Dynamic properties of sandy soil under medium-high strain rates are of great significance for protection engineering, pile penetration, ship anchoring, aircraft landing, and so on. This paper reviews the current research status of split Hopkinson pressure bar (SHPB) impact tests and numerical simulations on sandy soil. The key issues in the research of sandy soil impact characteristics are summarized as follows: (1) The SHPB test still faces uncertainties for granular materials, such as the lack of standardized test sample size, difficulties in controlling boundary conditions, and the immaturity of triaxial testing methods. Future triaxial SHPB tests need to address issues related to measuring radial deformation of the samples and maintaining consistent confining pressure. (2) Due to uncertainties in gas and water discharge under test conditions and the presence of inertial effects, the accurate determination of strain rate effects becomes challenging. (3) The impact characteristics of granular materials are influenced by moisture content, which is correlated with changes in pore water pressure and pore air pressure. However, measuring these related variables is difficult, making it challenging to analyze the results. It is necessary to develop a device that completely eliminates the effects of gas and water discharge to mitigate the influence of boundary conditions. (4) To study the impact characteristics of sandy soils, it is necessary to overcome computational limitations and establish numerical models that account for complex mechanisms such as water content and particle fragmentation. Existing methods such as the finite element method, discrete element method, and coupled methods are unable to uniformly simulate the continuity of wave propagation and particle fragmentation. (5) It is crucial to develop constitutive models that consider the strain rate effects and can simulate complex mechanisms such as water content and particle fragmentation. This will refine the theoretical framework of soil mechanics at medium to strain rates.

This study investigates the Strain characteristics of reinforced soft clay surrounding a tunnel subjected to cyclic loading, employing the Global Digital Systems cyclic triaxial test on the saturated reinforced clay near Shanghai Metro Line 4's Hailun Road station. Initially, the study examines the impacts of frequency, dynamic stress amplitude (DSA), and loading cycles on cumulative plastic strain. Following this, the orthogonal design method was employed to organize tests, and an evaluation method for assessing soil strain was developed through mathematical statistical analysis. The results indicate at the constant vibration frequency, cumulative plastic strain increases with an increase in DSA and decreases with as load frequency increases. DSA is the primary factor influencing the axial deformation of subway tunnels, whereas the interaction between load frequency and vibration frequency is negligible. The findings suggest that measures to prevent and control subway tunnel settlement should concentrate on DSA during the early stages of subway operation. A novel concept and calculation method for the influence rate of axial deformation of clay mass under cyclic loads were introduced, enabling the determination of a parameter's significant influence on deformation. The early stage of subway operation is the focus for preventing engineering geological disasters. Dynamic stress amplitude (DSA) is the primary factor influencing the axis deformation of subway tunnels, while the interaction between load frequency and vibration frequency is negligible.