Comparison of Rock Correction Methods for Compaction of Clayey Soils

The effect of varying percentages of large aggregate on the maximum dry density and optimum water content of clay is investigated through a series of laboratory compaction tests. Rock content (material retained on the No. 4 sieve) was varied from 0% to about 60% in the laboratory tests. The compaction tests are performed primarily using ASTM D698 method D, with replacement for oversized aggregate, i.e., the “scalp‐and‐replace” method. The maximum dry density obtained from ASTM D698 method D is compared with the maximum dry density estimated from rock correction equations in ASTM method 4718, U.S. Bureau of Reclamation method 5515‐89, and American Association of State Highway and Transportation Officials procedure T224. The optimum water content obtained from ASTM D698 method D is compared to the estimated optimum water content obtained from rock correction equations in ASTM method 4718. The data presented in this paper show that when soil fines are clayey, very significant differences in maximum dry density are obtained using scalp‐and‐replace procedures compared with the rock correction equations. The potential impact of these differences on construction compaction control are addressed.