Comparative Evaluation of 2.5-ton CPT, 10-ton CPT and SPT for Bearing Capacity Estimation in Swampy Tropical Soils of Akure, Southwestern Nigeria

Reliable estimation of foundation bearing capacity in swampy tropical soils is challenging due to weak, highly compressible and heterogeneous ground conditions. This study presents a comparative evaluation of bearing capacity estimates derived from 2.5-ton CPT, 10-ton CPT and Standard Penetration Test (SPT) data from lowland sites in Akure, southwestern Nigeria, underlain by weathered basement complex and transported soft soils. Cone tip resistance, sleeve friction and SPT N-values were analysed within a consistent depth framework, and bearing capacities were estimated using established empirical correlations. The results show a clear increase in soil resistance and bearing capacity with depth across all methods. However, systematic differences were observed in the magnitude of the estimates. The 2.5-ton CPT reached refusal in deeper, stiffer layers and generally produced more conservative values, whereas the 10-ton CPT provided continuous, higher-resolution profiles. The SPT yielded significantly higher bearing capacity values in intermediate and deeper layers, suggesting potential overestimation when used alone. The study highlights the strong influence of test method and equipment capacity on design outcomes and emphasises the need for site-specific calibration and combined use of in-situ tests in tropical lowland environments.