Shanghai soft clay is a typical marine clay with specific structural characteristics. The tunnel and overlying soft clay may undergo repeated surface surcharge loading, such as the temporary soil stacking. Assessing the extent of structured soft clay deformation and tunnel displacement caused by repeated surface surcharge loading is of great significance for evaluating of the safety of ground structures and underground tunnels. In this study, the effects of repeated surface surcharge loading on the soil and tunnel displacement were numerically investigated. The finite element code DBLEAVES with an elasto-plastic constitutive model (Shanghai model) that describes the mechanical properties and structural characteristics of natural clay was used to simulate the soil response. The parameters of the constitutive model were obtained through geotechnical testing. The effects of the soil structural characteristics, seepage conditions, and loading conditions on the soil response and tunnel displacement were analyzed. The numerical results show that the maximum excess pore pressure of clay decreased as the number of loading cycles increased. The effects of the structural characteristics cause greater displacement, whereas the effects of the degradation parameters of the structure are more significant than the initial degree of the structure. The differences in the vertical displacement of the tunnel and overlying soils owing to the structural characteristics become apparent with an increase in surface surcharge loading. However, the effects of structural characteristics become less significant as the depth increases. The seepage conditions and loading method primarily affect the build-up of excess pore pressure and the development of effective stress paths. For soils inside the surcharge area, a flexible surcharge produces a greater vertical displacement than a rigid surcharge. As the burial depth increased, the effects of the seepage conditions and loading method showed a declining tendency.

This paper presents an improved longitudinal beam-spring model on the Vlasov foundation for estimating the longitudinal deformation of the shield tunnel when subjected to the ground surface surcharge. This model incorporates an improved subgrade modulus and treats each segmental ring as a Timoshenko short beam, with each circumferential joint modeled by two mechanical springs. It can accurately reflect the discontinuous deformation, and capture the dislocation and opening deformation of shield tunnels. Two-stage analysis methodology is adopted to consider soil and tunnel interaction. The feasibility of this model is verified by comparing it with two well-documented field monitoring cases. The computed results are also compared with those based on other analytical models. The results show that the Timoshenko continuous beam overestimates the dislocation deformation, while underestimates the opening deformation. In addition, the settlement curve exhibits neither smooth nor differentiable features. Finally, this paper also conducted some parameter analysis to examine the impact on tunnel deformation, encompassing dimensions of ground surface surcharge, the dual-area loading, and the joint reinforcement. This approach provides valuable insights into how the deformation characteristics of shield tunnels are influenced by ground surface surcharge.