This study systematically scrutinized the influence of grain shape modification on the compaction characteristics of granular subgrade materials commonly employed in roadbed and subgrade construction. The process involved conducting compaction tests on granular crushed stones whose shape was altered through the grinding process facilitated by a granulating machine. As an initial step, the crushed stone was subjected to the grinding machine multiple times to induce changes in grain shape. This procedure resulted in crushed stone grains with fewer surface irregularities, smaller diameters, and a more circular shape tendency. Subsequently, image processing techniques were utilized to quantify these alterations in grain shape. Further, compaction tests were executed using a tamping method on the ground crushed stones, and their compaction characteristics were meticulously examined afterward. The results revealed no notable disparities in maximum dry density or optimal moisture content.