Rigorous plasticity solutions for the bearing capacity of two-layered clays

This paper applies numerical limit analysis to evaluate the undrained beari ng capacity of a rigid surface footing resting on a two-layer clay deposit. Rigorous bounds on the ultimate bearing capacity are obtained by employing finite elements in conjunction with the upper and lower bound limit theore ms of classical plasticity, Both methods assume a perfectly plastic soil mo del with a Tresca yield criterion and generate large linear programming pro blems. The solution to the lower bound linear programming problem is obtain ed by modelling a statically admissible stress field, whereas the upper bou nd problem is solved through modelling a kinematically admissible velocity held, Results from the limit theorems typically bracket the true collapse l oad to within approximately 12%, and have been presented in the form of bea ring capacity factors based on various layer properties and geometries. A c omparison is made between existing limit analysis, empirical and semi-empir ical solutions. This indicates that the latter can overestimate or underest imate the bearing capacity by as much as 20% for certain problem geometries .