DEM modeling and mechanical analysis of the soil-structure interface with different particle gradations under constant normal stiffness

Under constant normal stiffness (CNS) conditions, the mechanical behavior of the interface is very susceptible to the expansion effects of the surrounding soil particles. The expansion behavior of soils with different gradations also often varies. Therefore, it is of great significance to study the mechanical behavior of soil-structure interfaces with different particle grades under CNS conditions. In this study, a novel stable iterative algorithm considering computational efficiency is developed to establish the CNS conditions. Subsequently, a series of interface shear tests were conducted on assemblies with different particle gradations in the Discrete Element Method (DEM). The macroscopic and microscopic mechanical behaviors of interfaces with different particle gradations under CNS conditions were investigated. The shear bands were measured and quantitatively analyzed based on the concept of optimal solutions. The results indicate that an increase in the normal stiffness K of soil particles markedly enhances the sensitivity of the interface region to particle dilatancy, thereby influencing the shear resistance of specimens with different gradations. Broadening the particle-size distribution introduces a greater proportion of both coarse and fine particles, increasing the coordination number of the granular assembly. However, it may also promote coarse-particle clustering, which can disrupt force-chain transmission within shear band and ultimately reduce local load-bearing capacity. Overall, this work deepens the understanding of the impact of particle gradation on interface behavior, especially in terms of shear bands and microscopic parameter evolution.