide the only medium for transmission of such forces.

An alternative preferred construction (not illustrated) does not use grouting such as 34 within the bore hole 36. Instead an epoxy resin mixture containing hardener encapsulated in glass beads is poured into the bore hole 36. Insertion of the reinforcing rod 33 and vigorous agitation of the mixture tends to break the glass beads and release the hardener, causing rapid setting of the resin and bonding of the reinforcing rod 33 within the bore 2001-03-05,A:\320screwinlcmplct2.wpd7 -8hole 36. As with the previously described construction, grouting may be poured into the remaining void within the tube 31, and an end cap 39 and nut 38 applied to the exposed end of the tube 31.

In use the depth of the bore would depend upon the strength of the rock and upon the load supported by the anchor. The length of the anchor depends upon the depth of soil to be stabilised. Commonly the anchors will be made from commercially available pipe so ready made diameters would be used 89mm, 114mm and so on.

Throughout this specification:the words 'comprising' and 'comprises' mean including, but not limited to, or includes, without limitation; and any reference to a patent specification is not an admission that the contents of that specification are part of the common general knowledge of a person skilled in the *at in art in Australia.

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Claims (9)

1. A method for anchoring a soil layer to an adjacent rock layer comprising inserting a hollow ground anchor having a leading end and a trailing end, in the soil layer toward the boundary of the rock layer, boring through and beyond the anchor into the rock layer and filling the bore and hollow ground anchor with grout.

2. A method is claimed in Claim 1 and additionally inserting a tie through the anchor and at least part way into the bore.

3. A method is claimed in Claim 2 including inserting as a tie, a reinforcing rod through the anchor into the bore and after filling with grout, closing the trailing end of the anchor with a cap and securing the cap to the rod.

4. A ground anchor for anchoring a soil layer to a rock ground layer, the anchor comprising of first portion adapted for anchoring within the soil layer and the second portion for anchoring in the rock layer.

5. A method as claimed in any one of Claims 1-4 wherein the cross sectional area of the bore is substantially the same as the cross sectional area of the ground anchor.

6. An in situ ground anchor comprising an opened ended hollow shaft equipped with an exterior helical flight for screwing the shaft into the soil layer, a column of hardened grout cast within the anchor and extending beyond the leading end of the anchor and a tie extending through the anchor and into the column extending beyond the anchor.

7. An in situ ground anchor as claimed in Claim 6 wherein the open end of the anchor is closed by a cap fixed to the end of the tie.

8. An in situ ground anchor substantially herein described with reference to Figure 6. 200 l-3-0A:U\320scrwin.completc2.wpd9 10

9. A method of anchoring a penetrable ground layer to a resistant adjacent ground layer substantially herein described with reference to Figure 2 or as modified by Figure Dated this 6h day of March, 2001. SANDERCOCK COWIE PATENT ATTORNEYS FOR SCREW IN TECHNOLOGIES PTY. LTD.

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