## 1 Introduction  
Cross-river and cross-like passages are predominantly constructed in waterfront areas and confined water-rich zones, where suspension bridge solutions have become critical alternatives. These regions are characterized by highly permeable soil layers, elevated confined water heads, and significant construction challenges such as heavy overburden loads, deep soft foundations, low bearing capacity, small stiffness, and poor stability. Anchorage foundations built in such areas typically require embedment depths of tens of meters, necessitating ultra-deep excavation--a highly complex, uncertain, and risky engineering construction [1, 2, 3, 4, 5]. These conditions impose escalating demands on foundation treatment during excavation, as well as rigorous challenges in the rational selection, design theory, and construction of retaining structures. The circular diaphragm wall support system leverages the arch effect [6], converting lateral soil and water pressures into internal compressive forces while decreasing shear and bending moments, thereby fully utilizing the compressive resistance of concrete [7, 8]. Owing to its superior spatial load-bearing characteristics, this system has been progressively adopted in mega suspension bridge anchorage projects [9, 10, 11, 12]. Circular diaphragm walls are widely used in deep foundation pit engineering due to their efficient hoop-bearing characteristics. In recent years, systematic research has been conducted on their deformation patterns during construction, optimization of supporting structures, and adaptability to complex geological conditions. [PERSON] et al. [13] found, through monitoring a 121 m diameter and 31.1 m deep foundation pit, that symmetrical excavation maintains the wall in a hoop-dominated axial compression state, with maximum deformation concentrated 10-15 m above the excavation face. The wall deformation inversely correlates with hoop stiffness, and integral casting of ring beams improves stiffness by over 30%. [PERSON] et al. [14] conducted 3D elastoplastic finite element analysis showing that excavation sequences disrupt axisymmetric stress distribution, causing lateral stress variations behind walls, while reduced wall thickness decreases vertical and hoop sectional forces by 20-25%. [PERSON] et al. [15] studied a 56 m deep double-wall foundation pit (with inner circular diaphragm walls and outer rectangular cut-off walls), revealing that peak ground surface settlement occurs at 0.4-0.6 times the excavation depth, and that active zone earth and pore water pressures are less sensitive to excavation than those in the passive zone. [PERSON] et al. [16] compared top-down and optimized bottom-up schemes (5 ring beams) using a 3D beam-spring model, demonstrating a 40% increase in construction efficiency, with hoop axial compression accounting for 80% of wall stress and lateral displacement \(\leq\)0.1%H. [PERSON] et al. [8] proposed a hoop stiffness correction coefficient \(\alpha\) (0.485-0.514 at low stress; 0.545-0.581 at high stress) through joint mechanical experiments, providing quantitative guidelines for joint design. [PERSON] et al. [17] validated an axisymmetric BEF method for a 90 m diameter anchorage foundation pit using joint stiffness reduction coefficients, confirming a maximum displacement of only 0.018%H\({}_{\text{e}}\) and highlighting the superiority of circular diaphragm walls in controlling large-diameter pit deformation. [PERSON] et al. [18] monitored a 73 m deep shaft in London, revealing 15% higher-than-predicted hoop strains in chalk layers due to reduction in deep-layer hoop stiffness and construction verticality tolerances, emphasizing joint quality control. [PERSON] et al. [19] proposed a 3D elliptical deformation model for China's deepest circular pit (77.3 m), effectively predicting internal force distribution under non-uniform earth pressures.