Elastic Modulus Modelling of Soils under Deviatoric Stress-Strain Conditions
Abstract
Accurate characterisation of soil elastic properties is essential for predicting deformation and soil–structure interaction under loading. Young’s modulus, shear modulus, and bulk modulus are influenced by stress state, strain level, and soil characteristics, making their behaviour site-specific and potentially nonlinear. Reliable modelling of these parameters under deviatoric stress–strain conditions is therefore important for geotechnical design and performance assessment. This study evaluates the elastic response of cohesive soils from eight locations in Port Harcourt, Nigeria, under deviatoric stress-strain conditions. Forty-four soil samples were examined using unconsolidated undrained triaxial tests at confining pressures of 100 and 300 kPa. Young's modulus was derived from stress-strain models, while shear modulus and bulk modulus were calculated using elasticity relationships and assumed Poisson's ratio values ranging from 0.20 to 0.45. The results show that the elastic response varied with sampling location, strain level, confining pressure, and the assumed Poisson's ratio. Young's modulus plots generally indicated elastic behaviour at low strain, followed by location-dependent strain softening, plastic deformation, strain hardening, or very low stiffness at higher strain levels. Across the calculated values, bulk modulus increased markedly as Poisson's ratio increased, whereas shear modulus changed more gradually and generally decreased over the same range. The bulk-modulus relationships were represented by fourth-order polynomial models, while the shear-modulus relationships were represented by linear models. Differences were also observed between the 100 and 300 kPa loading conditions and among the investigated locations. These findings indicate that the calculated compressibility-related stiffness is more sensitive to changes in Poisson's ratio than the calculated shear stiffness within the adopted framework. The developed models provide site-specific relationships for evaluating soil compressibility and shear deformation under the investigated conditions and may support geotechnical assessments involving foundations, slopes, and dynamic loading.