Drain reinforcement

Abstract

 A particular problem with filter drains used beside highways is that they generally comprise a trench within which an aggregate infill is provided in order to allow soak away. Unfortunately, vehicles which drift off the highway and into the trench may tend to "plough" that aggregate and become dangerously embedded, etc. In accordance with the present invention, a reinforcing mesh is provided at an appropriate location within the filter drain in order to ensure retention of appropriate soak away whilst inhibiting ploughing such that it is easier for a vehicle to extract itself from the filter drain. The reinforcing mesh comprises a perforated plastic sheet having regular sized apertures in order to bind any compression of aggregate into those apertures for resistance to ploughing. The reinforcing mesh 5 is positioned at a desired spacing below the aggregate surface within the trench of the filter drain.

Description

[0001] The present invention relates to drain reinforcement and more particularly to reinforcement of filter drains adjacent to highways.

[0002] Drains and drain systems are invariably located underground in order to allow rapid dispersal and soakaway of surface water. A preferred drainage system adjacent to motorway highways is that known as a filter drain. Essentially, a filter drain comprises a trench or ditch filled with a depth of relatively coarse aggregate such that surface water is allowed to soak away through the filter drain either into the ground thereabout or a perforated drainage pipe located at the bottom of the drain. Filter drains are relatively cheap and easy to install with maintenance only required when the aggregate has become clogged by vegetation or other debris.

[0003] In order to be effective a filter drain must be relatively close and adjacent to a highway. In such circumstances, if a vehicle and in particular heavy goods vehicle should stray from the highway and so ride upon the aggregate of the filter drain there is a high possibility of wheel sinkage into the filter drain due to shear displacement of the aggregate under the load applied. Clearly, once a vehicle's wheels are sunk into the aggregate it is difficult for that vehicle to exit the drain due to the notional gradient presented to the wheel, the fluidity of the aggregate and instability of the vehicle. It will be understood that a vehicle which has sunk into a filter drain is unstable and liable to topple with dangerous consequences. In such circumstances, it is necessary to lift the vehicle from the filter drain and this may require closing the highway at least partially in order to allow appropriate lifting gear to be put into position. It will also be understood, after the vehicle has been removed from the filter drain there is a large scatter of aggregate on the highway which must be cleared if there are not be subsequent scree impact dangers as vehicles flick up individual aggregate stones at high speeds travelling along the highway.

[0004] In accordance with the present invention there is provided a drain arrangement for highways, the arrangement comprising a trench and aggregate filling to provide a soakaway path therethrough, the aggregate filling being associated with a reinforcing mesh, the reinforcing mesh extending substantially laterally across the trench at a desired depth below the aggregate filling surface so a portion of the aggregate filling above that reinforcing mesh provides greater compression strength under load.

[0005] Preferably, the portion of aggregate filling above the reinforcing mesh is preferentially compacted.

[0006] Typically, the reinforcing mesh is a perforated elastomeric sheet. Furthermore, that perforated elastomeric sheet is a plastics material of an open grid or net structure. Normally, the plastics material is polyurethane. Typically, the desired depth is between 100 and 300mm below the aggregate filling surface. Preferably, the desired depth is substantially 125mm ± 50mm below the aggregate filling surface. Alternatively, the desired depth is between 75mm and 175mm below the aggregate filling surface. However, the actual depth used in a matter of detailed design dependent upon aggregate type, angularity and desired performance requirements.

[0007] Possibly, two or more reinforcing mesh layers will be provided. Typically, such layers will be at substantially parallel and have a spacing such as 100mm and 200mm from the filling surface. Preferably, 150mm from the filling surface. However, spacing is again dependent upon aggregate type, angularity and desired performance.

[0008] Typically, the reinforcing mesh includes a uniform distribution of apertures. Advantageously, these apertures have dimensions whereby an aggregate constriction bias is provided. Typically, the aggregate bias is provided by the preferential compaction of the portion of the aggregate filling above the reinforcing mesh creates a bunching compression of aggregate into the apertures, that bunching compression causing lateral expansion of the aperture whereby when the preferential compaction of the portion of the aggregate filling is released the lateral expansion of the apertures creates an inward compression upon the aggregate held in the bunch compaction within the aperture and so creates an upward bias in the portion of the aggregate filling above the reinforcing mesh and so creates a degree of pre-stressing of that portion. Further advantageously, in order to enhance such bunch compression of the aggregate in contact with the reinforcing mesh in order to create pre-stressing of the portion of the aggregate filling above the reinforcing mesh, the apertures include lips for facilitating bunch compression. Additionally, interaction with and support by aggregates below is important for drain reinforcement.

[0009] Typically, the reinforcing mesh is presented substantially flat as well as laterally across the trench. Alternatively, the reinforcing mesh may be upturned at the trench side walls. Possibly, the reinforcing mesh, particularly where upturned at the trench side walls have no apertures.

[0010] Preferably, the reinforcing mesh includes drainage apertures for drainage, grip and reinforcement.

[0011] Preferably, the reinforcing mesh includes anchor means in order to hold mesh position and so stabilise presentation of the reinforcing mesh within the drain arrangement. Typically, such anchor means includes ribs and/or penetrative pegs secured between the reinforcing mesh and the aggregate filling and/or trench wall.

[0012] Possibly, the aggregate filling includes a proportion of ground or shredded tyre pellets or granules formed from used, worn or reject vehicle tyres.

[0013] Also in accordance with the present invention there is provided a method of forming a drain arrangement comprising digging a trench, filling that trench with aggregate until an upper surface of that aggregate is at a desired level, placing a reinforcing mesh upon that surface and adding further aggregate whereby an upper surface of that aggregate is such that the reinforcing mesh is at a desired depth from that upper surface.

[0014] Further in accordance with the present invention there is provided a method of renovating a drain arrangement comprising removing an upper portion of aggregate, placing a reinforcing mesh on the remaining aggregate and returning aggregate to an original drain surface level.

[0015] Additionally, the present invention includes a filter drain for highways formed from a trench filled with aggregate and wherein that aggregate includes at least a proportion of ground or shredded tyre pellets formed from used or reject vehicle tyres.

[0016] Typically, the upper portion of the drain arrangement is preferentially compacted.

[0017] Possibly, the removed aggregate is cleaned and returned to the drain arrangement.

[0018] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Fig. 1 is a schematic cross-section of a drain arrangement in accordance with the present invention;

Fig. 2 is a schematic plan view of a reinforcing mesh in accordance with the present invention; and,

Fig. 3 is a schematic plan view from underneath depicting aggregate filling associated with an aperture in a reinforcing mesh in accordance with the present invention.

[0019] Referring to Fig. 1 depicting a schematic cross-section of a drain arrangement 1 in accordance with the present invention. The drain arrangement 1 comprises a trench 2 within which there is an aggregate filling 3 such that rainwater presented in the direction of arrowheads A can soak away through the trench 2 into the ground 4 within which the trench 2 has been dug. Generally, this drain arrangement 1 is referred to as a filter drain and is used adjacent to the apron of a highway in order to allow soak away of rainwater from the highway. In short, the drain arrangement 1 provides a greater soakaway surface through the trench 2 walls and a volumetric capacity defined by the voids between aggregate stones of the aggregate filling 3 whereby standing water in the adjacent highway is eliminated.

[0020] In accordance with the present invention a reinforcing mesh 5 is located at a desired depth below the surface of the aggregate filling 3. The upper portion aggregate filling 3a may then be preferentially compacted or consolidated whereby that portion 3a of the aggregate filling 3 is forced into greater agglomeration by the preferential compaction or consolidation such that the portion 3a has a greater compression resistance compared to the aggregate filling 3. Aggregate is compacted if it is graded material of different sizes whilst it is consolidated where there is substantially a single size of aggregate component. Although there is preferential compaction of the portion 3a of the aggregate filling 3 it will be understood that there will still be voids between stones of the portion 3a of the aggregate filling 3 which constitute pathways for water soakway as described previously. In short, the preferential compaction of the portion 3a renders that portion 3a as having a higher compression load resistance than the aggregate filling 3 when normally loaded within the trench 2.

[0021] As described previously, a problem, with drain arrangements such as filter drains is that when a compression load such as that from a heavy goods vehicle which inadvertently strays onto the surface 6 causes ploughing of that aggregate filling 3 whereby the wheels of that vehicle become sunken or buried into the aggregate filling 3. Provision of the reinforcing mesh 5 in accordance with the present invention limits the depth of such ploughing or sinking whereby the vehicle can readily extradite itself from the drain arrangement 1. It will be understood that the reinforcing mesh 5 generally extends for a considerable distance in the longitudinal direction of the trench 2 such that the reinforcing mesh 5 is thereby substantially anchored by the weight of aggregate in the portion 3a of the aggregate filling 3 for that distance. In such circumstances, when a vehicle, even if it should displace the aggregate of the portion 3a, eventually impinges upon the reinforcing mesh 5, that mesh 5 due to its resilient nature prevents further ploughing and sinking of the wheels of the vehicle. In such circumstances, the vehicle can either extradite itself or there is a limit to the tilt of that vehicle determined by the depth d of the reinforcing mesh 5 within the trench 2. In terms of the vehicle expediting itself from the trench 2 it will be understood that passenger vehicles generally have smaller diameter wheels but a lower compression load weight such that the inclination angle for the vehicles wheels out of the trench 2 even when in direct contact with the reinforcing mesh will be such that it will normally be possible to drive or tow or manually push the vehicle from the trench 2 without slide ploughing further along that trench. Heavy goods vehicles present much larger compressive loads but have significantly greater diameter wheels such that the plough or sink depth to the reinforcing mesh will be a significantly lower proportion of the wheel diameter so that again extradition of the vehicle from the trench will normally be achievable by judicious driving or towing of the vehicle without slide ploughing of the aggregate due to the wheels being unable to climb the presented incline.

[0022] Essentially, it will be appreciated that the aggregate filling 3 is formed from a large number of stones or pebbles. These stones or pebbles when presented with a compression load can move relative to one another, that is to say shear, such that the aggregate filling has a "fluidity" which allows the ploughing described previously. In short, the pebbles are in compressive abutment but this compressive abutment is exceeded by the presented load such that there is shear slippage between the aggregate stones or pebbles. Provision of the reinforcing mesh 5 limits the depth of aggregate in the portion 3a that can be displaced. Furthermore, if that portion 3a is preferentially compressed then a hardened surface is provided to the drain arrangement 1 which is essentially prestressed and so more resistant to compressive loads applied to the surface 6.

[0023] Fig. 2 illustrates in schematic plan view a reinforcing mesh 25 in accordance with the present invention. The mesh 25 is essentially a perforated sheet of elastomeric material. Typically, this elastomeric material is a plastics material such as polyurethane or a similar geomaterial or textile. There are apertures 21 in the mesh 25. These apertures 21 allow drainage of water through them in order to facilitate the soakaway function of the drain arrangement. However, a reinforcing mesh 25 could be provided which rather than having an open aperture 23 structure includes regions of permeability through which water can soak away. It is the feature of the reinforcing mesh 25 inhibiting the depth of compressive load ploughing which is important in accordance with the present invention. Clearly, the apertures 21 may allow some keying between aggregate stones and pebbles which due to compression partially pass through the apertures 21. By such preferential compression of the aggregate through the apertures 21 there is a lateral grab or bunch compression of the aggregate stones and pebbles. The mesh 25 being made from an elastomeric material will allow radial expansion of the apertures 25 causing tension in the material from which the mesh 25 is formed. This tension causes an inward compression of the grabbed or bunched aggregate creating a bias or stress in the aggregate upwardly. Such pre-stressing of the aggregate (portion 3a in Fig. 1) upwards will further resist compressive loads applied to the surface 6 (Fig. 1) and diminish ploughing.

[0024] Fig. 3 illustrates an aperture 31 in a portion of a reinforcing mesh 35. As can be seen, aggregate from an aggregate filling 33 has been pushed towards the aperture 31 such that there is a grabbed compression pushing those individual aggregate stones and pebbles together radially inwards against the bias caused by tension expanding the aperture 33 through preferential compression. This radial compression and grab compaction of the aggregate stones in the filling 33 is inwardly in the direction of arrowheads b. The net effect of this compressive bias on the aggregate filling 33 is to pre-stress that aggregate so that there may be an upward bias direction and so further resistance to plough displacement of the aggregate stones and pebbles of the filling 33 under a compressive load.

[0025] In order to enhance this grab compression of the aggregate stones of the filling 33 the aperture 31 may include downwardly inclined lips to create a degree of lateral surface about the aperture 31 to engage the aggregate stones of the filling 33.

[0026] The apertures 31 in accordance with the present invention may be square or round or any shape determined necessary for performance.

[0027] In accordance with the present invention, stone displacement due to ploughing as described previously is resisted by the reinforcing mesh provided at a displaced depth below the upper surface of the aggregate filling. Typically, the aggregate has a size up to 40mm across its major dimension and so the reinforcing mesh will be designed to act with that aggregate in order to allow soak away in accordance with usual practice while resisting stone displacement as described. As indicated previously, the stone displacement causes a vehicle to sink into the aggregate filling and the aggregate is pushed into the side walls of the trench or out of the trench all together such that the aggregate can be dangerously scattered across an associated highway. Essentially, the aggregate cannot be compacted sufficiently through it's depth to provide adequate compression resistance to vehicle loads. In any event, it is still necessary to allow soak away through voids between the aggregate stones such that over compaction to achieve compression strength would result in detrimental limitation in soak away capacity. The reinforcing mesh in accordance with the present invention is of a type suitable for structural reinforcement. Known products which achieve the necessary performance criteria for the reinforcing mesh 5 are Tensar SSLA30 and Geogrid. A suitable grid composite is also described in International Patent Application No. PCT/US93/02278.

[0028] The reinforcing mesh is positioned typically at between 100mm to 300mm and preferably at a 125mm ± 50mm displacement from the upper surface of the aggregate filling. Clearly, the size of the aperture holes or interstices are determined to achieve necessary reinforcement as well as drainage therethrough for soakaway along with resistance to "fluid flow" or push through of the aggregate stones across the reinforcing mesh barrier.

[0029] Where desirable, more than one reinforcing mesh may be secured within the trench at differing displacements from the upper surface of the aggregate filling.

[0030] Side portions of the reinforcing mesh may be upturned as shown in Fig. 1 in order to cup the portion 3a of the aggregate filling for further anchoring and capture of that portion 3a for performance in accordance with the present invention. These side portions of the reinforcing mesh may include particular anchoring means to secure the reinforcing mesh 5 to the side walls of the trench 2. The side portions of the reinforcing mesh 5 may also incorporate apertures for drainage and therefore soakaway therethrough. Alternatively, side portions may be solid to again allow greater anchoring within the trench 2.

[0031] It will be understood that periodically the aggregate in the aggregate filling 3 must be cleaned. In such circumstances, the aggregate will be removed and any debris cleaned away. The aggregate will then be returned to the trench. Such cleaning is necessary in order to maintain the soakaway ability with the drain arrangement as debris would clog the voids between individual aggregate stones inhibiting such soakaway. The present reinforcement mesh 5 could be incorporated in such a cleaning procedure.

[0032] A typical installation of a drain arrangement 1 in accordance with the present invention would be to fill the trench 2 to a desired depth then locate the reinforcing mesh on top of that aggregate filling and subsequently apply the upper portion 3a of the aggregate filling. Alternatively, when cleaning the drain arrangement the upper portion 3a of the drain arrangement 1 will be removed and cleaned, a reinforcing mesh 5 located in the trench upon the remaining aggregate filling 3 and aggregate returned in order to recreate an upper portion 3a within the trench and therefore return the drain arrangement to its original surface level. As indicated previously, typically the reinforcing mesh 5 will be at a location of approximately 125mm ± 50mm below the surface 6. Where desirable, the upper portion 3a may be preferentially compacted against the reinforcing mesh 5 in order to achieve an enhanced compression strength for that portion 3a and therefore its resistance to compressive loads applied. Clearly an increased resistance to compression loads will limit the degree of sinking and ploughing due to a vehicle inadvertently riding upon the drain arrangement 1.

[0033] It will be appreciated that the aggregate used within the aggregate filling 3 will generally either be of a rounded or an angular type. The drain arrangement 1 may be constructed differently for rounded aggregate in comparison with angular aggregate.

[0034] With rounded aggregate generally two layers of reinforcing material will be installed in the drain arrangement. The first layer as indicated above will generally be at a depth of up to 200mm from the upper surface 6 possibly having the edges of that reinforcing material 5 upturned at the side of the drain. A volume of aggregate will then be introduced into the trench 2 such that at about half way between the first reinforcing mesh 5 and the eventual upper surface a further layer of reinforcing material will be provided. The second or further layer of reinforcing material will generally be flat and not have upturned side portions. The remainder of the aggregate to constitute the upper portion 3a will then be introduced. In such circumstances the drain arrangement will include respective reinforcing meshes at approximately 300mm from the surface 6 and approximately 150mm from the surface 6. The upper portion 3a will then be compacted as described previously in order to create preferential compactment of the upper portion 3a such that it is hardened and more resistant to compressive loads.

[0035] Where the aggregate is of an angular nature it will normally be possible through the greater aggregate to aggregate contact surfaces during compaction to provide an effective drain arrangement using only one layer of reinforcing mesh. This layer will generally be at approximately 125mm ± 50mm from the upper surface 6 or at such a depth deemed appropriate on site. As previously, the side or edge portions of the reinforcing material 5 may be upturned in order to cup the upper portion 3a as depicted in Fig. 1 for greater anchoring and reinforcement in accordance with the present invention. As previously, the upper portion 3a will generally be preferentially compacted in order to create a harder upper portion 3a with greater resistance to compressive loads and therefore reduced possibility for ploughing or aggregate displacement as described previously.

[0036] As indicated above the upper portion of the aggregate may be preferential compacted or consolidated to enhance compression strength. However, such compaction or consolidation may reduce drainage performance or simply may not be necessary so the upper portion of aggregate may be simply back filled without compaction or consolidation.

[0037] As an alternative to rock aggregate more recently it has been suggested that shredded or ground tyres from used, scrap or reject vehicle tyres could be used. This approach may limit the amount of such materials which are sent to land fill sites or for incineration. Typically, the tyres will be ground or shredded to a suitable pellet size which may be larger than traditionally prepared for land fill or incineration. The shredded tyre pellets will then be mixed with aggregate and used as a combination in the same manner as normal aggregate infill. Clearly, the relative proportion of rock aggregate to shredded tyre pellets will be dependent upon circumstances but will generally not exceed 50% shredded tyre pellets. Furthermore, there will normally be a similarity in nominal size between the rock aggregate used and the shredded tyre pellets or segments.

[0038] Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A drain arrangement for highways, the arrangement comprising a trench and aggregate filling to provide a soakaway path therethrough, the aggregate filling being associated with a reinforcing mesh, the reinforcing mesh extending substantially laterally across the trench at a desired depth below the aggregate filling surface so a portion of the aggregate filling above that reinforcing mesh provides greater compression strength under load.

2. An arrangement as claimed in claim 1 wherein the portion of aggregate filling above the reinforcing mesh is preferentially compacted.

3. An arrangement as claimed in claim 1 or claim 2 wherein the reinforcing mesh is a perforated elastomeric sheet.

4. An arrangement as claimed in any of claims 1 to 3 wherein the desired depth is between 100 and 300mm below the aggregate filling surface.

5. An arrangement as claimed in any preceding claim wherein two or more reinforcing mesh layers are provided.

6. An arrangement as claimed in claim 5 wherein such layers are substantially parallel and have a spacing such as 100mm and 200mm from the filling surface.

7. An arrangement as claimed in claim 6 wherein the reinforcing mesh includes apertures and these apertures have dimensions whereby an aggregate bunching bias is provided.

8. An arrangement as claimed in claim 7 wherein the aggregate bias is provided by the preferential compaction of the portion of the aggregate filling above the reinforcing mesh creating a bunch compression of aggregate into the apertures, that bunch compression causing lateral expansion of the aperture whereby when the preferential compaction of the portion of the aggregate filling is released the lateral expansion of the apertures creates an inward compression upon the aggregate held in the bunch compaction within the aperture and so creates an upward bias in the portion of the aggregate filling above the reinforcing mesh and so creates a degree of pre-stressing of that portion.

9. An arrangement as claimed in claim 8 wherein in order to enhance such bunch compression of the aggregate in contact with the reinforcing mesh in order to create pre-stressing of the portion of the aggregate filling above the reinforcing mesh, the apertures include lips for facilitating bunch compression.

10. An arrangement as claimed in any of claims 1 to 9 wherein the reinforcing mesh may be upturned at the trench side walls.

11. An arrangement as claimed in any preceding claim wherein the reinforcing mesh includes anchor means in order to stabilise presentation of the reinforcing mesh within the drain arrangement.

12. An arrangement as claimed in any preceding claim wherein possibly the aggregate fully includes a proportion of ground or shredded tyre pellets or granules formed from used or reject vehicle tyres.

13. A method of forming a drain arrangement comprising digging a trench, filling that trench with aggregate until an upper surface of that aggregate is at a desired level, placing a reinforcing mesh upon that surface and adding further aggregate whereby an upper surface of that aggregate is such that the reinforcing mesh is at a desired depth from that upper surface.

14. A method of renovating a drain arrangement comprising removing an upper portion of aggregate, placing a reinforcing mesh on the remaining aggregate and returning aggregate to an original drain surface level.

15. A drain for highways formed from a trench filled with aggregate and wherein that aggregate includes at least a proportion of ground or shredded tyre pellets formed from used or reject vehicle tyres.

16. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.

Drawing