This practice provides a calculation method for determining the number of constrictions m of a non-woven geotextile (or of a layer of a composite material). This standard is not applicable to woven geotextiles, knitted geotextiles, heat-bonded geotextiles or any other type of geosynthetic.

The number of constriction represents the number of x201C;windowsx201D; delimited by three or more fibers, in which soil particles could migrate. In that regard, it can be basically defined by the following equation: where t is the thickness and d_c the average distance between two constrictions. This value has been found to be relevant to explain the different filtration behaviors of non-woven geotextiles with similar opening sizes but different structures for various soil conditions (see Appendix X1 for details).

This value will be used in filtration research to evaluate the prediction of filtration efficiency and effectiveness of various non-woven geotextiles with similar opening sizes (Test Method D 6767).

Interpretation of the significance of m as calculated using this standard shall be done with care as some non-woven structures may not reflect the hypothesis used to establish the proposed equation (see Appendix X1 for details).

1.1 This practice describes the procedure used along with existing test method to determine the number of constrictions m of mechanically bonded non-woven geotextiles, based on thickness, mass per unit area and fiber properties

1.2 The number of constrictions is a property of non-woven geotextiles, which is complementary to opening size to predict their filtration behavio