WO2012035318A2

WO2012035318A2 - A permeable base

Info

Publication number: WO2012035318A2
Application number: PCT/GB2011/051680
Authority: WO
Inventors: Peter Leslie Lawrence
Original assignee: Peter Leslie Lawrence
Priority date: 2010-09-16
Filing date: 2011-09-08
Publication date: 2012-03-22
Also published as: GB2483690B; GB201015519D0; WO2012035318A3; GB2483690A

Abstract

The invention relates to a permeable base (10) for a road, path or playing surface (100). The base comprises a geotextile (20), a layer of aggregate material (30) above the geotextile, and a geonet (40) above the aggregate material. The base also comprises a binder (50) which adheres the aggregate material together to form a cohesive aggregate layer and which also adheres the geotextile (20) and geonet (40) to the respective bottom and top surfaces of the cohesive aggregate layer. The resulting bound aggregate base is durable, permeable and is relatively straightforward to install compared to known systems. The invention also extends to a sports or playing surface, a path, a road surface for vehicles, and to a golf bunker, comprising a base in accordance with the invention and a surface dressing layer (60) above the base. It also extends to a method of constructing a base.

Description

A Permeable Base

The present invention relates to a permeable base, and in particular it relates to a permeable base which is suitable for use in the construction of a road, path or recreational surface, or similar surface.

There is a wide variety of surface dressings which require a base of some form on which the surface dressing is laid. Examples of surface dressings which require a base include turf or artificial turf (e.g. golf courses, sports pitches), sand (e.g. golf bunkers), gravel (e.g. paths and driveways), tarmac (e.g. paths, roads, car parks, tennis courts), and composite materials (e.g. running tracks, play grounds, sports pitches or courts).

The purpose of the base is primarily to provide a stable foundation on which the top material is laid, but the base may also be needed to promote drainage. Another function of the base is to separate the surface dressing material from the soil underneath so that the two materials do not mix. This function is needed when the surface dressing is sand, as used in a golf bunker for example, or when using gravel in the construction of paths or driveways. A base may also have the function of providing shape or form to the surface dressing, as may be needed when constructing a three-dimensional structure such as a golf bunker or raised putting green on a golf course, for example. Depending on the application, the base may also have other functions, such as providing shock- absorbing properties to prevent injuries (in the case of a sports surface such as an artificial turf pitch) or to absorb the energy of a golf ball (in the case of a golf green made from artificial grass, to mimic real grass).

Traditionally, a base can be provided by excavating the site to a specified depth, importing a quantity of hardcore, graded stone and possibly crushed concrete, and compacting the material in layers. At this stage, the surface dressing can be added to complete the construction.

Certain applications may require a more solid base than the compacted material described above, in which case a layer of concrete or tarmac may be added on top of the compacted sub-base, before a top dressing is added if desired.

As mentioned above, some applications, such as turf, artificial turf, sand or gravel may require a solid base which also promotes drainage, in which case concrete or tarmac may not be suitable. For these applications, attempts have been made at providing a stable, permeable base by agglomerating a layer of aggregate material while attempting to keep passages between individual aggregate particles relatively open to allow water to pass through the agglomerated layer. All of the above base constructions have their disadvantages. The construction of a compacted base or sub-base requires the excavation and importation of a significant quantity of material, which can be labour-intensive and may not be desirable from an environmental standpoint.

The addition of a concrete or tarmac layer will render the base relatively impervious to rainwater, causing the water to run off at the sides of the area, potentially causing local flooding. This may be alleviated to some extent by providing drains or drainage channels in the base and/or sub-base, but this increases the overall complexity and cost of the construction. Furthermore, there is a general concern about the impact that large areas of impervious concrete or tarmac have on the environment, including their contribution to flooding, and some authorities have brought in legislation requiring the use of permeable materials and bases to alleviate this problem.

There are several commercial systems on the market which are designed to agglomerate the particles of an aggregate layer in an attempt to provide a stable, permeable base. They typically involve the construction of a compacted sub-base as described above, on top of which a layer of aggregate material is applied, to a specified depth. A liquid binder is then applied to the aggregate material which, once it solidifies or cures, is intended to adhere the individual aggregate particles together whilst maintaining the interstitial spaces, thereby permitting water still to permeate through the layer. One such system is described in WO 2007/070913, in which sodium silicate is used as a binder for the aggregate top layer of a playing field base. Another commercially-available system employs polymeric MDI (methylene diphenyl diisocyanate) as the binder, which is a moisture-cured polyurethane.

There are several problems with current bound aggregate systems. Sodium silicate, in the system referred to above, is applied to the aggregate in an aqueous solution which also contains a hardener/catalyst. After application, the hardener/catalyst produces a weak acid which lowers the pH of the alkaline sodium silicate solution, causing the sodium silicate to gel out of solution. After a period of time, the sodium silicate sets like a weak glass. In this form, sodium silicate is hard and inflexible, and it has no natural cohesion, so the aggregate layer cracks and breaks up over time. Furthermore, the sodium silicate can redissolve in water, so if any areas of the bound aggregate layer sit in water for any period of time, the sodium silicate will dissolve and become a liquid solution again. If any load is put on that area while in this state, the aggregate will move and break apart, allowing the sodium silicate to seep into the ground below. For this reason, installers of sodium silicate bound aggregate bases usually insist that the sub-base under the aggregate layer is constructed to be self-draining, either by means of drainage channels or by constructing drainage slopes into the sub-base, so that the bound aggregate layer never sits in water for any period of time.

The polymeric MDI binder system also requires the construction of a sub-base, since although the binder is more flexible compared to the sodium silicate binder, it nevertheless needs a stable base. This is because excessive flexing of the binder (if for example the base is not stable) will start to cause cracks in the binder. Once any of the material becomes unbound, the material around it starts to flex more, and the problem gets progressively worse. Another problem with the MDI binder system is that it is only permeable vertically, and even then not to a great extent. It does not promote drainage, or drain horizontally.

As mentioned above, both currently-available bound aggregate systems (sodium silicate and polymeric MDI) require the construction of a sub-base before the aggregate layer is laid down and the binder applied. It will be appreciated that this is not simply a levelling of the existing ground in the construction area, but typically involves excavation, importation of hardcore and other sub-base aggregates, and compaction of the materials in layers. The construction of drainage surfaces or channels may also be required.

There is therefore a need for a bound aggregate base for a road, path or playing surface (or similar) which is durable, permeable and which is relatively straightforward to install compared to known systems.

In accordance with a first aspect, the invention provides a permeable base comprising a geotextile, a layer of aggregate material above the geotextile, and a geonet above the aggregate material, the base further comprising a binder which adheres the aggregate material together to form a cohesive aggregate layer and which also adheres the geotextile and geonet to the respective bottom and top surfaces of the cohesive aggregate layer.

A geotextile is a type of permeable textile material used in construction or civil engineering. A geotextile is a permeable fabric used to separate, reinforce, protect or drain. It can be woven or nonwoven; if nonwoven, the material is typically heat-bonded (e.g. spunbond, meltblown or a combination) or needlepunched. It is often made from a polymer, such as polypropylene or polyester. Materials can have a range of basis weights, thicknesses, tensile strengths, water flow rates and fiber properties, with the most appropriate properties being chosen for the specific application and conditions.

A geonet (or sometimes "geospacer") is another material used in the construction industry. When viewed from above, a geonet can have a relatively open, net-like structure. When viewed in cross-section, the material typically comprises two or more layers of parallel sets of ribs, which are disposed at angles to one another and joined at their points of contact. By virtue of the layered sets of parallel ribs, geonets provide passages for fluids in the plane of the material, so they are useful where there is a need for horizontal drainage. In the present invention, a geonet can also provide shock- absorbing properties to the base, making the base suitable for use in sports applications.

The present invention relates to a composite, permeable base comprising a geotextile, a cohesive or agglomerated aggregate layer, and a geonet. The combination of these three materials results in a durable but relatively flexible base for a road, path or recreational surface. The binder adheres the geotextile and the geonet to the surfaces of the aggregate layer, as well as to bind the aggregate layer itself. However, it is not essential for the aggregate to be fully bound or for every part of the geotextile or geonet to be attached to the aggregate layer; it is simply necessary that enough of the base materials are bound together so that a cohesive three-layer structure results. The aim is to provide a stable, integrated base. Even if some of the aggregate is not fully bound and remains loose within the layer, the geonet and geotextile either side of the aggregate layer keep the aggregate bound together by preventing sideways movement of the material. Therefore, the aggregate is prevented from breaking up when under load. This is an important advantage over prior art systems, since they will tend to use quantities of binder sufficient to ensure that the structure is fully bound, which of course has an impact on the permeability of the structure. In the present invention, binder application levels can be reduced compared to prior art systems due to the presence of the geotextile and geonet layers, which help to keep the aggregate bound. By using less binder, the permeability of the structure is improved.

The base in accordance with the invention also has excellent drainage properties, and allows drainage in two directions. Under normal conditions, water will flow vertically down through the geonet, aggregate layer and geotextile, into the ground underneath. In periods of heavy rain, or if the ground underneath an area of the base becomes saturated, the geotextile will exert a back-pressure on the water, causing it to then move sideways through the aggregate layer and additionally the geonet until it can either flow down into the ground through another area of geotextile, or until it exits from the side edge of the base. The geonet, by virtue of its layered construction comprising sets of parallel ribs, is better able to convey the water horizontally across the base to an area where there is no back-pressure and it can then percolate down through the base to the ground underneath.

Because of the unified nature of the base, other than levelling and possibly some compaction of the ground underneath, there is no need for the construction of a sub-base, although in some cases this may be desirable, for example when building up a three- dimensional structure. For a typical two-dimensional structure such as a road, path or playing area therefore, the invention provides a significant saving in materials, transport and labour costs.

The aggregate material may be any material suitable for carrying out the desired function in the base. It can be stone or gravel, for example. The aggregate material may be or may include recycled aggregate, such as waste from industrial processes. One example of a suitable recycled aggregate is recycled modified waste expanded polystyrene (MEPS). If an aggregate material is being used as the top layer, the material used in the base can be the same as or different from the top material, allowing a cheaper, more environmentally-friendly or locally-available material to be used if more appropriate.

Preferably, the aggregate does not contain very small particles since these can block up the passageways between the larger particles. Preferably, therefore, the aggregate material comprises particles having a size greater than 5mm. It is also preferable to limit the upper size of the particles for the same reason, so that the passageways are optimised. Preferably, therefore, the aggregate material comprises particles having a size less than 20mm. Ideally, the two size requirements are combined so that the aggregate preferably comprises particles in the size range of 5-20mm. A more preferred size range is about 5-15mm, and about 10mm has been shown to work well in practice. Two particularly preferred types of aggregate are 10mm pea shingle or drive gravel, and 10mm road stone chippings.

The depth of the aggregate layer will largely depend on the specific site requirements (e.g. likely loads to be encountered) and also on the properties of the aggregate and the binder (specifically the binder's ability to penetrate to the lower surface of the aggregate to reach the geotextile). The applicant has found that a depth of between about 2cm and about 10cm will work in practice for a typical path construction, with a depth of between about 3cm and 5cm being ideal for this application.

As mentioned above, the geotextile component of the base is preferably either a woven material or a nonwoven material. Geotextile materials in use in the construction industry today will generally function well in the present invention, although the local requirements of the site and the purpose of the base being constructed will determine which specific materials may be more suited for the application than others. While other types of nonwoven materials should not be excluded, the applicant has found that a needlepunched material performs well and therefore such a material is preferred.

Preferably, the geotextile is a needlepunched nonwoven material, preferably made from polypropylene. As mentioned above, geonet materials are in use in some parts of the construction industry today and it is envisaged that many currently-available materials will be suitable for use in the present invention. Geonet materials are characterised by having a relatively open, net-like structure and the ability to channel fluids along the plane of the material. The geonet in the base of the present invention is designed to provide compressive strength, structural integrity and some degree of elasticity to the composite base. It can also help to form the finished surface of the base, by smoothing out or flattening the base surface. Certain geonets may provide smooth curves when used in three-dimensional structures, and this property may also be useful.

The geonet is preferably made from a polymer. As well as providing the desired physical properties, this allows adjacent sections of geonet to be heat-welded together when forming a base with a larger area than the size of geonet material available. The geonet may preferably be made from High Density Polyethylene (HDPE), and is usually made by extrusion.

Preferably, the geonet material in the present invention comprises two or more layers of parallel sets of ribs, the ribs of adjacent layers being disposed at an angle to one another. The ribs of adjacent layers are preferably joined to one another at their points of contact. The geonet material may comprise two, three, four or more layers of parallel sets of ribs. Preferably, the geonet comprises at least three layers of parallel sets of ribs. With three or more layers, the channels in between the ribs of the central layer(s) tend to remain open and are not occupied by aggregate particles above or below, so the fluid transmitting properties of the geonet are enhanced compared to two-layer materials. When the geonet has three layers, it is preferred that none of the three sets of ribs is parallel to another in the material, so that the ribs of all three layers lie in different directions. This has been found to provide a good combination of strength, flexibility and directional fluid transmission.

The base of the invention may additionally comprise a second geonet located below the cohesive aggregate layer, which may further be located above the geotextile. This provides greater strength and/or increased lateral drainage, if required.

As mentioned above, the base in accordance with the present invention includes a binder which adheres the aggregate material together to form a cohesive aggregate layer and which also adheres the geotextile and geonet to the respective bottom and top surfaces of the cohesive aggregate layer. It is important that the base has some level of flexibility, since very rigid bases such as those bound with sodium silicate mentioned above are prone to cracking. Therefore, it is preferred that the binder is inherently flexible and resilient. Further, the binder does not fill the interstitial voids in the aggregate, but only partially fills them so that the cohesive aggregate layer remains permeable.

Therefore, the binder will only contact the aggregate particles at certain points, binding the aggregate into a cohesive layer without making the layer rigid and inflexible.

Preferably, the binder is a polymeric binder. The binder is preferably applied to the base in liquid form, which then cures or otherwise solidifies into an inherently flexible binding material within the aggregate layer. Preferably therefore, the binder is a cured polymeric binder, such as a moisture-cured polyurethane binder or a moisture-cured polymeric MDI binder. Such a binder remains chemically inert once cured, and therefore does not seep into the surrounding ground, even when saturated. Commercially-available MDI binders would be suitable for use in the present invention, provided they possess the appropriate chemical and physical properties, which the skilled person will be able to determine.

The binder should preferably have a viscosity in the range of about 400 to about 700 centipoise (cps). A thick syrup consistency is preferred. The viscosity needs to be controlled such that, on application of the binder to the surface, the viscosity is high enough to coat the geonet and aggregate and remain in position there, but low enough so that sufficient binder flows down and reaches the geotextile, at least in some places. As discussed above, it is not critical in the invention that all three layers are fully bound together, or that the aggregate is fully bound in its layer; it is simply a requirement that the three-layer composite base is sufficiently bound such that a cohesive three-layer structure results.

The binder can be applied by means of a pump, with a nozzle or wand attached. The viscosity of the binder may need to be adjusted (e.g. by means of diluting or thickening agents) to compensate for the ambient temperature on the day, but this again will be within the scope of the skilled person.

If the binder is a moisture-cured MDI binder, curing generally starts well after the liquid has stopped flowing, at around 30 minutes for example, and fully cures over 24 hours typically. Chemicals could be added to the binder to speed up the start of the process, however, so that the reaction starts at around the same time as the binder has reached the geotextile (which may take approximately 2 minutes). In this case the chemicals may need to be premixed immediately prior to application.

The amount of binder used is dependent on the depth of aggregate required for a particular application, as well as the intended use of the base and its required strength. In a typical application such as a path or light vehicle drive with 4 cm deep aggregate, the coverage should be in the range from 1 .5 to 2.5 litres/m². In order to provide a base with greater depth and increased strength (such as may be required in the construction of a road, for example), multiple bases of the present invention may be layered vertically.

Once the base in accordance with the invention has been constructed, a top layer or surface dressing layer may be added, which will vary depending on the particular use of the finished surface. Clearly, while several examples have been given above, there is an infinite variety of uses for which a surface may be constructed and it is not practical to attempt to list them all. However, the invention extends to a recreational surface (such as a sports or playing surface, or a recreational lawn), a path, a road surface for vehicles (including a car park), and to a golf bunker, comprising a permeable base in accordance with the invention and a surface dressing layer above the base.

The surface dressing layer may be a single layer of material, or it may comprise two or more layers of different materials, depending on the application. The surface dressing layer preferably comprises one or more of the following materials: turf, artificial turf, sand, gravel, aggregate, tarmac, geotextile, composites (e.g. materials including plastics or rubber). A gravel drive, for example, may just require a top dressing of loose gravel, whereas the surface dressing layer for an artificial sports field may comprise a geotextile material, artificial turf and sand. It is useful to use a geotextile material above the geonet of the base when the surface dressing layer includes or comprises relatively fine material such as sand, which otherwise may impair the drainage function of the geonet through blocking of the geonet's pores and passageways. In the example of a golf bunker, the surface dressing may comprise a geotextile attached to the geonet of the base, and a sand layer above the geotextile. The sand may further include a binder, which forms a more cohesive layer and can also have the function of attaching the sand to the geotextile. The sand is then less able to migrate.

If the surface dressing layer comprises or includes sand, gravel or other aggregate, a binder may be used to form a cohesive layer. The binder may be the same binder as employed in the base. Depending on the materials being used, it may be possible to apply the binder to the base through the surface dressing layer, so that the binder is applied to the surface dressing layer, geonet, base aggregate and geotextile in a single operation. Alternatively, it may be preferably to apply the binder to the base (through the geonet) first, following up with a second application of binder to the top surface dressing once this layer is in place. Which technique is appropriate will depend on the materials making up the surface dressing layer and the base, and the properties of the binder being used.

In the case where the surface dressing layer includes a geotextile adjacent to the top surface of the base (i.e. the geonet), the polymeric nature of both materials allows them conveniently to be attached together by adhesive or by the application of heat. Alternatively, the layers may be attached by mechanical means such as staples, cable ties, clips, wire, etc.

The invention extends to a method of constructing a permeable base as described above, and therefore, in accordance with a second aspect, the invention provides a method of constructing a permeable base comprising the steps of laying a geotextile, forming a layer of aggregate material on top of the geotextile, laying a geonet on top of the aggregate material layer, and applying a binder to the base to form a cohesive aggregate layer and to adhere the geotextile and the geonet to the respective bottom and top surfaces of the cohesive aggregate layer.

The invention also extends to a method of constructing a recreational surface, a golf bunker, a road surface for vehicles, or a path, comprising the method of constructing a base in accordance with the invention and the further step of applying a surface dressing layer above the base. As discussed above, the binder may be applied to the base before the surface dressing is added, or it may be applied afterwards.

The base in accordance with the invention can be constructed on a level surface, but also on a sloping or curved surface. With a sloping or curved surface, once the geotextile is laid on the ground, a first area of aggregate is laid to the required depth at the lowermost point of the structure. The geonet is typically supplied in a roll, and with the initial area of aggregate in place, the geonet can be unrolled over the top as further aggregate is then added in between the geotextile and geonet. Weights can be used on top of the geonet to keep the aggregate at the right depth and to stop the new aggregate being added from accumulating and increasing the thickness of the layer beyond specification.

Further enhancements possible with the various structures made in accordance with the present invention include the addition of colour to the surface dressing binder (if being used) to generally colour the structure, or to mark out specific areas such as path edges, parking spaces, etc. The addition of a photoluminescent material to the surface dressing binder may be useful to increase the surface's visibility in low light or after dark, for example in the case of a golf course buggy track. Different grades or colours of surface aggregate may be used in the same structure to enable features such as road markings or symbols to be shown, or generally to enable different areas of the surface to be distinguished. Formers can be used to keep the aggregates separated until the binder has cured.

An embodiment of the invention will now be described, by way of example only and with reference to the accompanying drawings, in which: Fig. 1 shows a side view of a base in accordance with the invention;

Fig. 2 shows a perspective view of a base in accordance with the invention; and Fig. 3 shows a cross-sectional view of a gravel path including a base of the invention.

Referring to Figs. 1 and 2, base 10 generally comprises a geotextile 20, aggregate material 30, geonet 40 and binder 50. Each component of the base will be discussed separately before explaining the construction.

Geotextile 20 is a permeable construction fabric of sufficient strength to provide a separation between the underlying ground and the aggregate above. As discussed above, geotextiles are typically nonwoven materials, and in this preferred embodiment, geotextile 20 is a layer of needlepunched nonwoven. It is made from polypropylene fibers, and has a basis weight of about 300 gsm. The fabric is about 1.8mm thick and has a puncture resistance of about 3.3kN. Its liquid flow rate is about 70 litres/m²/second.

Aggregate material 30 in this preferred embodiment is 10mm road stone chippings, although as mentioned above, there are many suitable materials available including recycled aggregates. Road stone chippings are easily available and less expensive than decorative stone aggregates, for example, which may be used as the top surface dressing. In this application, showing a base construction for a path, the aggregate layer is about 4cm deep.

The structure of geonet 40 can be seen in Figs 1 and 2. The material comprises three layers of parallel sets of ribs, upper set 41 , middle set 42 and lower set 43. As can be seen from Fig. 2, each set is disposed at 45 degrees to the adjacent set and no set is parallel to another in the geonet. The geonet 40 is made from HDPE and is formed by continuous extrusion, with the ribs of adjacent layers being joined at their points of contact. When viewed from above, the geonet is a relatively open structure. The material in this embodiment has openings of about 5-10mm in size. With reference to Fig. 1 , the geonet structure defines passages 44 for fluids to move along the plane of the material. In this preferred embodiment, geonet 40 has a thickness of about 6mm, a basis weight of about l OOOgsm and a tensile strength of about 10kN/m. Other basis weights are available, such as 750gsm and 1300gsm for example, and these may also be suitable depending on the specific application.

The function of binder 50 is to adhere all of the base components sufficiently to form an integrated base which is still permeable, by preserving interstitial spaces in the aggregate layer and pores or voids in the other base materials. Properties of the binder such as viscosity and curing time will need to be controlled as discussed in the

introduction above. In the preferred embodiment, binder 50 is a moisture-cured polyurethane binder (MDI). In addition to MDI, the binder may contain other chemicals to control the speed and amount of curing, as well as the final hardness of the rubber. An organic ester such as tri-ethylene glycol diacetate may be suitable for this purpose. The properties of the binder are ideally controlled so that the binder starts to cure relatively soon after application (e.g. within about 30 minutes) and is fully cured within about 24 hours. Other chemicals may be present in the binder formulation to perform other functions as necessary.

The binder 50 is in liquid form and is therefore sprayed or poured onto the base once the geotextile 20, aggregate 30 and geonet 40 are all in position. In the construction of a path such as is being described, a typical application rate for the binder is 1.5 to 2.5 litres/m².

Turning to Fig. 3, the construction of a typical path 100 is shown. The path comprises a base 10 as described above together with a surface dressing layer 60 above the base, comprising decorative aggregate 70 and binder 80. Edging blocks 90 are used to provide separation between the surface dressing layer 60 and grass 95.

Path 100 is constructed by first excavating the site to a relatively shallow depth, bearing in mind that a sub-base is not required. The excavated area should be smoothed out and flattened, but significant compaction of the ground is not necessary. Next, geotextile 20 is laid on the bottom and side surfaces of the excavation, as well as a small section underneath the grass 95 to fully wrap the base 10, followed by aggregate material 30 and then geonet 40.

At this stage, base binder 50 may be applied to the base layers, or alternatively the binder may be applied once the surface dressing layer 60 has been added, in which case the binder will act on both the base materials and the surface dressing aggregate 70.

Once the geonet 40 is in place, and the base binder 50 applied if appropriate, edging blocks 90 can be put in position. It may be preferred to secure the edging blocks in place, in which case they could be designed to clip into or be attached to the geonet 40 by mechanical means or by adhesive, or even by the binder 50 or 80 used to bind the base aggregate 30 or the surface aggregate 70. In the final operation, decorative aggregate 70 is added on top of the base geonet 40, and binder 80 applied and allowed to cure.

Claims

Claims:

1. A permeable base comprising a geotextile, a layer of aggregate material above the geotextile, and a geonet above the aggregate material, the base further comprising a binder which adheres the aggregate material together to form a cohesive aggregate layer and which also adheres the geotextile and geonet to the respective bottom and top surfaces of the cohesive aggregate layer.

2. The base of claim 1 , wherein the aggregate comprises particles in the size range of 5-20mm.

3. The base of claim 1 or 2, wherein the aggregate layer is between 2-10cm in depth.

4. The base of any preceding claim, wherein the geotextile is a needlepunched nonwoven material.

5. The base of any preceding claim, wherein the geonet comprises two or more layers of parallel sets of ribs, the ribs of adjacent layers being disposed at an angle to one another.

6. The base of claim 5, wherein the geonet comprises at least three layers of parallel sets of ribs.

7. The base of claim 5, wherein the geonet comprises three layers of parallel sets of ribs, none of the three sets of ribs being parallel to another set in the material, so that the ribs of all three layers lie in different directions.

8. The base of any preceding claim, further including a second geonet located below the cohesive aggregate layer.

9. The base of claim 8, wherein the second geonet is located above the geotextile membrane.

10. The base of any preceding claim, wherein the geonet forms passageways for liquid to pass along the plane of the material in at least one direction.

1 1. The base of any preceding claim, wherein the binder is inherently flexible and resilient.

12. The base of any preceding claim, wherein the binder is a cured polymeric binder.

13. The base of any preceding claim, wherein the binder is a moisture-cured polyurethane binder, applied to the base in liquid form.

14. A base comprising two or more bases as claimed in any preceding claim.

15. A recreational surface comprising a base in accordance with any preceding claim and a surface dressing layer above the base.

16. The recreational surface of claim 15, in which the surface dressing layer includes one or more of the following materials: turf, artificial turf, sand, gravel, aggregate, geotextile, composite, binder.

17. The recreational surface of claim 15, in which the surface dressing layer comprises a geotextile, artificial turf and sand.

18. The recreational surface of claim 15, in which the surface dressing layer comprises a geotextile and sand.

19. A golf bunker comprising a base in accordance with any of claims 1 to 14 and a surface dressing layer above the base.

20. The golf bunker of claim 19, in which the surface dressing layer includes sand.

21. The golf bunker of claim 19, in which the surface dressing layer comprises or includes a geotextile material and sand.

22. The recreational surface or golf bunker of any of claims 15 to 21 , in which the surface dressing layer includes a geotextile adjacent the geonet of the base, the geotextile and geonet being attached together by mechanical means, or by adhesive or thermal bonding.

23. A road surface for vehicles comprising a base in accordance with any of claims 1 to 14 and a surface dressing layer above the base.

24. A path comprising a base in accordance with any of claims 1 to 14 and a surface dressing layer above the base.

25. The road surface or path of claim 23 or 24, in which the surface dressing layer comprises an aggregate material and a binder.

26. A method of constructing a permeable base comprising the steps of:

laying a geotextile,

forming a layer of aggregate material on top of the geotextile,

laying a geonet on top of the aggregate material layer, and

applying a binder to the base to form a cohesive aggregate layer and to adhere the geotextile and the geonet to the respective bottom and top surfaces of the cohesive aggregate layer.

27. A method of constructing a recreational surface, a golf bunker, a road surface for vehicles, or a path, comprising the method of constructing a base in accordance with claim 26 and the further step of applying a surface dressing layer above the base.

28. The method of claim 27, in which the step of applying a surface dressing layer is carried out before the step of applying a binder.