ASTM D4751-16 pdf free.Standard Test Methods for Determining Apparent Opening Size of a Geotextile. These test methods cover the determination of the apparent opening size (AOS) of a geotextile either by dry-sieving glass beads through a geotextile (Method A) or by using a capillary porometer (Method B). 1.2 Method B will not be used in lieu of Method A unless...