Accurate characterization of soil dynamic response is paramount for geotechnical and protective engineering. However, the impact properties of unsaturated cohesive soil have not been well characterized due to lack of sufficient research. For this purpose, impact tests using the Split Hopkinson Pressure Bar (SHPB) were elaborately designed to investigate the dynamic stress–strain response of unsaturated clay with strain rates of 204~590 s⁻¹. As the strain rate increased up to 500 s⁻¹, a lock-up behavior was observed in the plastic flow stage, which can be explained as the breakage and rearrangement of soil gains under a high level of stress. Further, the strain rate dependency of the dynamic strength was quantitatively characterized by the Cowper Symonds (CS) model and the CS coefficients were determined to be the intercept of 55 and slope of 0.8 in the double logarithmic scale of Dynamic Increase Factor (DIF) and strain rate space. Furthermore, the SHPB test was reproduced using a modified Material Particle Method (MPM), which involves an improved dynamic constitutive model for unsaturated soil considering the strain rate effect. The simulated stress–strain curves basically agree with the experimental results, indicating the feasibility of MPM for investigating the dynamic properties of unsaturated soil under SHPB impact loading.

The study of the damage and failure process of concrete medium under impact loading is an important research topic in the field of protection engineering. Due to the high peak value and short duration of impact loads, the dynamic response of concrete medium under such loading presents a high degree of complexity. The Material Point Method, as a mesh-free particle-based approach capable of conveniently handling large deformations, has seen rapid development in the field of computational mechanics due to its ease of programming implementation and high accuracy, providing a new approach to solving impact-related problems in concrete medium. Therefore, this research first investigated the fundamental theory and algorithms of the Material Point Method and developed a corresponding simulation program. Secondly, an HJC-TCK constitutive model was proposed and implemented in the simulation program to simulate the damage behavior of concrete medium under impact loading. Finally, the program was applied to the numerical simulation of concrete slabs subjected to impact. The numerical results demonstrate that this method can effectively reflect the crushing damage characteristics of concrete under compression and shear, as well as describe the mechanical behavior of crack propagation and collapse under tension.