Abstract: Given the insufficiency in research on the mechanism of fine particle impact on gravelly soil subgrade deterioration, a series of saturated gravelly soil consolidated drained triaxial shear tests was conducted using the GDS triaxial testing system under varying fines contents and effective confining pressures to investigate the effect of fine particle contamination on the static shear characteristics of gravelly soil. The results indicate that: (1) As the fines content increases, the stress-strain curve development pattern transitions from strain softening to strain hardening, with a critical threshold at a fines content of Fc=15%. (2) The addition of fine particles leads to a decrease in the principal stress ratio, brittleness index, peak strength, cohesion, and internal friction angle of the gravelly soil, while the degradation indices increase. The relationship between the degradation indices of peak strength and cohesion and fines content can be described by quadratic functions, and the degradation index of the internal friction angle by a cubic function. (3) With increasing fines content, critical state parameters decrease. The effective stress path shows retracing behavior, becomes shorter, and shifts to the left. (4) The addition of fine particles results in a decrease in the secant modulus, and the volumetric strain-axial strain curve changes from contractive-dilative to purely contractive.

Key words: fines content, gravelly soil, triaxial test, mechanical properties, deterioration mechanism