# Monitoring of the Variation in Pore Sizes of Woven Geotextiles with Uniaxial Tensile Strain
## 2 Materials and Methods
### Test Devices  
The woven slit-film geotextile specimen is gripped in the clamps with a gauge length of 100 mm, according to wide width tensile strength tests [24], then it is photographed by the image acquisition system, as shown in Figure 1.  
The tensile test machine consists of two clamps for securing the sample without slipping, a system for determining a tensile deformation rate of 12 mm/min, and software collecting data of tensile loads and tensile strains during tests. When the machine starts, the sample is stretched in a vertical test direction (warp direction), while the weft direction indicates the direction perpendicular to the warp direction.  
The image acquisition system consists of a Sony A7M3 digital camera with an FE 85 mm f/1.8 lens and a plane light source. This prime lens connected with a digital camera mounted on a tripped for synchronous image acquisition is used. The axis of the camera lens is perpendicular to the plane of the specimens. Figure 1b shows the sample illuminated by a plane light source upright standing behind the test machine. The power of the square LED plane light in this study is set to 15 W. The total area of the plane light is 200 mm \(\times\) 200 mm. The image is captured every 10 s. 1% tensile strain takes place in this duration, considering the tensile rate set to be 12 mm/min. The effective pixels of each  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Geotextile** & **Mass/Unit Area, g/m2** & **Thickness, mm** & **Percent Open** & **O95, cm** \\ \hline W1201 & 119.07 & 0.20 & 3.10 & 0.40–0.60 \\ W1202 & 121.30 & 0.22 & 3.03 & 0.50–0.65 \\ W1203 & 123.11 & 0.23 & 4.80 & 0.60–0.65 \\ W1504 & 149.76 & 0.27 & 1.98 & 0.30 \\ W2505 & 247.06 & 0.58 & 6.10 & 0.60–0.65 \\ \hline \hline \end{tabular}  
* Woven slit-film geotextile from manufacturer a. b Woven slit-film geotextile from manufacturer b. c Woven slit-film geotextile from manufacturer c.  
\end{table}
Table 1: Properties of woven slit-film geotextiles used in image analysis.  
Figure 1: Wide width tensile strength test system including: (**a**) Uniaxial tensile test machine; (**b**) Stretched woven slit-film geotextile illuminated by a plane light source.  
captured image are 6024 \(\times\) 4024 pixels, and the actual size of a pixel is calculated referring to the actual size of the picture.  
Figure 2 shows the uniaxial tensile load-strain plots for five woven geotextile specimens. The woven geotextiles have a wide range of peak tensile loads ranging from 22 kN/m (geotextile code W120\({}^{\text{b}}\)) to 41 kN/m (code W250\({}^{\text{c}}\)). The corresponding tensile strain under the peak tensile load varies from 13.1% (geotextile code W120\({}^{\text{a}}\) and W120\({}^{\text{b}}\)) to 16.8% (code W120\({}^{\text{c}}\)). The specimens subjected to the uniaxial tensile strain exhibit stronger load resistance for woven geotextile W120\({}^{\text{c}}\) and W250\({}^{\text{c}}\) than W120\({}^{\text{a}}\), W120\({}^{\text{b}}\), and W150\({}^{\text{c}}\). The geotextile W150\({}^{\text{c}}\) exhibits a larger strength than W120\({}^{\text{a}}\) and W120\({}^{\text{b}}\). Local failure of breaking slit films causes a drop-off in the tensile load-strain curve. The lateral contractions of tested woven geotextiles are less than 2%, which have a negligible impact on the deformation of pores in the illuminated regions of specimens.