Evaluating the Performance and Economic Viability of Wajir Metamorphosed Lime as a Stabiliser of Black Cotton Soil in Road Construction in Kenya

Road infrastructure remains a cornerstone of Kenya’s national development agenda; however, construction efforts are frequently impeded by geotechnical challenges, particularly the presence of expansive soils such as black cotton soil (BCS). In arid counties like Wajir, where BCS is prevalent and access to construction materials is limited, leveraging locally available resources becomes essential. This study investigated the potential of using locally produced metamorphosed lime from Wajir County as a sustainable stabilising agent for BCS in road subgrades. Laboratory tests were conducted to assess the effects of 5%, 10%, and 15% locally produced lime dosages on Atterberg limits, compaction characteristics, California Bearing Ratio (CBR), linear shrinkage, and swell potential. Results demonstrated significant improvement in soil properties with lime addition, notably a reduction in plasticity index from 31% to 6%, an increase in CBR from 5% to 19.2%, and a decrease in swell from 0.51% to 0.10%. The optimal lime dosage was determined to be 5%, balancing engineering performance and cost-effectiveness. A comparative cost analysis showed that lime stabilisation is substantially more economical than excavation and replacement with rockfill for a 1 km road section. The study concludes that locally available Wajir lime is both technically effective and economically viable for stabilising expansive soils, aligning with sustainable development goals. The findings advocate for integrating local lime into Kenya’s stabilisation practices, particularly in marginalised regions like Wajir