As underground structures' burial depth increases, buoyancy resistance due to groundwater becomes more pronounced. This study, through numerical simulation, analysis of field measurement data, and theoretical analysis, explores the impact of changes in groundwater level on the failure mode and uplift resistance of expanded base piles and proposes a new method for calculating the ultimate uplift capacity of expanded base piles considering the effect of groundwater. The research shows that the rise in groundwater level significantly affects the uplift performance of expanded base piles by altering the physical and mechanical properties of the soil and the morphology of the pile-soil failure surface, thereby affecting the pile's load-bearing capacity. The study identifies a three-segment failure mode for expanded base piles and notes that as the groundwater level rises, the extent of the failure surface gradually expands. Additionally, the paper underscores the importance of considering groundwater levels in practical engineering design and suggests re-evaluating the measured uplift capacity using the calculation method proposed in this study to ensure engineering safety. This research provides a theoretical basis and computational tools for designing belled uplift piles under the influence of groundwater, offering significant reference value for engineering practice.

The mechanical method for connecting aisle construction technology is gradually emerging in municipal underground engineering. In this method, a special segment structure that uses glass fiber or carbon fiber as the main reinforcement is installed in the main tunnel of the connecting aisle. During the construction process, because the fiber ribs are difficult to cut, additional lengths ranging from 20 to 40 cm are often left over. In order to solve this problem, a special segment structure is designed to replace the glass fiber or carbon fiber main reinforcement with short steel fiber, and a prestressed structure is added to the cutting area. The corresponding construction technology is also proposed for this special segment structure. Finally, the mechanical properties and feasibility of special segment structure of prestressed steel fiber reinforced concrete (SPSFC) are studied by numerical simulation. The results showed that under the same stratigraphic conditions, the deformation and stress of the SPSFC were similar to that of a reinforced concrete segment structure. The maximum vertical deformation of the soil induced by the SPSFC was smaller than that caused by the special segment structure of reinforced concrete (SRC). The study proposes an innovative research idea for special segment structure of the main tunnel.