Effect of Soil Nonlinearity on Analysis of Raft Foundation

Soil supporting foundations behave in a nonlinear manner at loading close to its bearing capacity. This behavior affects soil pressure distribution and the corresponding stresses in the raft foundation, which differs significantly from considering the soil as elastic linear material. The present research uses the finite element method to study the effect of soil nonlinearity on the behavior of raft foundations subjected to concentrated loads. The analysis is based on the Winkler type of foundation. The analysis considered different values of the average soil pressure to its bearing capacity. The supporting soil was modeled as elastic perfectly plastic material. The effects of soil nonlinearity on the intensity and distribution of soil pressure, punching shear force, and bending moments in the raft are investigated. The effects of the foundation stiffness evaluation factor L·λ on the behavior of rectangular raft foundations were studied. This parameter combines the effects of the modulus of subgrade reaction, raft thickness, modulus of elasticity of concrete, and column spacing, as these parameters are interrelated. The results indicated that considering the subgrade soil as a linear elastic material underestimates punching shear and bending moments compared to modeling the soil as an elastoplastic material.