## 5 Analysis of Monitoring Results  
### Deep Horizontal Displacement of Diaphragm Wall  
Figure 11 displays the deep lateral displacement curves of a typical monitoring point QWY-7 at different excavation stages (distributed in a 270\({}^{\circ}\) direction). The evolution patterns of the diaphragm wall's deep horizontal displacement during sequential excavation stages were systematically recorded by measurement devices, with the excavation stages corresponding to the sequence outlined in Table 2. In this context, positive horizontal displacement indicates outward deformation (away from the excavation pit), while negative values represent inward deformation. Since the monitoring point was not embedded within the diaphragm wall but located in the soil mass, and heavy construction machinery activity on-site significantly affected shallow lateral displacement measurements, data above \(-\)8.35 m depth were excluded. Horizontal displacement measurements at the top of the diaphragm wall were incorporated as a reference. As shown in Figure 11, the horizontal displacement at QWY-7 increased gradually during the initial excavation stages (prior to reaching \(-\)11.5 m depth) but surged significantly as excavation progressed to \(-\)16.5 m, followed by a gradual deceleration in displacement development during later stages. The displacement-depth profiles of the diaphragm wall across excavation stages exhibited consistent trends: Shallow displacements (0 m to \(-\)6.3 m) increased rapidly with  
Figure 10: Layout of monitoring points for earth pressure of diaphragm wall: (**a**) plan view; (**b**) elevation view (m). depth, peaking within the \(-6.3\) m to \(-10.65\) m range. Below this zone, displacements attenuated sharply with depth until reaching \(-15.7\) m, then slightly rebounded between \(-15.7\) m and \(-18.25\) m. From \(-18.25\) m to \(-29.55\) m, displacements stabilized, followed by a continued reduction until reaching a minimum at \(-37.8\) m. Displacements then increased again from \(-37.8\) m to \(-46.5\) m before gradually diminishing toward zero below \(-46.5\) m.  
Based on the structural dimensions of the circular diaphragm wall shown in Figure 2, the analysis of Figure 11 reveals that during initial excavation stages, maximum displacement occurs near the excavation face. This aligns closely with the finding of [PERSON] et al. [40] that peak displacement depth lies approximately 0.35 m below the actual excavation level. However, [PERSON] et al. [40] also reported progressive downward migration of maximum lateral displacement with excavation depth--a phenomenon not observed in this study where as excavation deepened, the peak displacement location did not migrate downward. [PERSON] et al. [41] demonstrated that effective basal restraint maintains near-constant displacement at the wall base, consistent with our observations: the high-stiffness reinforcement zone restricted displacement development near the pit bottom (\(-18.8\) m), while simultaneously explaining rapid displacement attenuation between \(-10.65\) m and \(-15.7\) m. Stable displacements from \(-18.25\) m to \(-29.55\) m are attributed to uniform earth pressure distribution within the reinforcement zone due to its substantial global stiffness. Below \(-29.55\) m, displacements further diminish owing to stronger constraints imposed by the full-area improvement zone (compared to the grillage reinforcement zone) on the diaphragm wall. According to the Technical Standard for Monitoring of Building Foundation Pit Engineering (GB 50497-2019) [42], the warning thresholds for diaphragm wall deep horizontal displacement monitoring of Grade I foundation pit in soils are listed in Table 3. For the circular diaphragm wall foundation pit of the South Anchorage of the Zhangjinggao north channel bridge, with an excavation depth of 21.3 m, the control standard for deep horizontal displacement is set at 30 mm. Based on field monitoring data, the maximum deep horizontal displacement of the diaphragm wall in this project meets the control criteria.