Combined Rupture Mechanism of Shallow Foundations under Drained Conditions

Current technical standards and codes of practice for shallow foundation design at the ultimate limit state require the analysis of rupture mechanisms that involve only the soil by assuming that the foundation structure does not undergo any yielding or rupture, but do not consider the case of combined rupture mechanisms in the soil and in the foundation structure, a situation that was recently observed in experiments on wind turbine foundations. By means of special numerical techniques for the analysis of soil–foundation interaction at the ultimate limit state under drained conditions, this work extends previous numerical investigations on undrained conditions and shows that the internal actions, the bearing contact pressures and the contact shear stresses beneath a yielding, flexible shallow foundation are much different with respect to those evaluated under undrained conditions. In any case, it is shown that foundation plasticisation leads to a potentially strong reduction of the bearing capacity depending on the loading condition. This work draws attention to some possible design situations that may be relevant for the optimised structural design of shallow foundations and paves the way to the development of simplified approaches that could be used in the usual design practice.