Abstract: The shear characteristics of continuously graded granular soils are closely related to their gradation characteristics. This paper aims to clarify the quantitative relationship between the apparent gradation of dense granular soils and their peak shear strength. Firstly, the influence of apparent gradation changes on the soil’s internal skeleton structure characteristics is investigated using a discrete element numerical model. Quantitative indices are introduced to characterize these structural characteristics. Subsequently, 16 continuous gradation granular soil samples are designed, and indoor direct shear tests are conducted to reveal the quantitative relationship between the skeleton structure characterization indices and the peak friction angle of the soils. The research results indicate that changes in the apparent gradation of granular soils can significantly alter the composition and network structure of the bearing skeleton. By using the dominant size of the skeleton structure (d_ed) and the coefficient of gradation non-uniformity (C_u) as characterization indices, a positive correlation is observed between these indices and the peak friction angle of continuously graded granular soils. An empirical shear strength model is established using d_ed and C_u as influencing factors, accurately fitting the peak friction angle results obtained from the direct shear tests. This model can be widely applied to various types of granular soils described in existing research. These findings provide a computational reference for predicting the strength of granular geomaterials in engineering practice.

Key words: granular soil, soil gradation, shear strength, skeleton structure, discrete element method, direct shear test