GB2462994A

GB2462994A - Composite material for use as a landfill liner

Info

Publication number: GB2462994A
Application number: GB0815560A
Authority: GB
Inventors: Robert Graham Warwick
Original assignee: Geofabrics Ltd
Current assignee: Geofabrics Ltd
Priority date: 2008-08-27
Filing date: 2008-08-27
Publication date: 2010-03-03
Anticipated expiration: 2028-08-27
Also published as: GB2462994B; GB0815560D0

Abstract

A composite material 10 for use as a landfill liner comprises a drainage layer 12 defining at least one flow path located between first and second permeable support sheets 16, 18 and a cushioning layer 20 located adjacent to one of the first and second support sheets. The first and second support sheets may be textiles formed of plastics material such as polypropylene having apertures for fluid passage between warp and weft fibres 26,28. The drainage layer may be an open cell mesh structure which may comprise spaced parallel first mesh elements 30 and second mesh elements 32 disposed transverse to the first mesh elements to define apertures. The cushioning layer may be permeable geotextile material such as needle punched plastics material such as polypropylene. The composite material has the advantage of reducing the amount of gravel required when lining a hole for landfill.

Description

COMPOSITE MATERIAL FOR USE AS A LINER

The present invention relates to a composite material for use as a liner. In particular, but not exclusively, the present invention relates to a composite material for use as a landfill liner, and to a composite landfill liner.

In many countries around the world, household waste is disposed of in landfill sites.

This involves excavating a large hole in the ground and progressively filling the hole to a desired level. The filled hole is then capped and, after a period of time, the land may be used for other purposes.

During the process of filling the excavated hole, the waste in the hole decomposes, and a by-product of the decomposition process is a toxic fluid run-off known as leachate. Whilst the hole is being filled, the waste is exposed to rainwater, which increases the amount of leachate. Thus during filling of the hole, which is a process that may take several years, a large volume of toxic leachate is produced.

Strict guidelines exist in most countries which restrict against discharge of the leachate into the ground. Accordingly, the landfill site operator must take steps to ensure that the leachate is collected, treated and disposed of in an appropriate manner.

To this end, the landfill site must be carefully prepared to ensure that the leachate is not discharged into the ground.

Usually, this includes lining the base and walls of the hole with a low-permeability soil, usually a clay-based soil. In the United Kingdom, the regulations concerning landfills are set out by the Environment Agency, which require that the base of a landfill site is provided with at least a 1 m depth of clay-based soil having a permeability of less than 1 x 10 rn/s. A thin impermeable membrane is then provided above the clay base layer, which provides a primary barrier to the leachate.

Suitable materials for the impermeable membrane include high density polyethylene (HDPE), which may be of the order of 2mm in thickness. A thick layer of gravel, typically of the order of 3 00mm to 5 00mm deep, is provided above the impermeable membrane, to improve drainage and assist in collection of the leachate, which flows down through the gravel to draw off points. The leachate is normally then pumped from the draw off points to a treatment plant.

To protect against the gravel puncturing or locally overstressing the impermeable membrane, a permeable geotextile material is provided between the membrane and the gravel layer. Suitable materials include the needle-punched polypropylene geotextile materials available from the present applicant under the GEOfabrics� Registered Trade Mark. Typically, the geotextile material is of the order of 5 to 20 mm in thickness, and cushions the loading of the gravel on the impermeable membrane.

Following filling of the landfill site, the hole can be capped using suitable further geosynthetics materials, and is then covered with soil, facilitating reuse of the land after an appropriate period of time. Typically the soil excavated during preparation of the hole is used for this purpose. After capping of the hole, the volume of leachate produced goes down significantly, due mainly to the reduced volume of rainwater flowing down into the waste. However, the operator continues to monitor the leachate for a further period of years following capping.

Whilst the above arrangement provides an effective solution to the problem of collecting leachate run-off from landfill sites, it is desired to improve upon the materials used and the method of preparing the site. In particular, the requirement to provide a thick layer of gravel above the impermeable membrane adds significantly to the costs of preparing the site in terms of: bulk material costs; costs involved in transportation of the gravel to the site; and handling costs associated with distributing and laying the gravel in the site. Furthermore, it diverts prime aggregate from construction applications into landfill.

It is therefore amongst the objects of at least one embodiment of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

According to a first aspect of the present invention, there is provided a composite material for use as a liner, the composite material comprising: a drainage layer defining at least one flow path for the passage of a fluid therealong; first and second permeable support sheets for the drainage layer, the drainage layer located between the permeable support sheets; and a cushioning layer located adjacent to one of the first and second permeable support sheets.

According to a second aspect of the present invention, there is provided a liner of a composite material, the composite material comprising: a drainage layer defining at least one flow path for the passage of a fluid therealong; first and second permeable support sheets for the drainage layer, the drainage layer located between the permeable support sheets; and a cushioning layer located adjacent to one of the first and second permeable support sheets.

The composite material of the present invention has a particular utility as a landfill liner, and may be a composite landfill liner. Providing a composite landfill liner having a drainage layer located between permeable support sheets and with a cushioning layer adjacent to one of the sheets offers advantages over prior materials used in the lining of a landfill. In particular, the invention permits the depth of a gravel layer in a landfill site to be reduced, typically by up to 150mm or more. Also, the liner of the present invention may provide enhanced support for an impermeable membrane positioned below the liner when compared to current geotextiles.

Furthermore, the structure of the liner may be such that cheaper cushioning layers (which may be thinner and/or of lower material strength) can be used than may otherwise be the case. Consequently, reductions in material costs; transportation costs; and/or handling costs can be obtained in use of the present invention.

Additionally, providing a composite liner including a drainage layer and a cushioning layer provides the above advantages without any additional burden on an operator preparing a landfill site for use. This is because current methods typically involve locating a geotextile above an impermeable membrane; a method using the composite liner of the present invention involves substituting such known geotextiles for a liner of the composite material of the present invention.

The composite material may be flexible which may facilitate reeling of the material.

Where the composite material is suitable for use as a landfill liner, and optionally takes the form of a composite landfill liner, the liner may be suitable for lining at least a base, andlor the walls of a landfill site, in particular of an excavated hole in the ground shaped to receive waste.

The first and second permeable support sheets of the present invention may act, in use, to support the drainage layer and to keep the flow path of the drainage layer open.

In particular, the first and second permeable support sheets may prevent solids materials from blocking the flow path in the drainage layer. For example, a landfill liner of the composite material may be located, in use, beneath a layer of gravel. The support sheet in contact with the gravel may restrict entry of the gravel into the drainage layer, to prevent the gravel from blocking the flow path in the drainage layer.

In a similar fashion, the cushioning layer may be of a resiliently deformable material, and the other one of the support sheets may prevent extrusion of the cushioning layer into the drainage layer which could otherwise block the flow path.

The first and second support sheets may be of a relatively inextensible material, and may have a mean 10% secant modulus of the order of l6OkN/m. The first and second support sheets may be textile or textile materials, and may be woven. The sheets may define apertures for fluid passage between warp and weft fibres of the textiles. The sheets may be of a plastics material, and may be of a polypropylene material. The sheets may be of a thickness of no more than 0.5 mm, and may be of a thickness no less than 0.25 mm. This may assist in maintaining flexibility of the composite material.

The drainage layer may be bonded to both the first and second support sheets. The cushioning layer may be bonded to the selected one of the first and second support sheets. Bonding may be achieved thermally, optionally by feeding the drainage layer, first and second support sheets and cushioning layer together into a thermal bonding machine. Bonding may be achieved using an adhesive or otherwise, optionally by bonding the first and second support sheets to the drainage layer, and then by bonding the cushioning layer to the selected one of the first and second support sheets.

The drainage layer may be an open cell structure, and may be a mesh or mesh-like structure, comprising a plurality of spaced, parallel first mesh elements and a plurality of spaced, parallel second mesh elements disposed transverse (non-parallel) to the first mesh elements, to thereby define a plurality of apertures extending through the drainage layer, which apertures may be arranged to define a flow path for fluid along a length of the drainage layer. The first and second mesh elements may be bonded together and may be thermally bonded. The drainage layer may comprise a plurality of spaced, parallel third mesh elements, the third mesh elements disposed transverse (non-parallel) to both the first and second mesh elements. The third mesh elements may be disposed between the first and second mesh elements and may define a spacing or gap between the first and second mesh elements, said spacing providing a primary flow path for the flow of fluid along a length of the drainage layer. The first mesh elements may be bonded to the third mesh elements, and the third mesh elements may be bonded to the second mesh elements; the mesh elements may be thermally bonded together. The first and second mesh elements may be disposed at 90° to one another and the third mesh elements may be disposed at 45 ° relative to both the first and second mesh elements. Other angles may be selected. The mesh elements may be elongate wires or the like, and may be of a plastics material. A suitable mesh material can be found in the applicant's commercially available composite material sold under the trade mark PROTEXIA, product code FnF 015.

The cushioning layer of the present invention may be designed to cushion the loading of gravel used to line the hole of a landfill site on an impermeable membrane such as the HDPE membranes typically found in current landfills. Additionally, the drainage layer may facilitate in reducing loading on the impermeable membrane.

The cushioning layer may comprise or take the form of a permeable geotextile material. The cushioning layer may be of a plastics material, typically a polypropylene. The cushioning layer may be of a needle punched material. The cushioning layer may be at least 5 mm in thickness, and may be at least 10 mm in thickness. The cushioning layer may be no more than 20 mm in thickness, optionally no more than 15 mm in thickness. Providing a cushioning layer having a thickness within this range may assist in maintaining flexibility of the composite material, thereby facilitating reeling of the material of the present invention.

The composite material may comprise a further cushioning layer which may be coupled to the other one of the first and second permeable support sheets. This may assist in further supporting the loading of gravel used in the lining of a landfill site.

The cushioning layer may be provided outermost in use of the liner; thus where the liner is a landfill liner, the cushioning layer may be spaced furthest from the waste in the landfill site. The first support sheet may be provided innermost in use of the liner, and the second sheet may be an intermediate support sheet provided between the mesh of the drainage layer and the cushioning layer.

Further support sheets, drainage layers and/or cushioning layers may be included in the composite material.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of part of a liner, comprising a composite material, in accordance with an embodiment of the present invention; Figure 2 is a schematic cross-sectional view of a landfill site with the liner of Figure 1 located therein; and Figure 3 is an enlarged view of the landfill site of Figure 2 in a region of a base of the site.

Turning firstly to Figure 1, there is shown a composite material for use as a liner, in accordance with an embodiment of the present invention, the material indicated generally by reference numeral 10. The composite material 10 generally comprises a drainage layer 12 defining a flow path 14 for the passage of a fluid therealong. The material 10 also comprises first and second permeable support sheets 16 and 18, and the drainage layer 12 is located between the support sheets 16, 18. Additionally, a cushioning layer 20 is provided adjacent to one of the first and second support sheets 16, 18. In the illustrated embodiment, the cushioning layer 20 is bonded to the second support sheet 18, which forms an intermediate support sheet of the material 10.

The composite material 10 has a particular utility as a liner and, in a preferred embodiment of the present invention, as a liner 22 for a landfill site 24, which is shown in the schematic cross-sectional view of Figure 2. It will be understood that the landfill site 24 is used for the disposal of household and other waste material.

In more detail, the structure of the composite material 10 shown in Figure 1 is as follows. The cushioning layer 20 is of a resilient geotextile material, typically of a needle-punched polypropylene material, such as is commercially available from the present applicant. The cushioning layer is typically provided at a thickness of around mm but the thickness will ultimately depend upon the particular set of circumstances in which the material is to be used, and the thickness may be in a range of 5 to 20 mm. Factors affecting thickness of the cushioning layer include the anticipated loading on the cushioning layer, and the quality and properties of other materials used in preparing the landfill site 24. For example, a thicker and/or more dense, less flexible material may be required in particular circumstances, and a thinner and/or less dense, more flexible material in other circumstances.

The first and second permeable support sheets 16 and 18 are woven textiles and typically also of a polypropylene material. Warp 26 and weft 28 fibres forming the first support sheet 16 are shown at a corner area of the support sheet in Figure 1. It will be understood that the second support sheet 18 is of similar construction. As the first and second support sheets 16 and 18 are woven materials, a number of apertures for the passage of fluid down through the respective sheets are defined at the junctions between the warp and weft threads 26, 28. In this fashion, fluid can permeate down through the support sheets 16 and 18.

The drainage layer 12 is in the form of an open cell structure, and takes the form of a mesh or mesh-like structure. The mesh 12 comprises a number of spaced, parallel first mesh elements and a number of spaced, parallel second mesh elements 32, both in the form of elongate wires. The wires 32 are disposed transverse to the wires 30, and are typically disposed at 90° relative to the first wires 30. A number of spaced, parallel third mesh elements 34, again in the form of elongate wires, are disposed between the first wires 30 and the second wires 32, and are transverse to both the first and second wires. In the illustrated embodiment, the third wires 34 are disposed at 45° relative to both the first wires 30 and the second wires 32.

The first wires 30 and second wires 32 are bonded to the third wires 34 such that the third wires are sandwiched between the first and second wires. The third wires 34 thereby define a spacing between the first and second wires 30, 32 which forms the flow path 14 along the drainage layer 12. Accordingly, it will be understood that fluid flowing down into the drainage layer 12 through the first permeable support textile 16 will enter the flow path 14 and can flow along the flow path. The direction of fluid flow along the flow path 14 will depend upon the positioning of the liner 22 comprising the composite material 10 within the landfill site 24. The drainage layer 12 thus facilitates flow of fluid out of the landfill site 24. However, and as will be described in more detail below, a portion of the fluid entering the drainage layer 12 will pass down through the second, intermediate permeable support textile 18 and thus will exit the drainage layer 12 through the intermediate textile.

The first, second and third wires 30, 32 and 34 of the drainage layer 12 are typically thermally bonded according to a manufacturing process which is known in the art of geotextile materials. The woven permeable support textiles 16 and 18 are also thermally bonded to the drainage layer 12. In the illustrated embodiment, the first support textile 16 is bonded to the first wires 30 of the drainage layer 12, whilst the second support textile 18 is bonded to the second wires 32 of the drainage layer 12.

The woven support textiles 16 and 18 are relatively inextensible in both warp and weft directions, and thus have relatively high modulii of elasticity. Typically, the textiles 16 and 18 may each have a mean 10% secant modulus of the order of 1 6OkN/m. In this fashion and as will be described below, the support textile 16, by being bonded to the first wires 30, resists entry of objects such as gravel into the drainage layer 12, which could otherwise block the flow path 14. In a similar fashion, the second support textile 18 resists extrusion of the cushioning layer 20 into the drainage layer 12, which may otherwise occur under load and which could block the flow path 14.

The cushioning layer 20 is thermally bonded to the second support textile 18. A manufacturing process of the composite material 10 will typically involve first manufacturing the drainage layer 12 and thus bonding the first, second and third wires 30, 32 and 34 together in the fashion described above. The first permeable support textile 16, assembled drainage layer 12, intermediate permeable support textile 18 and cushioning layer 20 will then be fed through an arrangement of rollers (not shown) into a thermal bonding machine (also not shown) of a type known in the art, which will bond the components together to produce the finished composite material 10 described above. However, in an alternative embodiment, the components may be bonded using an adhesive. In that event, the first and intermediate support textiles 16 and 18 will typically first be bonded to the assembled drainage layer 12, and the resultant sandwich of the first and second textiles and drainage layer will then be bonded to the cushioning layer 20.

When the composite material 10 is to be used as a liner such as the landfill liner 22 shown in Figure 2, the material 10 will typically be formed into sheets between 2m and 1 Om in width and may be around 25m to 1 OOm in length. The completed liner can be reeled, facilitating storage and onward transportation as well as subsequent installation at the landfill site 24.

Reference is now made to Figure 2 and also to Figure 3, which is an enlarged view of part of a base 36 of the landfill site 24. The landfill site 24 is prepared by first excavating a hole or depression 38 in the ground 40. A thick layer 42 of a low permeability soil such as a clay-based soil is provided as a lining in the base 36 of the hole 38, and which extends up the sides 44 of the hole. The clay layer 42 will typically around im in depth. An impermeable membrane 46, typically of a HDPE material and which is around 2mm in thickness is then positioned on the clay layer 42.

The liner 22 is then arranged above the HDPE membrane 46. This is achieved by providing a number of strips of the reeled composite material 10 in close abutment, covering the entire surface of the HDPE membrane 46. Finally, a layer 48 of gravel is provided on top of the liner 22. Typically, the gravel will be around 150mm to 3 50mm in depth, the depth ultimately depending upon material properties of the liner 22, selected according to parameters including the type and volume of waste. The site 24 is then ready to receive household or other waste, as indicated schematically at 50 in Figure 3.

In use of the liner 22, the cushioning layer 20 protects the HDPE membrane 46 against puncture or excessive strain by the gravel 48, under the loading of the gravel itself and of the waste 50. Leachate resulting from decomposition of the waste 50 passes down through the gravel layer 48, which filters out at least some of any solids particles present in the fluids. The leachate then passes down through the first or upper permeable support textile 16 into the drainage layer 12. Again, some of the solids particles may be filtered out by the textile 16. A portion of the leachate can then flow along the flow path 14 in the drainage layer 12, and will flow towards draw off points provided in a lowermost region of the hole base 36, one of which is shown and given the reference numeral 52. The remainder of the leachate will flow through the drainage layer 12, passing through the intermediate support textile 18 into the cushioning layer 20. Again, the intermediate textile 18 may filter out some of any remaining solids particles. The leachate then passes down through the cushioning layer 20, which may again filter out at least some of any remaining solids particles, and then comes into contact with the impermeable HDPE membrane 46. The leachate then flows along the membrane 46 towards the draw off points 52.

The leachate entering the draw off point 52 is pumped to a storage facility. This allows the leachate to be collected for subsequent treatment and disposal, as well as the volume of leachate flowing off the site to be monitored.

Various modifications may be made to the foregoing without departing from the spirit and scope of the present invention.

For example, it will be appreciated that the composite material of the present invention has a utility as alternative types of liner to landfill liners, and indeed has uses other than as a liner.

The drainage layer may comprise a plurality of spaced, parallel first mesh elements and a plurality of spaced, parallel second mesh elements disposed transverse (non-parallel) to the first mesh elements, to thereby define a plurality of apertures extending through the drainage layer, which apertures may be arranged to define a flow path for fluid along a length of the drainage layer. The first and second mesh elements may be bonded together and may be thermally bonded.

The first and second mesh elements may be disposed at angle other than 900 relative to one another, and the third mesh elements (where provided) may be disposed at an angle other than 45 0 relative to one or both of the first and second mesh elements.

Further support sheets, drainage layers and/or cushioning layers may be included in the composite material. The composite material may be used in a similar fashion in the base of landform waste disposal.

Alternative materials may be used for components of the composite. For example, the first and second support sheets may be of non-textile materials, and/or of other types of plastics or even non-plastics materials.

Claims

CLAIMS1. A composite material for use as a liner, the composite material comprising: a drainage layer defining at least one flow path for the passage of a fluid therealong; first and second permeable support sheets for the drainage layer, the drainage layer located between the permeable support sheets; and a cushioning layer located adjacent to one of the first and second permeable support sheets.
2. The composite material of claim 1, for use as a landfill liner.
3. The composite material of either of claims 1 or 2, wherein the material is flexible to facilitate reeling.
4. The composite material of any preceding claim, wherein the first and second permeable support sheets act, in use, to support the drainage layer and to keep the flow path of the drainage layer open.
5. The composite material of any preceding claim, wherein the first and second support sheets are of a relatively inextensible material.
6. The composite material of claim 5, wherein the first and second support sheets each have a mean 10% secant modulus of approximately l6OkN/m.
7. The composite material of any preceding claim, wherein the first and second support sheets are textiles.
8. The composite material of claim 7, wherein the first and second support sheets define apertures for fluid passage between warp and wefi fibres of the textiles.
9. The composite material of any preceding claim, wherein the first and second support sheets are of a plastics material.
10. The composite material of any preceding claim, wherein the first and second support sheets are of a thickness of no more than about 0.5 mm and no less than about 0.25 mm.
11. The composite material of any preceding claim, wherein the drainage layer is bonded to both the first and second support sheets.
12. The composite material of any preceding claim, wherein the cushioning layer is bonded to the selected one of the first and second support sheets located adjacent thereto.
13. The composite material of either of claims 11 or 12, wherein bonding is achieved thermally.
14. The composite material of any one of claims 11 to 13, wherein the drainage layer, first and second support sheets and cushioning layer are bonded by feeding them together into a thermal bonding machine.
15. The composite material of either of claims 11 or 12, wherein bonding is achieved using an adhesive.
16. The composite material of any one of claims 11, 12 or 15, wherein the first and second support sheets are first bonded to the drainage layer, and the cushioning layer then bonded to the selected one of the first and second support sheets to be located adjacent thereto.
17. The composite material of any preceding claim, wherein the drainage layer is an open cell mesh structure.
18. The composite material of any preceding claim, wherein the drainage layer comprises a plurality of spaced, parallel first mesh elements and a plurality of spaced, parallel second mesh elements disposed transverse to the first mesh elements, to thereby define a plurality of apertures extending through the drainage layer, which apertures may be arranged to define a flow path for fluid along a length of the drainage layer.
19. The composite material of claim 18, wherein the first and second mesh elements are bonded together.
20. The composite material of either of claims 18 or 19, wherein the drainage layer comprises a plurality of spaced, parallel third mesh elements, the third mesh elements disposed transverse to both the first and second mesh elements.
21. The composite material of claim 20, wherein the third mesh elements are disposed between the first and second mesh elements and define a spacing between the first and second mesh elements, said spacing providing a primary flow path for the flow of fluid along a length of the drainage layer.
22. The composite material of either of claims 20 or 21, wherein the first mesh elements are bonded to the third mesh elements, and the third mesh elements are bonded to the second mesh elements.
23. The composite material of any one of claims 20 to 22, wherein the first and second mesh elements are disposed at about 90° to one another and the third mesh elements are disposed at about 45 ° relative to both the first and second mesh elements.
24. The composite material of any preceding claim, wherein the cushioning layer takes the form of a permeable geotextile material.
25. The composite material of any preceding claim, wherein the cushioning layer is of a needle punched plastics material.
26. The composite material of any preceding claim, wherein the cushioning layer is at least about 5 mm in thickness.
27. The composite material of any preceding claim, wherein the cushioning layer is no more than about 20 mm in thickness.
28. The composite material of any preceding claim, comprising a further cushioning layer coupled to the other one of the first and second permeable support sheets.
29. The composite material of claim 17, or any one of claims 18 to 28 when dependent on claim 17, wherein, in use as a liner, the cushioning layer is provided outermost and thus spaced furthest from waste in a landfill site; the first support sheet is provided innermost; and the second support sheet is an intermediate support sheet provided between the mesh of the drainage layer and the cushioning layer.
30. A liner of a composite material, the composite material comprising: a drainage layer defining at least one flow path for the passage of a fluid therealong; first and second permeable support sheets for the drainage layer, the drainage layer located between the permeable support sheets; and a cushioning layer located adjacent to one of the first and second permeable support sheets.
31. The liner of claim 30, wherein the composite material comprises the composite material of any one of claims 2 to 29.