## 7 Conclusions  
The study on the foundation pit excavation for the south anchorage of the Zhangjing-gao Yangtze River Bridge north channel bridge demonstrates that employing high-pressure jet grouting pile technology to create an artificial composite foundation in soft soil layers--with permeability coefficients, bearing capacity, and base friction coefficients meeting design requirements--effectively enhances the engineering properties of the anchorage foundation. This approach not only increases the strength of the base soil to restrict diaphragm wall deformation but also simultaneously improves permeability characteristics and aquitard thickness, achieving coordinated enhancement against hydraulic uplift failures. Furthermore, it enhances the foundation's shear resistance, thereby ensuring anti-base heave stability of the excavation, ultimately improving project safety and stability. This study fills a critical research gap in the application of high-pressure jet grouting technology for deep ground improvement in anchorage foundation pit engineering. It not only provides an innovative solution for ultra-deep excavations in complex geological environments but also establishes a robust technical foundation for advancing jet grouting methodologies in future foundation pit projects. This study concludes the following key findings:  
1. During the final excavation stage, the maximum horizontal displacement developed within the circular diaphragm wall and concrete lining system. Simultaneously, the peak vertical displacement at the wall crown reached approximately 0.04% of the excavation depth. Both displacement metrics remained substantially below the code-specified control limits, demonstrating that the circular diaphragm wall and lining system effectively controlled pit deformation and ensured construction safety. 2. The earth pressure on the diaphragm wall exhibits a \"decrease followed by increase\" pattern during excavation. Initially, it transitions from at-rest earth pressure toward Rankine active earth pressure. However, the high-pressure jet grouting pile reinforcement at the pit bottom significantly enhances the embedment effect of the lower diaphragm wall, constraining deformation and redistributing earth pressures. This mechanism leads to temporary lower-than-active earth pressure values during intermediate excavation phases. As excavation progresses, progressive wall displacements enable gradual convergence with the theoretical Rankine active earth pressure limit. Figure 23: The schematic diagram of stability against base heave verification method. 3. The finite element simulation of the unreinforced excavation base revealed a distinct failure mechanism: confined aquifer water pressure induces sand particle suspension, triggering central heaving of overburden soil and interface shear failure along the soil-wall boundary. This failure mechanism confirms that the shear strength of ground improvement can effectively counter hydraulic uplift. The proposed calculation methodology, which incorporates the mobilization of side shear strength in the anti-uplift soil mass based on code-specified formulas, is particularly suitable for deep reinforcement techniques that enhance soil shear properties. 4. In the finite element model simulating the reinforced pit base, the soil failure mechanism of central uplift of the overburden soil layer and sliding shear failure in the external soil adjacent to the diaphragm wall demonstrate that ground improvement changes the soil failure mechanism of the pit base. The calculation method based on [PERSON]'s bearing capacity model for anti-heave stability verification, which accounts for the mobilization of side shear strength in the overburden soil, is better suited for deep reinforcement techniques that improve soil shear performance. This study did not conduct long-term monitoring, and the Mohr-Coulomb constitutive model adopted in the numerical analysis, while commonly used in engineering practice, cannot capture the creep behavior of soft soils.