## 3 Results and Discussion
### Sampling Intensity Testing in Natural Environments  
As shown in Table 6, the thickness of the geotextile sheets decreases to varying degrees over time, indicating the presence of aging and wear. From the changes in sheet strength, it is evident that the mud layer's attachment on the geotextile surface effectively mitigates aging. Except for the transverse strength retention rate of 61% observed in the 2-year-old sheets, the strength retention rates of sheets with different usage durations, both  
Figure 6: SEM scanning photos of geotextile samples under three working conditions at K135 of Tarim River: (**a**) new unused geotextile (X); (**b**) top geotextile for slope protection (D); (**c**) mud-covered geotextile (N). longitudinally and transversely, remain at or above 100%. Notably, even after 5 years of continuous exposure to sunlight, geotextile bags retain 105% of their original strength. Figure 7 shows the actual situation when sand adheres to the surface of the geotextile bag in the water level zone. It can be seen that the surface of the geotextile bag has been covered with a layer of mud, accompanied by the attachment of other aquatic plants. This situation is in sharp contrast to the geotextile bag at the top. The sand mixed in the internal fibers provides additional protective effect. As shown in Figure 8, the longitudinal and transverse strength values of the unused geotextile exhibit significant variability (\(\sigma\)). However, as the usage time of geotextile bags increases, the strength retention rate shows minimal changes. Based on the reduction in sheet thickness, it was inferred that the fibers themselves aged, transitioning from their original long-filament state to a shorter-filament state. In the tensile strength tests, the unused geotextile was tested in its original form, while the sampled sheets from used bags were tested as a combination of thinner geotextile and sand. The presence of sand enhances the strength of the geotextile to some extent, resulting in only minor variations in the strength retention rate. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Test** \\ **Sample** \\ **Source** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Construction** \\ **Time** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Sample** \\ **Time** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Thickness** \\ **(mm)** \\ \end{tabular} } & \multicolumn{2}{c}{**Tensile**} & \multirow{2}{*}{\begin{tabular}{c} **Strength** \\ **Strength** \\ **(KN/m)** \\ \end{tabular} } & \multicolumn{2}{c}{**Tensile**} & \multirow{2}{*}{\
\begin{tabular}{c} **Strength** \\ **Retention** \\ **(KN/m)** \\ \end{tabular} } & \multicolumn{2}{c}{**Strength**} & \multicolumn{2}{c}{**Retention**} \\  & & & & **(KN/m)** & & **Rate (\%)** & **(KN/m)** & **Rate (\%)** \\ \hline \hline \multirow{2}{*}{
\begin{tabular}{c} 1 \\ 2 \\ 3 \\ 4 \\ 4 \\ \end{tabular} } & 2018 & 0 & 1.62 & 5.13 & 100\% & 4.54 & 100\% \\  & 2 & At K135 & 2019.5 & 2021.03 & 1.05 & 5.77 & 112\% & 2.79 & 61\% \\  & 3 & At K135 & 2019.5 & 2023.02 & 1.25 & 5.52 & 107\% & 5.15 & 113\% \\  & 4 & At K135 & 2019.5 & 2023.11 & 1.16 & 5.43 & 105\% & 5.06 & 111\% \\ \hline \hline \end{tabular}  
* Note: 1 refers to the brand-new unused geotextile bag samples from the Usman Hub Station warehouse; 2 geotextile containers with 2-year service at the K135 location; 3 geotextile containers with 4-year service at the K135 location; 4 geotextile containers with 4.5-year service at the K135 location.  
\end{table} 
Table 6: Residual strength values of geotextile sampling samples (at K135 on the north bank). Figure 7: Sand adheres to the surface of the geotextile bag in the water level zone (19 May 2023): (a) geotextile bag revetment at K135; (b) geotextile bag revetment at K169. The test data reveal significant variability in the tensile strength values across different sections of the same geotextile.