# Monitoring of the Variation in Pore Sizes of Woven Geotextiles with Uniaxial Tensile Strain
## 1 Introduction  
Geotextiles have been utilized as filters in numerous geotechnical and environmental protection applications, such as drainage trenches and sludge dewatering [1; 2; 3]. To assure effective filtration performance, the filter design involves retention capability and the anti-clogging function of geotextiles. The percent open area (POA) and pore-opening size are commonly used as pore structure parameters defining filter design criteria of woven geotextiles [4; 5; 6]. In addition, the POA is usually dependent on the pore-opening size O\({}_{95}\)[5; 7]. Conventional standards suggest that apparent opening size (AOS or O\({}_{95}\)) and filtration opening size (FOS or O\({}_{98}\)) are characteristic pores for geotextile filter design [8; 9; 10; 11]. O\({}_{95}\) (or O\({}_{98}\)) describes that pore diameter for which 95% (or 98%) of the remaining pore diameters are smaller, obtained in sieving tests, in bubble point tests, or tests using image analysis [12]. The specific filtration opening size O\({}_{95}\) ignores that pore-opening sizes vary at a wide range in practice. As manufactured products, woven slit-film geotextiles show different frequency distributions for various pore sizes. Consequently, uncertainties still exist regarding the prediction about the influence of different characteristic pore sizes on the filtration performance of woven geotextiles. A series of tests carried out by [PERSON] suggested that the numbers of soil particles passing through two types of geotextiles were quite different despite the same filtrationopening size [13]. Compared with a specific pore-opening size value, the pore-size distribution (PSD) curve indicated various sizes of pore diameters, including O\({}_{98}\), O\({}_{50}\), O\({}_{10}\), etc., [14]. Considering various characteristic pore-opening sizes, [PERSON] et al. indicated smaller pore-opening sizes (O\({}_{50}\), O\({}_{30}\), and O\({}_{10}\)) of nonwoven geotextiles were less sensitive to tensile strain than larger characteristic pore-opening sizes (O\({}_{95}\) and O\({}_{98}\)) [12]. [PERSON] et al. determined two characteristic pore-opening sizes, O\({}_{95}\) and O\({}_{50}\), derived from the pore-size distribution of unstrained woven geotextiles [6]. There are limited studies carried out in predicting various characteristic pore sizes of woven slit-film geotextiles. In the practice of filtration, geotextiles are typically subjected to tensile strains [15]. Therefore, many laboratory tests have been conducted to investigate the filtration behaviors of woven and nonwoven geotextiles under various tensile loads [12; 16; 17]. [PERSON] et al. and [PERSON] et al. suggested that O\({}_{95}\) and O\({}_{98}\) increased linearly with notable tensile strain for woven slit-film geotextiles [18; 19]. However, problems exist with the currently available methods for determining characteristic pore sizes at every 3% or 5% tensile strain. The woven geotextile tubes suggested an insignificant tensile strain of less than 5%, and the tensile deformation increases slowly with time [20; 21]. The low tensile deformation of geotextiles has gained greater importance in engineering practice and laboratory experiments. Characteristic pore-opening sizes of woven geotextiles are generally determined by the direct method of image analysis [5] and indirect methods, including dry sieving test [8], wet sieving test [10], and hydrodynamic sieving test [22]. The image analysis is a rapid, accurate, and less user-dependent method in determining POA and pore-opening size for woven slit-film geotextiles subjected to tensile strain even for low tensile deformation [5; 18; 23]. The laboratory tests in this paper adopt five woven geotextiles from three manufacturers to assure the effective prediction about pore-opening sizes with uniaxial tensile strain. The image analysis method is used to determine the POA and pore size.