Abstract：The mechanical behavior of coarse soil is influenced by various factors, including relative density, stress level, and loading path, all of which exhibit distinct deformation characteristics, such as dilatancy under low confining pressure and contraction under high confining pressure. This paper develops a hypoplastic model for coarse soil by introducing an asymptotic state boundary surface, which can be used to determine the flow direction of rockfill during shearing. In addition, a new density factor is defined based on the relationship between the current state point and the critical state line in the e-p plane to account for the state-dependent behaviors of coarse soil. Model predictions are compared to the triaxial test data of Type I rockfill from the Changhe Dam to verify the proposed hypoplastic model. It indicates that the increase in confining pressure will reduce the tendency for dilatancy deformation, alongside the occurrence of strain-hardening behavior evident in the stress-strain curve under drained loading conditions. Conversely, excess pore water pressure within the specimen decreases as axial strain increases under undrained loading conditions. The proposed model can describe these behaviors and serves as a novel technical approach for geotechnical numerical analysis.
2025, Vol. 46 
