New Practice Provides a Calculation Method for Non-Woven Geotextiles

ASTM International Committee D35 on Geosynthetics has developed a new standard that is an important step toward the improvement of filtration design for non-woven geotextiles. The standard, D 7178, Practice for Determining the Number of Constrictions “m” of Non-Woven Geotextiles as a Complementary Filtration Property, will provide engineers and researchers a common basis for accurate determination of an important product property. Practice D 7178 is under the jurisdiction of Subcommittee D35.03 on Permeability and Filtration.

Practice D 7178 describes the procedure used along with existing test methods to determine the number of constrictions “m” of mechanically bonded non-woven geotextiles, based on thickness, mass per unit area and fiber properties. According to Eric Blond, director, geosynthetic division, CTT Group, the number of constrictions is the theoretical number of windows, delimited by three or more fibers, through which soil particles could migrate while passing through a geotextile during a filtration process. “Practically, this number can be used to differentiate non-woven geotextiles with similar opening sizes but different structures, which was found to be a significant issue in soil filtration,” says Blond. “Practice D 7178 helps with calculating the property that best reflects these differences in the structure of the product, along with other properties.” Blond also notes that standardization was necessary to maximize reproducibility and to clarify technical aspects of the calculations found in the practice.

“Practice D 7178 can be used by geotextile manufacturers for optimization of their products with regard to filtration behavior,” says Blond. “It can also be used by engineers and researchers for forensic investigation in the case of a failure, as well as for the design of projects in which filtration is a critical issue. For example, it was found at the design stage of a large sediment capping project [see photo above] that the number of constrictions was the best possible parameter correlating the materials behavior and the geotextiles intrinsic properties.”

In the coming years, Subcommittee D35.03 will be used as a technical platform dedicated to the investigation of the filtration behavior of geotextiles. Interested parties, particularly those involved in soil filtration, are encouraged to participate in the activities of the subcommittee.

CONTACT
Technical Information: Eric Blond, director, geosynthetic division, CTT Group, Quebec, Canada
Phone: 450/778-1870 ex. 229

ASTM Staff: Christine Sierk
Phone: 610/832-9728

Upcoming Meeting:
Jan. 31-Feb. 2, 2007
January Committee Week
Costa Mesa, Calif.