On the influence of progressive failure on the bearing capacity of shallow foundations in dense sand

ABSTRACT In designing the foundations for large-scale structures, it is important to take into account the scale effect of bearing capacity of foundation soils. In this paper the mechanism of the scale effect of bearing capacity of dense sand is investigated for shallow foundations. A series of loading tests using Toyoura sand are carried out in a centrifuge by which stresses in small-scale models can be made approximately identical to those in actual foundations. Deformations of the sand are measured by a set of electronic devices and slip lines in the sand mass are observed immediately after the peak load by an X-ray apparatus. It is found out by these observations that shearing strains in the foundation sand differ very much from place to place, which leads to a conclusion that the progressive failure generally exists in dense sand and that the assumption of constant shearing strain, which has been adopted in existing bearing capacity theories, cannot be accepted except for some limited cases. Kotter’s equations are solved by combining a unique relationship between the angle of shear stress and shearing strains for the sand, obtained from plane strain shear tests, with observed shearing strains in models. Resulted bearing capacities compare well with measured values for the sand in which shearing strains differ from place to place along the slip line. It is also shown that the rigidity of specimen containers gives significant influence to the magnitude of observed bearing capacities.