Geotechnical Characterisation of Expansive Soils Along the Abuja-Kaduna Rail Corridor

Expansive clay soils encountered along the Abuja-Kaduna standard gauge rail corridor in North Central Nigeria pose significant geotechnical challenges for long-term track stability, requiring systematic characterisation to support ongoing maintenance planning and prospective corridor extension. This study characterises the distribution and geotechnical properties of expansive soils at eight critical locations along the Abuja-Kaduna rail corridor identified from field observations of track distress. Undisturbed tube samples and disturbed bulk samples were collected from trial pits to depths of two metres at each location. Geotechnical tests performed included Atterberg limits, linear shrinkage, particle size distribution, free swell ratio, swell pressure measurement using an oedometer under vertical confinement, and consolidated undrained triaxial shear strength. The mineralogy of clay fractions was identified by X-ray diffraction to confirm the presence of smectite as the primary expansive mineral. Correlations between plasticity index, free swell ratio, and soil expansion potential were evaluated against classification systems by Chen and Nelson. Stabilisation options using lime, cement, and calcined clay pozzolan are assessed using treated sample swell pressure tests. Results and recommendations are presented to the Nigerian Railway Corporation and the infrastructure management contractor for adoption in the track maintenance programme. Keywords: expansive soils, swelling clay, rail corridor, geotechnical characterisation, Abuja-Kaduna.