Finite Element Evaluation of Vertical Bearing Capacity FactorsNc, Nq and N for Ring Footings

In this study, the vertical bearing capacity factors Nc, Nq and N are evaluated for smooth and rough base ring footings resting on c-phi soil using the finite element method. The radii ratio, (r(i)/r(o)), is the ratio of internal radius to the external radius of the ring footing, is varied from 0 to 0.75 with an increment of 0.25. The friction angle of the soil is varied from 5 degrees to 35 degrees, dilation angle is zero and the Mohr-Coulomb yield criterion and non-associative flow rule are used. The study is extended for the soil having a friction angle of 35 degrees considering the non-associative flow rule with a dilation angle of 5 degrees. The bearing capacity factors are evaluated considering cohesion, surcharge and unit weight as three separate components. Then the superposition of the three components of the bearing capacity equation is analysed. A numerical example is considered to illustrate the applicability of the finite element analysis by comparing the bearing capacities with those of the Terzaghi's classical equation. The finite element results are presented in the form of design charts and tables for practical use.