Since gradation greatly affects its compaction characteristics

the quantitative description of the effect of gradation on compaction properties is crucial. Based on the continuous gradation equations of soil

16 groups of experimental coarse-grained soils with different gradations were designed. Surface vibration compaction test and confined compression test were carried out to study the effect of gradation on compaction properties of coarse-grained soil. The results showed that the quadratic function relationship was found between the gradation curve area and dry density obtained by surface vibration compaction (dynamic stress) and confined compression (static stress). Besides

the gradation curve areas corresponding to the maximum values of dry density were close to 0.9. Both in surface vibration compaction test or confined compression test

there was optimal dry density of coarse-grained soil under certain gradation. Based on test results

the optimal gradation interval of coarse-grained soil with better compaction was given (upper and lower envelopes of gradation)

which was further demonstrated through similar grading method. Meanwhile

the universal applicability of this optimal gradation interval was verified by the design gradation of coarse-grained soil of several earth-rock dams. This paper can provide the important basis for the grading design of coarse-grained soil for earth-rock dam.