CONVENTIONAL AND CENTRIFUGE MODEL STUDIES OF THE MOMENT CARRYING-CAPACITY OF SHORT PIER FOUNDATIONS IN CLAY

An experimental investigation into the moment carrying capacity of sho rt rigid pier foundations in saturated clay is described. Scale models of square piers with different breadths and depths were used in both conventional and centrifugal studies. The results show that the relati onships between moment and rotation are nonlinear but do not exhibit a ny peak values, and that moment limits, defined by limiting angular ro tations, increase with increases in pier depth and breadth. Empirical equations are derived between moment carrying capacity and pier geomet ry, for a range of limiting rotations, and a very close fit is demonst rated between the moment-rotation relationships obtained using these e quations and the actual data obtained from the model tests. It is show n that, at the same pier rotations, the moment carrying capacities obs erved in the centrifugal model tests are significantly larger than tho se in the conventional model tests. Numerical analyses of the prototyp e geometries were also carried out using a three-dimensional nonlinear finite-element computer program. The results are shown to provide sat isfactory agreement with the moment-rotation behaviour and working lim its observed in the centrifuge model tests. Thus, even though conventi onal modelling is usually legitimate for determining the immediate bea ring capacity of rigid foundations in saturated clay, their rotational stability is shown to be significantly affected by self-weight stress es. Some of the existing methods for designing short piers subjected t o moments are examined and compared with the results from the centrifu ge model tests.