Dependency of N-gamma on footing diameter for circular footings

By incorporating a variation in soil internal friction angle phi with mean principal stress sigma(m) the dependency of bearing capacity factor N-gamma with footing diameter B has been evaluated for circular footings. The evaluation has been performed by a lower bound finite element limit analysis in combination with a linear optimization. Two phi-sigma(m) curves, available from literature, were used. The magnitude of N-gamma has been computed for several footing diameters, covering almost the entire possible range of model and field footing sizes. Factor N-gamma is seen to decrease significantly with an increase in B. For B approximately greater than (i) 0.7 m for smooth footings (delta=0) and (ii) 0.35 m for rough footings (delta=phi), N-gamma varies almost linearly with B on a log log scale. Once a relationship has been generated between N-gamma and B, for a given design load, the required footing diameter can always be obtained. (C) 2013 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved