Validity of SPT–CPT Correlation for Bearing Capacity Prediction of Reclaimed Soils in Lagos Island, Lagos State, Nigeria

Background: Engineers often apply published, generic SPT–CPT correlation ratios to estimate one test from the other when only one is available. These ratios were developed for natural soils, and their validity for reclaimed soils in Lagos Island, Nigeria, has not been tested. Methods: Secondary SPT, CPT and borehole data from six reclaimed sites in Ikoyi, Victoria Island, Lekki and Sangotedo were analysed. Allowable bearing capacity was computed from SPT data using Meyerhof’s general bearing capacity equation (factor of safety of 3) and from CPT data using Meyerhof’s (1956) direct method. The site-derived ratio qc/N was compared with published values from Brazil (Danziger et al., 0.39 MPa) and the United Arab Emirates (Akça, 0.30–0.45 MPa), including a one-sample t-test. Results: SPT-based allowable bearing capacity ranged from 237.5 to 404.5 kPa and CPT-based capacity from 245.2 to 653.8 kPa. The site-derived qc/N had a mean of 0.559 MPa (range 0.245–0.823 MPa), a coefficient of variation of 40.3% and a 95% confidence interval of 0.323–0.795 MPa. Only one of the six sites (Site A, 0.441 MPa) fell within the published range, although the mean did not differ significantly from the Danziger value (p = 0.13). Conclusion: Published generic SPT–CPT correlation ratios are not reliable for reclaimed soils in Lagos Island, because only one of the six sites fell within the published range. Site-specific data should be used or, where unavailable, the site-derived mean or the wider 95% confidence interval established here should be adopted as a fallback.