This study investigates the stability of multilayer shield tunnels beneath high-speed railway bases, with a particular focus on the influence of dynamic loads induced by high-speed rail vibrations and shield thrust. A self-designed scale test apparatus was employed to simulate the effects of these dynamic loads on tunnel soil stability, face integrity, formation stress, deformation, and settlement. The experimental setup was specifically designed to accurately replicate the deformation characteristics of the tunnel face and surrounding strata under the combined influence of shield tunneling and high-speed rail loads. The reliability of the experimental results was validated through comparison with numerical simulations performed using FLAC3D software. The study underscores the effectiveness of integrating physical model tests with numerical simulations to predict the failure characteristics and ultimate support forces of tunnel faces under dynamic loading conditions. The findings provide novel insights into the deformation and failure mechanisms of tunnel faces during shield excavation, particularly under the influence of high-speed rail loads. This research establishes a robust methodological framework for assessing tunnel face stability and offers valuable guidance for the design and construction of shield tunnels in analogous geological and operational contexts.

The fault zone represents one of the unfavorable geological conditions responsible for tunnel collapse in undersea tunnels. To reveal the collapse mechanism of an undersea tunnel triggered by the fault zone during excavation, a large-scale tunnel disaster model system was developed, capable of true triaxial loading and providing a sufficient supply of high-pressure water. A hydro-solid coupling similar model test was performed based on the engineering background of the under-construction second Jiaozhou Bay undersea tunnel. The results show that subsea tunnel fault collapse had an obvious progressive nature under excavation disturbance and seawater seepage. Soil arches repeatedly formed and moved upward during the collapse evolution process. When the overburden thickness was insufficient to form a soil arch, the tunnel collapse evolved into a water inrush. In addition, the multi-physics field changed obviously before the collapse, which could be used as precursor information for tunnel instability. Before the collapse, the horizontal stress rose slowly and then dropped suddenly, the pore water pressure drastically fluctuated and peaked, and the loosened zone's displacement rate increased suddenly. This study provided improved insight into the failure behavior of subsea tunnels and identified early warning signs of collapse.