Investigating the Distribution of the Modulus of Subgrade Reaction for the Structural Design of Mat Foundations in Clay

Abstract

The interaction between mat foundations and the supporting soil is often simplified by assuming that the mat foundation rests on uncoupled Winkler springs representing the soil medium. This assumption results in a uniform distribution of the modulus of subgrade reaction which leads to erroneous results that mispredicts bending moments within the mat foundation. Previous studies tackled these problems by examining the distribution of the Winkler spring stiffness throughout the mat foundation to achieve more realistic results by considering the soil as a continuum medium. However, these studies only focused on the elastic behavior of soil or elastoplastic behavior under constant volume (undrained conditions). This thesis aims to understand the effects of plastic strains and volume changes that happen due to the consolidation of clayey soils. For this purpose, three-dimensional parametric analysis of slabs resting on elastoplastic soil are performed using the finite element software ANSYS for various soil characteristics and loading configurations under drained conditions. The soil behavior is simulated using the Modified Cam Clay constitutive model. The results show that the assumption of a linear elastic soil overpredicts the soil’s stiffness and the bending moments in mat foundations. Acknowledging the elastoplastic behavior of the soil is crucial for mat foundation design. Effort was also made to provide a practical design method that would generate outcomes resembling those of an elastoplastic continuum finite element analysis by comparing different methods of subgrade analysis. It was found that the discrete area method is most suitable for this purpose.