EMPIRICAL PREDICTION MODELS FOR THE COMPRESSION INDEX (Cc) OF LAGOS COASTAL CLAYS USING INDEX PROPERTIES AND REGRESSION ANALYSIS

Author

Bello Abdulkabir Oluwadamilola


Abstract

 The prediction of compression index (Cc) is essential for estimating consolidation settlement in soft clay deposits, yet conventional oedometer testing may be constrained by cost, time and sample disturbance. This study developed and comparatively evaluated empirical regression models for predicting the compression index of Lagos coastal clays using routinely determined geotechnical index properties. A quantitative approach was adopted using 140 geotechnical observations obtained from borehole logs and site investigation reports across selected locations in Lagos State, alongside a primary laboratory control sample. Linear, logarithmic, exponential and power regression models were examined using natural moisture content, liquid limit, plastic limit, plasticity index and liquidity index as individual predictors. The best coefficient of determination was obtained by the linear plastic limit model (R2 = 0.5722) that gave Cc = 0.0445(PL) − 0.358. The two other important parameters, natural moisture content and liquid limit also showed moderate explanatory relationships, whereas, plasticity index and liquidity index showed comparatively weak performance. The results suggest that the index properties provide useful initial data for the estimate of compressibility, although they have a moderate level of explanatory power and there is still prediction uncertainty. The study suggests that prior to widespread engineering use, independent validation and further geological characterisation is needed. Proposed equations are therefore meant for preliminary geotechnical assessment and not to replace the direct consolidation testing in the design of settlement sensitive foundations.


Keywords

Compression index, Coastal clay, Consolidation settlement, Geotechnical properties, Soil compressibility, Plastic limit.



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