A DRAINAGE DEVICE

This invention relates to drainage devices.

More particularly, the invention relates to a drainage device which can be used for drainage of sub-surface water or in other sites where it is necessary to drain wet or damp ground.

According to the present invention there is provided a drainage device comprising a core and at least one water permeable web, said core being imperforate and having an array of protuberances and wherein said web spans said protuberances thereby defining interconnected spaces which constitute a passage between the web and the core whereby, in use, water can pass through said web and then run in said passage.

In a preferred embodiment of the invention, the core comprises a layer of plastics material which is formed with integral protuberances and wherein the web comprises a filter fabric which is held in engagement with the outer faces of the projections. Preferably further, the plastics layer has protuberances on both sides thereof and the fibrous fabric engages the protuberances on either side of the layer.

The invention will now be further described with reference to the accompanying drawings, in which:

Figure 1 is a cross-section through a core used in the drainage device of the invention,

Figure 2 is a plan view of the core shown in Figure 1,

Figure 3 is a cross-sectional view through one form of drainage device,

Figure 4 is a fragmentary side view of a sheet drainage device having the cross-section as shown in Figure 3,

Figure 5 shows the use of the sheet drainage device adjacent to a retaining wall,

Figure 6 shows one technique for interlocking the core with a perforated conduit,

Figure 7 shows a convenient arrangement for joining adjacent sheets of drainage devices,

Figure 8 shows an embodiment of the invention in which the drainage device is in strip form, Figure 9 is a cross-section through the drainage strip shown in Figure 8,

Figure 10 diagrammatically illustrates one technique for fabricating the drainage strip shown in Figures 8 and 9,

Figure 11 illustrates a typical application of the drainage strip,

Figures 12 and 13 illustrate techniques for forming joints of the drainage strips,

Figure 14 is a cross-section through another form of drainage strip of the invention,

Figure 15 illustrates a typical application of the drainage strip illustrated in Figure 14, and

Figure 16 illustrates one technique by which the strips are driven into a soil mass.

The core structure illustrates in Figure 1 comprises core2 of plastics material such as high impact resistance polystyrene and preferably comprises a layer of bi-cuspated material as disclosed in Australian Patent No. 460,849. The core 2 is formed with regular arrays of projections 4 and 6 which project from opposite sides of the layer respectively, as seen in cross-section in Figure 1 (which is a sectional view taken along the line 1-1 marked on Figure 2).

The outer extremities of the protuberances 4 and 6 are flat and lie in respective planes 8 and 10. The exact profile of the protuberances 4 and 6 is not important but it is desirable that they have flat outer faces as illustrated.

Figure 3 illustrates in cross-section one embodiment which comprises the core 2 in the form of a sheet and having a web or fabric layer 12 connected to the outer faces of the array of protuberances 4 by means of a hot melt adhesive. It will be appreciated that there will be interconnected voids 14 defined between the web 12 and the core 2. The web 12 comprises a flexible sheet of water permeable material such as a geotextile filter fabric. One form of filter fabric comprises polyester spun-bonded filter material which is sometimes used in soil stabilization applications, one suitable textile being made by I.C.I. Limited and known as "TEREAM".

Figure 4 illustrates the preferred form in which the sheets of material are formed. In this arrangement it will be seen that the web 12 is wider than the core 2 and is arranged to overhang the core on either side thereof so as to form an upper flap 20 and a lower flap 22 of the geotextile material. For a core width of say 1.2 metres the upper flap 20 is say 10cm in width whereas the lower flap 22 is 35cm. The material in this form can be formed in convenient lengths say 25 metres and transported in the form of a roll. The material in this form can be used most advantageously to form a sub-surface drain adjacent to a retaining wall, embankment or other structure which is at least partially covered by soil.

Figure 5 schematically illustrates the use of the device of Figure 4 in draining a retaining wall 24. The retaining wall has an inner face 26 against which the device is laid such that the projections 6 engage the face 26 a slotted conduit 28 is located adjacent to the foot 30 of the wall and the lower flap 22 of the device is wrapped about the conduit so as to prevent soil entering the slotted conduit 28. The backfill material 32 may be then placed behind the wall such that it bears directly against the fabric layer 12, as shown. Moisture in the backfill 32 can seep through the layer 12 into the voids 14 so that it will thereafter flow under gravity to the conduit 28 where it can be drained away, as required. The device is preferably fixed to the face 26 to avoid inadvertent displacement during backfilling.

Figure 7 shows one convenient technique for forming a joint between sheet drainage material of the type shown in Figure 4. It will be seen that the cores of the two sheets are overlapped in a manner which at least partially interlocks them and the flap 20 is made to overlie the fabric layer of the other device. A strip 33 of adhesive tape may be then applied to cover any gap between the edge of the flap 20 and the underlying fabric layer 12.

Figure 6 illustrates a preferred way of connecting the sheet material to the slotted conduit 28. In this arrangement, the conduit 28 is formed with an opening 34 which is large enough so that the lower edge of the core 2 can be inserted at least partially into the core of the conduit. The arrangement is such that the opening 34 forms a mechanical interlock with the protuberances 4 and 6 of the core so as to retain the conduit 28 in position. The flap 22 is then passed about the conduit 28 as illustrated.

Figures 8 and 9 illustrate another form of the invention in which the device is in the form of a drainage strip 35 which is more suited to drainage of water from damp ground, hillsides or highway shoulders. The core 2 is preferably of the same construction as that described in Figures 1, 2 and 3 except however that it is usually say 4cm thick i.e. the spacing between the planes 8 and 10 is 4cm. The strips 35 can be made in standard widths say 20cm, 30cm, 60cm and 90cm and supplied in roll form in lengths of say 50 metres. In this arrangement, the layer 12 is wrapped about the strip of core material so as to enclose the core. In the preferred construction the width of the fabric 12 is somewhat greater than the periphery of the core in transverse section so that an edge region of the fabric forms an overlapping flap 36 which is adhered to the underlying region of the fabric 12 by means of a line 38 of hot melt adhesive. One convenient arrangement for fabricating the drainage strips is diagrammatically illustrated in Figure 10. In this arrangement, the core material 2 is supplied from a roll 40 thereof to an enveloping station 42. The layer 12 is supplied from a roll 44 thereof to the station 42 where it is wrapped about the strip of core. Within the station 42, the line 38 of adhesive is applied to the fabric layer just prior to the flap 36 being pressed into engagement with the underlying layer. In this arrangement there is no need for the core 2 to be bonded to the fabric layer 12 since it is snuggly enveloped within the fabric layer.

Figure 11 illustrates a typical application of the drainage strips 35 shown in Figures 8 and 9. In this arrangement the strips are used for draining land which is prone to become sodden. The first step is to dig a trench 46 which can be as narrow as say 10cm and to an appropriate depth. The strip is then inserted and the trench is backfilled with soil 48 to complete the subterranean drain. In most applications, the depth of the trench can be kept constant and yet the drained water will still flow within the drainage strip, thus simplifying the trench digging.

Figure 12 illustrates a simple technique for forming a joint between ends of two adjacent drainage strips. First of all, the fabric layers 12 at the ends of .the drainage strips are peeled back so as to expose say 3 or 4 rows of protuberances. These rows of protuberances are interlocked as shown in Figure 12. Thereafter the fabric layer of one of the drainage strips is replaced and subsequently the end portion 50 of the fabric layer of the other drainage strip is then located so that it overlies the fabric layer of the other strip. A band 52 of adhesive tape completes the junction.

Figure 13 illustrates a technique whereby a T-joint can be conveniently made by a jointing technique analagous to that shown in Figure 12. Briefly, part of the fabric layer 12 of each of the strips to be joined is partially removed to expose core portions. The end portion is then bent laterally and interlocked with the exposed portion of the core of the continuous strip. The adjacent fabric layers are folded to overlie one another, as illustrated. Bands 52 of adhesive tape are then placed about the exposed edges of the fabric layers.

Buried ends of the strips can be covered by removal of part (say 7.5cm) of the core at the end of the strip and folding the free portions of the layer about the exposed end of the core. The folded layer can be retained in position by means of adhesive tape.

Figure 14 illustrates another form of drainage device in the form of a thin strip 53. In this arrangement the core 2 is made from plastic sheet material say 0.5mm thickness. The protuberances 4 and 6 are such that the overall thickness of the core is in the range 3-5mm and the spacing between the protuberances 4 being say 25mm (as for the spacing between the protuberances 6) . The width is preferably in the range 7.5 to 12.5cm and is supplied in rolls say 120m in length.

The drainage, strips 53 are particularly suitable for deep de-watering of swampy land where construction or dry-fill is to be located.

Figure 15 illustrates a typical application of the strips. As will be seen, the strips are disposed vertically and in a generally uniform array in the soil mass 54 to be drained. In a typical application, the strips 53 are located at 1.2 metre centres. The strips 53 extend to an appropriate depth usually in the range of say 5 to 30 metres. A porous layer 56 say of sand is then formed at approximately ground level and the ends of the strips 53 extend into the layer 56. A layer 58 of backfill or soil is then placed on the layer 56 so as to increase the pressure in the mass 54 to be drained. The arrangement is such that water will flow into the strips 53 and then will flow upwardly to the porous layer 56 where it is then free to drain laterally. In this manner, the mass 54 can be effectively drained. Figure 16 schematically illustrates one arrangement for placement of the strips 53. In this arrangement, the strips 53 are located within a hollow driving member 60 which is arranged to be driven into the soil mass 54 by means of a pile-driver (not shown). A head piece 62 having the profile as illustrated can be located over the lower end of the member 60 so as to prevent entry of soil to its interior. The member 60 is then driven to the desired depth in the mass 54 and thereafter the member 60 withdrawn. The head piece 62 and strip 53 will be retained in the soil mass 54 by virtue of the lateral pressure of the soil.