No abstract

The filtration performance of a geotextile is controlled by its pore opening size distribution ͑PSD͒. Current methods for determining PSD are mostly indirect and contain inherent disadvantages. Recent technological advancements in image analysis offer great potential for a more accurate and direct way of determining the PSD of nonwoven geotextiles. A new and accurate method of image analysis for PSD determination of nonwoven geotextiles is presented in this paper. The image analysis method was developed using various mathematical morphology algorithms to provide a complete PSD curve for each geotextile. The two characteristic pore opening sizes, O 95 and O 50 , were determined from image analysis and were compared to the results from laboratory tests, analytical equations, as well as manufacturer's reported apparent opening sizes ͑AOS͒. The image-based O 95 pore opening size of various geotextiles was comparable to the manufacturer's reported AOS as well as to those determined from the laboratory dry sieving test. However, the measured O 50 pore opening size was lower than the one determined using the analytical equations developed by two previous researchers. Overall, the image analysis method presented provides a unique and accurate method that can measure fiber thickness and pore opening sizes in a cross-sectional image of a woven geotextile.

Filtration performance of nonwoven geotextiles strongly depends on pore opening constriction size, i.e., the minimum opening size of flow channels across the geotextile. Currently available methods of pore opening characterizations do not provide accurate information about the constriction size. This paper presents the constriction size distributions of eleven nonwoven geotextiles commonly used as filters based on a probabilistic approach coupled with image analysis, named constriction size (CONS). The image analysis method was developed using mathematical morphology operations. Randomness in the structure of geotextile media was modeled using Markov chain processes. Two characteristic constriction sizes, C 95 and C 50 , were determined and compared with the available results from laboratory tests, theoretical equations, and manufacturer's reported apparent opening sizes. The CONS-based C 95 constriction size was comparable to C 95 determined using the bubble point test. On the other hand, the CONS-based C 95 was consistently lower than the manufacturer's reported apparent opening size, which is typically determined on the basis of the dry sieving test. Similarly, the CONSbased C 95 , was highly comparable with the value suggested by a theoretical equation. The observed differences in the constriction sizes determined by CONS versus the available physical tests may be reflective of the nature and indirectness of the physical tests rather than inaccuracies associated with CONS, which is based on direct observation of pore openings.