WO2004089506A1

WO2004089506A1 - Geosynthetic composite

Info

Publication number: WO2004089506A1
Application number: PCT/GB2004/001602
Authority: WO
Inventors: Harry Rolfe; Emanuel Olumuyiwa Adebayo Awoleye
Original assignee: Harry Rolfe; Awoleye Emanuel Olumuyiwa Adeb
Priority date: 2003-04-14
Filing date: 2004-04-13
Publication date: 2004-10-21
Also published as: GB0522440D0; GB2415644A; GB0308622D0; GB2415644B

Abstract

A composite device comprising two or more layers of geosynthetic material or any other similar laminate material, and a granular, filter, material. The composite device consists of pockets or cells, in which the granular material is contained, and is provided with a means or mechanism for folding the device; thereby making it easy to transport and install. One or more layers of the geosynthetic or laminate material can be provided with pores or perforations to encourage the flow of water through the filter material. The device is especially useful in railway trackbed, to assist in curing subgrade erosion, but can be used in any engineering application where a filtering or barrier layer is required.

Description

GEOSYNTHETIC COMPOSITE

The present invention relates to composite filter devices, and particularly but not exclusively to a composite filter device for use under railway tracks.

A filtering layer is often used in civil engineering applications for forming a separator between two materials that are usually of different properties, and/or as a drainage medium to convey fluid in any appropriate direction.

Traditionally, the filter material is a naturally occurring granular material, for example, naturally occurring sand and gravel, which may or may not be modified to meet the required purpose. However, filters can also be made from other materials. In recent years, geosynthetics, for example, geotextiles, have in some cases been used successfully to replace the traditional granular filters. A geotextile is a geosynthetic fabric, either woven or non woven, applied to either a soil surface or between materials. Geotextiles are generally used when there is a need for separation between two materials that are otherwise likely to interfere with each other. These materials have the advantage of being easier to transport and often easier and quicker to install than, for example, granular filtering layers.

There are, however, still many applications where a traditional granular filter is preferred. The bulk offered by traditional granular filtering layers can provide additional strength. There are also many instances where geotextiles do not possess sufficiently small pore sizes to enable them to act as efficient filters. For example, most modern geotextiles cannot filter out (or retain) clay and fine silt particles in an efficient manner. They are therefore not always suitable for use as separators where one of the materials to be separated contains clay or fine silt .

This filtering deficiency of the modern geosynthetics is particularly, but not exclusively, evident in railway applications to cure subgrade erosion or pumping failure problems . These problems occur when fine grained material

(such as clay) migrates from the underlying subgrade into the ballast layer, thus clogging the ballast and destroying its normally open structure. Consequently, the inability to drain properly and the lack of appropriate interlock between the ballast particles (due to the presence of the clay which acts to lubricate the ballast particles) prevents the ballast from effectively performing its main functions of distributing the traffic load and maintaining track alignment. A huge sum of money is spent annually within the railway industry to try and cure the problem.

Attempts at using modern geosynthetics (for example geotextiles, geomembranes and geocomposites) to solve the problem have not been successful. The most effective cure involves the use of a 'sand filtering layer¹ which is laid between the ballast and the fine grained subgrade. However, the 'sand' needed is not found in many areas and often has to be transported a long distance. In addition, the installation of a 'sand filtering layer' is time consuming and requires special machinery. In some cases, laying a 'sand filtering layer' is impractical. Similar problems are often encountered in unbound roadways, highways, runways, dams and other civil engineering structures.

Products known in the art have been suggested, but they suffer from either being impractical to transport, or difficult and time consuming to install.

Accordingly, a need exists for a device which will combine the advantages of the modern geosynthetics with the filtering efficiency of a traditional granular filter. This product will be easy to transport and install, and act effectively as a filter.

According to the first aspect of the present invention, there is provided a composite filter device comprising a first layer of material, a second layer of material and a granular filter material between said first and second layers, at least one of the first and second layers comprising a geosynthetic material, wherein the filter device is substantially foldable.

Disadvantageously, filters known in the art do not offer fσldability and are, therefore, either difficult to transport, difficult to install or both. Traditional filters come as unitary products, which must be precisely and accurately laid down next to each other with a small overlap. Each overlap between neighbouring filters provides a point of weakness where leakage may occur.

Advantageously, the composite filter device of the present invention is foldable and can therefore be pre- manufactured and stored in rolls, making it much easier to transport and install. Advantageously, the present invention provides a filter device which can be easily folded, packaged and transported. Hence, once on site, the filter device may be easily installed by unfolding and laying as appropriate, without the need for special machinery. Advantageously, the^' foldable. device minimises the risk of leakage.

Preferably, the composite filter device comprises one or more pockets. Preferably, the granular filter material is located in said pockets. Preferably, the granular filter comprises sand, gravel or pebbles.

Preferably, the composite filter device comprises one or more joints and/or flexible flaps and/or hinges between the pockets along which the device can be folded. Preferably, the other of the said first and second layers comprises a geosynthetic material.

Preferably, the first layer is an upper layer, and the second layer is a lower layer. Preferably, the upper layer comprises a geotextile, more preferably, a permeable geotextile. Preferably, the lower layer comprises a geomembrane. By the term "geomembrane" , we mean a substantially impermeable sheet of a resilient material for use in or on the ground. Preferably, the lower layer comprises a smooth material, for example, paper or some other smooth surfaced material. The lower layer may comprise polyethylene, polypropylene, polyester or rubber. The lower layer may be disintegratable or biodegradable. Preferably, the lower layer is substantially flexible. For railway applications, for example, to cure subgrade erosion, the layer of the filter device to be laid against the fine-grained subgrade, i.e. the lower layer is preferably smooth textured. Preferably, the lower layer comprises polyethylene, polypropylene, polyester, rubber, paper or any other similar material, to prevent the detrimental scouring action which is caused by rough textured materials, for example, a geotextile. Hence, for these applications, at least one side of any of the geosynthetic or any similar material to be used in the manufacture of the device is preferably smooth textured.

Preferably, the lower layer is perforated.

Preferably, the perforations are between approximately 0.5

- 50mm in diameter, more preferably between approximately 1.0 - 35mm, and most preferably between approximately 1.5

- 25mm. An especially preferred size of perforation is between approximately 2.0 - 5.0mm.

Preferably, the perforations are spaced apart between approximately 20 - 1000mm apart, more preferably between approximately 50 - 700mm apart, and most preferably between approximately 70 - 400mm apart. An especially preferred spacing is between approximately 75 - 100mm.

Preferably, at least one perforation is substantially covered by cover means during transport of the filter device. The cover means may comprise a disintegratable, or biodegradable material, for example, paper. Advantageously, the cover means disintegrates or degrades shortly after contact with water, thereby uncovering the perforation (s) . The cover means may be removed prior to placing the filter device in position prior to use. Preferably, the cover means is removable or may be peeled away from the at least one perforation. Preferably, the cover means covers over substantially all of the perforations during transport of the filter device.

Preferably, the cover means comprises a removable sealing layer which preferably, retains the granular filter within the geocomposite. Preferably, the cover means comprises a suitable plastic, such as polyethylene, polypropylene or polyvinylchloride.

Advantageously, the granular filter material is unable to escape through the perforations during transport of the filter device because of the removable cover means. Advantageously, when installing the filter device, the cover means may be peeled off to expose the perforations, prior to use.

The composite filter device may comprise more than two layers. For example, the composite filter may contain a third layer of material between the first layer and the second layer. Preferably, the third layer bisects the pockets and -creates cells therein. Preferably, the third layer comprises a geosynthetic material. The third layer may comprise a water-purifying matrix.

Advantageously, the composite filter device, encompasses the benefits of both the granular filter material and the geosynthetic material. According to a second aspect of the present invention there, is provided a method of filtering comprising use of the composite filter device as defined by the first aspect .

The present invention is a composite filter device which incorporates a granular filter material. The device comprises two or more layers of geomaterials and a granular filter. The layers of materials may be joined together at intervals to create one or more pockets. These pockets are then filled with appropriate granular filter material and sealed to prevent spillage of the filter material.

For some applications, the granular filter material may be replaced with concrete, reinforced or otherwise, metallic material or any other suitable material.

All of the features described herein may be combined with any of the above aspects, in any combination.

A specific embodiment of the invention will now be further described by way of example with reference to the accompanying drawings in whic : -

Figure 1 shows a perspective cross-sectional view of a first embodiment of a composite filter device;

Figure 2 shows a perspective cross-sectional view of a second embodiment of the composite filter device;

Figure 3 shows a perspective cross-sectional view of a third embodiment of the composite filter; and Figure 4 shows a perspective cross-sectional view of a fourth embodiment of the composite filter device.

Referring to Figures 1, 2, 3 and 4 there are shown four different embodiments of a composite filter device 10 having an upper layer 1 and a lower layer-2 which envelope a granular material 3. The upper layer 1 is a geotextile material, the lower layer 2 is a geomembrane. A geotextile is composed of woven or non woven fibrous strands of a synthetic material, for example, polyethylene. This construction results in a material with minute pores, for example, 30 μm and with an abrasive surface texture. In railtrack construction, this is ideal for the upper layer of the 10 device as it allows water to drain therethrough, is resilient, and will withstand abrasion by the layer of ballast placed thereon. A geomembrane is composed of extruded polymer sheets having a smooth surface, in the proposed application, railtrack construction, these sheets have holes cut in them after production to assist the drainage of water therethrough and prevent water being trapped between the geocomposite and the subgrade. Having a smooth material with pores cut in reduces the abrasion of the lower layer of the device 10 against the subgrade. In each embodiment, the composite filter device 10 is divided into pockets 11 in which the granular filter material 3 is housed.

Referring to Figure 2, there is shown a second embodiment of the composite filter device 10 having three layers 1, 2 and 8 which define two cells 12 within the pockets 11. The granular filter material 3 is used to fill the pockets 11, which can be partially or completely filled. The pockets 11 are then sealed at positions 4, 5, 6 and 7, for example, by stitching, heat bonding, glueing, stapling or any other suitable process to retain the granular filter material 3 within the pockets 11.

Referring to figure 3, there is shown a third embodiment of the composite filter device 10 having •a flexible flap 9 between the pockets 11. This flexible flap 9 assists in the folding of the device 10, for example, if one or more of the layers of materials is too stiff to enable the device 10 to fold easily. The flap 9 can be formed, for example, by creating more flexible strips in any of the two or more layers of materials during its manufacture, or by, for example, stitching, stapling, bonding or glueing a flexible flap between pockets 11 formed from less flexible material (s) .

Referring to Figure 4, there is shown a fourth embodiment of the composite filter device 10 having a flat second layer 2.

It should be appreciated that although the figures only show three pockets 11, it is intended that the composite filter device 10 can include many more pockets 11, the number of pockets 11 depending on the intended use of the device 10.

The choice of the two or more materials, for example materials 1, 2 and 8, will depend on the requirements of the application; with strength and pore size being some of the more important properties. It is desirable that the materials 1, 2 and 8, for example, are of appropriate strengths to ensure that, throughout their design life, they can withstand the stresses and strains imposed by the granular material 3 and adequately carry any other load that may be imposed on them during installation and in service.

It is desirable that the sizes and distribution of the pores or holes provided in any of the materials 1 and 2 enables appropriate drainage to be achieved in the required direction.

In accordance with the present invention, the materials 1, 2 and 8 may be produced by any one of the various techniques well known to persons of ordinary skill in the art, and any of the already available geosynthetics or similar products may be used.

The granular filter material 3 can be any suitable granular material, natural or synthetic, which may be a material designed in accordance with the normal methods of filter design. For example, sand, gravel, pebbles, granular plastics.

An example of a preferred size of a granular filter material 3 is:

BS sieve size Percentage passing

14mm 100

2.36mm 90

1.18mm 80

600micron 65 300micron 50

150micron 35

75micron 8

The composite filter device 10 is manufactured, for example, by attaching the layers of materials 1, 2 and 8 together at three edges 4, 5 and 6, to seal the edges. The materials 1, 2 and 8 are also joined at intervals to form joints 7, to create pockets 11. The joints 7 can be in any direction and can be of any length. The attachments at the edges 4, 5 and 6 and the joints 7 can be made by any suitable process, for example stitching, stapling, heat bonding or glueing. The attachments at the edges 4, 5, and 6 and at the joints 7 can be single or multipl .

Adequate flexibility of the materials 1, 2 and 8, or at least the materials of the flap 9, is desirable to enable the composite filter device to be easily folded, for example into a roll, for easy transportation and handling.

Instead of the flap 9, any other suitable mechanism can be employed to make the device foldable, such as hinges.

Another possible method of manufacturing the composite filter device 10 is to attach appropriately wide strips of a flexible or non-flexible material to a flexible material, leaving one end unattached, or open, to form the pocket 11 and leaving appropriate width of flexible material between the strips, thus forming pockets 11 and flexible flaps 9 between the pockets 11. The size of the pockets 11 will likely be determined by the required thickness of the granular filter material 3 to be contained therein. The shape of the pockets 11 can be changed to form other variations of the composite filter device 10.

A specific example of an embodiment of the present invention will now be described.

A two layered device 10 made from a geotextile (layer 1) and a smooth textured geomembrane (layer 2) .

Layer 1:

Thermally bonded non woven geotextile.

Mean peak tensile strength: 22.5kN/m - BS 6906: Part 1: 1987

Elongatio : 30%

CBR puncture resistance - Mean peak strength: 43ION - BS

6906 Part 4: 1989

Trapezoidal tear resistance - Mean peak strength: 900M - ASTM 04533:1991

Apparent pore size - Mean Apparent Opening Size, O₉₀: 35 microns - BS6906: Part 2: 1989.

Permeability - Mean Flow Rate at 10cm head: 40 l/m²/s - BS

6906: Part 3: 1989 Weight: 352 g/m².

Layer 2 :

Geomembrane: extruded High Density Polyethylene, HDPE, sheet.

Thickness: 320 microns. To encourage drainage, the polyethylene sheet was provided with 2.5mm diameter holes spaced at 80mm centre-to-centre, in a grid.

The geotextile and polythene materials were bonded together at the edges using an adhesive. Pockets 11 were then created, along the width of the materials by bonding 5mm strips of the geotextile and polyethylene materials together, using an adhesive. The strips were spaced at 200mm centres. These strips formed the joints/flaps along which the device could be folded.

The pockets 11 were filled with a granular material having the following grading:

BS sieve size Percentage passing

14mm 100

2.36mm 90

1.18mm 80

600micron 65

300micron 50

150micron 35

75micron 8

The pockets 11 were sealed using an adhesive.

While the preferred embodiments of the present invention have been illustrated and described, it will be understood that changes and modifications can be made without departing from the invention and its broader aspects. Various features of the invention are defined in the accompanying claims. Although the present invention has been described mainly with reference to use in civil engineering works, it is to be understood that the invention may be applied to a wide range of applications.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A composite filter device comprising a first layer of material, a second layer of material and a granular filter material between said first and second layers, at least one of the first and second layers comprising a geosynthetic material, wherein the filter device is substantially foldable.

2. A composite filter device as claimed in claim 1, wherein the composite filter device comprises one or more pockets .

3. A composite filter device as claimed in claim 2, wherein the granular filter material is located in the pockets .

4. A composite filter device as claimed in any preceding claim, wherein the granular filter material comprises sand, gravel or pebbles.

5. A composite filter device as claimed in any preceding claim, wherein the composite filter device comprises one or more joints and/or flexible flaps and/or hinges between the pockets along which the device can be folded.

6. A composite filter device as claimed in any preceding claim, wherein the other of the said first and second layers comprises a geosynthetic material.

7. A composite filter device as claimed in any preceding claim, wherein the first layer is an upper layer, and the second layer is a lower layer.

8. A composite filter device as claimed in claim 7, wherein the upper layer comprises a geotextile.

9. A composite filter device as claimed in either claim 7 or claim 8, wherein the upper layer comprises a permeable geotextile.

10. A composite filter device as claimed in any of claims 7 to 9, wherein the lower layer comprises a geomembrane.

11. A composite filter device as claimed in any of claims 7 to 10, wherein the lower layer comprises a smooth

^• material.

12. A composite filter device as claimed in any of claims 7 to 11, wherein the lower layer comprises polyethylene, polypropylene, polyester or rubber.

13. A composite filter device as claimed in any of claims 7 to 12, wherein the lower layer is substantially flexible.

14. A composite filter device as claimed in any of claims 7 to 13, wherein the lower layer is perforated.

15. A composite filter device as claimed in claim 1 , wherein the perforations are between approximately 0.5 - 50mm in diameter.

16. A composite filter device as claimed in either claim 14 or claim 15, wherein the perforations are spaced between approximately 20 - 1000mm apart .

17. A composite filter device as claimed in any of claims 14 to 16, wherein at least one perforation is substantially covered by cover means during transport of the. filter device.

18. A composite filter device as claimed in claim 17, wherein the cover means is either disintegrable or biodegradable or is removable from the at least one perforation.

19. A composite filter device as claimed in claim 17 or claim 18, wherein the cover means comprises a removable sealing layer which retains the granular filter layer within the geocomposit .

20. A composite filter device as claimed in any preceding claim, wherein the composite filter device comprises more than two layers.

21. A composite filter device as claimed in any preceding claim, wherein the composite filter contains a third layer of material between the first layer and the second layer.

22. A composite filter device as claimed in claim 21, wherein the third layer bisects the pockets and creates cells therein.

23. A composite filter device as claimed in claim 21 or claim 22, wherein the third layer comprises a geosynthetic material .

24. A composite filter device as claimed in any of claims 21 to 23, wherein the third layer comprises a water- purifying matrix.

25. A method of filtering comprising use of the composite filter device as defined by any of claims 1 to 24.

26. A geocomposite device substantially as herein described with reference to, and as illustrated by, the accompanying drawings.

27. A method of filtering comprising use of the composite filter device substantially as herein described with reference to, and as illustrated hγ_t the accompanying drawings.