A comparative analysis of foundations using prescriptive design and static loading test methods:(case study: the Karuma interconnection power project in Uganda)

Abstract

Foundations for overhead transmission line lattice towers are subjected to overturning loads imposed by winds and impact. Hence, they are designed to resist uplift, compression, lateral and interconnection cable line-tension forces. However, due to the non-linear nature of the load-displacement response for typical transmission line foundations, uncertainties in subsoil behavior and design models, variations in soil strata, limits of site explorations, and diversity in construction methodologies, the performance of the full scale foundation model was analyzed using the reliability-based Static loading test methods. The researcher used prescriptive design methods in geotechnical investigations, insitu and laboratory tests, geotechnical and structural designs using the load and resistance factor design approach, computer aided design tools, and static load test methods of static axial tensile, static axial compressive, and lateral load tests, to replicate and validate the foundation’s insitu long-term sustained load capacity and subsequent displacements. The findings showed moderately aggressive chemical and environmental conditions, fine-grained soils with low swell potential and medium-dense to hard soil consistencies under 0.3-10m ground water table levels. The static load test results showed a 20% increase in design efficiency, 15-35% cost savings, and 80% reduced displacement overdesigns based on the insitu displacement values of less than 20% of the prescriptive design values. Although this research has advanced the understanding about transmission line foundation designs using prescriptive design and static loading test methods, further research must be done in quantifying the influence of ambient temperature, weather variations, and rate of insitu backfill-soil compaction on static load test results. Key words: Foundations, Prescriptive design, Static load test, Transmission Towers