Using Dynamic Cone Penetrometer (DCP) to Assess Geotechnical Properties of Basra Subbase Soils

Abstract

The evaluation of subbase layers is essential for the performance of pavement structures, particularly in regions with variable soil conditions such as Basra, Iraq. The Dynamic Cone Penetrometer (DCP) test is widely used due to its simplicity, cost-effectiveness, and ability to provide continuous in-situ soil profiling without the need for sample extraction. This study investigates the relationship between the Dynamic Cone Penetration Index (DCPI), dry density, and moisture content for three commonly used subbase materials (Types B, C, and D) in Basra. A comprehensive experimental program was conducted using both DCP and Sand Replacement Method (SRM) tests under controlled laboratory conditions. Tests were performed at three moisture contents (4%, 6%, and 8.5%) and varying compaction efforts, resulting in a total of 270 test trials. The results revealed a clear inverse relationship between DCPI and dry density, while moisture content showed a significant influence on both parameters. A graphical method was developed to estimate in-situ dry density based on DCPI and moisture content. The proposed method demonstrated good agreement with SRM results, indicating its potential as a rapid and reliable alternative for field density estimation. This approach can significantly reduce testing time and cost in geotechnical site investigations.