Appraisal of Site Investigation Practices and Their Impact on Structural Costs in Kaduna State

Inadequate site investigation is widely recognised as a leading cause of unforeseen ground-related costs and structural difficulties in building projects. This study appraises the quality of site investigation practices and their impact on structural construction costs in Kaduna State. A descriptive quantitative design was adopted, with structured questionnaires administered to 82 quantity surveyors, civil engineers, and contractors working on building projects across Kaduna, Zaria, and Kafanchan. Data were analysed using mean item scores and correlation analysis. Findings reveal that comprehensive soil investigation reports are prepared for fewer than 30% of residential and commercial projects in the study area, with most developers relying on visual ground assessment or extrapolation from neighbouring sites. The study finds a significant positive correlation (r = 0.71) between inadequate site investigation and post-contract structural cost variations, particularly for foundation redesign, ground dewatering, and substructure modification. Projects on expansive clay soils in Kaduna's southern districts are disproportionately affected. Recommendations include making site investigation reports a mandatory condition for building permit approval in Kaduna State, training quantity surveyors in geotechnical risk pricing, and establishing a shared ground condition database for major urban areas. This research contributes to knowledge on site-related risk and its cost implications in the North West geopolitical zone. Keywords: site investigation, structural costs, Kaduna State, geotechnical risk, quantity surveying