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 geotextiles can comprise polypropylene or polyethylene. 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. 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.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional patent application Ser. No. 13/231,688, filed Sep. 13, 2011, which 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

Environmental covers are used to covers landfills, mines, stockpiles and other waste materials to minimize rain infiltration that can contaminate the groundwater table below. These covers 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 US EPA (40 CFR Sub. D) environmental regulations.

The prescribed covers required by the US EPA typically use a two feet 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.

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 them against strong wind uplift. The anchoring system can be very extensive resulting in large construction costs.

The prior art with exposed liners require anchoring and or ballasting the system to resist weather damage from wind uplift. Commonly, exposed covers require the liner 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 the material can be buried in them 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.

Exposed impermeable geomembranes in the prior art is 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.

Artificial grass or synthetic grass has been extensively used in sport's arenas as well as airport runways and general landscaping. However a primary consideration of artificial cover fields is the ability of the field to drain in order for the ballasting infill to stay on the steep sideslopes of landfills or mine stockpiles. This is not possible in environmental covers that require the use of an impermeable surface to avoid rainfall infiltration on the surface it covers.

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 covers 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

Briefly described, the present invention provides a new and useful system for covering (i.e., closing) various types of sites where waste is deposited. More particularly, the cover system of this invention comprises a composite of a one or more geotextiles consisting of polypropylene or polyethylene that are tufted with synthetic yarns and an impermeable geomembrane, which is comprised of a polymeric material.

The present invention comprises a wind-resistant textured synthetic surface that includes polymeric rod or blade-like geometry, referred also as vertical filaments, over a low-permeable polymer liner backing. The system does not rely on weight to resist wind forces. The cover of the present invention can be deployed over a large area with very minor ballasting or anchoring. This new cover breaks up the airflow over the cover providing wind uplift resistance. The cover that includes vertical filaments attached to the liner to break the wind aero-dynamics on the exposed cover. With this system, 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. The reaction of the filaments to the wind forces can also created a downward force on the membrane. This reaction is 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 filaments a radical departure from the typical exposed membranes or liners.

The wind-resistant cover in 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 breaks up the flow stream, increasing the boundary layer (distance from surface to free stream) to the point where uplift forces are very small. In comparison with a prior art of 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.

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.

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 extending the longevity of the geomembrane component over a much longer period of time in comparison with the old exposed geomembrane concept.

This invention, in a first preferred form uses the 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. The angle of friction shall be preferably higher than 18 degrees.

Alternatively, the liner can also be incorporated to the cover by spraying polypropylene or polyethylene to the back of the tufted or knitted geotextile(s).

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic view of prior art Subtitle D environmental cover as per US EPA where the anchoring of the impermeable geosynthetic membrane consists of a two feet soil cover.

FIG. 2 is a schematic view of a second prior art environmental cover with exposed geomembranes that require extensive anchoring system to resist wind uplift.

FIG. 2-1 depicts prior art arrangements and in general show 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. This type of prior art anchoring required to resist uplift is very expensive and it is not aesthetically pleasant.

FIG. 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 descriptions of these drawings are presented in the next section.

DETAILED DESCRIPTION OF THE PREFERRED EXAMPLE EMBODIMENTS

FIG. 1 depicts a cross sectional view of a typical cover system as described in current EPA Federal regulations and 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

FIG. 2 depicts also the prior art where the geomembrane is exposed to the environment. The system requires extensive anchoring in order to resist wind uplift forces.

FIG. 2-1 depicts prior art of exposed geomembrane arrangements and in general show a cross sectional view of anchor trenches (300) 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 figures show the geomembrane/raincoat cover (102), and the use of tires (200) tied with ropes as additional ballasting system of the exposed geomembrane (102). This type of prior art anchoring required to resist uplift is very expensive and it is not aesthetically pleasant.

FIG. 2A and 2B schematically depicts the current invention with an exposed geomembrane or raincoat liner (102) covered with synthetic strands that resemble grass (103) with a pile height ranging from ¾ inch to 2 inches depending on wind design velocities. The strands (103) will break the laminar flow of the wind and will also provide normal pressure on the geomembrane liner system when the strands bend onto the liner, creating normal pressure. Preferably, the pile height is ¾ inch to 2 inches or so.

Preferably, the chemical composition of the synthetic grass blades (103) should be selected to resist exposure to sunlight, which generates heat and contains ultraviolet resistance chemicals. The polymer yarns (103) should not become brittle when subjected to low temperatures. The selection of the synthetic grass color and texture should be aesthetically pleasing. While other materials may work well for the grass blades, it is presently believed that polyethylene fibers work best.

Optionally, the synthetic grass blades (103) are tufted to have a density of between about 20 ounces/square yard and about 130 ounces/square yard. The density spec is a measure of density of yarn (grass per yard or per foot). 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 teach tufted location. Preferably, the synthetic grass blades have a thickness of at least about 100 microns.

The synthetic grass (103) is tufted into the geotextile backing (104). The geotextile backing consist of one or more geotextiles made of polypropylene or polyethylene with UV stabilizers. The geotextiles can consist of 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 (104) typically have a cross section, which inherently provides for a smaller surface exposed to UV light to unit weight of Polypropylene or polyethylene to make the fabric.

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. Other materials can be used as well to coat the synthetic geotextile(s) such as polyurethane baking (109) that can be applied to both monofilament or slit film geotextiles. The polyurethane backing spray typically passes through the geotextile manifesting on to the upper surface thus adding additional protection of the geotextile(s) against UV.

The prior art technique of using tarps or geomembranes (102) 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 filaments like grass covering and protecting the impermeable geomembrane liner surface. The inventive wind-resistant cover and liner was laboratory tested (at the Georgia Institute of Technology aeronautical engineering 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 liner 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 30 to 40 mil thickness would exceed this weight-per-unit area threshold. The present inventors have confirmed the performance of this novel liner by installing same for landfill covers for mines and general covers for ore stockpiles, dams, embankments, general stockpiles and the like.

During the wind tunnel investigation, the inventors of this idea experimentally evaluated the aerodynamics 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 GTRI 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 in this patent application.

Pressure variations through the height of a boundary layer were measured in the wind tunnel. Pressure variations are due to viscous forces, which causes deficits in the total pressure as the bounding flat and level surface is approached. 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 condition (v=v inf).

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 cover=L−L amb+L geotex/geome

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 effects 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 is contra rested by building and anchor trench at the perimeters of the cover.

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 (0.75″). The blades (103) therefore experience a maximum 45% of the free stream. 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.

The wind-resistant cover in 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. In comparison with a prior art exposed membrane, there is a minuscule distance from the surface, where velocity is always 0 feet per second at the surface (as is the case for all materials and wind conditions) to free stream.

The cause for the deficient boundary layer is 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 that can simply be accomplished by the weight of the cover.

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.

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.

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.

Claims

1. A synthetic cover comprises:

a composite of a membrane covered with a tufted textile cover with upstanding synthetic slender elongate elements

wherein the synthetic slender elongate elements comprise polyethylene or polypropylene fibers.

2. A 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.

3. A cover system of claim 1 wherein the membrane is selected from the group consisting of high density polyethylene, linear low density polyethylene or polyvinyl chloride.

4. A cover system of claim 1 wherein the geomembrane is sprayed or applied directly on the textile(s) backing of the cover.

5. A cover system of claim 1 wherein the membrane is tufted directly on the textile backing of the cover.

6. A cover system of claim 1 wherein the synthetic cover comprises UV-resistant material.

7. The cover system of claim 1 wherein the flexible synthetic upstanding slender elongate elements comprise vertical filaments attached to a textile(s) backing.

8. A cover system as claimed in claim 1, wherein the membrane comprises 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.

9. A 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.

10. A cover system as claimed in claim 1 wherein the synthetic slender elongate elements comprise blade-like elements having the appearance of blades of grass.

11. A cover system as claimed in claim 10 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.

12. A cover system of claim 1 wherein the membrane comprises a geomembrane selected from the group consisting of high density polyethylene, linear low density polyethylene or polyvinyl chloride.

13. A cover system of claim 12 wherein the geomembrane is sprayed or applied directly on the geotextile(s) backing of the cover.

14. The 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 membrane below.