Model Test Study on the Deformation Behavior of Silty Sand Strata in the Yangtze River Floodplain under Shield Tunneling Disturbance

Silty clay stratum is one of the typical soil types in the Yangtze River floodplain, characterized by poor stability, which poses significant safety risks during shield tunneling. To ensure safety during shield construction, it is necessary to investigate the stability and deformation laws of the strata under the influence of key construction procedures, such as cutterhead excavation and tail void formation. Relying on the shield tunnel engineering of a section of Nanjing Metro Line 11, this study conducted research using model testing methods. Based on similarity theory, a surrogate soil was prepared with physical and mechanical parameters consistent with the undisturbed soil, and a simulation test device for shield construction was developed. Through the simulation of key excavation steps, the deformation characteristics of the silty clay strata were analyzed at different tunneling ring stages. Furthermore, embedded earth pressure cells and surface displacement meters were utilized to investigate the surface settlement characteristics and the evolution of formation stress in the floodplain silty clay under shield construction disturbance. The results indicate that both cutterhead excavation and tail void formation in the floodplain silty clay have significant impacts on ground deformation, stress distribution, and surface settlement. The influence of the tail void is more pronounced, approximately 1.6 times that of cutterhead excavation. During shield tunneling construction, the stress variation pattern along the springline monitoring line is consistent with that at the crown. For the referenced project, without considering synchronous grouting, the maximum surface displacement can reach 7.5 cm, highlighting the necessity for effective and timely synchronous grouting measures.