Evaluation of Bearing Capacity of Ring Footing with Varying Base Roughness Using Finite Element Limit Analysis

The ring footing problems are axisymmetric in nature and are used as foundation for supporting isolated structures like chimneys, storage tanks, and silos. The bearing capacity of ring footing is affected by its geometry, strength properties of soil, and footing roughness. This study attempts to evaluate the bearing capacity factors of the ring footing considering different base roughness between the footing and soil, varying friction angles of soil, and different radii ratios of the ring footing by performing two-dimensional lower and upper bound finite element limit analysis. The base roughness between the footing and soil (α) is varied from 0 to 1 with an increment of 0.2, where α = 0 represents a smooth base footing and α = 1 represents a perfectly rough base footing. The friction angle of soil (ϕ) is varied from 0 to 40°. The geometrical parameter of ring footing, i.e., the radii ratio (ri/ro) is varied from 0 to 0.75. The Mohr–Coulomb failure criterion and associative flow rule are used in the analyses. A multivariate adaptive regression splines model is developed to propose empirical equations for the evaluation of the bearing capacity factors and examine the influence of investigated parameters (i.e., α, ϕ, and ri/ro) on the bearing capacity factors of ring footing. The results from the numerical study are presented in the form of design charts and tables and the empirical equations are proposed which can be used to evaluate the ultimate bearing capacity of the ring footing.