<p>Compaction characteristics and maximum dry density control constitute critical considerations for over coarse-grained soil filler. In this study, DEM simulations of surface vibration tests were conducted and parametric analyses were carried out to investigate the effect of maximum particle size and gradation on compaction characteristics and maximum dry density behavior of over coarse-grained soil. The results show that the maximum dry density was positively correlated with the maximum particle size. Pores could be sufficiently filled when the content of small particles reached 25%, and soil skeleton was loosened when the content of small particles exceeded 35%. Giant and medium particles at a low content increased the maximum dry density by replacing small particles and void between them, and forming the soil skeleton when the content exceeded 40%. The increase in maximum dry density caused by small particles filling the pores and the decrease caused by the loosening of soil skeleton result in a peak value of maximum dry density when the content of small particles is between 25 and 35%. The effects of particles in soil can be concluded into four effects: framework effect, filling effect, substitution effect, and loosening effect. This study provides a scientific basis for predicting models and compaction methods of over coarse-grained soil. </p> Graphical abstract <p></p>