| This thesis presents research on the bearing capacity of ring footings on a dense sand under vertical loads. The effects of footing size, ring radii ratio and load eccentricity have been investigated by means of centrifuge modelling, the method of characteristics and the finite element technique.; Test results indicate that the bearing capacity is significantly affected by footing size, ring radii ratio and load eccentricity. It is found that the bearing capacity of circular footings increases linearly with footing diameter in a double-log scale diagram. The bearing capacity of a vertically loaded ring footing can be expressed in terms of a bearing capacity ratio (Br), a reduction factor (Re) and the bearing capacity of an axially loaded circular footing with the same area. Test results show that the value of Br is related only to the ring radii ratio (n), independent of footing size; when n is from 0 to 0.35, Br increases slightly with n. Further increase of n beyond 0.35 results in significant decrease of Br. The value of Re, decreases with load eccentricity and is independent of ring radii ratio.; Circular footings under axisymmetric conditions have been analyzed by the method of characteristics to further study the effect of footing size on bearing capacity. The compatibility of bearing capacities obtained from both variable and constant friction angle analysis provides a basis for the FE analysis using an equivalent constant friction angle for each footing.; The FE technique has been applied to circular and ring footings on the dense sand under axial vertical loads. In the analysis, a footing is represented by a rigid body consisting of rigid surface elements. Interface elements are used to model the interaction between the footing and soil. The elasto-plastic behaviour of soil is simulated by the Drucker-Prager/Cap constitutive model. Compared with centrifuge test data, the analytical results regarding the effect of footing size and ring radii ratio on bearing capacity are satisfactory. When calibrated with experimental data, the FE technique is very useful for analysis of very large foundations or for cases when experimental data are not available or difficult to obtain. (Abstract shortened by UMI.)... |
