To understand scale effect of coarse-grained materials

the forms of scale effect are systematically clarified. The scale effect is divided into dense degree scale effect and mechanical properties scale effect. We analyze results of previous studies and summarize the performance of the law. The scale effect of dense degree is that the maximum or minimum dry density increases with the growth of the maximum diameter

which is regardless of scale methods. The law can be explained in terms of gradation

particle shape and compaction energy. With regard to the scale effect of mechanical properties

for the specimens with the same dry density

both shear strength and modulus decrease with the increase of the maximum diameter

which is resulted from compaction degree and particle strength. However

under the criterion of the same relative density

the law of scale effect of mechanical properties is unclear

and thus further studies need to be conducted.