WO2000071638A1

WO2000071638A1 - Composition of soil having fibers and binding substance

Info

Publication number: WO2000071638A1
Application number: PCT/US2000/014577
Authority: WO
Inventors: Jonathan W. Hubbs
Original assignee: Stabilizer Solutions, Inc.
Priority date: 1999-05-26
Filing date: 2000-05-25
Publication date: 2000-11-30
Also published as: AU5295200A

Abstract

A composition of soil, fiber strands, and binder provides a material for a stable resilient ground surface. The material includes a mixture of an aggregate of particles having sizes within a first selected range; a selected amount of fiber strands having within a second selected range; and a selected amount of binder. The binder includes oil and polymer. Such a material provides relatively high load bearing shear strength and is easily maintained.

Description

COMPOSITION OF SOIL HAVING FIBERS AND BINDING SUBSTANCE

FIELD OF THE INVENTION

Embodiments of the present invention relate to compositions of soil and to methods of preparing compositions of soil having fibers and binding substance.

BACKGROUND OF THE INVENTION

Tracks utilized in horse racing are typically designed to absorb shock and provide traction for the running of a safe race. To this end, tracks generally comprise a mixture of sand, clay, and silt and generally include three layers: a top "cushion" layer, a middle "pad" layer, and a "base" layer. The base layer is typically consolidated matter for supporting the other layers. The pad layer is typically a layer of dirt or sand from about four to about twelve inches thick, that is laid upon the base layer and compacted to a bulk density of about 1.1 g/cc. The cushion layer is typically made of soil about three inches thick and comprises loose, fluffy, rakable material with a bulk density of about 1 g/cc. The cushion layer may be initially laid upon the pad, or derived from the pad, for example, by raking. In the care and maintenance of the track, the cushion layer is "worked" with a harrow, while the pad and base layers remain compacted. The pad layer may occasionally be disturbed.

Proper track maintenance typically requires a harrowing program and a moisture control program. Harrowing is intended to break up the cushion layer that becomes compacted by horse's hooves. Harrowing may also maintain uniformity in the cushion layer's density and depth. The cost of harrowing equipment and the cost of labor for frequent harrowing may become substantial.

Track characteristics vary considerably with the amount of moisture in the cushion layer. Typically the cushion layer is suitable for use with a moisture content of about 7 to about 11 percent water to soil by weight. At a low moisture content the cushion layer will, especially in a turn, tend to fall away from the horses' hooves. At a high moisture content (e.g., above 14 percent) water and water-laden cushion material may squirt out from under the horses' hooves. Such a cushion layer provides little support to the horses.

General uniformity of the moisture content across the surface of the dirt track is desirable, yet difficult to achieve. Evaporation rates may be dramatically different from place to place across the track. The moisture content of the track is typically improved by applying water from a truck. The water truck may increase moisture content by as little as 0.3 percent per pass. On a hot, dry day, the water truck may be unable to increase moisture content due to evaporation between passes. In summary, maintaining a uniformly suitable moisture content adds considerable cost above the costs of harrowing discussed above. A nonuniform track surface may lead to unsafe conditions during use. Consequential costs to the health and strength of race horses may be incurred immediately upon injury or may accrue over time, shortening the career of the race horse. Without improved material compositions for use on tracks, ground surfaces, and earthen structures generally (e.g., sloped landscape surfaces, paths, race tracks, sports courts, drive ways, and roads), increasing maintenance costs may force the early abandonment of parks and income producing facilities with consequent general economic decline. SUMMARY OF THE INVENTION

The present invention provides a material for a stable resilient ground surface. The material includes a mixture of an aggregate of particles having sizes within a first selected range; a selected amount of fiber strands having lengths within a second selected range; and a selected amount of binder. The binder includes oil and polymer. Such a material provides relatively high load bearing shear strength and is easily maintained.

Particular synergies are obtained by the combination of binder and fiber to aggregate in appropriate proportions. According to a first aspect, adding fiber to a subcombination of aggregate and binder provides a material having greater cohesion, extended life (duration) of adequate cohesion, and greater load bearing strength. According to a second aspect, adding binder to a subcombination of aggregate and soil provides a material having increased cohesion and resiliency

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the present invention will now be further described with reference to the drawing consisting of a sole figure being a schematic cross-section view of a track according to various aspects of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The practice of the present invention is based upon mixing soil, fiber, and binder. In general, a material of the present invention includes a granular portion, a fiber portion, and a binder portion in proportions as described below. Such a material provides relatively high load bearing shear strength, as well as elasticity and flexibility, and is easily maintained. Referring now to the drawing, a track 10 (e.g., a horse race track) in accordance with the present invention includes a base layer 12, a pad layer 14, and a cushion layer 16. A base layer provides drainage and support in a conventional manner and may be formed of any suitable combination of materials of appropriate size such as rock, pavement, gravel, sand, and soil. For example, base layer 12 may be formed of compacted gravel for a horse race track. A pad layer provides shock absorption and water retention in a conventional manner and may be formed of any suitable combination of paniculate materials of appropriate size such as gravel, sand, silt, and clay. For example, pad layer 14 may be formed of compacted sand and silt for a horse race track.

Pad layer 14 may be omitted, for example, when shock absorption and water retention are adequately provided by a thicker than usual cushion layer 16. Alternatively, pad layer

14 may comprise aggregate and binder or may comprise aggregate, binder, and fiber, in composition different from cushion layer 16. A cushion layer, according to various aspects of the present invention, may comprise any material that provides a stable resilient ground surface as a result of a mixture of an aggregate of particles, numerous fiber strands, and a binder. For example, cushion layer 16 is suitably formed of a particulate aggregate 30 (e.g., sand, silt, and/or clay), fiber strands 28 of predetermined length, and a binder (not shown) comprising polymer enriched oil. Aggregate 30 may be primarily any sand, silt, or clay type soil. The basic types of soils are gravel, sand, silt, and clay. Mixtures of these types of soils give rise to coarse-grained soils (e.g., more than 50% retained on a No. 200 sieve) and fine-grained soils (e.g., 50% or more passes through a No. 200 sieve). Soils with which the present invention may be practiced include gravel, sand, silt, and clay of the types described in the Unified Soil Classification System published as ASTM Standard D2487, incorporated herein by reference.

Aggregate 30 (also called the granular portion) may generally comprise sand, sand with silt, sand with clay, or sand with silt and clay. Preferably, there is little or no gravel in the granular portion. For a horse race track, the granular portion most preferably primarily includes sand. Generally, the percentage composition of the sand, clay, and silt is sufficient to cooperate with the binder to maintain cohesion in the material of the present invention. Any naturally occurring mixture of sand, clay, and silt may provide the proper cohesion and may be utilized. The granular portion suitably comprises in the range of about 70 to about 90 weight percent sand having an average diameter in the range of about 0.05 to about 1 millimeters. For example, the granular portion may comprise in the range of about 30 to about 40 weight percent course sand 20 having an average diameter in the range of about 0.5 to about 1 millimeters, and further comprise in the range of about

40 to about 50 weight percent fine sand 22 having an average diameter in the range of about 0.05 to about 0.5 millimeters.

The silt or clay 26 utilized in the present invention suitably comprises particles with diameters in the range of about 0.05 to about 0.002 millimeters. When both silt and clay are present, the ratio of silt to clay may be in the range of about 1 :3 to about 3:1, preferably in the range of about

1 :2 to about 2:1, and most preferably about 1 :1. For most applications, the granular portion suitably includes about 10 to about 30 weight percent clay or silt. Preferably, the granular portion comprises in the range of about 10 to about 25 weight percent clay or silt, and most preferably in the range of about 12 to about 22 weight percent clay or silt. Fiber strands 28 provide tensile strength and a wicking effect that permits water to be distributed within the aggregate during installation, water to be retained, and excess water to be carried into pad layer 14. Fiber strands 28 may be formed of any material that is relatively inert, and impervious to water, salts, acids, and fertilizers in the soil. Fiber material should be selected for flexibility, elasticity, durability under use and weather conditions, and resistence to sunlight (e.g., heat and ultra-violet light). For an outdoor horse race track, a suitable material is polypropylene. For example, fiber strands 28 are preferably flat, ribbon-like, fibrillated fiber having a denier of at least 360 and preferably in the range of about 360 to about 1000. Fiber strands are suitably of a length chosen to provide adequate tensile strength to the material, but not so long as to be subject to balling or present difficulties in mechanical application. The longer the fiber, the more tensile strength is provided. However, the longer fibers are not amenable to mechanical application, and are difficult to mix uniformly with the aggregate. Fiber strands may be selected from the broad class of commercially available man-made fiber forming substances as well as fiberglass and conventional slit films. Fiber length may range from about 0.5 to about 4 inches (1.25 to 10 cm) with about 0.75 to about 1.5 inches (1.9 to 3.8 cm) being preferred. Fiber diameter is suitably between about 0.003 to about 0.10 inches (0.076 to 2.5 mm). Any combination of different fiber diameters may be used. Fiber yield, i.e., denier, which is a length to weight ratio, may be between about 50 to about 41,000. For long useful life, the fiber material should neither affect the soil nor be affected by the soil and therefore, the fiber material should not mold, rot, mildew, dissolve or otherwise deteriorate in the soil environment but should maintain its basic integrity throughout its useful life. For temporary use, any suitable fiber, e.g., a degradable fiber, may be used. In coastal areas, for instance, severe storms may erode the natural dune structure. Use of a degradable fiber could provide temporary reinforcement of the soil structure. Other instances may be envisioned where environmental considerations could be satisfied by employing biodegradable materials as opposed to the non-degrading types and thus, the present invention should not be limited to either type because in specific situations one type may be preferred over the other. Preferred fiber materials include the olefins, particularly polypropylene, polyesters, nylons, acrylics and glass, but should not be limited to these. Degradable man-made fiber forming substances would include rayon, acetate, triacetate, and biodegradable or degradable polyolefins. Practical considerations include creep resistance (a strong trait of polyesters), and dispersibility of the fiber material in the soil, although the absence of either one of these properties should not eliminate a particular polymer. Typically, man-made fibers having specific gravities ranging from about 0.80 to about 2.4 are suitable.

Slit film fibers may be used having any length, width, or cross-sectional dimensions comparable to the above mentioned fiber materials. Hence, the term "fiber strands" has been employed herein to connote both conventional fibers and slit film fibers. Slit film materials are formed from films and sheets of any conventional man-made fiber forming substances that have been slit into thin strips. These thin strips may be further split or treated by conventional processes into fibrillated or roll embossed film constructions. The films and sheets may be cut with conventional apparatus into narrow strips having both pairs of opposed sides parallel (e.g., rectangles and parallelograms), two sides parallel (e.g., trapezoids), or no sides parallel (e.g., quadrangles and other polygons). Thickness of these strips may range from about 0.001 to about 0.02 inches (0.025 to 0.5 mm) and widths may vary to achieve the final weight of the product desired. Lengths of the strips may be comparable to that for the fiber materials discussed above, namely from about 0.5 to about 4.0 inches (1.25 to 10 cm). The strips may also be deformed in any conventional manner to promote, for example, cohesion of the aggregate, fiber, binder material.

Any combination of fibers and slit film fibers may be used. With respect first to the conventional fibers, configuration may be important, but is also not a controlling feature. Monofilaments may be used. Other cross-sectional configurations such as rectangular, square, round, oval, hollow, and the like may further enhance soil cohesion or other properties. Additionally, embossed, multi-lobal, collated or bonded fibers, triangular, entangled multifilaments, filaments, monofilaments, fibrids, and fibrils may be used provided they may be combined with the granular and binder portions to produce a homogeneous material. The fiber configuration may also be slubbed, spiraled, gear crimped, saw-tooth configured, gnarled, cork-screwed or otherwise deformed, for example, to promote cohesion of the aggregate, fiber, and binder material.

In the case of fibrids and fibrils, length and cross-section dimensions are typically variable and nonuniform. Fibrid and fibril lengths or bundle lengths of from about 0.04 to about 0.5 inches (1 to 12 mm) are preferred, with individual fiber diameters being subject to the manufacturing process. Generally, fibrids and fibrils may range from micro-deniers to about 90 denier.

As noted above, cushion layer 16 includes a predetermined proportion of fiber strands 28. More particularly, cushion layer 16 includes about 0.05 to about 2.0 percent by dry weight of fiber strands 28, and preferably about 0.25 percent (i.e., 0.5 pound per U.S. ton or 1 Kg/MT). The amount of fiber strands 28 is chosen to provide desired strength, and flexibility, and additionally, to provide desirable water distribution characteristics in the cushion layer.

The amount of fiber necessary for strength, tends to be inversely proportional to the amount of larger sized particles in the aggregate, and concomitantly, directly proportional to the amount of silt and clay. If too little fiber is included, the cushion layer tends to become rather hard and inflexible. On the other hand, if too much fiber is included, the cushion layer becomes too soft, and does not provide sufficient tensile and shear strength. In addition, the amount of fiber strands 28 included tends to affect the wicking action that maintains and distributes water within cushion layer 16 and into pad layer 14. If too much fiber strands 28 is included, water is conducted too quickly through cushion layer 16.

The amount of fiber in a material of the present invention ranges from about 0J percent by weight up to about 5 percent by weight with about 0.1 to about 2 percent being preferred.

Practically speaking, the upper limit is not dictated by operability but more a matter of diminishing returns. Thus, for many fibers, when more than about 2 percent has been added, higher performance values are offset by economics unless specific engineering properties (e.g., increased shear strength) are sought. Nevertheless, amounts in excess of 5 percent are not beyond the scope of this invention if such additions may be justified.

A binder includes any material that adheres to the particles in the aggregate and/or to the fibers, and binds these components together. A binder promotes cohesion of coated particles and coated fibers. In various embodiments of the present invention, the binder suitably includes an amorphous polymer (e.g., any copolymer or interpolymer) dissolved or dispersed in a non-aromatic or low-aromatic oil may be used. The binder used in cushion layer 16, for example, comprises in the range of about 2 to about 10 weight percent polymer. Preferably, the binder comprises in the range of about 4 to about 8 weight percent polymer. More polymer to oil may be needed for coarser soils including for example volcanic soils. More oil to polymer may be permissible when using finer soils including for example limestone and other sedimentary soils.

Polymers suitable for use in the binder portion of a material of the present invention include any amorphous polymers that are soluble or dispersable in a non-aromatic or low-aromatic oil. Suitable polymers include poly alpha-olefin interpolymers derived from ethylene, propylene, butene, and higher order alpha-olefins. Commercially available examples of suitable poly alpha-olefin interpolymers include Vestoplast 608 or 708 from Huls. Other polymers suitable for use in the present invention include interpolymers of ethylene and or propylene with ethylenically unsaturated monomers, including vinyl acetate, methyl acrylate, ethyl acrylate, and the like. Oils suitable for use in extended life materials of the present invention preferably are resistant to evaporation and rapid degradation or oxidation from heat or ultraviolet light. Suitable oils contain low or no aromatic fractions, have a flash point generally suitable to maintain the oil on the track after application, and are suitably fluid at granular contacting temperatures. While oils with lower flash points may possibly be utilized, the oil of the present invention generally has a flash point above about 350 degrees Fahrenheit. Examples of suitable oils include paraffϊnic oils and low-aromatic naphthenic oils. A commercially available example of a paraffinic oil includes Exxon's 150 SE solvent extracted bright stock FN-2507. An example of a low-aromatic naphthenic oil includes Cyclolube No. 2290 available from Witco.

Suitable oils may include any biodegradable oil, for example, vegetable oil, preferably canola oil. For applications exposed to wide temperature ranges, any conventional multi- viscosity oil may be used. Synthetic oils may be used.

The binder portion of a material of the present invention may be brought into contact with the granular material in "neat" form (i.e., as an oil and polymer mixture) or in aqueous emulsion form. When the binder portion of the present invention is prepared as an emulsion, the emulsion suitably comprises water and binder (e.g., an oil and polymer mixture) in a ratio in the range of about

10:1 to about 1 :10. Preferably, the composition of water and binder in the emulsion is in the range of about 5: 1 to about 1:5, and most preferably in the range of about 3:1 to about 1 :3. The emulsion may further comprise an emulsifying agent in an amount suitable to form an emulsion of the binder and water. Suitable emulsifying agents include ionic surfactants, non-ionic surfactants, and mixtures thereof, comprising in the range of about 0.01 to about 10 weight percent of the emulsion. Preferably, the emulsifying agent comprises in the range of about 0.1 to about 2 weight percent of the emulsion and most preferably in the range of about 0.5 to about 1.5 weight percent. Emulsion preparation is well known to those of skill in the art and suitably includes contacting the binder, water, and emulsifier under conditions suitable to form an emulsion. Some stirring or shaking is generally necessary to form the emulsion. In the practice of the present invention, the prepared emulsion may be suitably applied, for example, to an existing track to form a new surface in-situ. As the emulsion has a viscosity approximating that of water, it percolates into the aggregate cushion (with or without fiber) thereby coating the aggregate particles (and fiber strands) evenly. As the water evaporates, a thin uniform binder layer is left on the particles.

The emulsion of the present invention may be applied to a horse race track surface by any suitable means. The binder is suitably applied as part of an emulsion or if applied neat, under temperature conditions suitable to liquify the binder. Such suitable means for applying the neat binder or binder emulsion include spraying, pouring, sprinkling, etc. The emulsion may also be worked into the track utilizing conventional track surface maintenance equipment. Preferably, the prepared emulsion is applied to the track via an oil spray truck.

The binder portion of the present invention may be applied to the granular portion (with or without fiber) away from the track. The combined binder and granular portions may then be laid upon the track. The binder of the present invention may be applied to the granular portion either in neat form or as an aqueous solution, or with any other suitable carrier material or liquid. Preferably in the practice of the present invention, the first application of the binder is as an aqueous emulsion.

A material of the present invention suitably includes aggregate and fiber as discussed above mixed with a binder. For track 10, cushion layer 16 suitably includes about 80 to about 99 weight percent aggregate, about 0.1 to about 5 weight percent fiber, and about 0.5 to about 5 weight percent fluid binder. Preferably, cushion layer 16 includes about 96 to about 99 weight percent aggregate, about 0.1 to about 1 weight percent fiber, and about 1 to about 3 weight percent binder. Most preferably, cushion layer 16 includes about 97.75 percent aggregate, about 0.25 weight percent fiber, and about 2.0 weight percent binder.

When the granular portion contains little or no silt or clay, the binder may be about 2 to about 3 weight percent. When the aggregate includes higher proportions of smaller particles (e.g., a fine sand with higher silt content), more binder may be needed to adequately coat the particles.

While the binder of the present invention may be used to create new track material, it may also be used to recondition old, used, or weathered track surfaces (natural or synthetic) generally having unsuitable cohesion properties. The binder may be directly applied to the old track either in neat or emulsion form. Additional aggregate may first be added to the old track. When additional aggregate is added, the weight ratio of additional aggregate to old track material is in the range of about 0.01 :1 to about 4: 1. Preferably, the weight ratio of additional aggregate to old track material is in the range of about 0.35 : 1 to about 1 :1.

Binder may be prepared in any manner resulting in a homogeneous fluid that is stable for a period long enough to assure desired mixing of the binder portion with one or more of the granular and fiber portions. For example, five parts of Huls Vestoplast 708 polymer may be dispersed in 95 parts of Witco Cyclolube 2290 by stirring with the temperature of the mixture raised to 265 degrees Fahrenheit. After approximately 30 minutes of stirring the polymer may be completely dissolved. The resulting binder may then be cooled to room temperature. Alternately, six parts of Huls Vestoplast 708 may be added to 94 parts of Exxon bright stock oil by stirring with the temperature of the mixture raised to 265 degrees Fahrenheit. After approximately 30 minutes of stirring the polymer may be completely dissolved. The resulting binder may then be cooled to room temperature. As yet another example, five parts of Du Pont's ethylene vinyl acetate copolymer #250 may be dissolved as above in Exxon bright stock and later cooled to room temperature. Copolymer #250 includes 25% vinyl acetate content and is a medium mole weight copolymer.

An emulsion of any binder as described above may be prepared in a water mixture of, for example, 0.3 g of an emulsifying agent (e.g., comprising a mixture of anionic and/or non-ionic surfactants) to 66 g of water. The binder may be mixed in any manner in a ratio of, for example, 33 g of binder to 66.3 g of the water mixture discussed above. If separation becomes noticeable, agitation may be repeated or continuously applied to obtain complete re-emulsification. In commercial practice, a re-circulation pump may be used to keep the emulsion homogenized. Alternatively, an emulsion of water (preferably with surfactants) and binder may be prepared at a ratio of about 1:1.

Binder may be mixed in any manner with aggregate (or aggregate premixed with fiber). For example, a sand/clay/silt mixture having dry weight of 50 g may be added to 3.5 g of a 1 :1 emulsion, as discussed above. After evaporation of the water a second addition of 3.5 g of the emulsion may be made followed by mixing and evaporation. The resulting material contains about 7% by weight binder (0.35% polymer) coated particulates. Material formed in this manner may be formed in situ, for example, on a track using an asphalt/oil spray truck with a 14 foot wide spray bar for distributing the emulsion. Even coating of aggregate particles and fiber strands may result from use of a 1:1 emulsion water and binder. For example, binder in the amount of 6% for the emulsion (3% for the neat form) may be applied to either dry aggregate or moist aggregate with modest mixing. After the water from the emulsion has evaporated, binder in neat form may be applied. With only modest mixing the binder quickly disperses coating the aggregate particles and fiber strands evenly. A cushion layer 16 may be formed in a number of ways. If the native earth has a suitable aggregate mix, or may readily be modified to bring it into the suitable ranges (e.g., all particles larger than the predetermined maximum size, e.g., 2 mm removed, and/or particles added to attain the appropriate percentages of the various sized particles), fiber strands 28 and binder may be added to the aggregate in situ, by, for example, spreading the fibers and binder over the surface of the aggregate, and then mixing (e.g., tilling) the fibers and binder into the aggregate to a depth of from about 1.5 to 6 inches (3.8 to 15 cm), preferably about 2 inches (5 cm). The mix may be raked and shaped after mixing, and if desired compacted, for example, with rollers and/or hand tampers. Alternatively, material for a cushion layer (or other suitable application) may be premixed and manually "plastered" onto surfaces and/or slopes. It may be particularly advantageous to premix the material and apply it by blowing it under pressure onto surfaces and slopes, in a manner analogous to the "Gunnite" process of applying concrete in swimming pools. The material is blown onto a surface or slope at a predetermined pressure, for example, about 2800 to 3600 pounds per square inch (955 to 1227 Kg/cm²) and impacts the surface or slope with a predetermined force, for example, in the range of about 900 to about 1,000 pounds per square inch (307 to 341 Kg/cm²). In addition to being quicker and requiring less labor, applying the aggregate in such a manner provides a number of advantages. The necessity of a separate compacting step is avoided; the compacting is more consistent, particularly on slopes; the depth and contour of the applied layer (e.g., cushion) is more readily controlled, and consistent, particularly on slopes; and the finished top surface of the material (e.g., cushion layer) tends to be smoother. A smooth surface provides a more aesthetic appearance. More significantly, the blowing process itself tends to mix the constituents of the material, and in particular, fiber strands and binder-coated particles, providing desirable homogeneity. Moreover, where fibrillated fibers are employed, a blowing process tends to open and spread the fibrils of fibers, creating spread net structures within the aggregate, increasing the load bearing strength of the applied material, as well as the water retention and distribution properties. The blowing process may tend to separate the material in mid-air so that the larger materials are deposited on the surface first, with the finer materials applied thereover. Separation causes the finer materials to settle between the coarser particles, filling interstices and binding the aggregate together.

The material described above provides greater load bearing and shear strength, while, at the same time, being particularly elastic and flexible. In addition, fiber strands 28 provide particularly advantageous water retention and distribution properties. Additionally, fiber strands 28 permit excess water to quickly percolate through the material. A material formed with aggregate, fiber, and binder as discussed above has excellent water resistance in that (1) it sheds water sprayed on its surface; and (2) upon saturation with water, for example, 15% or more water "worked" into the material, it retains a measure of cohesiveness versus going sloppy.

A material in accordance with the present invention provides the following desirable properties: (a) water retention, water distribution, or resistence to drought or saturation; (b) shear strength or tensile strength; (c) resiliency, flexibility, or shock absorption; or (d) positional stability or resistence to separation of a soil mixture. Variations in the granular portion, fiber portion, and binder portion may be made to trade-off economic factors with one or more of the desirable properties discussed above. Certain such variations are shown in TABLE 1. Variations of the type described in TABLE 1 may be accomplished by a method as follows: determining a design goal for the material in terms of desirable properties; preparing a set of candidate materials, each candidate having a different variation in one or more constituents (e.g., materials, size distributions, configuration distributions, relative amounts, etc.); selecting a candidate having the most desirable properties by analysis, inspection, or test (e.g., a conventional California bearing ratio (CBR) or friction angle test); determining a more limited range of variation; preparing a second set of candidates having a variation within the limited range; and repeating the steps of selecting, determining, and preparing until the step of selection provides a candidate having characteristics that meet or exceed the design goal. Various materials according to aspects of the present invention may be used for stabilizing soil in the presence of shock, vibration, or traffic as described by example in TABLE 2. TABLE 1

Positional stability, volume Uniform particle sizes and Stability increases with cohesion change, angle of internal friction uniform fiber lengths aid yet brittleness may upset maintaining homogeneity; longer homogeneity over time; highly fibers may improve angle of cohesive materials may provide internal friction; increased binder poor water distribution; may increase cohesion

TABLE 2

A material of the present invention provides a resilient surface with significant load bearing strength without using large gravel. It is also particularly advantageous for environments that require the surface to retain its consistency and resiliency over a wide range of weather conditions, and quickly recover consistency and resiliency after the range is exceeded.

For a golf bunker, the top layer of sand is supported on an intermediate layer comprising aggregate, fiber, and binder. The aggregate preferably comprises angular particles of a plurality of sizes, ranging downward from a predetermined maximum size (e.g., 2 mm) chosen to assure that no particles of potentially harmful size are present. More particularly, an intermediate layer comprises, in predetermined proportion, an aggregate of fine gravel/very coarse sand (e.g., particle size of approximately 2 mm); coarse sand (particles of from about 0.5 to 2 mm); fine sand (e.g., particles in the range of 0.05 to 0.5 mm); silt and clay (particles from 0.0002 to 0.05 mm); fiber strands; and binder that adheres to the particles and fiber strands and may fill interstices. The aggregate preferably includes no particles more than a predetermined maximum size, e.g., 2 mm in diameter. The aggregate suitably includes: 1 -6% by volume of particles (gravel/very coarse sand) of the maximum size 20%-50% coarse sand; 20%-50% fine sand; and 10%-40% silt and clay. Preferably, the aggregate includes l%-3% gravel (e.g., 2 mm); 30%-45% course sand; 25%-45% fine sand; and 15%-30% silt and clay. Ideally, the aggregate includes approximately 1.3% gravel (es, 2 mm), 38.2%o coarse sand, 36.3% fine sand, and 24.2% silt and clay. Such aggregates are particularly advantageous in that they do not include any rock particles that are sufficiently large to cause injury or damage under normal circumstances to golfers or equipment. For example, fiber strands are suitably in the range of about 0.1 to about 3.0 inches (0.25 to 7.6 cm), typically in the range of about 0.125 to about 2.0 inches (0J to 5 cm), preferably in the range of about 0J25 to about 0.5 inch (0.32 to 1.3 cm) and most preferably, 0.25 inch (0.6 cm). For blown application, fibers with lengths in the range of one-eighth inch to three-quarters inch, and particularly one-quarter inch to one-half inch, are preferred. Fibrillated (multi-strand) fiber quarter-inch length, and 360 denier (approximately one-eighth inch wide) is preferred. During the mixing process the fibrillated fibers, in effect, open up to present a spread net structure.

A material of the present invention may be used as the surface for unpaved roads, athletic fields, sports courts, and pedestrian paths. Here, for example, relatively wet conditions must be tolerated and recovery should be quick after a substantial rain or freeze thaw. The fiber portion provides for relatively fast distribution of water and for speedy percolation of excess water through the surface. The surface is more quickly playable after a rainstorm or watering. The surface is advantageous because the surface is safer in that slippery conditions from excess water are quickly eliminated. As discussed above, the particular fiber strand size, the relative amounts of the various sized components of the aggregate, and the amount and composition of binder may be varied to provide the desired performance characteristics for each particular surface. For surfaces designed to accommodate vehicular as well as foot traffic, the maximum size of the aggregate particles is preferably relatively large, for example, about 0.375 inch (0.95 cm); about 2 to 15%, preferably about 2 to 10%, and most preferred, about 5 to 6% by volume. In such applications, fiber strands would suitably be in the range of about 0.25 to about 2 inches (0.6 to 5 cm) in length, preferably in the range of about 0.5 to about 1.5 inches (1.2 to 3.8 cm), and most preferably, about 0.75 inch (1.9 cm). For roadway applications, a material of the present invention should be about 2 to 10 inches (5 to 25 cm) thick.

To provide a relatively tight, hard surface, as needed for example in a baseball infield, it may be preferable to use relatively short fiber strands (e.g., about 0J25 inch (0.25 cm) or shorter) with an aggregate similar to that described above in connection with a track. Consistent resiliency is provided for predictable baseball trajectories off the surface.

In a turf football field, it may be preferable to use relatively long fiber (e.g., about 1.5 inch (3.8 cm) or longer) in greater relative amounts (e.g., about 4 to about 12 pounds per U.S. ton (8 to 24 Kg/MT)) to provide greater shear strength, and for better drainage and to facilitate turf growth, less binder and more uniformly sized aggregate particles with less clay and silt. Aggregate meeting the USGA sand specification is preferred for turf fields. If desired, fertilizer may also be included.

The amount of fiber strands in strip form for various applications may range from about 0J percent by weight up to about 5 percent by weight, with about 0.25 percent being preferred. A landscaping material of the present invention may include a sandy silt, about a 0.03 inch (0.76 mm) cross-section polypropylene fiber about 1 inch (2.54 cm) long, and a binder as discussed above. The relatively large fiber diameter and short length may provide resistance to wind disturbance, bulking, curling, and the like. The fiber portion may include a monofilament configuration having a round cross-section and a cylindrical design. The fiber portion may amount from about 0.2 to about 1.5 weight percent fiber.

For mass fills to supports for buildings, roads, and other uses, the material may be first mixed and then graded. Addition of the fiber portion may be accomplished at the site using a conventional mixing technique, for example, by broadcasting or laying the fibers or slit film fibers or both and then blending via blade, grader, disc, or harrow, or via mixing with pulverizing mobile mixer, hydrostatic travel mixer, shredder mixer, or the like. Steeper side slopes for embankments are possible inasmuch as the average angle of internal friction is improved significantly by the addition of the fiber portion discussed above. As a result, less fill dirt is necessary and transportation costs may be reduced. Moreover, because space is often at a premium in highway and embankment construction, by using soil having improved properties, lateral spacing may be reduced. Soil reinforced according to the present invention also provides the ability to reduce volume change or settlement in high fills because of the improved modulus. Likewise, the long term strength of backfill soils behind walls, retaining structures and the like are improved since greater cohesion and angle of internal friction values, or shear strength, produce lower earth pressures thereby reducing the potential for lateral movement. Also, less structural support is required for soils placed behind retaining structures. Finally, stabilizing the face of fill slopes, whether they be landfill slopes or dredge spoil (underwater) slopes, is accomplished by this invention based upon the extremely favorable enhancement of soil strength and deflection characteristics.

It should be appreciated that the foregoing description is of preferred embodiments of the present invention contemplated by the inventors at the time of filing. Such embodiments, however, are merely exemplary. The invention is not limited to the specific components and ranges described. Modifications to the embodiments described above are contemplated, and may be made within the scope of the invention, as defined by the claims.

Claims

What is claimed is:

1. A material for providing a stable resilient ground surface, the material comprising a mixture of: a particulate aggregate of particles having sizes within a first selected range; a selected amount of fiber strands having lengths within a second selected range; and 5 a selected amount of binder comprising oil and polymer.

2. The material of claim 1 wherein the first selected range comprises a maximum particle size of about 2.0 millimeters.

3. The material claim 1 wherein the aggregate comprises sand, silt, and clay.

4. The material of claim 3 wherein the aggregate comprises from about 10 to 90 weight percent 10 sand particles having size from about 0.05 to about 1.0 millimeter diameter.

5. The material of claim 3 wherein the aggregate comprises: from about 40 to about 50 weight percent sand particles having size from about 0.05 to about 0.5 millimeter; and from about 30 to about 40 weight percent sand particles having size from about 0.5 to about 1.0 millimeter diameter.

6. The material of claim 3 wherein the aggregate comprises from about 10 to about 30 weight percent silt and/or clay.

7. The material of claim 1 wherein the aggregate comprises from about 10 to 25 weight percent silt/or clay.

20

8. The material of claim 1 wherein the aggregate comprises from about 12 to 22 weight percent silt and/or clay.

9. The material of claim 6, 7, or 8 wherein a weight composition ratio of silt and clay is in the range from about 1 :3 to about 3: 1.

10. The material of claim 6, 7, or 8 wherein a weight composition ratio of silt and clay is in the

25 range from about 1 :2 to about 2: 1.

11. The material of claim 6, 7, or 8 wherein a weight composition ratio of silt and clay is about 1:1.

12. The material of claim 1 wherein the fiber has a denier in the range from about 360 to about 1000.

13. The material of claim 1 wherein the second selected range comprises from about 1.9 to about

30

3.8 centimeters.

14. The material of claim 1 wherein the fiber has a specific gravity in the range from about 0.8 to about 2.4.

15. The material of claim 1 wherein the fiber comprises at least one of polyproplylene, polyester, , , nylon, acrylic, rayon, acetate, triacetate, olefin, and polyolefin.

16. The material of claim 1 wherein the fiber comprises monofilament strands and slit film strands.

17. The material of claim 1 where the fiber comprises at least one shape of flat, fϊbrilated, embossed, collated, entangled, slubbed, spiraled, gnarled, crimped, multilobal, triangular, bundled, saw-toothed, and cork-screwed.

18. The material of claim 1 comprising about 80 to about 90 weight percent aggregate; about 0.05 to about 5 weight percent fiber; and about 0.5 to about 5 weight percent binder.

19. The material of claim 1 comprising about 96 to about 99 weight percent aggregate; about 0J to about 2 weight percent fiber; and about 1 to about 3 weight percent binder.

20. The material of claim 1 comprising about 97.75 weight percent aggregate; about 0.25 weight percent fiber; and about 2 weight percent binder.

21. The material of claim 1 wherein the binder comprises from about 2 to about 10 weight percent polymer.

22. The material of claim 1 wherein the binder comprises from about 4 to about 8 weight percent polymer

23. The material of claim 1 wherein the polymer comprises at least poly-alpha olefin, interpolymer, ethylene, propylene, vinyl acetate, methylacrylate, ethylacetate, and butene.