The coarse particles in mixed soils can be cobbles or gravels,with the main difference being their round-ness(an indicator describing particle shape characteristics at an intermediate scale).The influence of coarse particle shape(i.e.,roundness)on the macroscopic and microscopic shear behaviours of cohe-sionless mixed soils with various fines contents(FCs)was investigated via the discrete element method in this study.The shapes of coarse particles were formed using the rotation-invariant spherical harmonic method proposed by previous investigators.An equation was proposed to predict the initial void ratios of samples in this study.A decrease in the roundness of coarse particles can increase the peak friction angle(FC ≤ 40％)and critical friction angle(FC ≤ 30％).As the roundness of coarse particles decreases,the peak dilatancy angle initially increases and then decreases(FC≤20％).Furthermore,it was found that the roundness of coarse particles hardly affects the classification of cohesionless mixed soils,as deter-mined by probing the percentage contributions of coarse-coarse,coarse-fine,and fine-fine contacts.When cohesionless mixed soils change from an underfilled structure to an interactive-underfilled struc-ture at the critical state,the main forms of coarse-coarse contacts were discovered.Additionally,the force-fabric anisotropy mechanisms of the influences of the roundness and rolling resistance coefficient of coarse particles on the shear strengths of cohesionless mixed soils were found to be different.