## 3 Results
### Ground Surface Settlement Distribution and Analysis behind the Wall  
Figure 17 depicts the ground surface settlement distribution curve behind the wall. As the excavation depth increased, so did the settlement, and the closer it was to the wall, the greater the settlement. When the excavation depth was shallow (the excavation of the first layer \(Z\) = \(0.37\) m), the maximum settlement value was measured at the first measuring point \(25\) mm away from the retaining structure. The results for the two groups of tests were \(-2.05\) mm and \(-1.97\) mm, respectively. The settlement distribution was similar to the exponential function curve distribution mode. When the excavation depth was relatively deep (the excavation of the second layer \(Z\) = \(0.74\) m), the maximum settlement remained at the first measurement point, with settlement values of \(-2.31\) mm and \(-2.38\) mm, respec  
Figure 15: “Recurve bow”-type lateral displacement mode. (**a**) The single-layer strut group; (**b**) the double-layer strut group. tively. The second measuring point had the most variation in settlement, with measured settlements of \(-\)1.97 mm and \(-\)1.86 mm, respectively. There was also a trend of \"concave\" surface settlement, which resembled a triangular distribution mode, similar to the retaining structure protruding into the excavation side. When the excavation depth was high (the excavation of the third layer \(Z\) = 1.11 m), the maximum settlement value was moved to the second measuring point position, which was \(-\)2.78 mm and \(-\)2.68 mm, respectively. There were differences in settlement distribution, with the settlement of the single-layer strutted test exhibiting a \"trough\" distribution mode and the settlement of the double-layer strutted test exhibiting a \"trapezoid\" distribution mode. The above evolution phenomenon of the ground surface settlement distribution mode reflected the control effect of struts on the fill behind the wall, dividing its settlement into primary and secondary influence zones. Figure 18 shows the relationship between the maximum ground surface settlement and the excavation depth of the single-layer and double-layer strutted retaining structures. The maximum ground surface settlement value gradually increased at each excavation depth, ranging from 1% \(Z\) to 0.1% \(Z\), which met [PERSON]'s statistical description of the maximum ground surface settlement of a deep-excavation steel sheet pile flexible retaining structure (\(s_{max}<\) 1% \(Z\)) [25]. The average maximum ground surface settlement of these tests was 0.375% \(Z\), which was larger than the value of 0.15% \(Z\) calculated by [PERSON] for solid piles, steel sheet piles, diaphragm walls, and bored pile retaining structures [2]. The right axis  
Figure 16: Relationship between the maximum lateral displacement and the nondimensionalized maximum lateral displacement of the retaining structure and the excavation depth [24]. Figure 17: Measured values of the ground surface settlement behind the wall. (**a**) The single-layer strut group; (**b**) the double-layer strut group. represents the nondimensionalized maximum ground settlement. When the first layer of the excavation was excavated, the ratio of the two groups of the strutted retaining structures increased sharply to a maximum of 0.0055 and 0.0053, respectively. Subsequently, under the action of the strut, the ratio decreased continuously with an increasing excavation depth. The nondimensionalized ground surface settlement profiles behind the wall are shown in Figure 19. Firstly, the settlement profile of \(s/Z\) is shown in Figure 19a. [PERSON] summarized the typical normalized surface settlement distribution profiles of a steel sheet pile retaining structure [25]; defined three types of surface settlement areas; and divided them into zones I, II, and III by three dotted lines. Obviously, the ground surface settlement was not significant, and most of the data points were scattered in zone I, corresponding to the excavation area in the sand and soft to hard clay soil layers.