CA2352934A1

CA2352934A1 - Drainage system for artificial grass using spacing grid

Info

Publication number: CA2352934A1
Application number: CA002352934A
Authority: CA
Inventors: Jean Prevost
Original assignee: Fieldturf Inc
Current assignee: Individual
Priority date: 2001-07-12
Filing date: 2001-07-12
Publication date: 2003-01-12

Abstract

A drainage system is provided for a synthetic grass turf assembly having a flexible and water permeable sheet backing for installation on a supporting soil substrate to provide a game playing surface. The draining system of the present invention prevents water from accumulating on the turf surface, which could cause the top-dressing layer to "float" and be moved by inundation.
The draining system of the present invention includes a spacing grid disposed between the backing of the turf and a porous aggregate layer over the supporting soil substrate.
The spacing grid is structured to permit water not only to be drained vertically through the spacing grid into the porous aggregate layer, but also to be drained horizontally through the spacing grid to the edges of the field when water is accumulated in the porous aggregate layer beneath the spacing grid and cannot be drained away promptly. The spacing grid is made from one or more types of geotextile or plastics material with an adequate flexibility to improve the impact absorption capabilities and resilience of the synthetic grass turf assembly.

Description

"DRAINAGE SYSTEM FOR ARTIFICIAL
GRASS USING SPACING GRID"
The invention relates to a synthetic grass turf to provide a game playing surface, and more particularly relates to a drainage system for a synthetic grass turf assembly for installation on a supporting substrate to provide a game playing surface.
Synthetic grass sport surfaces are well known.
They are used to replace natural grass surfaces which do ~o not stand up well to wear and which require a great deal of maintenance. Also, natural grass surfaces do not grow well in partly or fully enclosed sport stadiums. The synthetic grass surfaces stand up to wear much better than the natural grass surfaces, do not require as much maintenance, and can be used in closed stadiums. Some synthetic grass surfaces comprise rows of strips or ribbons of a synthetic material, extending vertically from a backing mat with particulate material in-filled in between the ribbons on the mat. The ribbons of synthetic material usually extend zo a short distance above the layer of particulate material and represent blades of grass.
In order to reduce the abrasive nature of the synthetic grass infills and stabilize the top surface of the infills to retain a resilient grass-like surface that does not deteriorate in quality, or compact over time through use, a unique infilled layer of multiple distinct courses of a particulate material, for example, is disclosed in U. S. Patent 5,958,527 which issued to Prevost on September 28, 1999 and was assigned to the Assignee of 3o this application. In Assignee's Canadian patent appli-cation No. 2,218,314, filed October 16, 1997 and published on September 10, 1998, the Assignee discloses a synthetic grass turf assembly.

When the synthetic grass turf assembly is installed on a sport field, however, an efficient drainage system under the grass turf assembly is needed because the water permeable backing cannot function well without a drainage system underneath to prevent water from accumulating on the turf surface, which could cause the top course of the infills to "float" and be moved by inundation.
For example, U. S. Patent 5,976,645, issued to ~o Daluise et al on November 2, 1999 discloses a vertically.
draining system for a rubber-filled synthetic turf. The draining system disclosed in this patent is deployed below a fabric backing layer of a synthetic turf and incorporates a porous geotextile membrane between an open graded aggregate layer and a sand layer above the aggregate layer to prevent the movement of one aggregate layer into the other. The draining passages generally formed with the 2 inch thick porous layer of sand and the 6 inch thick layer of sand and stone mixture. The draining rate depends on 2o the particulate sizes and compact conditions of those layers. The porous geotextile membrane is used only for separating those two different layers and does not facilitate drainage because the porous geotextile membrane generally is a two-dimensional sheet made of needle punched polypropylene. As a matter of fact, the small holes in the geotextile membrane get filled with sand particles and thus the use of the geotextile membrane does not provide any additional draining space to the draining system.
A multiple-layer net structure for fluid 3o drainage, particularly for geotechnical use, is well known in the art. A triplannar net, described in U. S. Patent 5,255,998, which issued to Beretta on October 26, 1993, for example, includes a first layer of mutually parallel wires which is rigidly associated with a second or intermediate layer of substantially mutually parallel wires, which are inclined with respect to the wires of the first layer. A
third layer of wires is rigidly associated with the intermediate layer, on the opposite side thereof with respect to the first layer, and has substantially mutually parallel wires which are inclined with respect to the wires of the second or intermediate layer. In general and geotechnical use, such multiple-layer nets are buried and to inclined with respect to the horizontal plane, so as to allow the drainage of any liquids to be eliminated from the region in which the drainage nets are located collecting them in another region.
However, those multiple layer nets have not been suggested to be used in a drainage system for a synthetic grass turf assembly. Unlike other environments in which the multiple layer nets are used for drainage, a synthetic grass turf assembly to provide a game playing surface is a dynamic system continuously in movement under the influence zo of bouncing balls, vibration and impacts from the feet and bodies of players in contact with the top surface of the turf. The multiple layer nets conventionally used for geotechnical use generally are quite rigid and lack adequate resilience to meet the dynamic requirements for the resilience and impact absorption capabilities of a synthetic grass turf . Many efforts have so far been made for improving such dynamic properties of synthetic grass turf assemblies, and negative effects resulted from inadequate use of the multiple layer nets are not so acceptable.
Another problem with regard to the use of multiple layer net in synthetic grass turf assembly is deformation resulting from radiant heat from the sun. A

deformed multiple layer net not only statically affects the formation of a planar game playing surface but also jeopardizes the dynamic property thereof. For instance, the synthetic grass surface weight with an infill will not always correct the deformations caused by the curling of the edges of the net caused by absorbing heat from the sun.
The net itself can form undulations by heat absorption both prior to and after the installation of the artificial grass system.
~o Therefore, there exists a need for a more efficient drainage system for a synthetic grass turf assembly, which meets the dynamic requirements for a game playing surface.
It is one object of the invention to provide a drainage system for a synthetic grass turf assembly for installation on a supporting substrate to provide a game playing surface.
It is another object of the invention to provide an improved drainage system for a synthetic grass turf zo assembly using a spacing grid to provide additional draining capacity to the system to facilitate drainage.
It is a further object of the invention to provide a synthetic grass turf assembly for installation on a supporting substrate to provide a game playing surface, which includes an efficient drainage system to prevent water from accumulating on the turf surface.
It is also contemplated to use the drainage system in combination with drainage tiles. Such drainage tiles are in the form of one foot square interlocking tiles 30 of molded plastic with vertical through openings.
A drainage system for a synthetic grass turf assembly having a flexible and water permeable sheet backing for installation on a supporting substrate to provide a game playing surface generally comprises a flexible, three-dimensional spacing grid positioned between the backing and the supporting substrate, supporting the undersurface of the backing and having the backing spaced apart from the supporting substrate to form draining passages in both vertical and substantially horizontal directions.
The spacing grid is preferably selected from geotextile materials, having a plurality of elongated grid to members preferably parallel to each other, bonded with link elements in a manner such that water is enabled to flow through the grid in a direction perpendicular to a major plane defined by the grid, and also in another direction from one edge of the grid to an opposite edge. It is desirable to have the supporting substrate sloped downwardly from a field centerline to two opposed edges to facilitate drainage. It is also desirable to place a porous aggregate layer, preferably formed with selectively sized crushed rocks between the supporting substrate and 2o the spacing grid so that water is enabled to be drained through the spacing grid into the porous aggregate layer.
Woven and non-woven geotextiles are well known in the industry. They provide drainage, filtration, reinforcement, protection and separation of soils in construction and civil engineering markets. However, most types of geotextiles are generally two-dimensional and are not suitable for use in the drainage system according to the present invention. The drainage device used in the present invention is a grid type of plastics material which 3o preferably comprises a plurality of longitudinal grid members in a base layer to form the substantially horizontal drainage passages therebetween when the grid is positioned between the backing and the supporting substrate. A plurality of link elements in two outer layers associated with two opposite sides of the base layer bond the grid members in position to form the grid without blocking either the vertical draining passages or the substantially horizontal draining passages. The spacing grid is preferably made of an extruded triplanar plastic structure having adequate properties in regard to flexibility, firmness and resilience. V~Ihite colour is preferred to reduce heat absorption and, therefore, to to prevent or minimize deformation of the spacing grid.
The use of this drainage device as a spacing grid in the drainage system is adapted to significantly increase the draining capacity. The thickness of the crushed rock layer placed over the supporting substrate which conventionally provides drainage passages can be reduced because the spacing grid not only provides vertical draining passages from the synthetic grass turf assembly to the layer of crushed rocks on the supporting substrate but also enables substantially horizontal drainage through the 2o space provided between the backing of the turf assembly and the layer of crushed rocks when water is accumulated in the layer of crushed rocks and does not drain promptly.
An additional advantage of using the spacing grid relates to the property of the adequate combination of resilience and firmness of the material. The resilience yet firmness of the spacing grid will further improve the impact absorption capability of the synthetic grass turf assembly which is an important property of a game playing surface .
3o Other features and advantages will be better understood with reference to a preferred embodiment described below.

-Having thus generally described the nature of the invention, reference is now given to drawings by way of examples only illustrating a preferred embodiment in which:
Fig. 1 is a cross-sectional view of an installed synthetic grass turf assembly with a drainage system according to a preferred embodiment of the invention;
Fig. 2 is a plan view of a spacing grid used in the embodiment shown in Fig. 1; and Fig. 3 is a plan view of a layer of drainage ~o tiles.
With reference to Fig. 1, a synthetic grass turf assembly generally indicated at numeral 10 is installed on a supporting soil substrate to provide a game playing surface. The synthetic grass turf assembly 10 has a pile fabric including a flexible sheet backing 14 that in the embodiment shown is a two-ply open weave fabric. Extending upwardly from an upper surface of the backing 14 is a large number of upstanding synthetic ribbons 16. As indicated in Fig. 1, the ribbons 16 are tufted through the backing 14 zo spaced apart in rows by a distance W and of a length L.
The length is selected depending upon the depth of an infill 18 and the desired resilience of the completed synthetic grass turf assembly.
The ribbons 16 may include a mixture of multiple fibers and the single ribbons fibrillated on site or left in their original state. The on-site fibrillation can be done by passing over the turf surface with a wire brush, for example, or other brushing means after installation of the infill 18. Thin fibers cannot be easily top-dressed on 3o site since they are more fragile and fall more easily than thicker fibers, especially in high heat environments. The mix of thick and thin fibers on the ribbons causes a ball to roll in a more predictable manner depending on the resistance of the fibers to the moving ball. Modification of the ribbon width and density in the turf will also modify the ball-rolling characteristics.
The ribbons 16 are made from suitable synthetic plastic material which is extruded in a strip that is relatively wide and thin. The details of the synthetic ribbons 16 and the porous sheet backing 14 as well as the method for attaching the ribbons 16 to the sheet backing 14 are described in Canadian Patent Application 2,218,314 ~o which is incorporated herein by reference.
Deposited interstitially between the upstanding ribbons 16 upon the upper surface of the backing 14 is the infill layer 18 of particulate matter. The particulate matter may be selected from any number of commonly available hard granules, such as sand, small rocks or other graded particulate matter, and resilient granulars, such as crumb rubber.
The infill layer 18 is made up of a base course 20, a middle course 22 and a top course 24. The base zo course 20 is substantially exclusively of hard sand granules disposed immediately upon the top surface of the backing 14. The middle course 22 is of intermixed hard sand granules and resilient rubber granules. The mix is selected on the basis of a weight ratio greater than 2 to 1 of hard and resilient granules respectively. The top course 24 is substantially exclusively of resilient rubber granules.
An upper portion 26 of the synthetic ribbons 16 extends upwardly from a top surface 28 of the top course 30 24. The resulting artificial turf surface can be adapted for several indoor and outdoor uses, such as athletic playing fields, horse racing and recreational areas. The detailed characteristics of the infill layer 18 and the selection, in particular, of the particulate sizes and unit weights of the respective courses are described in U. S.
Patent 5,958,527 which is incorporated herein by reference.
The supporting soil substrate 12 is formed, for example, by removing turf, loam, etc., and grading and compacting the earth. Excavation of materials is necessary to establish a proper grade of the supporting soil substrate 12 to a tolerance of about 1 inch per 10 feet.
Preferably the slope of the supporting soil substrate 12 is to 0.5~ to about 1~ from the field center line downwards to opposed edges of the field in order to facilitate drainage, and the supporting soil substrate 12 is compacted to about 95°s Proctor density, if possible, to form a firm and stable surface. A porous aggregate layer 30 is disposed over the supporting soil substrate 12. Preferably the porous aggregate 30 is comprised of free-draining stone, such as crushed rock or graded sand. It is also preferable to install the aggregate so as to maintain a finished grade slope of 0.5~ or greater toward the edges of the field.
2o Situated over the entire graded porous aggregate layer 30 is a spacing grid 32, preferably made of extruded triplanar polypropylene or polyethylene material. The spacing grid 32 directly supports the undersurface of the backing 14, and as a result, the backing 14 is spaced apart from the supporting soil substrate 12 and the porous aggregate layer 30.
The spacing grid 32, more clearly shown in Figs.
2 and 3, includes a plurality of longitudinal grid members 34 which are parallel to each other and form a base layer 30 of the grid, and a plurality of link elements 36 at one side and link members 38 at the other side of the spacing grid 32 which form two respective outer layers of the grid to bond the longitudinal grid members 34 in position. The link elements 36 and 38 are elongated and extend diagonally with respect to the longitudinal grid members 34 according to this preferred embodiment of the invention. The diagonal directions of the respective link elements 36 and 38 at the opposite sides of the spacing grid are angularly crossed, preferably perpendicular to each other, as shown in Fig. 2. The spacing grid has a thickness that is 1/ inch in accordance with this embodiment to provide an adequate draining space between the backing 14 and the porous ~o aggregate layer 30.
The spacing grid 32 with such a structure provides a plurality of draining apertures 40 defined by the longitudinal grid members 34 and the diagonal link elements 36 and 38 to permit water drained vertically from the grass turf through the spacing grid 32 into the porous aggregate layer 30 in which water is drained toward the field edges.
The spacing grid 32 further provides substantially horizontal draining passages defined between 2o adjacent longitudinal grid members 34, as indicated by numeral 42 in Fig. l, which permits water to flow freely along the passage 42, horizontally through the spacing grid 32 when water is accumulated in the porous aggregate layer 30 and is enabled to be drained promptly through the layer 30. For this purpose, the thickness of the base layer formed by the grid members 34 should be much greater than the thickness of the outer layers formed by the link elements 36 and 38. The spacing grid 32 is preferably positioned in a direction such that the longitudinal grid 3o members extend from the field center line to the opposed edges, aligning with the slope direction of the supporting soil substrate to achieve the best drainage result.

The spacing grid 32 is preferably manufactured in a light colour such as white because a dark coloured plastic spacing grid absorbs more heat energy which results in deformation thereof.
In high rainfall areas, a geotextile, that is, a non-woven porous membrane made of needle-punch polypropylene, may be placed immediately underneath the spacing grid 32. In fact, the geotextile membrane could be attached directly to the spacing grid 32 at the ~o manufacturing plant.
The geotextile membrane prevents sand or other infill material from entering the interstices formed in the aggregate layer which would tend to block the passages so formed in the aggregate layer 30.
In a preferred embodiment, the backing 14 is made in accordance with Canadian patent application 2,218,314 and U. S. Patent 5,958,927. This backing prevents the infill from passing through the backing into the spacing grid 32, thereby blocking the drainage passages. If the 2o present invention is utilized with an artificial turf assembly having a different backing sheet, it may be necessary to provide a geotextile membrane between the spacing grid 32 and the sheet backing 14 in order to prevent the infill material from moving into the grid 32.
This, however, would reduce the function between the grass surface and the geo-grid and could cause movement of the grass surface which may result in line deformation.
Fig. 3 shows a layer 50 of tiles, such as drainage tiles 52, that can also be used in combination 3o with the spacing grid 32. The tiles 52 are typically square, interlocking tiles made of molded plastics material with spaced-apart openings 54 defined therein. The layer 50 of tiles 52 can be placed between the spacing grid 32 and the backing 14. The tiles 52 with the openings 54 create a further drainage in the vertical direction.
Although the above description and accompanying drawings relate to a specific preferred embodiment as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described and illustrated. Modifications and improvements to the above-described embodiment of the invention may ~o become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the invention is intended to be limited solely by the scope of the appended claims.

Claims

1. ~A drainage system for a synthetic grass turf assembly having a flexible and water permeable sheet backing for installation on a supporting substrate to provide a game playing surface, the drainage system comprising:
a flexible three-dimensional spacing grid positioned between the backing and the supporting substrate, supporting an undersurface of the backing and having the backing spaced apart from the supporting substrate to form draining passages in both vertical and substantially horizontal directions.

2. ~A drainage system as claimed in claim 1, wherein the grid comprises a plurality of longitudinal grid members to form the substantially horizontal drainage passages therebetween when the grid is positioned between the backing and the supporting substrate.

3. ~A drainage system as claimed in claim 2, wherein the spacing grid comprises a plurality of link elements to bond the grid members in position to form the grid without blocking either the vertical draining passages or the substantially horizontal draining passages.

4. ~A drainage system as claimed in claim 3, wherein the grid members form a base layer and the link elements form two outer layers associated with two opposite sides respectively.

5. ~A drainage system as claimed in claim 4, wherein the spacing grid is made from a firm yet resilient plastic.

6. ~A drainage system as claimed in claim 1, wherein the supporting substrate is sloped downwards from a field centerline to two opposed edges of the game playing surface to facilitate drainage.

7. ~A drainage system as claimed in claim 6, wherein the grid is positioned so that the elongated grid members extend in a direction from the field centerline to either one of the opposed edges.

8. ~A drainage system as claimed in claim 1, further comprising a porous aggregate layer between the supporting substrate and the spacing grid.

9. ~A drainage system as claimed in claim 8, wherein the porous aggregate layer is selected from crushed rock, graded sand, lava rock, and rubber granules.

10. ~A method for providing a drainage system for a synthetic grass turf assembly installed on a supporting substrate to provide a game playing surface, the turf assembly including at least a plurality of upstanding synthetic ribbons of selected length, representing grass blades, extending upwardly from an upper surface of a flexible and water permeable sheet backing, the method comprising the steps of:
a) preparing the supporting substrate in a slope extending downwards from a field centerline to two opposed edges of the game playing surface; and b) placing a flexible three-dimensional spacing grid between the supporting substrate and the backing to form draining passages in both vertical and substantially horizontal directions.

11. ~A method as claimed in claim 10, wherein the spacing grid is selected from plastic materials, having a plurality of elongated grid members bonded with link elements in a manner such that water is enabled to flow through the grid in a direction perpendicular to a major plane defined by the grid and also in another direction from one edge of the grid to an opposite edge.

12. ~A method as claimed in claim 10, further comprising a step of placing a porous aggregate layer between the supporting substrate and the spacing grid so that water is enabled to be drained through the spacing grid into the porous aggregate layer.

13. ~A method as claimed in claim 12, wherein the porous layer is selected from sized crushed rocks, graded sand, and rubber.

14. ~A synthetic grass turf assembly for installation on a supporting substrate to provide a game playing surface, the turf assembly comprising:
a) a pile fabric with a flexible and water permeable sheet backing and a plurality of upstanding synthetic ribbons of selected length, representing grass blades, extending upwardly from an upper surface of the backing;
b) an infill layer of particulate material disposed interstitially between the upstanding ribbons upon the upper surface of the backing and of a depth less than the length of the ribbons, the particulate material selected from the group consisting of hard and resilient granules, the infill including:
i) a base course substantially exclusively of hard granules disposed upon the upper surface of the backing;
ii) a middle course of intermixed hard and resilient granules of a selected relative weight ratio, disposed upon the base course; and a top course substantially exclusively of resilient granules disposed upon the middle course, an upper portion of the synthetic ribbons extending upwardly from a top surface of the top course; and c) a flexible, resilient, three-dimensional spacing grid positioned over the supporting substrate, supporting the backing spaced apart from the substrate to form draining passages adapted to drain water from the turf assembly both vertically and substantially horizontally through the spacing grid.

15. A synthetic grass turf assembly as claimed in claim 14, further comprising a porous aggregate layer between the supporting substrate and the spacing grid to facilitate the vertical drainage through the spacing grid.

16. A synthetic grass turf assembly as claimed in claim 15, wherein the porous layer comprises selectively sized crushed rocks, graded sand, and rubber granules.

17. A synthetic grass turf assembly as claimed in claim 14, wherein the supporting substrate is sloped downwardly from a field centerline to opposed edges of the game playing surface.

18. A synthetic grass turf assembly as claimed in claim 14, wherein the spacing grid comprises:
a first layer of cords arranged substantially parallel to each other and defining a plane;
a second layer of cords arranged substantially parallel to each other and superimposed on the first layer of cords parallel to the plane, the second layer of cords being inclined with respect to the first layer of cords, and connected thereto at a plurality of intersection rods;
and a third layer of cords arranged substantially parallel to each other and superimposed on the second layer of cords, the third layer of cords being inclined with respect to the pespective first and second layers of cords and connected at a plurality of intersection nodes.

19. A synthetic grass turf assembly as defined in claim 14, wherein a layer of spacing tiles having drainage apertures extending in the vertical direction is provided between the spacing grid and the backing in order to increase the vertical component for the drainage.