GB2284459A - Stabilisation of soil contours - Google Patents

Abstract

A polymeric sheet with longitudinal load carrying components (7) and flexible transverse components (8) is rolled or folded into a spiral or zig-zag cross-section to form an elongate load-bearing member for use as a "soil nail" to be grouted into a correspondingly elongate bore in a soil contour to be stabilised. Such a construction gives good grout adhesion between the walls of the bore and the polymeric components e.g. components 7, and is proof against corrosion. <IMAGE>

Description

STABILISATION OF SOIL CONTOURS This invention relates to the stabilisation of soil contours and to devices which may be used for that purpose.

It is commonplace in civil engineering to re-contour the land surface whether for structural reasons e.g.

cuttings or embankments or for cosmetic reasons e.g.

berms for noise shielding. There is also a large body of old-established existing artificial land contours i.e. from the civil engineering of past generations, and there is occasionally encountered a destabilised natural contour e.g. a deforested ravine or the like. Moreover, accumulations of mine waste or the like are still piled high to take the natural gravitational, or a subsequently manipulated, form. All of such contours potentially need to be safeguarded against bulk material movement, whether slippage under gravity, or bursting by accumulations of water, or other bulk movement.

Of recent years, it has become common to incorporate stabilising members into accumulating piles of soil or waste. A typical example of a stabilising member is a very large calibre polymeric mesh, which can be applied at intervals inside an accumulating embankment (for example) as a spaced succession of sheets laid horizontally or at a small angle to the horizontal.

While this is very effective for stabilising work in progress, it cannot readily be used on preexisting soil contours. For these, a different technique is known, which basically involves drilling a hole into the contour and passing into the hole an elongate metal bar. If desired, the bar can be hammered home past the end of the hole, although this is not invariably done.

In any event, the hole is then filled round the bar with a suitable grout or like hardened cementitious material. The process is repeated at such intervals as may be necessary. The procedure is known as "soil nailing" and the elongate metal bar a "soil nail". The present invention is concerned primarily with improvements in such "soil nailing and associated "soil nails", although the equipment evolved for this purpose could also be used for "in progress" soil stabilisation. We have observed that corrosion can be a problem with such existing "soil nails. Since all of the forces are taken up essentially by one corrodible tensile member in each case, corrosion can lead to an area of weakness and eventual failure.

In one aspect the invention consists in a method of stabilisation of soil contours in which there is used as a stabilising member at least one flexible expanse of material rolled or folded into an elongate body so that longitudinal stress carrying members extend along the roll or folded body.

The term "folded" covers a configuration of zigzag or other irrgular nature in cross-section; a rolled expanse is generally spiral in cross-section.

The expanse of material can be a grid, i.e. an open structure with longitudinal and transverse elements, adhered or integral, intersecting to define orifices.

It can be an interwoven material, of all grades ranging from flat-interwoven contiguous strips (e.g. of polymer) to a flexible fabric material, provided that the rolled or folded expanse of material, or at least one component thereof if more than one is present, gives longitudinal stress - carrying members.

A valuable form of the invention utilises two such expanses, one being a resistant high-strength woven fabric and the other, rolled up or folded up with such fabric, being an open polymeric grid. The composite roll or folded body has longitudinally extending voids down which, as discussed below, a grout (i.e.

cement/water mixture) can be forced, to set and unite tl,e soil and the rolled material.

Preferably the method is applied to post stabilisation of pre-existing soil contours, in which case the method comprises drilling into the contour an elongate hole into which the rolled or folded material is introduced for stabilisation purposes. A grout can be introduced into the hole in the usual way either before or after the introduction of the rolled or folded material. Of course, in practice an array or pattern of such holes will typically be drilled and filed with the reinforcing roll or folded elongate body of material.

These holes can be placed at any angle, but are usually drilled horizontally, or angled downwards. The length of the holes and corresponding length of the rolled or folded material can be widely variable, but 2 to 20 metres is preferred, more preferably 3 to lOm e.g. about 7m. While the broad scope of the invention is not to be limited in this respect, it is envisaged that in many cases the penetration of the "soil nail" may be of the order of the vertical height of the bank to be stabilised.

Where the expanse of material is a grid, it is typically fabricated of resistant polymer, as known per se for the flat grid material, from which indeed the "soil nails1: as proposed with this invention can in many cases be rolled. Such a grid can have orifices which are typically from 2 to 20 cms square mesh. It will be appreciated that such an expanse should be rollable into a form spiral in cross-section. For this purpose the transverse links can be much less substantial than the longitudinal components, since their primary purpose is to locate the longitudinal components prior to grout arrival. A secondary role is to give good grout bonding with the material. In contrast, when grids are used as in the prior art, on the flat, they can stabilise both ways, i.e. can utilize the tensile strength of substantial transverse links.

The invention extends to soil contours when reinforced by the above method, and to a rollable or foldable sheet of polymeric soil-reinforcing material dimensioned to fit a drilled hole for soil reinforcement, or acombination of two or more such expanses or such an expanse or expanses when rolled (or folded) and secured for use.

A valuable optional feature of such a rolled or folded expanse is the provision of (a) external longitudinal 'skids' i.e. members facilitating introduction of the roll or folded body into the drilled hole, and spacing it from the wall thereof to assist grout bonding and/or (b) surrounding ties or straps to keep the roll or folded body to a predetermined diameter.

The invention may moreover be operated in such a way that the amount of polymeric material used is equivalent to or less than that used in the incorporation of flat grids.

The invention will be further described by way of example only with reference to the accompanying drawings, in which: Fig 1 shows a prior art form of soil contour stabilization, Fig 2 shows diagrammatically the installation of soil nails in accordance with an embodiment of the present invention, Fig 3 shows a soil nail itself in accordance with an embodiment of the present invention, Fig 4 shows such a soil nail unrolled, and Fig 5 shows part of such an unrolled soil nail on a larger scale.

Figure 1 shows diagrammatically the formation of a positive soil contour, i.e. an earth bank or embankment. As earth arrives- to form the embankment from the direction of the arrow A it covers a grid laid upon the existing earth surface. When a predetermined thickness of earth covers the grid a further grid is laid upon the surface, and so on. Earlier, and covered, grids are shown in 1A, 1B etc.

It will be appreciated that the size and shape of the grids shown in Figure 1 is diagrammatic, and that in practice such grids, or accumulations of grids, may extend over a wide area. Nonetheless, and as shown in Figure 1 in the prior art the grids are generally laid parallel and more or less horizontally in building up such a protection against loss of soil contour.

Figure 2 shows in general terms soil stabilization of an existing contour by the procedure in accordance with the present invention. In this, an earth bank 3 is drilled with suitable holes 4 and into each hole is fed a spiral rolled expanse 5 of synthetic polymeric material. This can be a grid of the nature shown in Fig. 1, used for example with an inter-rolled fabric.

When such a grid-like rolled material, and any fabric inter-roll, is completely taken into the hole, grout 6 is pumped into the hole to give a good bond between the rolled up material 5 and the earth bank. It will be apparent from Figure 2 that the material is used with major members lying in a longitudinal direction to absorb tensile stresses. It is again envisaged to use such reinforcements 5 generally in layers, so that the holes are drilled to occupy spaced parallel planes. The total loading of synthetic polymer in the preformed contour or bank is generally equivaient to the loading which would be achieved if the polymer was incorporated as flat grids during the initial formation of the bank.

Figure 3 shows a rolled up synthetic polymeric material 5 of a calibre suitable as the sole component, or as one component of a composite, for soil stabilization. This expanse possesses elongate and load carrying components 7 held together by transverse components 8. The transverse components 8 form a useful function, since they interconnect the material 5 for rolling and incorporation, and since they help to grip the eventual grout 6 which is forced into the hole.

However, they are not otherwise needed for strength, and can be quite small or even almost vestigial in character.

Although not shown, the expanses can be rolled up with a heavy duty fabric material as a composite roll still permitting grout incorporation.

As shown in Figure 4, a polymer grid essentially comprising straight bars 7 interconnected by polymer straps 8 could be envisaged as a potential component.

The invention also extends to incorporate the use of synthetic polymeric grids even when these are formed by cutting or by expansion of a sheet or by adhesion of flat components.

Figure 5 shows a magnified version of part of Figure 4, utilising such flat component, with load bearing component 7 and interconnecting component 8. If desired the internal void 9 can be much smaller or indeed non-existent (not shown).

Various modifications may be made to the above embodiment. For instance, the roll of material could alternatively be an elongate folded structure, in other respects having the same properties and uses.

Claims (3)

CLAIMS:

1. A sheet of polymeric soil-reinforcing material dimensioned and rolled or folded to fit within a drilled hole for soil reinforcement, alone or in combination with at least one other rolled or folded sheet, in a roll or elongate body secured for such use.

2. A rolled or folded sheet according to claim 1, secured by surrounding ties or straps to keep the roll or elongate folded body to a predetermined diameter.

3. A rolled or folded sheet as claimed in claim 1, further comprising external longitudinal members to facilitate introduction of the rolled or folded body into the drilled hole, and to space it from the wall thereof in order to assist grout bonding.