Numerical Simulation of Bearing Capacity Characteristics of Strip Footing on Sand

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This study aims at numerically simulating the bearing capacity characteristics of strip footing on sand, and consequently explaining the scale effects observed in a series of plane strain model tests carried out on a particular type of sand (Toyoura sand). The model tests were performed using different sizes of footing, with the largest width being 50 cm, under normal gravity and in a centrifuge. A constitutive model developed for Toyoura sand based on the results from an extensive series of plane strain compression tests is used. A number of factors which affect the strength and deformation of sand are taken into account, including; 1) confining pressure; 2) anisotropy; 3) non-linear strainhardening and strain-softening; 4) dilatancy; and 5) strain localization into a shear band(s). This material model is coupled with an isotropically hardening, non-associated, elasto-plastic material description. A widely used numerical technique, FEM, is applied to solve the non-linear equations. A parametric study is performed to evaluate the effects of using different assumptions for the material model. The simulation of bearing capacity compares well with the physical model test results. It is shown that the isotropic perfectly plastic modelling of soil property, assumed in most of the classical bearing capacity theories, is an overly simplified approximation to be used in FEM analysis of this issue. It is explained that the scale effect consists of the pressure level effect and the particle size effect.