When modeling the flexible behavior of a mat foundation under load, it is crucial to carefully select the appropriate modulus of subgrade reaction (MSR). The MSR represents the soil’s stiffness and varies across the mat, influenced by factors like the mat’s width, shape, and founding depth. In particular, the MSR is typically lower at the center and higher near the edges of the mat.
Assuming a constant MSR throughout the mat’s width, as is often done in simplified analyses, can lead to inaccurate results. Under a uniform load, this assumption would predict a relatively uniform settlement pattern. However, in reality, the center of the mat experiences greater settlement than the edges. This discrepancy, as noted by Donald P. Coduto (1994), can underestimate the bending moment by 18% to 25%, potentially compromising the structural design.
Therefore, a variable MSR that accounts for the changing soil stiffness across the mat is essential for accurate analysis. This approach is particularly crucial when dealing with non-rigid superstructures or when the foundation’s rigidity is not dominant. It allows for the realistic simulation of the pressure bulb distribution, which represents how loads are transmitted from the foundation to the underlying soil.
In summary, the selection of an appropriate MSR model is fundamental for the accurate analysis and design of mat foundations. While a constant MSR may suffice for rigid systems, a variable MSR is necessary to capture the complex behavior of flexible foundations and ensure their structural integrity.