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.

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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!

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