The scale effect is considered one of the primary reasons for the inaccuracy in predicting the deformation of rockfill dams. However

the scaling behaviors of blasted rockfill and gravel materials differ significantly. Preliminary analyses suggest that this is due to particle-shape differences manifesting in packing densification and crushability

yet a comprehensive mechanistic explanation remains lacking. To address this

discrete element method (DEM) simulations were conducted on both prototype and scaled specimens of rockfill and gravel

considering the size-dependent crushing strength of particles and the effect of coordination number on particle strength. Rockfill numerical specimens were generated based on 3D-scanned blasted rock fragments

while gravel was simplified as an assembly of spherical particles. The results reveal that the particle shape’s influence on the contact force chain network is the main factor responsible for the differences in scale effects between rockfill and gravel. The strong interlocking effect among irregular particles weakens the densification effect induced by broader gradation

resulting in decreased mechanical coordination number and lower anisotropy coefficients of both normal and tangential contact forces. This ultimately leads to reductions in deformation modulus and shear strength. In contrast

spherical particle assemblies exhibit the opposite trend: enhanced packing densification

a more stable force chain network

and increased stiffness and strength with scaling. Moreover

the decrease in particle strength mitigates modulus variations induced by scaling in the spherical system

whereas this influence is less significant in the irregular particle system.