U.S. patent application number 13/231688 was filed with the patent office on 2012-03-15 for wind-resistant environmental synthetic cover.
Invention is credited to Michael AYERS, Jose URRUTIA.
Application Number | 20120064263 13/231688 |
Document ID | / |
Family ID | 44654522 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120064263 |
Kind Code |
A1 |
AYERS; Michael ; et
al. |
March 15, 2012 |
WIND-RESISTANT ENVIRONMENTAL SYNTHETIC COVER
Abstract
A system for covering (i.e., closing) various types of sites
where waste is deposited comprises a composite of one or more
geotextiles that are tufted with synthetic yarns and an impermeable
geomembrane, which is comprised of a polymeric material. The cover
can include wind-resistant textured synthetic blade-like elements,
such as vertical filaments, secured over a low-permeable polymer
liner backing. Advantageously, the system does not rely on piled-on
weight to resist wind forces and the cover can be deployed over a
large area with little or no ballasting or anchoring. Optionally,
the cover includes vertical filaments attached to the liner to
break the wind aero-dynamics on the exposed cover.
Inventors: |
AYERS; Michael; (Alpharetta,
GA) ; URRUTIA; Jose; (Suwanee, GA) |
Family ID: |
44654522 |
Appl. No.: |
13/231688 |
Filed: |
September 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61382322 |
Sep 13, 2010 |
|
|
|
Current U.S.
Class: |
428/17 ; 428/221;
428/92; 428/95 |
Current CPC
Class: |
B09B 1/004 20130101;
Y10T 428/2395 20150401; Y10T 428/23957 20150401; D06N 2201/0254
20130101; Y10T 428/249921 20150401; Y10T 428/23979 20150401; D06N
7/0092 20130101; D06N 2209/103 20130101; Y02W 30/30 20150501 |
Class at
Publication: |
428/17 ; 428/95;
428/92; 428/221 |
International
Class: |
D05C 17/02 20060101
D05C017/02; E01C 13/08 20060101 E01C013/08; E02D 17/20 20060101
E02D017/20; A41G 1/00 20060101 A41G001/00 |
Claims
1. A wind-resistant synthetic cover system for landfills,
stockpiles, soil erosion protection, dry ponds, phosphogypsum
stacks, environmentally impacted lands, leach pads, ash fills, and
similar environmental sites or material stockpiles that require a
water-resistant closure system or a plastic rain barrier, wherein
the wind-resistant synthetic cover system comprises: a composite of
a geomembrane covered with a synthetic turf-like cover with
upstanding synthetic slender elongate elements selected to have
reacting forces when exposed to wind, so that uplift of the
wind-resistant synthetic cover system is prevented when wind loads
are applied.
2. A wind-resistant synthetic cover system as claimed in claim 1
wherein the synthetic slender elongate elements comprise
polyethylene or polypropylene fibers.
3. A wind-resistant synthetic cover system as claimed in claim 1
wherein the synthetic slender elongate elements comprise
monofilament fibers or slit film.
4. A wind-resistant synthetic cover system as claimed in claim 1
wherein the synthetic slender elongate elements are formed to have
a blade length ranging between 0.5 inches and 4 inches.
5. A wind-resistant synthetic cover system as claimed in claim 1
wherein the synthetic slender elongate elements are tufted to have
a density of between about 15 ounces/square yard and about 120
ounces/square yard.
6. A wind-resistant synthetic cover system as claimed in claim 1
wherein the synthetic slender elongate elements comprise blade-like
elements having the appearance of blades of grass.
7. A wind-resistant synthetic cover system as claimed in claim 1
wherein the cover is adapted to resist wind uplift by the weight of
the material itself without the need for subterranean anchoring
and/or ballast system or the conventional sand in-fill.
8. A wind-resistant synthetic cover system of claim 1 wherein the
geomembrane is selected from the group consisting of high density
polyethylene, linear low density polyethylene or polyvinyl
chloride.
9. A wind-resistant synthetic cover system of claim 1 wherein the
geomembrane is sprayed or applied directly on the geotextile(s)
backing of the cover.
10. A wind-resistant synthetic cover system of claim 1 wherein the
synthetic turf-like cover comprises UV-resistant material.
11. The wind-resistant synthetic cover system of claim 1 wherein
the flexible synthetic upstanding slender elongate elements
comprise vertical filaments attached to a geotextile(s) backing to
create wind aero-dynamic conditions that prevent uplift of the
exposed cover and impermeable geomembrane below.
12. An exposed cover system for landfills, stockpiles, dry ponds
and/or general raincoat covers for ore materials, wherein the cover
system comprises: a composite of a geomembrane covered with
synthetic cover selected of sufficient weight that when exposed to
wind, unwanted uplift of the cover system is prevented, even when
wind loads are applied, without the use of subterranean anchoring
or ballasting system and wherein the weight of the material itself
provides the primary resistance to uplifting due to wind.
13. The exposed cover system of claim 12 further comprising
flexible synthetic upstanding slender elongate elements comprise
vertical filaments attached to a geotextile(s) backing to create
wind aero-dynamic conditions that prevent uplift of the exposed
cover and impermeable geomembrane below.
14. The exposed cover system of claim 12 further comprising
flexible synthetic upstanding slender elongate elements creating a
synthetic turf-like upper portion selected to have reacting forces
when exposed to wind, so that uplift of the wind-resistant
synthetic cover system is prevented when wind loads are
applied.
15. The exposed cover system of claim 13 wherein the synthetic
slender elongate elements comprise monofilament fibers or slit
film.
16. The exposed cover system of claim 13 wherein the synthetic
slender elongate elements are formed to have a blade length ranging
between 0.5 inches and 4 inches.
17. The exposed cover system of claim 13 wherein the synthetic
slender elongate elements comprise blade-like elements having the
appearance of blades of grass.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of U.S.
Provisional Patent Application Ser. No. 61/382,322, filed Sep. 13,
2010, which is hereby incorporated herein by reference.
BACKGROUND
[0002] Environmental covers (or caps) are used to covers landfills,
mines, stockpiles and other waste materials to minimize rain
infiltration that can contaminate the groundwater table below.
These covers often use synthetic liner materials that are typically
covered with two feet of soil that can support natural vegetation.
Some of these environmental caps are described in the United States
Environmental Protection Agency (40 CFR Sub. D) environmental
regulations.
[0003] The prescribed covers required by the United States
Environmental Protection Agency typically use a two foot soil layer
to cover the impermeable geosynthetic layers below. This soil layer
can erode easily under major storm events and can be very difficult
to maintain, particularly on the steep slopes of landfills and mine
stockpiles.
[0004] Environmental covers are also used with geosynthetic liner
materials that are not covered with soil. In this case the
impermeable geomembrane is exposed to the environment. However this
type of exposed geosynthetic cover requires extensive anchoring and
or ballasting to protect the cover against wind uplift in the
presence of strong winds. The anchoring system can be very
extensive resulting in large construction costs. Commonly, exposed
covers require the cover to be held down by the use of ropes and
tires (ballast) spaced a few feet apart and/or numerous anchor
trenches across the slope where ballast material can be placed atop
the cover in the anchor trenches to protect the liners against the
wind uplift. In other applications sand tubes are used to ballast
the geosynthetic liner/synthetic cover against the wind. The
exposed geosynthetic liner material also weathers more rapidly as a
result of lack of a protective cover.
[0005] Exposed impermeable geomembranes have been used for the
closures of landfills and various man made stockpiles. However,
such covers with an exposed membrane generally have negative
aesthetics and require extensive anchoring or ballasting.
[0006] Artificial grass or synthetic grass has been extensively
used in sports arenas as well as airport runways and general
landscaping. However, a primary consideration of artificial turf
fields is the ability of the field to drain moisture therethrough,
such as to keep the athletic field playable by avoiding puddling.
In environmental covers, the opposite is desired. In environmental
covers, it is desired that moisture not drain through the cover and
environmental covers generally require the use of an impermeable
surface to avoid rainfall infiltration through the cover and into
the soil below.
[0007] The prior art ballasting techniques are expensive, often
impractical and their effectiveness is typically limited to winds
below about 40 mph. Additionally, this type of cover only last a
few years due to damage from wind. Accordingly, it can be seen that
there exists a need for a wind-resistant liner that doesn't require
the expense and trouble of ballasts. It is to the provision of
solutions to this and other problems that the present invention is
primarily directed.
SUMMARY OF THE INVENTION
[0008] Briefly described, the present invention provides a new and
useful system for covering (i.e., closing) various types of sites
where waste is deposited. In general, the cover system of this
invention comprises a composite of one or more geotextiles that are
tufted with synthetic yarns and an impermeable geomembrane, which
is comprised of a polymeric material. Optionally, the geotextiles
can comprise polypropylene or polyethylene.
[0009] In one preferred form the present invention comprises a
wind-resistant cover, including textured synthetic slender elongate
elements, such as vertical filaments, secured over a low-permeable
polymer liner backing. Advantageously, the system does not rely on
piled-on weight to resist wind forces and optionally the cover of
the present invention can be deployed over a large area with little
or no ballasting or anchoring. This new cover breaks up the airflow
over the cover, providing wind uplift resistance.
[0010] Optionally, the cover includes vertical filaments attached
to the liner to break the wind aero-dynamics on the exposed cover.
With this system, it is believed that the wind velocity on the
impermeable surface (membrane) now becomes turbulent near the
surface of the cover, thus greatly reducing the actual wind
velocity at the liner surface and decreasing associated uplift.
[0011] The reaction of the slender elongate elements to the wind
forces may also create a downward force on the membrane. This
reaction may be caused by the filaments applying an opposing force
against the wind which is transferred as a downward force on the
membrane. The use of vertical slender elongate elements amounts to
a radical departure from the typical exposed membranes or liners.
Optional examples of slender elongate elements contemplated as
encompassed by the present invention or in conjunction therewith
include structures that resemble blades of grass, rods, filaments,
tufts, follicle-like elements, fibers, narrow cone-shaped elements,
etc.
[0012] Advantageously, the wind-resistant cover in this invention
can create a larger distance from the material surface to the "free
stream" (free stream occurs where the wind flow is unaffected by
the material). The cover breaks up the flow stream, increasing the
boundary layer (distance from surface to free stream) to the point
where uplift forces are very small. This is in stark contrast to a
prior art cover with an exposed membrane, where there is a
minuscule distance to the uninterrupted free-stream air flow. This
small boundary means that there is a large velocity differential
over a very short distance creating much higher uplift.
[0013] The positive/downward force is a result of a reaction of the
synthetic cover, with the individual blades acting as spring
pushing against the wind. This reaction and opposing force will
vary based on the type of cover and the length of the synthetic
blade of grass. The blade will be shorter or longer depending on
the wind design flow for the disruption provided by the synthetic
cover of this invention.
[0014] The synthetic cover portion of this environmental closure
also acts as a protective layer providing protection from physical
damage and weathering to the geomembrane liner below. Thus, the
present invention can extend the longevity of the geomembrane
component over a much longer period of time in comparison with the
conventional exposed geomembrane covers.
[0015] This invention, in a preferred form, uses a lower
geomembrane with roughened or structural components to increase the
friction resistance against the lower soil and interface friction
between the cover and the geomembrane. Preferably, the angle of
friction can be higher than 18 degrees.
[0016] Alternatively, the liner can also be affixed to the cover by
spraying polypropylene or polyethylene to the back of tufted or
knitted geotextile(s).
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0017] FIG. 1 is a schematic view of prior art environmental cover
as per the United States Environmental Protection Agency where the
anchoring of the impermeable geosynthetic membrane consists of a
two foot soil cover.
[0018] FIG. 2 is a schematic view of a second prior art
environmental cover with exposed geomembranes that require
extensive anchoring to resist wind uplift.
[0019] FIG. 2.1 depicts prior art arrangements and in general shows
a cross sectional view of anchor trenches used along the slope of
an exposed geomembrane cover to secure it in place in the face of
wind which would otherwise tend to lift the cover.
[0020] FIGS. 2A, 2B, 3, 3.1, 4, and 5 consist of schematic views of
a wind-resistant environmental cover/liner according to a first
preferred form of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EXAMPLE EMBODIMENTS
[0021] FIG. 1 depicts a cross sectional view of a typical cover
system as described in current United States Environmental
Protection Agency federal regulations and as used in the covers for
landfills and mines. In this case the two feet of soil is used to
cover the geomembrane against wind uplift.
[0022] FIG. 2 depicts a prior art cover where the geomembrane is
exposed to the environment. The system requires extensive anchoring
in order to resist wind uplift forces.
[0023] FIG. 2.1 depicts prior art covers of exposed geomembrane
arrangements and in general shows a cross sectional view of anchor
trenches (30) used along the slope of an exposed geomembrane cover
to secure it in place in the face of wind which would otherwise
tend to lift the cover. The figure shows the geomembrane/raincoat
cover (12), and the use of tires (20) tied with ropes as additional
ballasting system of the exposed geomembrane (12). This type of
prior art anchoring required to resist uplift is very expensive and
it is not aesthetically pleasant.
[0024] FIG. 2A and 2B schematically depict the current invention
with an exposed geomembrane or raincoat liner (102) covered with
synthetic strands (103) that resemble grass with a pile height
ranging from about 3/4 inch to 2 inches depending on wind design
velocities. The strands (103) tend to break the laminar flow of the
wind and also provide normal pressure on the geomembrane liner
system when the strands bend onto the liner, creating normal
pressure. Preferably, the pile height is 3/4 inch to 2 inches or
so. More preferably, the pile height is about 1 inch to 1-1/2
inches.
[0025] Preferably, the synthetic strands (103) are slender elongate
elements. As used herein, "slender" indicates a length that is much
greater than its transverse dimension(s). Examples of slender
elongate elements contemplated as encompassed by the present
invention or in conjunction therewith are structures that resemble
blades of grass, rods, filaments, tufts, follicle-like elements,
fibers, narrow cone-shaped elements, etc. The synthetic strands
extend upwardly from a base and form a mat or field of such
strands. Such can simulate a field of grass, pine straw or similar.
Moreover, while the invention will be described below in connection
with blade-like elements (grass blade-like, not necessarily like
cutting blades) as an example embodiment, those skilled in the art
will readily appreciate that the invention is not to be limited to
the example form.
[0026] Preferably, the chemical composition of the synthetic grass
blades (103) should be selected to be heat-resistant and
UV-resistant (and to withstand exposure to sunlight, which
generates heat in the blades and contains ultraviolet rays).
Furthermore, the polymer yarns (103) should not become brittle when
subjected to low temperatures. The selected synthetic grass color
and texture should be aesthetically pleasing. While various other
materials may work well for the grass blades, it is presently
believed that polyethylene fibers work best.
[0027] Optionally, the synthetic grass blades (103) are tufted to
have a density of between about 20 ounces/square yard and about 100
ounces/square yard. Preferably, the synthetic grass blades have a
density of between about 20 and 40 ounces/square yard. The tufting
is fairly homogeneous. In general, a "loop" is inserted at a gauge
spacing to achieve the desired density. Each loop shows as two
blades of grass at each tufted location. Preferably, the synthetic
grass blades have a thickness of at least about 100 microns.
[0028] The synthetic grass blades (103) are tufted into the
geotextile backing (104). The geotextile backing preferably
consists of one or more geotextiles made of polypropylene or
polyethylene with UV stabilizers. The geotextiles can comprise slit
film (tape yarn) or monofilament. Generally speaking, the lower the
surface area of the yarn per unit weight of raw material, the
better the ultraviolet (UV) performance. Monofilament geotextiles
typically have a small cross section relative to their length,
which inherently provides for a smaller surface exposed to UV light
per unit weight of polypropylene or polyethylene. In other words, a
yarn with a round cross-section typically will exhibit better UV
resistance than a flat geometric shape.
[0029] Optionally, the geotextile backing (104) can be a single
layer backing, a double layer backing, or can have more than two
layers. But it is preferred that a single layer or double layer
backing be used. Optionally, the backing can be made of
polypropylene or polyethylene. Also, optionally a separate membrane
can be dispensed with, such as by applying a membrane-like layer to
the back side of the synthetic geotextile. For example, a urethane
coating can be sprayed onto the back of the synthetic geotextile
and allowed to cure.
[0030] The prior art technique of using tarps or geomembranes to
cover leach pads, landfills and stockpiles to protect the ore,
waste and soil stockpiles from rain and weather damage typically
requires substantial ballast or anchorage as shown on FIG. 2.1.
This new invention allows the use of a membrane over large areas
without such ballast or anchorage. Instead, a synthetic cover layer
(100) is provided that can resist wind uplift and thus protecting
the impermeable geomembrane (102) below. The synthetic cover (100,
103) contains grass-like filaments covering and protecting the
impermeable geomembrane liner surface.
[0031] The inventive wind-resistant cover and liner was laboratory
tested (at the Georgia Tech Research Institute ("GTRI") Wind Tunnel
Lab) using wind tunnels to determine the uplift vertical pressures
and shear pressures on the synthetic cover. The wind tunnel trials
indicated that this novel cover resists the uplift forces of the
wind. Minimal product weight of 0.3 lbs/sq-ft typically will be
required to counteract the shear forces from the wind. Synthetic
grass and geomembranes in the range of 30 to 40 mil thickness would
exceed this minimum weight-per-unit area threshold. The present
inventors have confirmed the performance of this novel cover by
testing the same as landfill covers for mines and general covers
for ore stockpiles, dams, embankments, general stockpiles and the
like.
[0032] During the wind tunnel investigation, the inventors of this
idea experimentally evaluated the aerodynamic properties and
ballast requirements of the novel synthetic ground cover system
under a range of wind speed conditions. The cover system was tested
full scale in a subsonic model test facility wind tunnel wherein
the normal forces loading (lbs/sq ft) and the shear stresses
(lbs/sq ft) were determined for the proposed section of the
materials (synthetic cover and geomembrane) as described
herein.
[0033] Pressure variations across the height of a boundary layer
were measured in the wind tunnel. Pressure variations are due to
viscous forces. In order to investigate the unique characteristics
of the flexible and permeable cover layer (100) a traverse system
was built into the model to actuate a pitot static probe vertically
through the boundary layer. This allowed the measurement of the
total and static pressure as a function of the probe height defined
as h=0 at the upper surface of the geomembrane or geotextile
backing. From these measurements the flow velocity was determined.
This characterized the shape of the boundary layer that is by its
nature a transition from the no slip condition at the surface (v=0)
to the free stream.
[0034] A sophisticated 6-component force balance was utilized to
measure the aerodynamic lift (L) and the total drag (D). These
forces were transmitted to the balance through a vertical strut
mounted underneath the model base. These forces represent the total
sum of all pressure distribution acting on the model resolved
vertically and tangentially as shown in the equation below:
L.sub.cover=L-L.sub.amb+L.sub.geotex/geome
[0035] FIG. 4 shows the boundary layer profile for two conditions.
The lower curve shows the wind profile at the edges and the upper
curves represents the wind profile in the interior conditions of
the cover defined in this invention. At the edges the wind subjects
the cover (103) to up to 89% of the total free stream. The blades
are subject to higher velocities and thus higher increasing drag as
the wind speed increases. The higher drag increases the bending of
the blades back onto the backing geotextile(s) (104). The effect of
this has two counteracting impacts on the net lift. At lower
velocities the synthetic blades (103) are bent slightly with flow
being deflected and accelerated over the edges. This flow
acceleration increases the local velocity and lowers the local
static pressure below that of the stream static, which creates the
pressure differential building up with the associated uplift of the
cover geotextiles (104). This force can be counteracted by building
an anchor trench at the perimeter of the cover.
[0036] For the interior condition FIG. 4 (upper curve)
approximately 18 inches from the edge, the curve is drastically
different than the perimeter boundary. Compared with the perimeter
profile it is 25% thicker with no measurable velocity until the
height is greater than 50% of the cover length. The blades (103)
therefore experience a maximum 45% of the free stream velocity.
This reduces the drag action on the cover layer. Furthermore, the
static pressure remains constant as a function of height through
the boundary which effectively prevents the formation of pressure
differential (i.e., no uplift) at the geomembrane/geotextile
surface.
[0037] The wind-resistant cover of this invention creates a larger
distance from the material surface to the "free stream" (free
stream occurs where the wind flow is unaffected by the material).
The cover radically breaks up the flow stream, increasing the
boundary layer (distance from surface to free stream) to the point
where uplift forces are very small. This is in stark contrast to a
prior art exposed membrane cover, in which there is a minuscule
distance from the surface (where velocity is 0 feet per second,
which is the case for all materials and wind conditions) to free
stream.
[0038] The boundary layer conditions are created by longer flow
paths over a given surface and all boundaries grow in thickness and
increase in turbulence with increasing distance. In the case of
this invention, the interaction of the flow with the flexible
blades causes the boundary layer growth to occur quite rapidly. It
is also clearly seen in our experiments that little to no
deflection occurred in the cover at a distance just over 6 inches
from the perimeter edge. The measured uplift results show values
requiring minimal uplift resistance that can simply be achieved by
the weight of the cover itself.
[0039] Exposed geomembrane covers have been used extensively in the
past as covers for landfills and stockpiles in the solid waste and
mining industries in order to prevent or minimize rainwater
infiltration into the waste or the ore. In such prior art
geomembrane applications, UV-resistance of the liner materials has
not been a concern when HDPE and LLDPE, PVC materials are used as
the plastic materials. For the synthetic grass used in the present
invention, the blades can be made of polyethylene, HDPE, LLDPE,
PVC, or other UV-resistant material. While UV resistance is not an
absolute requirement, it does provide an important long-term
stability for the synthetic grass blades, adding to the overall
performance of the system.
[0040] It is to be understood that this invention is not limited to
the specific devices, methods, conditions, or parameters described
and/or shown herein, and that the terminology used herein is for
the purpose of describing particular embodiments by way of example
only. Thus, the terminology is intended to be broadly construed and
is not intended to be limiting of the claimed invention. For
example, as used in the specification including the appended
claims, the singular forms "a," "an," and "one" include the plural,
the term "or" means "and/or," and reference to a particular
numerical value includes at least that particular value, unless the
context clearly dictates otherwise. In addition, any methods
described herein are not intended to be limited to the sequence of
steps described but can be carried out in other sequences, unless
expressly stated otherwise herein.
[0041] While the invention has been shown and described in
exemplary forms, it will be apparent to those skilled in the art
that many modifications, additions, and deletions can be made
therein without departing from the spirit and scope of the
invention as defined by the following claims.
DETAILED DESCRIPTION OF THE PREFERRED EXAMPLE EMBODIMENTS
[0042] FIG. 1 depicts a cross sectional view of a typical cover
system as described in current United States Environmental
Protection Agency federal regulations and as used in the covers for
landfills and mines. In this case the two feet of soil is used to
cover the geomembrane against wind uplift. As shown, the waste W is
covered by eighteen inches of soil (11), then a 40 mil. geomembrane
GM, a geocomposite drainage media D, eighteen more inches of soil
S, six inches of topsoil TS, and finally vegetive grass G.
[0043] FIG. 2 depicts a prior art cover where the geomembrane is
exposed to the environment. The system requires extensive anchoring
in order to resist wind uplift forces. As shown, the waste W is
covered by eighteen inches of soil S and an exposed geomembrane
12.
[0044] FIG. 2.1 depicts prior art covers of exposed geomembrane
arrangements and in general shows a cross sectional view of anchor
trenches (30) used along the slope of an exposed geomembrane cover
to secure it in place in the face of wind which would otherwise
tend to lift the cover. The figure shows the geomembrane/raincoat
cover (12), and the use of tires (20) tied with ropes as additional
ballasting system of the exposed geomembrane (12). This type of
prior art anchoring required to resist uplift is very expensive and
it is not aesthetically pleasant.
[0045] FIG. 2A and 2B schematically depict the current invention
over waste W covered with soil (101) with an exposed geomembrane or
raincoat liner (102) covered with synthetic strands (103) that
resemble grass with a pile height ranging from about 3/4 inch to 2
inches depending on wind design velocities. The strands (103) tend
to break the laminar flow of the wind and also provide normal
pressure on the geomembrane liner system when the strands bend onto
the liner, creating normal pressure. Preferably, the pile height is
% inch to 2 inches or so. More preferably, the pile height is about
1 inch to 1-1/2 inches.
[0046] Preferably, the synthetic strands (103) are slender elongate
elements. As used herein, "slender" indicates a length that is much
greater than its transverse dimension(s). Examples of slender
elongate elements contemplated as encompassed by the present
invention or in conjunction therewith are structures that resemble
blades of grass, rods, filaments, tufts, follicle-like elements,
fibers, narrow cone-shaped elements, etc. The synthetic strands
extend upwardly from a base and form a mat or field of such
strands. Such can simulate a field of grass, pine straw or similar.
Moreover, while the invention will be described below in connection
with blade-like elements (grass blade-like, not necessarily like
cutting blades) as an example embodiment, those skilled in the art
will readily appreciate that the invention is not to be limited to
the example form.
[0047] Preferably, the chemical composition of the synthetic grass
blades (103) should be selected to be heat-resistant and
UV-resistant (and to withstand exposure to sunlight, which
generates heat in the blades and contains ultraviolet rays).
Furthermore, the polymer yarns (103) should not become brittle when
subjected to low temperatures. The selected synthetic grass color
and texture should be aesthetically pleasing. While various other
materials may work well for the grass blades, it is presently
believed that polyethylene fibers work best.
[0048] Optionally, the synthetic grass blades (103) are tufted to
have a density of between about 20 ounces/square yard and about 100
ounces/square yard. Preferably, the synthetic grass blades have a
density of between about 20 and 40 ounces/square yard. The tufting
is fairly homogeneous. In general, a "loop" is inserted at a gauge
spacing to achieve the desired density. Each loop shows as two
blades of grass at each tufted location. Preferably, the synthetic
grass blades have a thickness of at least about 100 microns.
[0049] The synthetic grass blades (103) are tufted into the
geotextile backing (104). The geotextile backing preferably
consists of one or more geotextiles made of polypropylene or
polyethylene with UV stabilizers. The geotextiles can comprise slit
film (tape yarn) or monofilament. Generally speaking, the lower the
surface area of the yarn per unit weight of raw material, the
better the ultraviolet (UV) performance. Monofilament geotextiles
typically have a small cross section relative to their length,
which inherently provides for a smaller surface exposed to UV light
per unit weight of polypropylene or polyethylene. In other words, a
yarn with a round cross-section typically will exhibit better UV
resistance than a flat geometric shape.
[0050] Optionally, the geotextile backing (104) can be a single
layer backing, a double layer backing, or can have more than two
layers. But it is preferred that a single layer or double layer
backing be used. Optionally, the backing can be made of
polypropylene or polyethylene. Also, optionally a separate membrane
can be dispensed with, such as by applying a membrane-like layer to
the back side of the synthetic geotextile. For example, a urethane
coating can be sprayed onto the back of the synthetic geotextile
and allowed to cure.
[0051] The prior art technique of using tarps or geomembranes to
cover leach pads, landfills and stockpiles to protect the ore,
waste and soil stockpiles from rain and weather damage typically
requires substantial ballast or anchorage as shown on FIG. 2.1.
This new invention allows the use of a membrane over large areas
without such ballast or anchorage. Instead, a synthetic cover layer
(100) is provided that can resist wind uplift and thus protecting
the impermeable geomembrane (102) below. The synthetic cover (100,
103) contains grass-like filaments covering and protecting the
impermeable geomembrane liner surface.
[0052] The inventive wind-resistant cover and liner was laboratory
tested (at the Georgia Tech Research Institute ("GTRI") Wind Tunnel
Lab) using wind tunnels to determine the uplift vertical pressures
and shear pressures on the synthetic cover. The wind tunnel trials
indicated that this novel cover resists the uplift forces of the
wind. Minimal product weight of 0.3 lbs/sq-ft typically will be
required to counteract the shear forces from the wind. Synthetic
grass and geomembranes in the range of 30 to 40 mil thickness would
exceed this minimum weight-per-unit area threshold. The present
inventors have confirmed the performance of this novel cover by
testing the same as landfill covers for mines and general covers
for ore stockpiles, dams, embankments, general stockpiles and the
like.
[0053] During the wind tunnel investigation, the inventors of this
idea experimentally evaluated the aerodynamic properties and
ballast requirements of the novel synthetic ground cover system
under a range of wind speed conditions. The cover system was tested
full scale in a subsonic model test facility wind tunnel wherein
the normal forces loading (lbs/sq ft) and the shear stresses
(lbs/sq ft) were determined for the proposed section of the
materials (synthetic cover and geomembrane) as described
herein.
[0054] Pressure variations across the height of a boundary layer
were measured in the wind tunnel. Pressure variations are due to
viscous forces. In order to investigate the unique characteristics
of the flexible and permeable cover layer (100) a traverse system
was built into the model to actuate a pitot static probe vertically
through the boundary layer. This allowed the measurement of the
total and static pressure as a function of the probe height defined
as h=0 at the upper surface of the geomembrane or geotextile
backing. From these measurements the flow velocity was determined.
This characterized the shape of the boundary layer that is by its
nature a transition from the no slip condition at the surface (v=0)
to the free stream.
[0055] A sophisticated 6-component force balance was utilized to
measure the aerodynamic lift (L) and the total drag (D). These
forces were transmitted to the balance through a vertical strut
mounted underneath the model base. These forces represent the total
sum of all pressure distribution acting on the model resolved
vertically and tangentially as shown in the equation below:
L.sub.cover=L-L.sub.ambL.sub.geotex/geome
[0056] FIG. 4 shows the boundary layer profile for two conditions.
The lower curve shows the wind profile at the edges and the upper
curves represents the wind profile in the interior conditions of
the cover defined in this invention. At the edges the wind subjects
the cover (103) to up to 89% of the total free stream. The blades
are subject to higher velocities and thus higher increasing drag as
the wind speed increases. The higher drag increases the bending of
the blades back onto the backing geotextile(s) (104). The effect of
this has two counteracting impacts on the net lift. At lower
velocities the synthetic blades (103) are bent slightly with flow
being deflected and accelerated over the edges. This flow
acceleration increases the local velocity and lowers the local
static pressure below that of the stream static, which creates the
pressure differential building up with the associated uplift of the
cover geotextiles (104). This force can be counteracted by building
an anchor trench at the perimeter of the cover.
[0057] For the interior condition FIG. 4 (upper curve)
approximately 18 inches from the edge, the curve is drastically
different than the perimeter boundary. Compared with the perimeter
profile it is 25% thicker with no measurable velocity until the
height is greater than 50% of the cover length. The blades (103)
therefore experience a maximum 45% of the free stream velocity.
This reduces the drag action on the cover layer. Furthermore, the
static pressure remains constant as a function of height through
the boundary which effectively prevents the formation of pressure
differential (i.e., no uplift) at the geomembrane/geotextile
surface.
[0058] The wind-resistant cover of this invention creates a larger
distance from the material surface to the "free stream" (free
stream occurs where the wind flow is unaffected by the material).
The cover radically breaks up the flow stream, increasing the
boundary layer (distance from surface to free stream) to the point
where uplift forces are very small. This is in stark contrast to a
prior art exposed membrane cover, in which there is a minuscule
distance from the surface (where velocity is 0 feet per second,
which is the case for all materials and wind conditions) to free
stream.
[0059] The boundary layer conditions are created by longer flow
paths over a given surface and all boundaries grow in thickness and
increase in turbulence with increasing distance. In the case of
this invention, the interaction of the flow with the flexible
blades causes the boundary layer growth to occur quite rapidly. It
is also clearly seen in our experiments that little to no
deflection occurred in the cover at a distance just over 6 inches
from the perimeter edge. The measured uplift results show values
requiring minimal uplift resistance that can simply be achieved by
the weight of the cover itself.
[0060] Exposed geomembrane covers have been used extensively in the
past as covers for landfills and stockpiles in the solid waste and
mining industries in order to prevent or minimize rainwater
infiltration into the waste or the ore. In such prior art
geomembrane applications, UV-resistance of the liner materials has
not been a concern when HDPE and LLDPE, PVC materials are used as
the plastic materials. For the synthetic grass used in the present
invention, the blades can be made of polyethylene, HDPE, LLDPE,
PVC, or other UV-resistant material. While UV resistance is not an
absolute requirement, it does provide an important long-term
stability for the synthetic grass blades, adding to the overall
performance of the system.
[0061] FIG. 5 shows synthetic strands (103) over a geomembrane
(102) atop subgrade soil (101), with anchor trenches (300) at the
leading edges only.
[0062] It is to be understood that this invention is not limited to
the specific devices, methods, conditions, or parameters described
and/or shown herein, and that the terminology used herein is for
the purpose of describing particular embodiments by way of example
only. Thus, the terminology is intended to be broadly construed and
is not intended to be limiting of the claimed invention. For
example, as used in the specification including the appended
claims, the singular forms "a," "an," and "one" include the plural,
the term "or" means "and/or," and reference to a particular
numerical value includes at least that particular value, unless the
context clearly dictates otherwise. In addition, any methods
described herein are not intended to be limited to the sequence of
steps described but can be carried out in other sequences, unless
expressly stated otherwise herein.
[0063] While the invention has been shown and described in
exemplary forms, it will be apparent to those skilled in the art
that many modifications, additions, and deletions can be made
therein without departing from the spirit and scope of the
invention as defined by the following claims.
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