Cumulative Plastic Deformation Characteristics of Saturated Silty Sand under Variable Frequency Cyclic Loading of Subway Entrance/Exit

The acceleration and deceleration movement of the subway near the subway station have a certain impact on the foundation soil. After the samples have been reconstituted in an inclined slope using sand rain method, undrained dynamic cyclic triaxial experiments were designed under specific variable frequency loading condition according to on-site monitoring data and theoretical calculation results. Effects of subway entrance/exit distance, subway entrance/exit acceleration, vibration amplitude, effective confining pressure on the cumulative deformation characteristics of Nanjing saturated silty sand were explored under experimental program. The results show that the cumulative plastic strain development of the Nanjing silty sand under the variable frequency cyclic loading of subway entrance/ exit can be roughly divided into three stages: explosive growth, rapid growth and gradual stability. The increase of the distance from the subway station can reduce the vibration cycles of subway entrance/exit loading to enter the gradual stabilization phase; it can also lower the shear deformation and increase the vertical deformation. Greater the vibration amplitude or lower the effective confining pressure can also have the same effect on soil deformation characteristics. Instead, greater the subway entrance/ exit acceleration, smaller the vertical deformation and larger the shear deformation. For practical engineering, the initial stage of subway line in operation is the focus of engineering geological disaster prevention. The settlement deformation of the soil in subway entrance interval, the horizontal displacement of the soil in subway exit interval are more serious. The soil closer to subway station is more prone to deformation hazard