Note: Descriptions are shown in the official language in which they were submitted.
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"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.
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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
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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
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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
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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
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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.
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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
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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
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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
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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.
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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
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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.
