Examining Shear Behavior in Sandy Gravel Interfaces: The Role of Relative Density and Material Interactions

Current research on soil–structure interface properties mainly focuses on sand, clay, and silt, with little attention given to sandy gravel. In order to study the effects of relative density and interface materials on the shear behavior of the sandy gravel–structure interface, a series of large-scale direct shear tests on sandy gravel were carried out, and stress–strain relationships, volume change curves, and shear strengths were investigated. The results show that the angle of internal friction of sandy gravel increases linearly with relative density (R2 is 0.998), from 43.0° to 48.0° when the relative density increases from 0.3 to 0.9. The growth trend of cohesion increases, the shear behavior transitions from strain hardening to strain softening, and the shear strength increases linearly with the increase in relative density. The interfacial shear strengths and interface adhesion of sandy gravel with steel and concrete interfaces increase linearly with relative density, and the shear curves are strain hardening. Furthermore, the interface friction angle of concrete increases linearly with relative density (R2 is 0.985), from 30.2° to 34.2°, while the interface friction angle of the steel interface remains relatively constant around 28.9°. Finally, relative density was introduced into the Mohr–Coulomb shear strength formula, and the relationship equations of relative density and normal pressure with the shear strength and interfacial shear strength of sandy gravel were established. The validation results show that the error margin of the formula is within 4%. This formula can be used to evaluate changes in the mechanical properties of sandy gravel formations and the bearing capacity of pile foundations after they have been disturbed by factors such as construction.

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