A frequent problem when constructing metro tunnels is the uneven settlement of adjacent buildings, which results in huge economic losses. Due to shields causing the settlement of adjacent buildings, this study took the Nantong Metro Line 1 as the research object. The metro runs from the East Huancheng Road Station to the Nantong Intermediate People’s Court Station and passes under the old residential area of the Community Sendadi-Huayuan building. Based on the settlement monitoring data, this study analyzed the impact of tunnel shield construction on the foundation settlement of adjacent buildings. The computational analysis of the shield tunnel was performed by numerical simulation, taking into account the upper building load and the construction disturbance to the surrounding rock. Afterward, the study summarized the law behind the settlement. The results show that when the boring machine was tunneling through sandy soil and silt rich in water, its head was prone to twisting due to soil disturbance and the dissipation of pore water, causing instability in the excavation process and eventual ground settlement. In the sandy strata, the relationship between foundation settlement caused by shield construction and time can be approximated as an exponential function in a certain area. The vibrations from shield excavation caused the foundations to vibrate for a short period of time. Therefore, the average settlement of buildings directly above the underpass reached 7mm/d. Likewise, the tunneling shield caused a 1.5mm settlement before passing under the building. It caused a peak settlement of 4.0 and 5.1mm during and after passing under the buildings, respectively. The width of the settlement troughs of approximately 7D formed after the tunnel was excavated. Shield excavation placed the soil at the top of the excavation face in a state of tensile stress, causing tensile and shear damage to the soil and forming a local plastic zone.

Tunnel engineering is frequently undertaken in complex geological environments, which present heightened risks during construction and operation, particularly in active fault zones. This necessitates the enhancement of fault resistance. This study investigates the combined application of Steel–polypropylene Fiber Concrete Linings and Combined Seismic Joints through numerical simulation using ABAQUS 2023 (Dassault Systèmes, France). The findings demonstrate that this combination significantly enhances the fault resistance of tunnel structures, exhibiting substantial synergistic effects. In comparison with the utilization of Steel–polypropylene Fiber Concrete Linings as a standalone measure, the maximum reductions in longitudinal tensile and compressive strain were found to be 40.1% and 46.7%, respectively. Furthermore, peak equivalent compressive and tensile plastic strains were reduced by 60.3% and 51.1%, and tensile and compressive damage by 4.9% and 17.3%. Further analysis reveals that the steel fiber aspect ratio and the content of both steel and polypropylene fibers have varying effects on suppressing different damage forms in tunnel linings. It is evident that an augmentation in the steel fiber aspect ratio most effectively suppresses plastic zone deformation, while an increase in polypropylene fiber content significantly reduces tensile strain and tensile damage. The optimal level of fault resistance performance is achieved when the steel fiber content is set at 1.90%, the aspect ratio is 60, and the polypropylene fiber content is 0.15%. Furthermore, the adjustment of the combined arrangement parameters enables tunnel structures to adapt more effectively to diverse operational conditions, thus providing flexible design solutions for practical engineering applications.

With the increasing complexity of engineering environments in tunnel construction, the vibrations generated by shield tunneling in hard rock strata pose significant challenges to the operation and maintenance of adjacent tunnels. This study investigates the vibration characteristics induced by shield tunneling and provides an in-depth analysis of the propagation behavior of these vibrations within tunnel segments and surrounding soil layers. Through a combination of theoretical derivations, on-site monitoring, and numerical simulations, the research examines the distribution of vibration energy and its attenuation patterns with increasing propagation distance. The findings reveal that vibration energy is primarily concentrated in the low-frequency range (3–4 Hz) and follows an exponential decay trend as distance increases. Furthermore, the vibration response of neighboring tunnels is heavily influenced by the construction vibration source, with rapid energy attenuation observed over short distances. Numerical simulations conducted using PFC3D6.0 (Particle Flow Code) software validate the theoretical model and emphasize the critical roles of soil-damping properties and tunnel segment material characteristics in vibration attenuation. This study offers a robust theoretical framework and valuable data to support the control of tunnel vibrations and the optimization of construction practices.