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.