Investigation of Ground Improvement Options for Soft Clay Foundations in Coastal Communities of Rivers State

Coastal communities in Rivers State, South South Nigeria, are frequently located on weak soft clay deposits that pose significant challenges for building and infrastructure foundations. This study investigates ground improvement options appropriate for soft clay foundation conditions in coastal communities in Bonny, Asari-Toru, and Akuku-Toru LGAs of Rivers State. Undisturbed soft clay samples were collected from three depth profiles (0.5 to 3.0 m) at six locations in the study area. Laboratory tests including Unconfined Compressive Strength, consolidation, and Atterberg limits characterised the native soil. Ground improvement methods assessed include preloading with vertical drains, lime column installation, stone column construction, and geosynthetic reinforcement. Feasibility and cost-effectiveness were evaluated relative to the soil profile and available local materials. Results indicate that undrained shear strength ranges from 8 to 24 kPa across sample sites, consistent with very soft to soft clay requiring ground improvement for any loading above 20 kPa. Liquid Limit values of 58 to 84 percent indicate highly plastic clay. Settlement calculations predict 120 to 320 mm of consolidation settlement for a typical building floor load on untreated ground. Preloading with prefabricated vertical drains is identified as the most cost-effective solution for large footprint structures. The study recommends minimum geotechnical investigation standards for coastal construction in Rivers State.

Keywords: soft clay foundations, ground improvement, coastal engineering, Rivers State, South South Nigeria