ASTM D-4833 “Pin Puncture” Versus ASTM D-6241 “CBR Puncture.”

ASTM D-4833 “Pin Puncture” Versus ASTM D-6241 “CBR Puncture.”

Puncture strength measures a geotextile’s ability to resist damage from the stresses associated with the installation process. Until recently, ASTM D4833, “Standard Test Method for Index Puncture Resistance of Geomembranes and Related Products,” also known as “Pin Puncture,” was used to determine a geotextile’s puncture resistance. This test was adopted from standard textile testing and the ability to withstand the puncture of an 8mm, beveled pin was more relevant to a shirt or pair of pants than a geotextile.

As such, the geotextile industry determined Pin Puncture was an insufficient method for measuring a geotextile’s performance and have replaced it with ASTM D6241, “Standard Test Method for the Static Puncture Strength of Geotextiles and Geotextile related Products Using a 50-mm Probe.” This test utilizes a 50mm diameter, flat-ended probe (plunger) that is pushed slowly through the geotextile. The relatively large size of the plunger provides a multidirectional force on the geotextile and simulates the stress of big stones being pressed onto a geotextile laying on a relatively soft sub-base.

 

 

 

 

 

 

 

Unfortunately, it will take many years for specifications requiring Pin-Puncture to filter out of the specifying community. Additionally, some current products may not currently have the CBR testing included in their data. This creates a problem for those in charge of approving geotextiles. How does Pin Puncture and CBR Puncture correlate, if at all?

Many studies have passively compared ASTMs D-4833 and D-6241 or determined a trend, but a correlation of Pin Puncture and CBR Puncture testing methods, independent of manufacturing or material type, has not been attempted.

A May 2014 Thesis by Stacy Van Dyke of the University of Milwaukee-Wisconsin undertook determining a correlation. Her final formulas allow one to estimate a decent ball-park CBR value (and vice-versa) when only one set of data is available. Below are the two formulas for woven and nonwoven geotextiles. This is only offered as a way for an engineer to get a feel for the CBR puncture of a fabric when Pin Puncture is the only available value submitted (or vice-versa). The formulas tend to run a little high in our opinion, but give a good estimate regardless.

Pin Strength x 5.27 = Estimated CBR for Nonwovens.

Pin Strength x 7.378 = Estimated CBR for Wovens.

I hope this is helpful!

Permittivity Vs Permeability

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]

Permittivity 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

ILLUSTRATION B

Asking The Right Questions

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.

Do Not Create “Ala Carte” Geotextile 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 “Geotextile Used As Filters” 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

The table requires ASTM D-4833 pin puncture and ASTM D-4884 mullen burst. 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 existing, 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!

Construction Entrance: Chatfield College, Fayetteville, OH

Construction Entrance: Chatfield College, Fayetteville, OH

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

CALL US ABOUT YOUR PROJECT

If you have a project that you would like to discuss, please contact us a (800)518-2290 or email us at info@usfabrics.com.

 

Commercial Parking and Coal Storage: Champaign Coal & Stove Co.

Commercial Parking and Coal Storage: Champaign Coal & Stove Co. Urbana, OH.

US Fabrics was approached 8 years ago by Champaign Coal & Stove owner Pete Aksenczuk, regarding the construction of a parking lot and coal storage facility for his business. The facilities’ regular traffic includes fully loaded semi’s weighing approximately 44,000 lbs.

Pete was skeptical regarding the value of using a geotextile fabric. He had been told by several people that geotextiles did not work well and added little value. This is not uncommon, as many contractors are unfamiliar with the use of geotextiles and rock suppliers see them as a detriment to business.

After speaking with US Fabrics’ Dan Bonn regarding the long track record of success with geotextiles for this specific application, he decided to move forward. Dan recommended US 200, a woven geotextile that meets AASHTO M-288 Class 3 for separation and stabilization applications.

This area was cut out to approximately 4 to 6 inches deep. The US 200 was placed and then covered with 6 inches of compacted rail-road gravel.

 US 200: An “Amazing” Product.

8 years later, US Fabrics received a call from Pete looking to purchase US 200 for another project. He wanted us to know how pleased he was with his decision to use a geotextile. According to Pete, “I have never had to add gravel or re-grade it other than adding a top coating of limestone to the coal storage area this spring.” THAT’S 8 YEARS LATER! Pete is now a true believer in what he describes as an “amazing” product. As the photos below demonstrate, US 200 is an exceptional value and performer:

(8 Years After Insallation)

 

 

 

 

 

 

 

 

 

 

PAY US ONCE OR PAY THE GRAVEL GUY EVERY YEAR!

 

 

 

 

 

 

 

US 200 minimizes rutting and prevents intermixing of the aggregate with the soft soils below. Think of US 200 as affordable insurance for your aggregate. It saves time and money by reducing or eliminating the need for additional rock.

US 200 is placed between the aggregate and the subgrade to stabilize the soil, preserve the aggregate and reinforce the surrounding soil. It will also keep mud below the rock from “pumping” up and help keep cleanup to a minimum.

If you are building a road, constructing a parking lot, stabilizing material staging areas or repairing/installing a gravel driveway, US 200 performs at a high level and saves time and money.

  • Minimizes Rutting
  • Improves Performance
  • Reduces Maintenance Costs
  • Prevents Intermixing of Aggregate & Soil
  • Cost-Effective
  • Affordable “Aggregate Insurance”
  • Saves Time & Money
  • High Tensile Strength

 CALL US ABOUT YOUR PROJECT

If you have a project that you would like to discuss, please contact us a (800)518-2290 or email us at info@usfabrics.com.

Problematic Specifications – An Example

Our “Guide to Better Geotextile Specifying,” detailed many issues we encounter with geotextile specifications. Our first blog post discusses a problematic specification that was recently forwarded to us. This specification was for a park-on/drive-on, separation and stabilization project. It required a geotextile and geogrid be laid on the subgrade with a sand/shell mix placed on top.

Click Here for the Spec

This specification has numerous concerns and is an excellent example of several of the points we made in the guide. Our intent is not to single out one specification or engineer.  Unfortunately, most engineers receive only a cursory education in geotextiles. As such, it is commendable that some well-crafted geotextile specifications exist. However, citing specific problems with current specifications is an excellent way to engage these issues with specifiers.

WOVEN OR NONWOVEN?

A strong specification is clear regarding which geotextile styles are acceptable. Section 2.05 C. describes the geotextile as a “woven continuous filament polyester or polypropylene. Fabric shall be spun-bonded, needle-punched, or otherwise mechanically interlocked.” This description is very problematic. Here is why:

A woven geotextile is manufactured in these structures or types:

  • slit-film (tape)
  • monofilament
  • combination of the two
  • fibrillated

A nonwoven geotextile is manufactured from two different fiber types:

  • continuous filament
  • staple fiber

A nonwoven geotextile is manufactured in several types including:

  • spun-bonded
  • heat-bonded
  • needle-punched

As you can see, 2.05 C. requires an impossibility: a woven geotextile made with nonwoven fibers and possibly manufactured like a nonwoven.

Further confusion is introduced in Section 2.05 I.2. It describes the product as being installed “bearded or fuzzy side down and smooth side up.” This is a clear reference to a nonwoven geotextile. However, the specification mentions “woven fabric” in sections 2.05 D. and 2.05 E.

It is completely unclear if the specifier is requiring a woven or a nonwoven.

MARV WEIGHT ISSUE

Section 2.05 D.1 requires the weight be “6 oz. per sq. yard minimum.”

As we discussed in our “Guide to Better Geotextile Specifying,” MARV weight is almost exclusively specified for nonwoven geotextiles used in environmental applications such as landfills. MARV weight does not apply to woven geotextiles. In fact, typical weight is rarely specified for woven geotextiles. This adds further confusion as to which type is required.

CONFLICTING PROPERTIES

A MARV 6oz nonwoven would typically have a Grab Tensile Strength of 165 pounds. However, the spec calls for 300 pounds, which equates to a 12 ounce MARV. This is why we recommend steering clear of specifying weights with nonwovens. The strength is the more important property.

DISCONTINUED, INCORRECT or NO ASTM TEST METHODS

The geotextile industry in the United States relies on ASTM for useful and consistent test methodologies. However some of these methods are misunderstood by the specifying community. Additionally, ASTM methods are dynamic and can become obsolete, modified or replaced with newer methods. Section 2.05 D has several issues with obsolete and incorrect test methods:

  • ASTM D-1682 is for grab tensile textiles, not geotextiles and was withdrawn by ASTM in 1992.
  • ASTM D-117 is listed as the method for Trapezoid Tear. The correct method is ASTM D-4533. ASTM D-117 refers to “Standard Guide for Evaluating Nonwoven Fabrics” which was withdrawn in 2009.
  • There is no test method listed for Puncture Resistance. Regardless, it is no longer recognized by ASTM as an acceptable geotextile test and has been replaced by ASTM D-6241CBR Puncture.

SPECIFYING OUTDATED, INCORRECT OR VAGUE PRODUCTS

Products that have not been manufactured for decades regularly show up in specifications. Without a reliable way to cross-reference these products the geotextile supplier is left to guess the specifier’s intentions.

2.05 E. lists acceptable fabrics that are:

Companies and brands no longer in business:

  • Exxon
  • Phillips Fibers Corporation
  • Supac
  • 6WS

Generic terms for all types of geotextiles:

  • “Engineered Fabrics”
  • “Stabilization Fabrics”
  • “Exxon Geotextile”

Incorrect product nomenclature:

  • “GFT 300” is probably GTF 300 by Thrace/Linq (formerly Exxon)

Products that do not meet the specification:

  • GTF 300 does not meet the 6 oz. MARV weight requirement

PLACING RESPONSIBILITY OF CHOOSING PRODUCT ON MANUFACTURER

Section 2.06 requires a geogrid, but leaves the specifics up to “manufacturer’s recommendations.” Most manufacturer sales reps are not engineers, nor would they have the site specific information required to make such a recommendation. The specifier needs to be clear on all products.

OUR RECCOMENDATION

US Fabrics recommended US 315 and BaseGrid 11 for this project. US 315 meets AASHTO Class 1 for separation and stabilization and is an equal to the GTF 300 product listed as acceptable. BaseGrid 11 is a “Type 1” punched and drawn geogrid and the most popular for this type of application.

MAKING THE SPEC CLEARER

An excellent starting point for many specifiers is the American Association of State Highway and Transportation Officials (AASHTO) “Geotextile Specification for Highway Applications” or M288-06(2011). An AASHTO Type 1 is an excellent choice for a geotextile for this application.

For the past 20 years a “Type 1” or “Type 2” punched and drawn geogrid has been used with a geotextile for this type of application.

We would suggest writing the specification in this manner:

  • Geotextile fabric shall be: AASHTO M288-06(2011), Stabilization, Class 1, <50%.

Acceptable products include: US 315 as sold by US Fabrics Inc., 3904 Virginia Ave, Cincinnati, Ohio 45227. (800)518-2290. Or equal.

  • Geogrid shall be: Biaxial, punched and drawn, Type 1.

Acceptable products include: BaseGrid 11 as sold by US Fabrics Inc., 3904 Virginia Ave, Cincinnati, Ohio 45227. (800)518-2290. Or equal.

We hope you found this information useful. If you have a specific application you would like to discuss or require further information, please feel free to phone us at 800-518-2290 or email us at info@usfabrics.com. We would love to help. 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!

 

DO NOT USE AASHTO SPECIFICATION WITH QUALIFIERS.

DO NOT USE AASHTO SPECIFICATION WITH QUALIFIERS.

An oft 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 attached specification 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 special 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

CALL US ABOUT YOUR PROJECT

If you have a project that you would like to discuss, please contact us a (800)518-2290 or email us at info@usfabrics.com.

Reducing System Thickness with Cellular Confinement

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)

* 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:

  • 15” of crushed stone (.14 SC Value)
    1. (15 x .14) + (2 x .41) = 2.92
  • 6” EnviroGrid® with sandy soil (.35 SC Value)
    1. (6 x .35) + (2 x .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: