Abstract: The compaction rate of gravel soil is usually characterized by the "relative density", which is used to evaluate the compaction quality of dam construction. Restricted by the size and energy limitation of the laboratory test equipment, the laboratory tests are difficult to reflect the actual situation of high strength compaction of gravel soil by large rolling equipment;and the maximum dry density of the gravel soils obtained in laboratory tests is often much lower than the actual one, so it cannot be directly used in practical engineering. To the sand and gravel materials for the Dashixia high concrete faced rock-fill dam, the field large-scale relative density test of original gravel soil was carried out by using the actual rolling equipment and large relative density bucket on the site, the compaction characteristics of soil was studied, and further the relative density characteristic indexes of soils with different gradation (coarse grain content) were determined. The test results show that the maximum dry density of gravel soil determined by field test is greatly improved compared to a general laboratory test; the minimum and maximum dry densities of gravel soil show a tendency of increasing at first and then decreasing with the increase of the coarse grain content, and there is an optimal coarse grain content value with the highest compaction density of soil; the strong vibration compaction results in different degrees of particle crushing effect on weakly cemented gravel materials, and the degree of particle crushing is related to the original grading characteristics of soil materials.

Key words: gravel soil of dam, field relative density test, maximum dry density, three factors chart, particle crushing, Dashixia high concrete faced rock-fill dam