Abstract
The authors studied the classification system for coarse soils based on the maximum dry density and the optimum moisture content of the modified AASHO compaction test, the soaked CBR at 95 percent of the maximum dry density, and the coefficient of permeability of compacted soils. After this study, the best boundaries between clean gravels or sands, gravels or sands with some fines, gravels or sands with fines, and fine soils were found to be 5%, 15% and 50%, respectively. And the criteria of well-graded gravels or sands were found to be the coefficient of uniformity Cu greater than 10 and the coefficient of curvature Cz between 1 and √(Cu).Based on these considerations, the authors proposed a modification of the Unified Soil Classification System using the above-mentioned criteria and 2.0 mm for the gravel-sand boundary, and showed the relationships between the engineering properties and the modified classification system for coarse soils.
