Research and application of relative density test method for large coarse-grained soil

Based on the design filling gradation of rockfill materials for Lawa super-high face dam, the main factors affecting the test accuracy of large density barrel are studied by means of numerical and field tests. The double-control index of rockfill porosity and relative density is proposed, and its applicability is verified by the results of rolling tests. The results show that: (1) For the field density barrel tests on the coarse-grained soil with a large particle size, which is difficult to be fully mixed, the method of artificial layering can effectively reduce the discreteness of the test results. (2) The selection of container size has a great influence on the test results, and too large size will bring higher test cost, even difficult to implement, while too small size will bring obvious container boundary size effect. Considering the actual situation in the field, the size effect of the test results is relatively small when the density barrel test size meets the minimum 'diameter to diameter ratio' and the 'height to diameter ratio' is about 4.0 and 2.0, respectively. (3) With the increase of the maximum particle size, the extreme dry density of density barrel tests shows an increasing trend. However, when the maximum particle size reaches 400 mm, the extreme dry density is basically stable. The test results can be used as the basis for compaction design and filling quality control. (4) The porosity is not higher than 19% and the relative density is not less than 0.75. The requirements can be met by using 32T vibration rolling 12 times. (5) For the soil with a large particle size with horizontal layered compaction, the ratio of the thickness of compaction layer to the maximum particle size can be appropriately increased, which can achieve better compaction efficiency. It is an optimal compaction scheme for rockfill materials to take a loose paving layer with a thickness of about 1.0 m and a maximum particle size of 400~600 mm. The research results can be directly applied to the compaction design and evaluation of coarse-grained soil with large particle size, which has a great application value.