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 repro-ducibility and to clarify technical aspects of the calculations found in the practice.
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