Geotechnical Investigation of Soils at Settlement of Bridge Approach Slab in Kaduna State, Nigeria

The study was conducted to investigate the geotechnical properties of soils at settlements of bridges approach slabs in Kaduna State, Nigeria. Five soil samples were collected from bridge settlement sites within Zaria and Kaduna Metropolis of Kaduna State, and were designated as KDM-A, KDM-B, KDM-C, KDM-D, KDZAR-A, and KDZAR-B. The index properties of the soils were determined, and tests conducted on the soil samples were in- situ dry density, dynamic cone penetration test, California bearing ratio, unconfined compressive strength, vane shear test, direct shear test, and consolidation test in accordance with British Standard (BS) and American Society for Testing and Materials (ASTM) standards. Results from the findings showed that the soils at KDM-A, KDM-B, KDM-C, KDM-D, KDZAR-A, and KDZAR-B were classified as A-2-6(2), A-6(4), A-6(3), A-2-6(1), A-2-6(2), and A-2-6(3) respectively, having OMC and MDD values ranging from 9.1 to 16.4% to 1.66 – 2.29 mg/m³ respectively. More results showed that KDM-A had the highest CBR at 0 – 150mm, and 151 – 300mm depth of 20 and 24 % respectively, whereas KDZAR-B had the highest CBR value of 20 % at >300mm depth for dry soil samples, while KDM-A and KDM-D sites had the highest soaked CBR values. Furthermore, KDM-A had the highest shear strength of 130kPa, and 7, 14, 28 days UCS at various compaction efforts, while KDM-B had the highest cohesion value of 16, 17, and 19 kPa, and lower angle on internal friction for BSL, WASC, and BSH compaction efforts. Finally, KDM-B has a soil settlement of 0.903 mm followed by KDM-A with settlement of 1.003 mm, indicating that these soil samples has better geotechnical properties compared to others.