## 2 Research Methods  
### Model Test  
[PERSON] et al. [28] investigated the symmetry of the embankment, a half-symmetric model was established in a finite element software, and the performance of a fixed-geosynthetic-reinforced and pile-supported embankment (called FGT embankment) was studied. [PERSON] et al. [29] established a half-symmetric centrifugal test model based on the Maputo Bridge and Link Roads Project in Mozambique, and studied the deformation and failure modes of the embankment supported by geogrid reinforced piles. As mentioned above, the test results of the half-symmetric test could represent the variation of analysis results if a full-section test was difficult to establish. Based on [PERSON] et al. [30; 31], the large-scale model tests had been conducted with the dimensions of 1.5 m \(\times\) 0.6 m \(\times\) 1.5 m (length \(\times\) width \(\times\) height). This paper presents a half-symmetric test model based on the size dimensions of the full-section test conducted by [PERSON] et al. [30; 31]. Only a half size of the full-section test was used to build the test model. Table 1 lists the model tests performed in this paper. According to the prototype size and scale factor N = 5.0, the anchorage length \(L\) of the geotextile was set as 600 mm in the model test. The tests H1, H2, H3, and H4 represented the test with the subsidence width (denoted as \(B\)) of 300 mm, 150 mm, 300 mm, and 600 mm, respectively, which were conducted to research the influence of the subsidence width on the geotextile control of a subgrade collapse. \(L/B\) represented the anchorage length of the geotextile \(L\) to the subsidence width \(B\). Figure 1 shows the layout of the half-symmetric model test. In the middle of the model box, the rigid baffle treated was wrapped by a double-layer Teflon film. On the left side of the rigid baffle was the test soil, and on the right side was the rigid support. The rigid baffle was connected with the rigid support and its position could be adjusted. The model geotextile was laid in the rigid stable area. As a comparison, the geotextiles did not fold upwards at the position of rigid baffle in the full-section model test. The geotextile on one side of rigid baffle was folded upwards and extended to contact the movable side plate and fixed with thumbtacks. The test conditions of the different subsidence widths were realized by changing the width of the movable bottom plate. The movable side plate was in contact with the rigid baffle, and the double-layer Teflon film was placed between them. The model geotextile on the rigid baffle side was fixed and the vertical settlement was allowed during the test. During the subgrade collapse test, the soil pressure cells were used to record soil stress and the strain gauges recorded the deformation of the geotextile. The settlement of the movable bottom plate was measured with an electromechanical dial indicator. Additionally, the soil settlement within the subsidence area was captured and analyzed with particle image velocimetry (PIV) equipment. All monitoring equipment were connected to the static strain gauge, and the computer collected real-time data once per second. Figure 2a,b \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Variation** & **Test No.** & \begin{tabular}{c} **Subsidence** \\ **Width, \(B\) (mm)** \\ \end{tabular} & \begin{tabular}{c} **Anchorage Length of** \\ **the Geotextile, \(L\) (mm)** \\ \end{tabular} & \begin{tabular}{c} **Anchorage Ratio,** \\ **L/B** \\ \end{tabular} & \
\begin{tabular}{c} **Buried Depth of the** \\ **Geotextile, \(H\) (mm)** \\ \end{tabular} \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Subsidence \\ width \\ \end{tabular} } & H1 & 300 & 1200 & 4.0 & 1000 \\  & H2 & 150 & 600 & 4.0 & 1000 \\  & H3 & 300 & 600 & 2.0 & 1000 \\  & H4 & 600 & 600 & 1.0 & 1000 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Model test program. Figure 1: Sketch graph of the geotextile of half-symmetric model. show the model size and layout of the instruments (unit: mm).