An Original Theoretical Framework for Poro-Elasto-Plastic Modelling of Soft Clay Consolidation Under Infrastructure Loading in the Niger Delta

Ground settlement under infrastructure loads in the Niger Delta's soft organic clay environment involves coupled mechanisms including Terzaghi primary consolidation, secondary creep, plastic deformation under cyclic loading, and pore pressure generation from organic decomposition, none of which are comprehensively captured by existing consolidation theory as applied to the region. This study develops an original poro-elasto-plastic theoretical framework for soft clay consolidation in the Niger Delta environment, integrating novel constitutive components specific to the region's highly organic, gas-generating soft clay deposits. Three original theoretical contributions are developed: a modified Cam Clay yield surface extended to accommodate the gas voids that characterise organic soft clays of the Niger Delta; a secondary consolidation law incorporating pore gas exsolution effects during load application and stress relaxation; and a finite element implementation scheme that handles the extreme deformation magnitudes characteristic of very soft clay under embankment loading. The framework is validated against field settlement monitoring data from three embankment constructions on Niger Delta soft deposits, including vertical and horizontal deformation measurements. The constitutive model implementation is benchmarked against Terzaghi, Biot, and Modified Cam Clay predictions. Results confirm that the original framework reduces settlement prediction error from 38 to 12 percent relative to Modified Cam Clay for organic clay sites. The theoretical contribution advances the fundamental understanding of gas-bearing organic soft clay behaviour under infrastructure loading.

Keywords: soft clay consolidation, Niger Delta, poro-elasto-plastic, organic clay, finite element modelling