The cyclic behavior of calcareous sands containing non-plastic fines is a critical issue in coastal regions vulnerable to seismic loading. This study examines the effect of non-plastic silt on the liquefaction resistance of calcareous sand obtained from Bushehr Port, located on the northern coast of the Persian Gulf. A total of 30 undrained cyclic triaxial tests were performed on sand–silt mixtures with five fines contents (0, 10, 20, 30, and 40%) under isotropic ( \(\alpha\) = 0) and anisotropic ( \(\alpha\) = 0.1) consolidation conditions. The results reveal that liquefaction resistance generally decreases with increasing silt content, except for a marked increase at 10% fines. At low silt contents (0 and 10%), where particle breakage exceeded 3%, the 10% mixture exhibited lower breakage and a stronger microstructural arrangement, resulting in greater dilative behavior and higher resistance than clean sand. At higher fines contents (20–40%), where particle breakage fell below 3%, the response was controlled mainly by microstructure, and increasing fines led to more contractive behavior and reduced resistance. The application of initial static shear stress enhanced the cyclic resistance of clean sand and mixtures with 10–20% fines, had negligible effect at 30%, and reduced resistance at 40% fines due to the loose silty skeleton. Furthermore, a soil-specific correlation was established between the residual excess pore pressure ratio and the normalized number of loading cycles, calibrated separately for clean and silty calcareous sands under isotropic and anisotropic consolidations.
