NUMERICAL-STUDIES OF THE MOMENT CARRYING-CAPACITY OF A SHORT PIER FOUNDATION IN A CLAY SOIL

Numerical predictions of the immediate moment carrying capacity of a s hort pier foundation in saturated clay are presented. Three-dimensiona l finite element analyses are carried out using linear and non-linear programs and using a linear axi-symmetric program. Preliminary investi gations are made to determine suitable boundary distances for analysis at full-scale and size of loading increment for non-linear analyses. Predictions of the behaviour of prototype pier and of conventional and centrifuge models of this pier are then made. It is shown that the ax i-symmetric program yields significantly higher rotations per unit mom ent than the linear three-dimensional program and that, using both of these programs, elastic analyses of the conventional and centrifuge mo dels and of the prototype yield very similar results. It is also shown that non-linear analyses of the conventional and centrifuge models yi eld significantly different moment/rotation relationship in accordance with the behaviour actually observed in the model tests. The relation ship obtained for the centrifuge model is shown to differ only slightl y from that obtained for the prototype, due to the boundary restrictio ns in the model, and to be of the same order as the centrifuge test re sult at working condition but not at ultimate capacity.