## 4 Discussion  
In this article, to explore the complex deformation issues of strutted flexible retaining structures in deep and large excavations, we adopted an indoor model test investigation. We analyzed some deformation phenomena of the excavations and found that the lateral displacement of the flexible retaining structures of the excavations in sand varied with the excavation depth, which conformed to the descriptions of the deformation modes of retaining structures by scholars such as [PERSON] [2], [PERSON] [3], and [PERSON] [4]. However, the flexible retaining structures eventually evolved into a complex displacement mode of the \"recurve bow\" type, which was characterized by recurring on both sides and protruding in the middle. The above deformation differed from the conventional mode for three main reasons. Firstly, the flexural rigidity of the retaining structure itself was not large, belonging to the flexible category, and it was prone to deformation under external forces. Secondly, the strut's stiffness was high enough to limit the retaining structure's further displacement, resulting in recurve deformation. Finally, there was interaction between the structure and the soil, which was the least intuitive but most complex reason. This meant that during excavation, the structure and the soil were in dynamic equilibrium, and the uneven deformation generated a vertical soil arch. The earth pressure behind the wall redistributed to the arch feet on both sides [26], so its impact on the lateral deformation of the retaining structure was reflected in the reduction in the protruding deformation trend in the middle of the retaining structure, and there was a trend of deformation towards the excavation side at the strut and a certain position below the excavation bottom. This showed that there was more significant structure-soil interaction in the strutted flexible retaining structure. Furthermore, the test results showed that the lateral deformation of the single-layer strutted retaining structure was greater than that of the double-layer strutted structure, and its \"recurve bow\"-type displacement mode was more obvious. There are two explanations for the emergence of such a unique \"recurve bow\" displacement mode. The first factor is the number of struts. The more struts there are, the more load they bear behind the wall; additionally, the lower the recurve deformation of the retaining structure, the lower the total displacement. As a result, it could be boldly predicted that the overall lateral displacement  
Figure 21: Bending moment. (**a**) The single-layer strut group; (**b**) the double-layer strut group. of the multi-layer strutted retaining structure would be small, and the displacement mode would be of the \"wave\" type. The second factor is the strut's location. Closer to the pile top, the smaller the lateral displacement at the top of the retaining structure, the smaller the recurve deformation, presenting a \"bow\"-type displacement mode. Closer to the middle, the greater the lateral displacement at the top of the retaining structure, the greater the recurve deformation, and the more obvious the \"recurve bow\"- type displacement mode. In addition, it was also discovered from the experimental investigation that the tendency of the ground surface settlement behind the wall to alter with the excavation depth was comparable with the findings of investigators such as [PERSON] [25], [PERSON] [2], and [PERSON] [6]. The distribution of the ground surface settlement ultimately evolved into \"trough\" or \"trapezoid\" mode, which may have been due to three reasons. Firstly, it was closely related to the lateral deformation of the retaining structure. The lateral protrusion deformation of the single-layer strut was more severe, resulting in more significant surface subsidence, thus presenting a \"trough\" type. Secondly, there was an interaction between the structure and the soil.