Particle size plays a critical role in the cyclic liquefaction resistance of sandy soils, as variations in grain size can significantly influence their response to cyclic loading. Accordingly, the present study investigated the effect of changes in the mean sand grain size (D50) on liquefaction characteristics within a laboratory framework. For this purpose, six classified groups of medium-dense clean sand specimens (i.e., CS1–CS6) with an almost identical relative density (Dr = 52%) were tested under three initial vertical effective stresses (σ'v0). Hence, a total of 54 drained constant-volume cyclic simple shear tests (CSSTs) were performed. The cyclic responses at three initial vertical effective stresses, σ'v0 = 100, 200, and 300 kPa, were measured to evaluate the cyclic resistance ratio (CRR) of the specimens. Furthermore, the effect of sand particle size on the overburden correction factor, Kσ, was examined for all specimens. The results of this study show that variations in particle size of a specific sand influence both the cyclic stress ratio (CSR) and CRR. These results were used to calculate the Kσ factor. It was observed that Kσ decreases with increasing σ'v0 and that a larger D50 decelerates this reduction. An empirical relationship for Kσ is proposed. This study provides new experimental insight into the particle-size dependency of liquefaction resistance under controlled-density conditions, highlighting the importance of explicitly considering grain-size effects in cyclic liquefaction assessments.
