“Do Not Create ‘Ala Carte’ Specifications”

Writing geotextile specifications can be an excursion into unfamiliar territory for specifiers. The best intentions can result in a confusing specification or one for which there are no conforming products.

It’s important to note that geotextiles cannot be created ala carte. Specifiers must review existing geotextile products and choose the product with the combination of strength and hydraulic properties that best fit the project’s needs.

Click here for an example of a specification that appears to be the result of this ala carte approach to specifying. I want to discuss the issues that arise with this particular specification.

Woven or Nonwoven?

Section “2.1 Materials, A” calls out for a “woven pervious sheet.” However, the accompanying “Table – Geotextile Physical Properties” requires the geotextile to “equal or exceed” a grab tensile of 180 at 50% elongation. A woven geotextile will typically only meet a maximum elongation of 15-20%. However, nonwoven geotextiles will meet the 50% requirement.

The property table requires a minimum apparent opening size (AOS) of #100 US sieve. There are currently no woven geotextiles on the market with an AOS meeting or exceeding #100.

A 7 oz. nonwoven meets the grab tensile strength requirement, but has an AOS of #70 US sieve. A 10 oz. would be required to meet #100. But an increase in weight (and hence grab tensile strength) corresponds with a decrease in flow rate. This could be an issue for a geotextile being used as a filter.

Sieve Size (Bead or Number)?

Sieve size is confusing because the SMALLER the US Sieve number, the LARGER the bead size that will pass through the geotextile. As such, a #70 sieve fabric may actually meet the specification since it filters out a larger bead size (0.21 mm) than the #100 sieve (0.149 mm).

Perhaps the specifier understands this, but how do you know for sure? Listing only the bead size eliminates any doubt as to the intent of the specification. You can read more about Sieve Size here.

Antiquated Properties And Incorrect Test Methods

The table requires ASTM D-4833 pin puncture and mullen burst which is listed incorrectly as ASTM D-4884. The correct method is  ASTM D-3786. Regardless, these two properties are no longer recognized by AASHTO and have been replaced by the more appropriate ASTM D-6241 CBR puncture. CBR puncture is more relevant since it simulates big stones pressed onto a geotextile laying on a relatively soft sub-base.

Abrasion Resistance

While ASTM D-3884 abrasion resistance is a valid ASTM test method, it has several issues. According to ASTM: “. . . caution is advised since information on the precision of the test is lacking.” They further note: “The resistance of abrasion is also greatly affected by the conditions of the tests, such as the nature of abradant, variable action of the abradant over the area of specimen abraded, the tension of the specimen, the pressure between the specimen and abradant.” They also state that “the dimensional changes in the specimens; and the resistance of geotextile materials to abrasion as measured on a testing machine in the laboratory is generally only one of several factors contributing to performance or durability as experienced in the actual use of the material.” The result is an index property that offers little practical value to the engineer.

As such, abrasion resistance is not performed as part of standard geotextile conformance testing. It may be difficult to get a value from the geotextile manufacturer, much less a certification.

What is a Specifier to Do?

Choose a product best suited to the job’s requirements from current, published manufacturer’s technical data sheets. Do not make any changes or add any qualifiers to the description and table data on the data sheet.

Most geotextile manufacturers publish their current technical geotextile data sheets by product type on their websites. US Fabrics has a “Product Data Sheets” drop down menu box on most pages to locate current data sheets by product type/application.

We Can Help!

You can always call us at (800)518-2290 and we will be glad to point you in the right direction. We also offer a free account with access to detailed product information as well as drop in specifications for many of our products for various applications. Above any product data sheet you will see a green button that says “Detailed Product View” or “Drop In Specification”. Click on either and you will be directed to a sign up page.

You can also sign up to download our “Guide to Better Geotextile Specifications” to learn more.

Thanks for reading and happy specifying!

AOS (ASTM D-4751) – A Straightforward Method a Confusing Result

AOS (ASTM D-4751) – A Straightforward Method a Confusing Result.

AOS (Apparent Opening Size) is a straightforward test. During the test, spherical, solid glass beads are dry sieved through a geotextile for a specified time and at a specified frequency of vibration. The amount of beads retained by the geotextile sample is then measured. The test is carried out on a range of sizes of glass beads. The apparent opening size is the pore size, measured in millimeters, at which 90% of the glass beads are retained on and within the fabric.

US Sieve in Relation to Millimeter Bead Size

Unfortunately, AOS is reported in a confusing manner. The problem lies in the relationship between the U.S. Mesh or Sieve number and the correlating millimeter bead size. For example, a 60 Sieve has a corresponding bead size of .250 mm. A 40 Sieve has a corresponding bead size of .400 mm. So the SMALLER the US Sieve number, the LARGER the particle size that will pass through the geotextile.

The Devil is in the Details

The most common way this property is reported is: “No. 60 sieve, maximum.” This is problematic. What is the intent here? Does the specifier want a fabric that will not pass any larger than a .250 mm bead? Or does he want a fabric with no larger than 60 Sieve number? In the first case, a 40 Sieve would not meet the specification, since the corresponding BEAD SIZE is .400mm, which is larger than the 60 Sieve .250 mm bead size. In the second case, a 40 Sieve is a smaller NUMBER than the required 60 Sieve, so it would be acceptable. How is one to know for sure? Leaving the intent of a specification to a geotextile company or contractor is certainly not what most specifiers have in mind.

Here’s How It Can Go Wrong

The attached specification is a perfect example of how the relationship between sieve number and bead size can really create confusion. In section 2.02 B, the specifier has required an AASHTO M-288, woven class 2 geotextile. The properties listed are taken verbatim from the AASHTO tables. However, the specifier has added the bead size in parentheses after the AOS Sieve Size. The M-288 specification does not include the bead size. While we believe this to be un-intentional, if interpreted as written, this specification now requires a maximum bead size of .250 mm. This would eliminate a 250# tensile strength woven slit-film; the very product the AASHTO M-288 specification was meant to require.

The Solution

Always resist the temptation to add the millimeter bead size if the specification only lists the US Sieve number and vice-versa. However, it is our belief that specifiers should list only the bead size to eliminate any doubt as to the intent of the specification. In the case of the attached specification it should read: “AOS .250 mm, minimum.”

  • US Mesh or Sieve is a NUMBER that correlates to a specific millimeter bead size
  • The LARGER the US Sieve number, the SMALLER the bead size
    • 60 Sieve = .250 mm
    • 40 Sieve = .400 mm
  • Avoid confusion by specifying only the millimeter bead size
    • “AOS .250 mm, minimum.”

We hope you found this information helpful. Thanks for reading our blog!

The Mistake Of Adding Qualifier’s To The AASHTO Specification

DO NOT USE AASHTO SPECIFICATION WITH QUALIFIERS.

An often repeated mistake of the specifying community is to add qualifiers to the AASHTO M-288 standard specification. It’s important to keep in mind that each AASHTO Class refers to a set of specific physical and hydraulic properties. These are not “stand alone” properties. For example, increasing the tensile strength or mass per unit of a nonwoven geotextile will negatively impact the hydraulic properties of that geotextile.

A Specification That Cannot Be Met

The specification found here is a good example of this issue. Here the specifier is requiring an “AASHTO M 288 Class 1”. However, the qualifier of “and weighs at least 15 oz/yd2” is added. It is important to note that AASHTO does not currently include ASTM D-5261 Mass Per Unit Area in its specification. However, we can determine a weight. An AASHTO Class 1 nonwoven has a tensile strength of 205 pounds. A typical weight for a 205-pound nonwoven is 8 oz/sy2.

A second issue arises because a 15 oz/sy2 nonwoven is not a standard product. The closest standard product is a typical 16 oz/sy2. The chart below compares the physical and hydraulic properties of a typical 16 oz nonwoven with an AASHTO Class 1 nonwoven. While the 16 oz will surpass the strength requirements of AASHTO Class 1, notice what happens to the hydraulic properties:

PROPERTY TEST METHOD 16 oz/yd2 AASHTO CLASS 1
Weight – Typical ASTM D-5261 16.0 oz/yd2 8 oz/yd2
Tensile Strength ASTM D-4632 380 lbs 205 lbs
Elongation @ Break ASTM D-4632 50% 50%
CBR Puncture ASTM D-6241 1,080 lbs 535 lbs
Trapezoidal Tear ASTM D-4533 145 lbs 85 lbs
Apparent Opening Size ASTM D-4751 100 US Sieve 80 US Sieve
Permittivity ASTM D-4491 0.70 Sec-1 1.35 Sec-1
Water Flow Rate ASTM D-4491 50 g/min/sf 90 g/min/sf

A 15 oz/sy2 nonwoven geotextile cannot meet the Permittivity and Water Flow Rate requirements of a Class 1 AASHTO nonwoven. The oz/sy2 qualifier has created a contradictory specification that cannot be met.

What Was The Intent of the Specifier?

So what is important? Is it weight, hydraulic properties or something else? It falls on the geotextile supplier to answer these questions and determine the intent of the specification. This is a scenario specifiers want to avoid. Many suppliers do not have the product knowledge to understand the issues with this specification since geotextiles are an auxiliary item they offer along with their main product line. Many would simply offer a Class 1 nonwoven. Others may offer a typical 16 oz/yd2. Neither of these would be correct for the intended use, but could be reasonably perceived as meeting the specification.

We believed this to be a “bond-breaker” application since a common specification for a bond-breaker requires a 15.0 oz/yd2 weight. We were able to verify this with the contractor. As such, we took exception to the specification and submitted product data for a specially manufactured bond-breaker product. That data included the properties of Thickness (under load), Permeability (under load) and Hydraulic Conductivity (under load) which are not part of the AASHTO specification, but important for a bond breaker application. So in this case, the important properties were weight as well as something else not addressed in the specification. Adding 15 oz/sy2 to the AASHTO Class 1 specification did not create a bond breaker specification. It created confusion and left room for serious error.

What Product Was Installed?

Since our contractor was not awarded the job, we do not know if the desired product was actually installed. More than likely, neither does the specifier.

  • Do Not Attach Qualifiers to AASHTO Spec
  • Do Not Leave Interpretation of Intent to Suppliers or Contractors
  • Call US Fabrics For Guidance
  • Reduce Possibility of Utilizing the Wrong Geotextile

If you have a project that you would like to discuss, please contact us at (800) 518-2290 or contact us through our website.

 

The Correct Product Every Time!

US Fabrics takes customer service seriously. Before offering you a quotation, we do our best to make sure we have a thorough understanding of the application and all the pertinent specifications and drawings. Then we carefully interpret the information so you can be assured we quote the correct product.

We Know Which Questions To Ask

But this isn’t always easy. Sometimes the information given on the drawings contradicts the specification. Other times, the specification is incomplete, obsolete or mix of properties that can’t be met by a product on the market. In these cases, we know which questions to ask and will work with you to clarify these issues. This may seem like a hassle compared to a construction supply house that will quickly, and often incorrectly, throw out a product and price. But you are not saving any time by submitting, or even worse installing, the wrong product.

Example

We recently received a Request for Quote that asked for: “Geotextile Filter Fabric with the following qualifications: ASTM D4759, ASTM D4873, Minimum puncture strength of 200lbs.” This information was pulled off the project drawings by the contractor.

Incomplete Information

In addition to being incomplete, there are two problems with the information provided. First, it lists two test methods without listing the required values for these tests. Second, it lists a required value for Puncture Strength, but does not give the ASTM test method. Since there are two puncture test methods, we do not know if this value is for ASTM D4833 Pin Puncture or ASTM D 6241 CBR Puncture.

US Fabrics pointed out the ambiguity with the spec to the contractor. We asked if they could verify how the geotextile would be used and if they could find any additional information in the project specifications.

Correct Information Found

Two days later the contractor forwarded the full geotextile specification along with a drawing demonstrating its use. The specification gave a list of properties and called specifically for Mirafi HP 370 or equal. He also included information on a product offered by a construction supply house that was submitted and rejected by the project engineer. It was a very lightweight, nonwoven filter fabric. HP 370 is a high strength woven, erosion control and separation geotextile.

Product Quoted & Submitted

The same day we submitted a quote for our equivalent product, US 3600, along with a side by side data comparison to the HP 370. We are the only company that offers these comparisons with our quotes. We also make them available through our website.

Product Accepted!

The next day we received an email that the project engineer requested additional information which we provided immediately. 3 days later our US 3600 was approved and the Purchase Order was received. This is how it’s supposed to work. We are geotextile experts. It’s our job to make sure you get the correct product, not to just throw out a price and hope for an order. It’s no surprise that our customer loyalty is very high.

Subgrade Thickness

Engineers have the option of utilizing a geosynthetic to reduce overall road system thickness. The following is a quick overview of the benefits of cellular confinement and bi-axial, base stabilization geogrids in reducing overall required layer thickness.

Reducing System Thickness with EnviroGrid® Cellular Confinement

The following table shows the system thickness required to achieve a structural coefficient value of 0.35 for various materials, including EnviroGrid® filled with sandy soil*:

MATERIAL

TYPE

ENVIROGRID® FILLED WITH SANDY SOIL ASPHALTIC

CONCRETE

CRUSHED

STONE

SANDY

GRAVEL

LIME

STABILIZED

SOIL

SANDY

SOIL

REQUIRED LAYER

THICKNESS

FOR S.C. = 0.35

4 inches

(10 cm)

3.4 inches

(8.6 cm)

10 inches

(25 cm)

12.7 inches

(32 cm)

17.5 inches

(45 cm)

20 inches

(51 cm)

6 inches

(15 cm)

5.1 inches

(13 cm)

15 inches

(38 cm)

19.1 inches

(49 cm)

26.3 inches

(67 cm)

30 inches

(76 cm)

8 inches

(20 cm)

6.8 inches

(17 cm)

20 inches

(51 cm)

20 inches

(51 cm)

35 inches

(89 cm)

40 inches

(102 cm)

15” of crushed stone (.14 SC Value)* Utilizing AASHTO design methodology. A complete description of the AASHTO design procedure can be found at www.aashto.org.

Multiplying the SC of a material by the thickness of the layer determines the material layer’s SN. To achieve a SN of 2.90 with a top layer of 2” of asphalt concrete (.41 SC Value), the following are two possible options for the remainder of the base:

  1.  15″ of crushed stone (0.14 SC Value)
    • (15 x 0.14) + (2 x 0.41) = 2.92
  2. 6″ EnviroGrid® with sandy soil (0.35 SC Value)
    • (6 x 0.35) + (2 x 0.41) = 2.92

 

Alternatively, if the structural coefficient of a material in an existing design is known, an engineer can relate the structural coefficient of EnviroGrid® to the material in the design. For example, EnviroGrid® filled with sandy soil has an SC of 0.35 and sandy soil alone has an SC .07. Thus, 4” of EnviroGrid® filled with sandy soil has the same load bearing strength as 20” of sandy soil without EnviroGrid®. Therefore, a road design calling for 18” of a sandy soil fill could be reduced to 4” of EnviroGrid® with sandy soil.

 

Reducing System Thickness with BaseGrid Bi-Axial Geogrids

Bi-Axial base stabilization geogrids can also be used to reduce road system thickness. Utilizing the values calculated by the “RoadWorx, v1.0 Design Prescriptions for Better Roads” we can determine the required road system thickness for an unreinforced road system and one reinforced with a “Type 1” (BaseGrid 11) or a “Type 2” (BaseGrid 12) geogrid:

 

image005.png
Loading Conditions:

20,000 lb / axle load

100 psi tire pressure 1,200 passes

Subbase CBR = 20 (min) 1.5″ wheel rut depth

 

image006.png

 

Loading Conditions:

20,000 lb / axle load

100 psi tire pressure 1,200 passes

Subbase CBR = 20 (min) 3.0″ wheel rut depth

 

Specifying Permittivity in Geotextiles

There is much confusion surrounding permittivity and permeability relating to geotextiles. As a specifier, the most important point is to understand is that permeability as a geotextile property is not supported by the geosynthetic industry. The following will hopefully clarify the differences and underscore why specifying permeability is very problematic.

Permittivity [ASTM D 4491]
first-image-sm_360.jpgPermittivity is the mechanism by which water moves through the fabric. ASTM defines it as “the volumetric flow rate of water per unit cross sectional area per unit head under laminar flow conditions, in the normal direction through a geotextile” (Illustration B) The permittivity test measures the quantity of water which can pass through a geotextile perpendicular to the surface of the geotextile. The permittivity may be measured either in a constant head or falling head test, although constant head testing is more common due to the high flow rates through geotextiles which makes it difficult to obtain readings of head change versus time in the falling head test.

In the constant head test, a head of 50 mm water is maintained on the geotextile throughout the test. The quantity of flow is measured versus time.

In the falling head test, a column of water is allowed to flow through the geotextile and a reading of head change versus time is taken. The flow rate of water through the geotextile needs to be slow enough to obtain accurate readings.

Permeability [ASTM D 4491]

ASTM defines permeability as “the rate of flow of a liquid under differential pressure through a material.” (Illustration B) Geotextile permeability is derived from pemittivity using the nominal thickness of the geotextile. (Illustration A) ASTM notes that “nominal thickness is used as it is difficult to evaluate the pressure on the geotextile during the test, thereby making it difficult to determine the thickness of the fabric under these test conditions.” Keep in mind that nonwoven thickness will decrease under load. It is also important to note that nominal thickness is just that: “existing in name only.” In addition, the geotextile thickness value is only relevant at the time of manufacture. Packaging of the product and method of shipment can negatively impact the geotextile’s thickness. All of these factors make permeability an unreliable property for geotextiles.

History

Permeability soil coefficients are well established and used in various calculations such as structural coefficient for subgrades. The thought was defining a permeability for geotextiles would allow one to compare the geotextile’s permeability to the soil’s permeability. But adding a geotextile’s thickness to the equation does not make the geotextile a “soil” or create a test value to compare to soil just because both now have cm/sec as their units.

At least, it would seem to offer an index test to compare one geotextile to another. However, because geotextiles vary in thickness using permeability nullifies a designer’s ability to compare them, since the permeability value is related to geotextile thickness rather than geotextile cross-plane flow.

Summary

Permittivity is the volumetric flow through a cross section of material. Permeability is the advancement of that water in conjunction with thickness. Geotextile thicknesses vary and are easily impacted by packaging, shipping and load. Furthermore, permeability relies on the nearly meaningless “nominal” thickness value. As such, permeability is an unreliable index test that offers little understanding in how a geotextile will function in situ or how one geotextile will perform compared to another.

Permittivity [ASTM D 4491] is the test method preferred by the geosynthetic industry.

ILLUSTRATION A

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ILLUSTRATION B

image3.png

Pedestrian Trail Installation Guide

Designing and Implementing Your Trail 

If budget permits, trail designers often prefer to surface trails with asphalt or concrete. However, a gravel surfaced trail with a geotextile separator provides an excellent alternative surfacing option. “Crusher run” gravel surfaced trails are eco-friendly, more aesthetically pleasing and economical compared to asphalt or concrete.

Nonwoven geotextiles perform well as separators and are also excellent for drainage, making them exceptional options for such challenging applications as pedestrian trails. They allow water to pass at a high rate while preventing the gravel surface from being pushed down into the subgrade and mud from “pumping” into and mixing with the gravel. Nonwoven geotextiles are made from staple filaments of polypropylene fiber and are needle-punched and heat set, in strengths ranging from lightweight to heavyweight.


Trail.jpg

1.0 General

  • This guideline is for building a relatively flat pedestrian trail with a crusher run (rock) surface.
  • Trail tread grades over 6% will require significantly more maintenance since they tend to unravel or erode faster.
  • If water is an issue that cannot be addressed, do not use crusher run since it is highly susceptible to washouts.
  • French drains can be used to drain a spring or direct water under the trail. See our French Drain Installation Guide for more information.
  • Where contradictions occur follow the instructions of the project engineer.

2.0 Alternate Surface Options

  • Other surface options include wood chips and saw dust.
    1. Sawdust compacts fairly well, but can draw moisture from the ground.
    2. Wood chips are a maintenance issue, can be slippery when wet and will need to be replaced every 3 years.
      1. Avoid cedar chips since toxic leachates could enter watercourses.
      2. Use hemlock, spruce, pine or fir chips.

3.0 Edging

  • Typically, edging a trail should be avoided.
    1. Edges can create a berm or dam that holds water on the trail causing erosion and other trail maintenance issues.
  • Trails surfaced with wood chips must be edged.
    1. Wood chips do not compact well and will spread.
  • If edges are required, install hard, continuous edging:
    1. 4 x 4 ft. landscape timbers.
    2. 7 x 9 inch x 8 ft. railroad ties.

4.0 Trail Widths

  • Trail widths vary depending on use.
    1. 24 to 48 inch widths for standard hiking trails.
    2. 36 to 60 inch widths for more accessible trails.

5.0 Excavate Trail

  • Excavate the trail area to a depth of 4 to 6 inches.
  • Make sure all organic material has been removed from the subgrade and the bed is thoroughly compacted.

 

6.0 Place Geotextile

  • Roll the geotextile out flat in the roll direction, minimizing folds and creases.
    1. It can be easily cut with a quality utility knife.
  • You can cut the entire roll with a Sawzall equipped with a metal cutting blade.
    1. Start your cut until you get through the top of the core and then roll the product forward to finish the cut.
  • Pins or staples are typically not required to hold the fabric in place.
    1. If needed, 6 inch sod staples work well.
  • Overlap adjoining pieces 6 inch to 1 foot.

7.0 Place Gravel

  • The preferred gravel is 3/8” minus crusher run with fines.
    1. Crusher run with fines, unlike washed stone, contains natural binders.
    2. When combined with water and compacted it produces a solid surface that resists deformations from hiking boots and bikes.
  • Crown the finished trail surface at ¼ inches per 1 ft.

8.0 Gravel Coverage Formula

  • Convert trail surface area into square feet (length x width = square feet).
  • Square feet/324 = number of cubic yards needed to cover 1inch deep.
  • Multiply cubic yards by depth of surface desired.
  • Multiply this figure by 1.25 = tons of surface material needed.
    1. Example:

How many tons of gravel is needed for 1/4 mile trail that is 6 foot wide and 4 inches deep?

  1. 1,320 ft. X 6 ft. = 7920 sq. ft.
  2. 7920/324 = 24.44 cubic yds. For 1inch deep surface.
  • 44 x 4 inch deep = 97.6 cubic yds.
  1. 76 x 1.25 = 122.2 tons gravel needed.

9.0 Repair & Maintenance

  • Any damage to the geotextile should be repaired using a second piece with a minimum 1 foot overlap in all directions.
  • If the surface of a crusher fines trail becomes loose and uncompacted it can often be wetted and reshaped.

10.0 Storage

  • Geotextile rolls are wrapped in a UV protective cover.
  • If stored outdoors for a prolonged period, elevate the geotextile from the ground and cover with a tarpaulin or opaque plastic.
    1. Contractor must insure rolls are adequately protected from:
      1. Moisture
      2. Ultraviolet radiation
      3. Chemicals that are strong acids or bases
      4. Temperature in excess of 140ºF
      5. Animal destruction
  • Chemicals that are strong acids or bases

 

 

This material is presented for general information only.  Always verify the suitability for a specific application with the project engineer.  Where contradictions occur, follow the instructions of the project engineer. There is no implied or expressed warranty regarding the installation procedures or the geosynthetic products in this guide. Installation procedure and product choice is the sole responsibility of the contractor and contractor assumes all liability.

 

Installation Guide – Cow Carpet Trail Crossing

Cow Carpet Trail Crossing Installation

According to the Pennsylvania Small Scale Livestock Committee: “Mud creates an unhealthy environment for both horses and livestock.” Mud is a pervasive and expensive problem facing beef and dairy producers as well as horse farms. US 180NW Cow Carpet® is the solution.

Compromised soil conditions in high-traffic livestock gathering areas cause problems for animals, producers and the environment. Grazing cattle congregate in concentrated areas damaging soil, an effect which is exacerbated by farm vehicle and equipment traffic. During periods of wet weather, soil in these areas turns to mud, creating an unhealthy environment for livestock, unsafe traction for farm equipment and the potential for poor surface water quality. Even after the areas dry, they could lead to rough and possibly dangerous footing for the animals.

US 180NW Cow Carpet® will keep your cover material from disappearing into the subgrade and prevent the mud below from intermixing with your cover material. In addition, US 180NW Cow Carpet® will improve the footing and hoof health of your horses and cows. US 180NW Cow Carpet® meets the Natural Resources Conservation Service Class 1 Nonwoven Geotextile Fabric Specification.

1.0 General

  1. This guideline covers general installation of Cow Carpet in trail crossings.
  2. Where contradictions occur follow the instructions of the project engineer.

2.0 Dewater & Excavate

Dewater and excavate the bed of the channel to the necessary depth and width.

3.0 Place Geotextile

  1. Roll the Cow Carpet out flat in the roll direction, minimizing folds and creases.
    • Pins or staples are typically not required to hold the fabric in place.
      • If needed, 6 inch sod staples work well.
  2. Start on the surface of one bank and extend it across the bottom of the stream and up the opposite bank.
  3. Extend fabric past the expected high water mark of the banks.
  4. If overlapping is required, use a minimum of 3 foot overlap.
  5. Cow Carpet can be easily cut with a quality utility knife.
  6. You can also cut the entire roll with a Sawzall equipped with a metal cutting blade.
    • Start your cut until you get through the top of the core and then roll the product forward to finish the cut.

4.0 Place Gravel

  1. Place and compact the gravel.
    • 8 to12 inches is typically sufficient depending on the finished grade.
    • For very weak subgrades, thicker lifts may be required.
  2. The preferred placement method is to dump the stone onto the Cow Carpet and then push it further out onto the fabric.
  3. Try to keep the finished grade of the crossing as close as possible to the natural stream bed bottom.
  4. Dump trucks and rubber tired loaders can be driven directly on the Cow Carpet if needed.
    • Avoid quick stops, starts and turns.
    • Keep speeds less than 10 mph.
  5. The gravel should be spread in the same direction as overlaps to avoid separation between the pieces.

5.0 Type of Stone

  1. The preferred aggregate is crushed and angular and should be large enough so it cannot be washed away by the stream.
    • Limestone is a good option, but other stone will work fine.
    • If the crossing is for livestock, use an appropriate surfacing material over the rock to protect the animal’s hooves.
      • Some names for this type of stone are dense grade aggregate (DGA) or crusher run.

6.0 Repair & Maintenance

Any damage to the Cow Carpet should be repaired using a second piece with a minimum 3 foot overlap in all directions.

7.0 NRCS Class I

Cow Carpet meets most Natural Resources Conservation Service (NRCS) Class 1 Nonwoven Geotextile Fabric Specifications for stream crossings.

8.0 Storage

  1. Cow Carpet rolls are wrapped in a UV protective cover.
  2. If stored outdoors for a prolonged period, elevate the overlay geotextile from the ground and cover with a tarpaulin or opaque plastic.
    • Contractor must insure rolls are adequately protected from:
      • Moisture
      • Ultraviolet radiation
      • Chemicals that are strong acids or bases
      • Temperatures in excess of 140ºF
      • Animal destruction

 

This material is presented for general information only.  Always verify the suitability for a specific application with the project engineer.  Where contradictions occur, follow the instructions of the project engineer. There is no implied or expressed warranty regarding the installation procedures or the geosynthetic products in this guide. Installation procedure and product choice is the sole responsibility of the contractor and contractor assumes all liability.

 

Cost Effective Use Of Woven Geotextile Separation

THE PROJECT

US Fabrics was approached by a contractor regarding the construction of a 2,800 foot long temporary construction entrance through existing farmland. The entrance would eventually be paved and become a permanent entrance for the college. The original specification called for HP370, a costly high strength woven geotextile.

A COST-EFFECTIVE SOLUTION

Due to the cost of the HP370 geotextile, the contractor called US Fabrics looking for a less-expensive option. US Fabrics’ representative Dan Bonn agreed that US 200 woven geotextile would work well given the site conditions, type of rock to be used and expected traffic conditions. US 200 meets the AASHTO M228-06 Class 3 specification for Separation and Stabilization and is US Fabrics’ most popular product for these types of applications. Since the material savings would be nearly $1.00 per foot, the contractor submitted US 200 for approval.

SUCCESS!

US 200 was accepted by the project engineer and installed. The contractor was very pleased with the installation process and two years later the entrance looks like the day it was installed, as the photo below demonstrates.

CORRECT PRODUCT FOR THE APPLICATION

US Fabrics takes pride in making sure our contractors are using the right product for their project. As we have discussed in our “Guide to Better Geotextile Specifying” and on this blog, geotextile specifications are not always correct or optimal. We try to understand the application as well as the specification. If we believe there is a more cost-effective option or the specified product is incorrect for the application, we will offer an alternative to the specified product. If the specification is in error, we will do our best to offer a product that meets the intent of the specification or the requirements of the application.

  • Cost-effective solutions
  • Knowledgeable representatives
  • Proper spec interpretation
  • Correct product for the application
  • AASHTO grade products