Geotechnical Assessment of Subsurface Conditions along the Proposed Kano–Maradi Rail Project Using Standard Penetration Test (SPT): A Case Study of the Yargaya-Gaya Section, Northwestern Nigeria

Abstract

This research investigates the subsurface conditions along the Yargaya–Gaya section of the proposed Kano–Maradi rail line in Northwestern Nigeria, focusing on geotechnical assessment using the Standard Penetration Test (SPT). The study involved conducting SPTs at 82 borehole locations along the rail alignment to evaluate soil strength, bearing capacity, and foundation suitability for rail construction. Field SPT N-values ranged from 4 to 99, with relative density classifications varying from Loose to Very Dense across the explored depths. Predominantly, the subsurface soils exhibited medium-dense conditions at depths between 1.5 m and 6.0 m. Laboratory analysis revealed natural moisture content ranging from 1.9% to 40.3%, liquid limits between 17% and 49%, and plasticity index (PI) values spanning non-plastic to 37%. Grain size analysis classified the soils into groups such as SM (Silty Sand), SC (Clayey Sand), SP-SM (Poorly Graded Silty Sand), SP (Poorly Graded Sand), ML (Silt of Low Plasticity), and CL (Lean Clay). Pile capacity analysis using effective stress methods indicated that the soils have moderate to high allowable bearing capacities depending on depth and soil type. The coefficient of consolidation ranged from 6.9 m²/year to 8.3 m²/year, suggesting moderate compressibility. Rock samples exhibited uniaxial compressive strengths ranging from 4.56 N/mm² to 10.84 N/mm², confirming competent rock layers at depth. Based on the results, the study concludes that most sections of the rail alignment are suitable for shallow foundations or pile foundations, with some locations requiring soil improvement or deeper foundation solutions due to loose sands or highly plastic clays.