Note: Descriptions are shown in the official language in which they were submitted.
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DRAINAGE SYSTEM AND METHOD 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
io known. They are used to replace natural grass
surfaces which do 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
20 backing mat with particulate material in-filled in
between the ribbons on the mat. The ribbons of
synthetic material usually extend 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
30 of multiple distinct courses of a particulate
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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 this
application. In Assignee's Canadian patent
application 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
io 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.
With certain infill materials, slow water evacuation
could cause the infill material to float off of the
surface, thereby creating an additional maintenance
cost issue.
For example, U. S. Patent 5,976,645, issued
to Daluise et al on November 2, 1999, discloses a
20 vertical drainage system for a rubber-filled synthetic
turf. The drainage 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
drainage passages are 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
30 on the particulate sizes and compact conditions of
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those layers. The porous geotextile membrane is used
only for separating those two different layers.
A multiple-layer net structure for fluid
drainage, particularly for geotechnical use, is well
known in the art. A triplanar 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
io 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 inclined with
respect to the horizontal plane, so as to allow the
20 drainage of any liquids to be eliminated from the
region in which the drainage nets are located.
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 for
providing a game playing surface is a dynamic system
continuously in movement under the influence of
bouncing balls, vibration, and impacts from the feet
30 and bodies of players in contact with the top surface
of the turf. The more rigid grids do not alleviate the
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resilience of the synthetic turf. Many efforts have
so far been made for improving such dynamic properties
of synthetic grass turf assemblies.
Another problem with regard to the use of
multiple layer nets 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
io 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.
Therefore, there exists a need for a more
efficient drainage system for a synthetic grass turf
assembly, which meets the dynamic requirements for a
20 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 assembly using a spacing device to provide
additional draining capacity to the system to
facilitate drainage.
30 It is a further object of the invention to
provide a synthetic grass turf assembly for
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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 surf ace .
It is also contemplated to use the drainage
system embodying drainage tiles. Such drainage tiles
are in the form of one-foot square, or more,
interlocking tiles 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 device 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 device may be an assembly of
interconnecting tiles preferably selected from
plastics materials, having a plurality of elongated
channels preferably parallel to each other, on at
least one surface of the tile as well as through
openings extending from one surface of the tile to the
other, in a manner such that water is enabled to flow
through the tile in a direction perpendicular to a
major plane defined by the tile, and also in another
direction from one edge of the tile to another edge
such that the water to be drained can flow throughout
the interconnected tile assembly. It is desirable to
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have the supporting substrate sloped to facilitate
drainage.
The spacing device may alternatively be a
grid preferably selected from geotextile materials,
having a plurality of elongated grid 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
io 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.
In one embodiment, it is desirable that the
support substrate has a non-porous and stable crushed
stone base directly under the spacing grid or tiles.
This stone is readily available and is lower in cost
than specially graded stone. This method would reduce
the cost of the substrate construction by allowing the
20 water to drain horizontally to the edges, thus
reducing the need for a more complicated and costlier
drainage system under the support substrate. This in
effect simulates the characteristics of having a non-
porous asphalt or concrete base. A geotextile fabric
or impermeable liner could be placed directly on the
stone base to prevent the water from percolating
through the stone base.
The latter drainage device is a grid type of
plastics material which preferably comprises a
30 plurality of longitudinal grid members in a base layer
to form the substantially horizontal drainage passages
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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
io flexibility, firmness, and resilience. white colour
is preferred to reduce heat absorption and, therefore,
to prevent or minimize deformation of the spacing grid
from the heat of the sun.
It may also be desirable to place a porous
aggYegate layer, preferably formed with selectively
sized crushed rocks, between the supporting substrate
and the spacing device so that water is enabled to be
drained through the spacing device into the porous
aggregate layer.
20 An additional advantage of using the spacing
device 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
especially in shorter pile infilled synthetic grasses.
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In accordance with another aspect of the present
invention, there is also provided, a synthetic grass turf
drainage system for installation on a supporting soil
substrate to provide an easily drained synthetic grass turf
surface, the drainage system comprising: a synthetic grass
turf assembly having a flexible and water permeable sheet
backing from which a plurality of upstanding synthetic
ribbons extend, the sheet backing defining an upper surface
and an under surface, an infill layer of particulate
material being disposed interstitially between the
upstanding ribbons on the upper surface of the sheet
backing; an impermeable membrane disposed on top of the soil
substrate; and a structurally self-supporting three-
dimensional spacing device having a top and a bottom surface
defining a spacing distance there between, said spacing
device being disposed between the impermeable membrane and
the synthetic grass turf assembly such that bottom surface
thereof abuts the impermeable membrane and the top surface
thereof abuts the under surface of the sheet backing, the
spacing device thereby elevating the sheet backing away from
the impermeable membrane on the soil substrate by said
spacing distance, the spacing device having draining
passages in both vertical and substantially horizontal
directions throughout said spacing distance such that
drainage in both vertical and substantially horizontal
directions is possible at any elevation between said sheet
backing and said impermeable membrane.
In accordance with yet another aspect of the present
invention, there is also provided, a method for providing a
=30 drainage system for a synthetic grass turf assembly
installed on a supporting soil substrate to provide a
synthetic grass turf surface, the turf assembly including at
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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 soil substrate in a slope; b)
placing an impermeable membrane on top of the supporting
soil substrate; c) placing a structurally self-supporting
and flexible three-dimensional spacing device on top of the
impermeable membrane, the spacing device having draining
passages in both vertical and substantially horizontal
directions throughout; and d) laying the turf assembly on
top of the spacing device without performing any further
preparation to the spacing device, the spacing device
defining a spacing distance between the impermeable member
and the sheet backing of the turf
assembly, the draining passages permitting draining in both
vertical and substantially horizontal directions at any
elevation within the spacing distance.
In accordance with yet another aspect of. the present
invention, there is also provided, a synthetic grass turf
assembly for installation on a supporting soil substrate to
provide a synthetic grass turf 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 comprising at least
one of hard and resilient granules, the infill including: i)
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a base course substantially exclusively of hard and
resilient granules disposed upon the upper surface of the
backing; ii) a top course substantially exclusively of
resilient granules disposed upon the base course extending
upwardly; and c) an impermeable membrane disposed on top of
the supporting soil substrate; d) a flexible, structurally
self-supporting three-dimensional spacing device elevating
an undersurface of the backing away from the impermeable
membrane and being disposed there between such that a
spacing distance between the impermeable membrane and the
undersurface is defined, the spacing device having draining
passages in both vertical and substantially horizontal
directions throughout the spacing distance such that water
drainage both vertically and substantially horizontally is
possible through the spacing device at any elevation between
the backing and the impermeable membrane.
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. la 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. lb is a cross-sectional view of an installed
synthetic grass turf assembly with a drainage system
according to an alternate embodiment of the invention;
Fig. 2 is a plan view of a spacing grid used in the
embodiment shown in Fig. la;
Fig. 3 is a plan view of a layer of drainage tiles;
Fig. 4 is a perspective view taken from the bottom of
another embodiment of a drainage tile;
Fig. 5 is a perspective view taken from the top of
still another embodiment of a drainage tile; and
Fig. 6 is a perspective view, taken from the side, of
the embodiment shown in Fig. 5.
With reference to Figs. la-lb, 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. la, the ribbons 16 are tufted through the backing 14
spaced apart in rows by a distance W and of a length L. The
length is selected depending upon the depth of
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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
when manufactured, or 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. Generally, thin fibers
cannot be easily top-dressed on 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 can cause 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.
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
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as sand, small rocks or other graded particulate
matter, and resilient granular, 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 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
a.o weight ratio greater than 2 to 1 of hard and resilient
granules respectively. The top course 24 is
substantially exclusively of resilient rubber
granules. It is noted that the inf ill can be all
rubber.
An upper portion 26 of the synthetic.ribbons
16 extends upwardly from a top surface 28 of the top
course 24. The resulting artificial turf surface can
be adapted for several indoor and outdoor uses, such
as athletic playing fields, horee racing, and
2o 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.
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
30 1-inch per 10 feet. The supporting soil substrate 12
is compacted to about 95t Proctor density, if
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possible, to form a firm and stable surface. Then a layer of
concrete or asphalt is placed on the compacted earth, in
order to ensure the grade and to provide an impervious
barrier to the water being drained. Instead of the concrete
or asphalt, a layer of non-porous stone may be provided
which is compacted to form a stone base 31. This stone base
may be relatively inexpensive, as it need not be graded. An
impermeable membrane 33 can then be placed on the stone base
31 to complete the water barrier, as seen in Fig. lb.
Preferably, the slope of the supporting substrate 12 is 0.5%
to about 1%, depending on the IDF rainfall curves for
specific areas from the field center line downwards to
opposed edges of the field in order to facilitate drainage.
Situated over the support substrate 12, in one
embodiment, 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 substrate 12.
The spacing grid 32, more clearly shown in Figs. la to
2, includes a plurality of longitudinal grid members 34
which are parallel to each other and form a base layer 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
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according to this 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 can be from 1/5 inch
(5.08 mm) to 1 inch (38.1 mm) in accordance with this
embodiment to provide an adequate draining space between the
backing 14 and the porous aggregate layer 30. The thickness
of the spacing device is inversely proportional to the
degree of slope of the field.
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 in which water is drained
toward the field edges.
The spacing grid 32 provides substantially horizontal
draining passages defined between adjacent longitudinal grid
members 34, as indicated by numeral 42 in Fig. la, 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 members extend from the
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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, installed outdoors 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
poly-propylene, may be placed immediately over the spacing
grid 32. In fact, the geotextile membrane could be attached
directly to the spacing grid 32 at the manufacturing plant.
The membrane could also be woven.
The geotextile membrane prevents sand or other infill
material from entering the interstices formed in the grid 32
which would tend to block the passages so formed in the grid
32. This, however, would reduce the function between the
grass surface and the geogrid and could cause movement of
the grass surface which may result in line deformation
unless the backing material has a non-slip characteristic
that does not allow the grass to slide on it.
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 preventing blocking of the drainage passages.
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Another preferred embodiment is illustrated
in Fig. 3. In this embodiment, the drainage device is
in the form of interconnecting tiles 50 made up of
individual tiles 52. The tiles 52 are generally
square but could be made up of various shapes. The
tiles 52 include intersecting grooves or channels 53
defining square lugs 54. The opposite surface of the
tile 52 would have similar channels 53 and lugs 54.
Through openings 55 extend from one surface to the
io other and provide drainage passages for the vertical
flow of the water, and communicate with the channels
53 in order to evacuate the water horizontally. The
interconnected tiles would normally sit on the support
substrate 12 and would be in direct contact with the
backing 14 in order to allow the water to pass through
the backing 14 and then along the channels 53, on the
top of the tiles 52, or through the openings 55 to
access the channels 53 on the bottom of tiles 50.
Fig. 4 shows another embodiment of the tile
20 152, in accordance with the present invention, having
a bottom surface 152a and a plurality of lugs 154
extending from the bottom surface 152a. The lugs 154
define channels 153 to provide the necessary drainage
from edge to edge. Through openings 155 are provided
to allow drainage perpendicular to the tile 152.
Nails 156 are provided for anchoring the tiles to the
support substrate 12.
In yet another embodiment, the tiles 252
shown in Figs. 5 and 6 show the through openings 255
30 as a pattern of openings defined by links 257. Lugs
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254 are provided on the bottom surface 252a to define
the channels 253.
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 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.
