Geotechnical Characterization of Subgrade Soils Using the AASHTO Classification System: A Case Study

Abstract

This study presents the geotechnical characterization of soils in the vicinity of Shaheed Benazir Bhutto University (SBBU), Nawabshah, employing the American Association of State Highway and Transportation Officials (AASHTO) classification system. Soil samples were obtained from two distinct locations using a hand auger, and subsequent laboratory testing included sieve analysis, liquid limit determination via the Casagrande cup method, and plastic limit testing. The experimental outcomes demonstrated that Soil Sample A contained 31.54% fines passing the No. 200 sieve, with a liquid limit of 31.5%, a plastic limit of 13.73%, and a plasticity index of 17.77%, which classifies it as A-2-6, indicating silty or clayey gravel sand. In contrast, Soil Sample B exhibited 38.34% fines passing the No. 200 sieve, with a liquid limit of 41%, a plastic limit of 25.51%, and a plasticity index of 15.49%, thereby classifying it as A-7-6, indicative of a clayey soil. These findings reveal that the soils in the SBBU vicinity range from silty-clayey gravel sands to clayey soils, thereby providing essential baseline data to inform future construction planning, foundation design, and the development of soil improvement strategies for the area.