AU770393B2 - Apparatus and method for producing cement mix columns - Google Patents

Description

WO 01/12906 PCT/AUOO/00960 -1- APPARATUS AND METHOD FOR PRODUCING CEMENT MIX COLUMNS FIELD OF THE INVENTION The present invention relates to an apparatus and method for producing cement mix columns, for example, along an intended retaining wall line and relates particularly, though not exclusively, to a method of forming a soilnail wall.

BACKGROUND TO THE INVENTION Soilnailing is a known technique for retaining excavations in unstable sand and soil. The technique involves an iterative process of excavating the soil to a prescribed depth and reinforcing the exposed cut. The soil is initially cut vertically to a depth of say one metre on a lineal run. When the vertical cut has been completed, reinforcing mesh is placed against the exposed face of the cut soil and then concrete is sprayed against the mesh to cover the face to a thickness of say 100mm to form a wall. Block-outs are placed at spaced intervals in the mesh to provide voids for grout anchor holes to be driven into the soil behind the wall. Reinforcing anchor bars are then inserted in the holes with the outer end protruding beyond the face of the concrete wall. The anchor bars are then cement grouted into the soil and the face of the wall. When the grout is set, holding steel plates are placed against the bars and against the wall and secured with a nut to hold the plates in place and to support the wall. The soil is then cut vertically to a depth of 1 metre below the first metre cut. The process of forming the soilnail wall described above is then repeated.

One of the difficulties with the known soilnail wall technique is the risk of soil collapsing, (particularly in sandy soils), prior to completion of the process of forming the concrete wall. This creates all sorts of problems in constructing the concrete wall, incurring extra concrete usage and time and labour costs. Furthermore, if soil collapses at a lower level there is a substantial risk that the upper level(s) of the wall will slide down, causing a total collapse and endangering lives.

111 1 I.~ilririml ii~cmr :iril .Inrrurri~~ ;iih~nnq~wu:ii.~;u;lirr I jl~isnjlm;j~.~ iu;lu** +zir~i~i~ iitl~i~i~Y~"~YUli~i" dl.f Received 16 May 2001 -2- SUMMARY OF THE INVENTION The present invention was developed with a view to providing an apparatus and method for producing grout columns along an intended soilnail wall line that substantially reduces the risk of soil collapsing during construction of a soilnail wall. It was further developed to provide an apparatus and method for producing cement mix columns that can be used, for example, for making a retaining wall that in certain situations can replace lightweight sheet piling or other retaining methods.

Throughout this specification the term "comprising" is used inclusively, in the sense that there may be other features and/or steps included in the invention not expressly defined or comprehended in the features or steps subsequently defined or described. What such other features and/or steps may include will be apparent from the specification read as a whole.

According to one aspect of the present invention there is provided an apparatus for producing cement mix columns, the apparatus comprising: a manifold having an elongate hollow tube adapted to be driven into soil, a bottom end of the tube, which first enters the soil, having a first opening sufficiently large to permit cement mix to pass therethrough, and a top end of the tube having a second opening to permit cement mix to be pumped into the hollow interior of the tube, said manifold being capable of being held in a vibratory piling hammer and further comprising a transverse plate fixed to said tube and extending transversely to the longitudinal axis of the tube so as to protrude outwardly from at least one side of the tube whereby, in use, when the elongate tube has been driven into the soil to a predetermined depth and is then withdrawn, cement mix pumped through the tube can be injected into a void left in the soil by the tube and into a groove-shaped void formed by the transverse plate as the manifold is withdrawn.

Throughout this specification the term "cement mix" is intended to be used in the broadest sense to cover any suitable mixture of cement and water, and possibly other additives and fillers such as sand and/or gravel, capable of being pumped through the tube and injected into the void left in the soil as the tube is withdrawn. It includes cement grout, (a "neat" mixture of cement and water), including superfine cement grout, as well as a sand, cement AMENDED SHEET

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Received 16 May 2001 -3and water slurry. The cement may be conventional Portland cement or any other suitable cement material.

Preferably said elongate hollow tube is one of a plurality of tubes of the manifold extending substantially parallel and provided in a spaced array. Preferably the apparatus further comprises a sacrificial tip element provided at the bottom end of the tubes, said tip element being left behind at the bottom of said voids when the tubes are withdrawn.

Typically each tube of the manifold is of substantially circular cross-section throughout its length, said bottom end being partially flattened to form a taper. Preferably said tip element is wedge-shaped and is removably received over said taper to prevent soil from entering the tube as it is driven into the soil.

Preferably said plurality of tubes are provided in a linear spaced array. Preferably said manifold further comprises a transverse plate fixed to said plurality of tubes and extending transversely to the longitudinal axis of one or more of the tubes for stiffening the manifold and keeping the tubes in substantially parallel alignment. One or more transverse plates may be provided at spaced intervals along the length of the tubes. Alternatively, said transverse plate may extend throughout the full length of the tubes. Preferably said transverse plate protrudes beyond the respective outermost tubes on each side of the manifold whereby, in use, as the tubes are withdrawn a groove-shaped void, formed by the transverse plate, is left in the soil both between the voids formed by the tubes and on the outer sides of the voids formed by the respective outermost tubes.

According to another aspect of the present invention there is provided a method for producing cement mix columns, the method comprising the steps of: driving a manifold having an elongate hollow tube into soil, a bottom end of the tube which first enters the soil, having a first opening sufficiently large to permit cement mix to pass therethrough, and a top end of the tube having a second opening to permit cement mix to be pumped into the hollow interior of the tube hammer and further comprising a transverse plate fixed to said tube and extending transversely to the longitudinal axis of the AMEDE c8HEET IPEA/Au ~a ~;rulrnm hr- M M~~ri~r~iY"' liii~B~~iiai*~iiu~r~ Received 16 May 2001 -4tube so as to protrude outwardly from at least one side of the tube; withdrawing the elongate tube, when it has been driven into the soil to a predetermined depth, so as to leave a void in the soil in the space formerly occupied by the tube and a groove-shaped void in the space formerly occupied by the transverse plate; pumping cement mix through the tube so that the mix is injected into said voids through said first opening; and, allowing said cement mix to set in said voids to form a cement mix column which helps to stabilise the soil when excavation of the soil adjacent the column commences.

Preferably said step of withdrawing the tube involves vibrating the tube as it is withdrawn so that the cement mix injected into the voids fills the voids.

Preferably the method further comprises moving the manifold along an intended retaining wall line and repeating the above steps to form a line of cement mix columns along the intended retaining wall line.

Preferably the method further comprises temporarily fixing a length of reinforcing mesh to the manifold, prior to said step of driving the manifold into the soil, whereby the mesh is driven into the soil with the manifold, and wherein when the manifold is withdrawn the mesh is retained in the soil and becomes embedded in the cement mix injected into the voids left in the soil.

In one form of the invention a separate length of reinforcing mesh is attached to the manifold between each tube of the manifold. In another form of the invention a single length of reinforcing mesh is attached to the manifold, the mesh having a transverse profile adapted to match the transverse profile of the manifold.

According to a further aspect of the present invention there is provided a method of AMENDED SHEET 111 MMON-- liV. if ;'MiBi~Br~rW Y WO 01/12906 PCT/AU00/00960 forming a soilnail wall which employs the above method of producing cement mix columns, along the intended soilnail wall line.

BRIEF DESCRIPTION OF DRAWINGS In order to facilitate a more comprehensive understanding of the nature of the invention a preferred embodiment of the apparatus and method for producing cement mix columns will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1(a) and illustrate a preferred embodiment of an apparatus for producing cement grout columns according to the invention; Figures 2 and 3 illustrate steps in a preferred method of forming a soilnail wall according to the invention; Figure 4 illustrates a completed soilnail wall formed according to a preferred method of the invention; Figure 5 is a plan view of the soilnail wall of Figure 4; Figure 6 is a front view of the soilnail wall of Figure 4; Figure 7(a) and illustrate the apparatus of Figure 1 having reinforcing mesh temporarily attached to the manifold; Figure 8 illustrates a preferred method of forming a cantilever retaining wall according to the invention; Figure 9 is a front elevation of a completed retaining wall built according to a preferred method of the invention; Figure 10 is a section view through the retaining wall of Figure 9; IMPMOMIA104 0*AWNilYi~ii~ iii.n-~' 'Iif *WV~iiliI1 iil~iff*M.iliI WO 01/12906 PCT/AU00/00960 -6- Figure 11 is a section view through another retaining wall built according to a preferred method of the invention; Figure 12 is a section view through a further retaining wall built according to a preferred method of the invention; Figure 13 is a section view through a manifold of the apparatus illustrated in Figure 7; Figure 14 is a section view through a second embodiment of a manifold of the apparatus according to the present invention; Figure 15 is a section view through a third embodiment of a manifold of the apparatus according to the present invention; Figure 16 is a section view through a fourth embodiment of a manifold of the apparatus according to the present invention; Figure 17 is a section view through a fifth embodiment of a manifold of the apparatus according to the present invention; and, Figure 18 is a section view through a sixth embodiment of a manifold of the apparatus according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A preferred embodiment of the apparatus for producing cement grout columns as illustrated in Figure 1 comprises a manifold 10 having a plurality of elongate hollow tubes 12 extending substantially parallel and provided in a linear spaced array. In this embodiment the manifold 10 has three tubes 12 adapted to be driven into soil, a bottom end 14 of each tube, which first enters the soil, being tapered. Each of the tubes 12 of this embodiment is of substantially circular cross section throughout its length, with the bottom end 14 being partially flattened to form the taper but leaving a first opening WO 01/12906 PCT/AU00/00960 -7sufficiently large to permit cement grout to pass through (approximately 10mm wide).

The tubes 12 may be of any suitable diameter and typically have an internal diameter of between 80 to 120mm. The tubes 12 may also be of any required length, and in this embodiment are about 5 metres in length. They are preferably made from seamless, hard drawn steel of the type used for drill casings. Each tube is also provided with a second openings 16 at a top end of the tube to permit cement grout to be pumped into the hollow interior of the tube 12. Bleed holes (not shown) may be provided adjacent the top ends of the tubes 12 to allow air to escape from within the tubes as the cement grout is pumped in through the opening 16. If necessary, the bleed holes may be closed in order to pressurise the cement grout within the tubes 12.

The manifold 10 further comprises a steel mounting plate 18 to which the top ends of the tubes 12 are welded, in this case at 500mm centres. The mounting plate 18 may be gripped in the jaws of a high frequency, vibratory piling hammer 20 for driving the elongate tubes 12 into the soil. The jaws 22 of the piling hammer 20 may be of the kind described in co-pending Australian patent application No. PP 9736 for A Set of Jaws for Sheet Pile, the contents of which are incorporated herein by reference. A sacrificial tip element 24 is preferably provided at the bottom end 14 of the tubes 12, the tip element being left behind in the soil when the tubes are withdrawn. The tip element is typically wedge-shaped as can be seen most clearly in Figure 1 and is removably received over the taper at the bottom end 14 of the tubes 12 to prevent soil from entering the tubes as they are driven into the soil. (The tip element 24 has been omitted from Figure 1 for clarity). Individual tip elements 24 may be provided on each of the ends 14 of the tubes, or alternatively a single elongate tip element extending the full width of the manifold may be provided, formed from a length of hardened metal plate in the shape of a The manifold 10 further comprises one or more transverse plates 26 fixed to the tubes 12 and extending transversely in the plane of the linear array for stiffening the manifold and keeping the tubes in parallel alignment. Preferably the transverse plate 26 provided at the bottom ends 14 of the tubes protrudes beyond the respective outermost tubes on each side of the manifold by approximately 100mm. In this way, as the tubes are withdrawn, a groove-shaped void, formed by the transverse plate 26, is left in the soil both between the J~.~~mi~r.lu*i'*"'"~~"~""l:lunrana~llli WO 01/12906 PCT/AU00/00960 -8voids formed by the tubes and on the respective sides of the voids formed by the outermost tubes. The significance of the groove-shaped voids thus formed will be described further below.

A preferred method for producing cement grout columns along an intended soilnail wall line, and of forming a soilnail wall will now be described with reference to Figures 2 to 6.

The hollow tubes 12 of the manifold 10 are first driven into the soil using a piling hammer with a sacrificial tip element 24 attached to the bottom ends 14 of the tubes. The manifold is driven into the soil with the tubes aligned and adjacent to the intended soilnail wall line. When the tubes have been driven into the soil to a predetermined depth, the tubes are withdrawn by, lifting the manifold 10 using the piling hammer 20, so as to leave voids in the soil in the spaces formerly occupied by the tubes 12. As the tubes are withdrawn, cement grout is simultaneously pumped through the tubes through the second opening 16 so that grout is injected into the voids through the first openings at the bottom ends 14 of the tubes. Preferably the piling hammer 20 continues to vibrate the manifold during withdrawal of the tubes so that the cement grout injected into the voids fills the voids. The sacrificial tip element 24 remains in the soil at the bottom of the voids as the tubes are withdrawn. As the grout is pumped through the tubes into the voids under pressure, it will also tend to fill the groove-shaped voids formed by the transverse plate 26 both between the voids formed by the tubes and on the outer sides of the voids formed by the respective outermost tubes. Hence, there will be a transverse spreading of the grout columns as can be seen most clearly in Figure When the tubes 12 have been fully removed from the soil and the voids are full of grout, a reinforcing bar is pushed down into the grout to substantially the full length of the column.

The cement grout is then allowed to set in each of the voids to form three reinforced grout columns 30 extending downwards into the soil adjacent the intended soilnail wall line.

The grout columns 30 are preferably formed down to a depth extending slightly below the base of the intended soilnail wall. The above process is then repeated along the intended soilnail wall line, starting 500mm from the last grout column. This distance may vary depending on the required wall strength or the soil condition.

NXI

WO 01/12906 PCT/AU00/00960 -9- When the cement grout in the columns has set and hardened, excavation of the soil in front of the grout columns can proceed. When the tubes 12 are driven into the soil, the soil is displaced rather than being removed, and therefore the soil between the columns is compacted which allows the soil to arch from column to column. This helps to further stabilise the soil preventing it from collapsing during excavation. The soil is initially cut vertically to a depth of between 1 to 2 metres as shown in Figure 2. In view of the improved soil stabilisation provided by the grout columns 30, the soil can be cut vertically to a greater depth compared to conventional soilnailing techniques. The soil is cut back between the columns 30 to half the diameter of the columns. Then reinforcing mesh 32 is placed against the grout columns 30 and concrete is then sprayed over the reinforcing mesh 32 and the exposed faces of the grout columns 30, so that the grout columns 30 are integrated into the structure of the concrete wall 34, as illustrated in Figure 3. Block-outs are inserted at spaced intervals between columns 30 for insertion of anchor bars prior to spraying of the concrete. Grout anchors 36 can then be installed in the normal manner.

When the concrete wall 34 has set and hardened, the next layer of soil can be excavated along the line of the soilnail wall. As before, the soil is cut back between the columns to half the diameter of the columns and then reinforcing mesh 32 is placed against the grout columns. Concrete is then sprayed over the reinforcing mesh 42 and the exposed faces of the grout columns 30 to the same depth as the concrete wall 34 already formed above. Grout anchors 36 are also installed as before. The finished soilnail wall 34 down to the predetermined depth is illustrated in Figure 4. As the grout columns 36 extend downwards the full length of the depth of the soilnail wall, they support the upper section of the wall 34 from slipping during the next stage of soil excavation. The void left by the transverse plate 26 will also be partially filled with cement grout as can be seen in Figure This allows the grout to extend transversally from one column 30 to the other, further reducing the possibility of soil collapse during excavation. Steel anchor plates 38 are fastened to the exposed ends of the anchor bars 36 as illustrated in Figure 6.

In some situations, for example, in long street frontages, it is not permissible to use anchors in retaining walls, and therefore a soilnail wall cannot be used. In these a m -l1"RIMM "Mr, WO 01/12906 PCT/AU00/00960 circumstances, a timber (lagging) and beam system of retaining wall is employed. More recently, lightweight sheet piling has been used to replace the timber and beam type system of retaining wall. In some situations a cement mix column retaining wall made in accordance with the method of the present invention may be just as effective and will be less expensive than lightweight sheet piling. Additional reinforcing material may be required in order to strengthen the retaining wall. However, the total cost of the cement mix and steel reinforcing material will be significantly less than the cost of the sheet piling.

Figure 7 illustrates a technique for inserting construction/reinforcing mesh into a retaining wall made with cement mix columns in accordance with a preferred method of the present invention. The apparatus illustrated in Figure 7 is substantially identical to that illustrated in Figure 1, and therefore the like parts have been identified with identical reference numerals and will not be described in detail again. The most significant difference in the apparatus of Figure 7 is the addition of two lengths of reinforcing mesh 40 which are temporarily attached to the manifold 10. The reinforcing mesh is typically conventional construction/reinforcing galvanized steel mesh made, for example, from 5 mm diameter reinforcing bar welded together in a 100 mm 2 grid. In this embodiment, the reinforcing mesh is cut into two separate lengths which are attached to the manifold between the tubes 12 (see Figure 13). The length of the reinforcing mesh corresponds to approximately twice the height of the retaining wall. The lower end 42 of the reinforcing mesh is bent over and temporarily retained on the lower transverse plate 26 of the manifold as can be seen most clearly in Figure With the manifold 10 carrying the lengths of mesh 40 a slightly increased driving force will be required to drive the manifold into soil. However, as the manifold is being driven into the soil, the mesh 40 occupies the groove-shaped voids created between the tubes 12 by the lower transverse plate 26. When the manifold is withdrawn the lengths of mesh 40 are retained in the soil as the lower end 42 grips into the walls of the groove-shaped voids formed by the transverse plate 26. The method for producing cement mix columns along an intended retaining wall line is similar to the method described with reference to Figures 2-6. A preferred method of forming a retaining wall with reinforced cement mix columns will now be described with reference to Figures 8-10.

~lll!yWW OR'WMllnhr!iRii~ ~YC~Ali~.~Oerw WO 01/12906 PCT/AU00/00960 11 As illustrated in Figure 8, a cantilever retaining wall 50 has been formed using the cement mix column technique of the present invention. To form the retaining wall 50, the manifold 10 was first driven into the soil with the tubes aligned along the intended retaining wall line and with the reinforcing mesh 40 temporarily attached to the manifold as described above. When the manifold has been driven into the soil to the desired depth, the tubes are withdrawn by lifting the manifold 10, leaving voids in the soil in the spaces formerly occupied by the tubes 12 and the transverse plates 26. As the tubes are withdrawn, the lengths of wire mesh 40 are retained in the soil, and simultaneously the cement mix is pumped through the tubes and injected into the voids at the bottom end of the tubes. As the cement mix is pumped through the tubes into the voids under pressure, it will fill both the voids left by the tubes .as well as the groove-shaped voids formed by the transverse plate 26. The groove-shaped voids formed by the transverse plates 26 are now occupied by the reinforcing mesh 40, and therefore become embedded in the cement mix.

When the tubes 12 have been fully removed from the soil and the voids are full of cement mix, reinforcing bars 52 may be pushed into the columns to substantially the full length of the columns (see Figure 10). One or more reinforcing bars 52 may be inserted in each column, and for larger diameter columns, a small cage of reinforcing bar may be used in the columns to provide additional strength.

The cement mix is then allowed to set in each of the voids to form three reinforced cement mix columns joined by two webs of reinforced cement mix extending between the columns along the intended retaining wall line. In this embodiment the cement mix columns 54 are preferably formed down to a depth extending approximately twice the height of the retaining wall 50 that will be exposed above ground level as shown in Figure 8. The above process is then repeated along the intended retaining wall line, starting a predetermined distance, (corresponding to the spacing between the tubes 12 of the manifold), from the last cement column 54.

When the cement mix in the columns has set and hardened, excavation of the soil in front of the retaining wall 50 can proceed. The soil is cut vertically to a depth approximately halfway down the full height of the columns 54, (say 1.5 metres for 3 metre columns). If nil 0. R INVIVINIOU firci IMM"11 NARMINW161h ON IMAIN14 PIP WHAMON WWI RMUMMINI RRAIRM pwo v wARM ApTf NNAM I

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WO 01/12906 PCT/AU00/00960 -12necessary, a footing 60 may be formed at the base of the wall and a concrete wall 62 formed integral to the exposed faces of the cement columns 54.

As can be seen most clearly in Figure 10, the groove-shaped voids between the cement columns 54 substantially fill with the cement mix to form a continuous web between each of the columns 54. In this connection, the transverse plate 26 provided at the bottom ends 14 of the tubes on the manifold 10 have been lengthened in the present embodiment, so that they now protrude beyond the respective outermost tubes on each side of the manifold by approximately 250 mm (see Figures 7(a) and 13). Hence, when the process of driving the manifold into the soil and injecting the cement mix is repeated along the intended retaining wall line, starting (in this case) approximately 500 mm from the last cement column, the outer most grooves formed by the transverse plate will adjoin.

Furthermore, in the described embodiment, the reinforcing mesh is attached to the manifold in separate lengths between each tube of the manifold. However, in an alternative embodiment the reinforcing mesh may be attached to the manifold in the form of a single length of mesh having a transverse profile adapted to match the transverse profile of the manifold, ie, crimped at the locations of the tubes so as to minimise soil resistance when driving the manifold into the soil. This form of reinforcing mesh 44 is also illustrated in Figure 10. One advantage of this form of reinforcing mesh 44 is that the mesh in 44 is more firmly embedded in the cement columns 54, further improving the strength of the retaining wall.

Figure 11 illustrates another retaining wall made in accordance with a preferred method of the invention. The retaining wall 66 is made in a similar manner to that of Figure except that in this case a different form of manifold 68 is employed as illustrated in Figure 14. The manifold 68 shown in section view in Figure 14, has three tubes 70 arranged in a linear spaced array similar to that of Figure 13, except that the tubes 70 are of slightly larger diameter, (say 200 mm) and a transverse plate 72 is also arranged differently. In this embodiment, the transverse plate 72 still extends transversely in the plane of the linear array but is now displaced closer towards one edge of the linear array. Whereas in Figure 13 the transverse plate 26 is aligned with the centre axis of each of the tubes 12, the plane WO 01/12906 PCT/AUOO/00960 13of the transverse plate 72 in the manifold of Figure 14 is displaced from the centre axis of each of the tubes This means that the groove-shaped voids created by the transverse plate 72 are also displaced closer to one edge of the row of cement mix columns 74 as can be clearly seen in Figure 11. This arrangement makes it easier to attach a single sheet of reinforcing mesh 76 to the manifold. Furthermore, because the tubes 70 are of larger diameter, the size of the cement mix columns 74 is increased sufficiently to allow a reinforcing "cage" 78 to be inserted in each of the columns. Individual reinforcing bars in the cages 78 may be designed to be in tension or compression, depending on the orientation of the cage relative to the load bearing face of the retaining wall. The exposed face of the retaining wall 66 in Figure 11 has been rendered with shotcrete 80, which then becomes an integral part of the wall as well as providing a more aesthetically acceptable wall face.

Figure 12 illustrates a further retaining wall built according to a preferred method of the invention, using a third embodiment of a manifold 82 in accordance with the present invention (see Figure 15). The manifold 82 also comprises a linear spaced array of hollow tubes 84, in this case having a pair of facing transverse plates 86 fixed tangentially to the outer circumference of the tubes 84. Here again, the method of forming the retaining wall 88 is substantially the same as the method described above in relation to the retaining wall of Figure 10, except that in this case two sheets of reinforcing mesh 90 are temporarily attached to the transverse plates 86 and driven into the soil with the manifold. When the manifold 82 is withdrawn and cement mix is pumped into the voids left in the soil, the reinforcing mesh 90 is retained in the voids and becomes embedded in the cement mix so as to form two reinforced webs of cement mix 92 as shown in Figure 12.

As in the previous embodiment, each of the cement mix columns 94 is sufficiently large to allow a reinforcing cage to be inserted, after the tubes have been fully withdrawn. When the cement mix has been injected into the voids, sections of soil 96 will be captured between the columns 94 and webs 92. This soil 96 will have been partly compacted when the manifold 82 was being driven into the soil. If desired, smaller diameter tubes may be inserted into these sections of soil 96 for injecting a microfine grout into this soil. The II1 F~Fm~l r* lrl B61 H NilYH .IRI~IHHI C II IjI 'I(IIIIRH!~li I)K !lrJBVI J I~~RR I II I II H H -'HI IYlRlilrIO~ I~*HW~Y L M If Hf 1k 'HHII1 III I~f WO 01112906 PCT/AU00/00960 -14microfine grout is injected under pressure and will disperse through the soil 96 so that it becomes an integral part of the structure of the retaining wall 88.

The apparatus for producing cement columns in accordance with the invention may also be utilised for making other types of underground structures, in addition to soilnail walls and retaining walls. For example, Figures 16 and 17 illustrate a fourth and fifth embodiment respectively of a manifold of the apparatus which can be used to construct a so called "cluster pile". In both cases, the manifold comprises a central tube 100 having three or more radial tubes 102 extending parallel thereto in a polygonal spaced array. The manifold of Figure 16 has the tubes 102 arranged in a square armray, whereas the manifold of Figure 17 has the tubes 102 arranged in a hexagonal array. In each case, the radial tubes 102 are joined to the central tube 100 by means of transverse plates 104 which perform a similar function to the transverse plates of the previous embodiments. If desired, lengths of reinforcing mesh may be temporarily attached to the transverse plates 104 to be driven into the soil with the manifold, in a similar fashion to that described above.

Figure 18 illustrates a sixth embodiment of a manifold of the apparatus in accordance with the present invention in which a plurality of tubes 106 are provided in a rectangular spaced array. Each of the tubes 106 is joined to at least two adjacent tubes by means of transverse plates 108. When the manifold of Figure 18 is employed in the method of forming cement mix columns in accordance with the invention, a box-like cement column structure is formed in the ground. This type of manifold may be employed to facilitate a more costeffective method of producing a diaphragm wall.

From the above description of various embodiments of the manifold according to the present invention, it will be apparent that the tubes can be arranged in a spaced array of any desired configuration, in order to facilitate the construction of a wide variety of soil stabilisation structures or support structures which utilise reinforced or unreinforced cement mix columns. The size and configuration of the manifold is limited only by the strength of the materials and the force required to drive the manifold into the soil.

WO 01/12906 PCT/AUOO/00960 From the above description of preferred embodiments of the apparatus and method for producing cement mix columns it will be apparent that the method and apparatus provides a number of significant advantages over prior art techniques for constructing a retaining wall, including the following: the risk of soil collapse is substantially reduced, if not eliminated; (ii) slippage of the upper section of a soilnail wall during succeeding stages of soil excavation is prevented, as the cement columns help to support the wall; (iii) each stage of soil excavation can be cut to a greater depth and length due to the reduced possibility of soil collapsing, thereby improving efficiencies; (iv) less concrete need be employed since the cement columns not only stabilise the soil but also improve the structural integrity of the retaining wall; incorporating reinforcing mesh into the webs of cement mix formed between the columns provides further strength allowing the method to be extended to produce cluster piles and retaining walls without anchors; and, the apparatus is relatively inexpensive to manufacture and simple to use with a conventional vibratory piling hammer.

Numerous variations and modifications will suggest themselves to persons skilled in the pile driving and earthmoving arts, in addition to those already described, without departing from the basis inventive concepts. For example, the tubes may be of any suitable crosssection, for example, of rectangular cross-section. If tubes of square cross-section are employed, each tube is preferably aligned with a comer pointing towards the intended retaining wall. All such variations and modifications are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description and the appended claims.

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Claims (19)

1. An apparatus for producing cement mix columns, the apparatus comprising: a manifold having an elongate hollow tube adapted to be driven into soil, a bottom end of the tube, which first enters the soil, having a first opening sufficiently large to permit cement mix to pass therethrough, and a top end of the tube having a second opening to permit cement mix to be pumped into the hollow interior of the tube, said manifold being capable of being held in a vibratory piling hammer and further comprising a transverse plate fixed to said tube and extending transversely to the longitudinal axis of the tube so as to protrude outwardly from at least one side of the tube whereby, in use, when the elongate tube has been driven into the soil to a predetermined depth and is then withdrawn, cement mix pumped through the tube can be injected into a void left in the soil by the tube and into a groove-shaped void formed by the transverse plate as the manifold is withdrawn.

2. An apparatus for producing cement mix columns as defined in Claim 1, wherein said elongate hollow tube is one of a plurality of tubes of the manifold extending substantially parallel and provided in a spaced array.

3. An apparatus for producing cement mix columns as defined in Claim 2, wherein the apparatus further comprises a sacrificial tip element provided at the bottom end of the tubes, said tip element being left behind at the bottom of said voids when the tubes are withdrawn.

4. An apparatus for producing cement mix columns as defined in Claim 3, wherein each tube of the manifold is of substantially circular cross-section throughout its length, said bottom end being partially flattened to form a taper.

5. An apparatus for producing cement mix columns as defined in Claim 4, wherein said tip element is wedge-shaped and is removably received over said taper to prevent soil from entering the tube as it is driven into the soil. 'ME DS SHEET i PIA'AiJ *%vJS1A V %A A.hAM, -17-

6. An apparatus for producing cement mix columns as defined in Claim 2, wherein said transverse plate is fixed to said plurality of tubes for stiffening the manifold and keeping the tubes in substantially parallel alignment.

7. An apparatus for producing cement mix columns as defined in Claim 6, wherein one or more transverse plates may be provided at spaced intervals along the length of the tubes.

8. An apparatus for producing cement mix columns as defined in Claim 6, wherein said transverse plate may extend throughout the full length of the tubes.

9. An apparatus for producing cement mix columns as defined in Claim 6, wherein said transverse plate protrudes beyond the respective outermost tubes on each side of the manifold whereby, in use, as the tubes are withdrawn a groove-shaped void, formed by the transverse plate, is left in the soil both between the voids formed by the tubes and on the outer sides of the voids formed by the respective outermost tubes.

An apparatus for producing cement mix columns as defined in Claim 2, wherein said plurality of tubes are provided in a linear spaced array.

11. A method for producing cement mix columns, the method comprising the steps of: driving a manifold having an elongate hollow tube into soil, a bottom end of the tube which first enters the soil, having a first opening sufficiently large to permit cement mix to pass therethrough, and a top end of the tube having a second opening to permit cement mix to be pumped into the hollow interior of the tube hammer and further comprising a transverse plate fixed to said tube and extending transversely to the longitudinal axis of the tube so as to protrude outwardly from at least one side of the tube; withdrawing the elongate tube, when it has been driven into the soil to a predetermined A4MENiD SHEET Received 16 May 2001 -18- depth, so as to leave a void in the soil in the space formerly occupied by the tube and a groove-shaped void in the space formerly occupied by the transverse plate; pumping cement mix through the tube so that the mix is injected into said voids through said first opening; and, allowing said cement mix to set in said voids to form a cement mix column which helps to stabilise the soil when excavation of the soil adjacent the column commences.

12. A method of producing cement mix columns as defined in Claim 11, wherein the method further comprises inserting a reinforcing bar down into the cement mix, prior to allowing the mix to set.

13. A method of producing cement mix columns as defined in Claim 11, wherein said step of withdrawing the tube involves vibrating the tube as it is withdrawn so that the cement mix injected into the voids fills the voids.

14. A method of producing cement mix columns as defined in Claim 11, wherein the manifold has a plurality of said elongate tubes provided in a spaced array whereby, in use, a plurality of cement mix columns can be formed simultaneously.

A method of producing cement mix columns as defined in Claim 14, wherein said plurality of elongate tubes are provided in a linear spaced array.

16. A method of producing cement mix columns as defined in Claim 11, wherein the method further comprises moving the manifold along an intended retaining wall line and repeating the above steps to form a line of cement mix columns along the intended retaining wall line.

17. A method of producing cement mix columns as defined in Claim 11, wherein the method further comprises temporarily fixing a length of reinforcing mesh to the manifold, prior to said step of driving the manifold into the soil, whereby the mesh is driven into the AMEiNDD ,SE-T !P _T fiffiYAWPAW I9QWfflIVMl ZEN&MCm' Received 16 May 2001 -19- soil with the manifold, and wherein when the manifold is withdrawn the mesh is retained in the soil and becomes embedded in the cement mix injected into the voids left in the soil.

18. A method of producing cement mix columns as defined in Claim 17, wherein a separate length of reinforcing mesh is attached to the manifold between each tube of the manifold.

19. A method of producing cement mix columns as defined in Claim 18, wherein a single length of reinforcing mesh is attached to the manifold, the mesh having a transverse profile adapted to match the transverse profile of the manifold. A method of forming a soilnail wall which employs the method of producing cement mix columns as defined in any one of claims of 11 to 19, along the intended soilnail wall line. AMENDED SHEET *PEAF-4 MblaApWi on(,1 Val. if