GEOLOGICAL AND GEOTECHNICAL CHARACTERISATION OF SHALE-DERIVED MATERIALS AND THEIR ENGINEERING IMPLICATIONS IN UGWUAJI AND ENVIRONS, SOUTHEASTERN NIGERIA

Abstract

This study conducted in Ugwuaji and Environs, Enugu South L.G.A, scrutinized the geological and geotechnical features of the area. Two distinct units, A and B, were identified. Unit A consisted of fissile dark grey shale with pronounced weathering and cracking, while Unit B comprised fissile light grey shale displaying reddish-brown stains from overburden. A variety of sedimentary structures, such as cracks, lamination, joints, Orphiamorphar burrows, fractures, bedding planes, and mud cracks, characterized the Lithofacies of the region. Geo-technical assessments on six disturbed soil samples unveiled a stiff soil with the capacity to withstand load and pressure. Triaxial test outcomes revealed a cohesion range of 20-31 KNm-², an angle of internal friction range of 16-18, and an undrained compressive strength range of 111.05-144.2 KNm-². Atterberg's limit results indicated a low to medium swelling potential, with liquid limit ranging from 24-35.70%, plastic limit from 16.72-25.97%, and plasticity index from 5.71-12.35%. The particle size distribution test emphasized the prevalence of sands, clay, silt, and gravel in the soil composition. According to the Unified Soil Classification System (USCS), the area was classified as well-graded sands with gravel, poorly graded sand, and sands with fines. The AASHTO classification system categorized the soils predominantly as A-1-a, signifying granular, low-plasticity clay suitable for sub-grade material. In essence, this study provides a comprehensive understanding of the geological and geotechnical attributes of Ugwuaji and Environs within a 240-word framework.