## 2 Experimental Test
### Experimental Results
#### 2.5.3 Sand Deformation
Under pull \(u_{\rm t}\), at the dashed line AB, the sand moves downwards from the point \(x_{\rm 2b}\) on the sand surface along the horizontal angle \(\theta_{\rm 2b}\) from B to A; at the dashed line CD, the sand moves downwards from the point \(x_{\rm 2a}\) on the sand surface along the horizontal angle of \(\theta_{\rm 2a}\) from D to C; and at the dashed line EF, the sand moves upwards to the point \(x_{\rm 1b}\) on the sand surface along the horizontal angle of \(\theta_{\rm 1b}\) from E to F. Consequently, a bump with a width of \(w_{1}\) and a height of \(v_{\rm s1}\) can be found on the sand surface from \(x_{\rm 1a}\) to \(x_{\rm 1b}\) near the proximal end of the FAS specimen and a void with a width of \(w_{2}\) and a depth of \(v_{\rm s2}\) can be found on the sand surface from \(x_{\rm 2a}\) to \(x_{\rm 2b}\) near the distal end of the FAS specimen;  
The reason for these observed deformations is that under push \(u_{\rm t}\), the sand zone EFG at the proximal end of the FAS specimen moves far away from the front wall, resulting in a deformation trend of sliding downwards. The sand surface subsides and forms a void. The sand zone ABD at the distal end of the FAS specimen is compressed by the FAS specimen, resulting in a deformation trend of sliding upwards. The sand surface uplifts and forms a bump. Under pull \(u_{\rm t}\), the sand zone EFG at the proximal end of the FAS specimen moves towards the front wall, resulting in a deformation trend of sliding upwards. The sand surface uplifts and forms a bump. The FAS specimen moves far away from the sand zone ABD at its distal end, resulting in a deformation trend of sliding downwards. The sand surface subsides and forms a void. The sand around the FAS specimen has formed a plastic zone. With an increase in \(u\), the sand deformation around the FAS specimen is gradually transferred to the sand surface. Because one part of \(u\) can be absorbed by sand deformation, the deformation of the sand surface increases slowly. Failure stage  
When \(u\) is larger than \(u_{\rm b}\), with an increase in \(u\), the deformations of the sand zones EFG and ABD at the distal and proximal ends of the FAS specimen increase rapidly under push and pull \(u_{\rm t}\). Shear failure can be found in the sand around the FAS specimens, and the plastic region inside the sand expands continuously to form a plastic zone extending from the FAS specimen to the sand surface along a certain horizontal angle \(\theta\). With the development of the plastic zone, a continuous slip surface is finally formed, such as the zones shown by the dotted line in Figure 10.  
Under push \(u_{\rm t}\), at the distal end of the FAS specimen, a passive deformation zone ABD in a compressive state is formed by the slip surfaces AB and CD and the sand surface. At the proximal end of the FAS specimen, an active deformation zone EFG in a tensile state is formed by the slip surface EF, the front wall EG, and the sand surface. Under pull \(u_{\rm t}\), at the distal end of the FAS specimen, an active deformation zone ABD in a tensile state is formed by the slip surfaces AB and CD and the sand surface. At the proximal end of the FAS specimen, a passive deformation zone EFG in a compressive state is formed by the slip surface EF, the front wall EG, and the sand surface. The parameters of the sand deformation and slip surface of different test cases are summarized in Figure 8.0 It can be found that with an increase in \(H\), \(w_{2}\) increases, while \(v_{\rm s2}\) decreases. The reason for this is that the sand deformation zone is a wedge-shaped zone that gradually enlarges from the bottom to the top. The larger the \(H\), the larger the area of the wedge-shaped zone, and the more \(u\) that can be absorbed. With an increase in \(H\), the pavement deformation decreases, and the risk of pavement settlement and cracking can be reduced, which is similar to the conclusions in [21; 34; 47].