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.
