Development of Relative Rigidity Measure for Shallow Foundations

- This study investigates the influence of the structure-to-soil relative rigidity on the structural behaviour of shallow foundation. The effect of change in the material and geometrical properties on the critical soil pressure intensity, bending moment and shear force of spread footings and rafts is investigated numerically using the finite element method. The parameters that are addressed in the analysis include the foundation thickness, soil modulus of subgrade reaction, concrete modulus of elasticity and plan geometry of the foundation. The foundation is modelled by thick shell elements while the soil by Winkler elastic springs. Findings of the study showed that the most important variables that affect the structural response of shallow foundations are the thickness and plan dimensions of the foundation, and to a lesser extent the soil modulus of subgrade reaction and concrete modulus of elasticity. A relative foundation-to-soil rigidity measure that can quantitatively predict the degree of stiffness of a shallow foundation was developed. The rigidity measure can help engineers in forecasting whether the traditional rigid foundation approach can be safely used to analyse a given spread footing or raft.