Stability of pile groups

Stability analysis of pile groups is an inherent ingredient in the design of new structures and is an integral part of maintenance of scoured pile foundations. It also represents an important part of nonlinear structural analysis, including computational techniques to trace nonlinear equilibrium path and to detect bifurcation and limit points on that path.; The main goal of the present research is the advancement of the existing capabilities for stability analysis of pile foundations. To this end, the new development in several relevant areas is included in stability analysis presented in this thesis, among which are modeling of soil-structure interface, nonlinear structural analysis and modern aspects of computational mechanics. Considering these aspects, a continuum model and a structural model are developed for three-dimensional nonlinear stability analysis of pile groups as a system.; In the continuum model, three-dimensional solid finite elements and mapped infinite elements are employed for modeling the three-dimensional geometry, pile-soil-pile interaction, and unbounded domain whereas three-dimensional thin-layer interface elements are used for modeling interaction behavior between the pile and the soil. In contrast, thin-walled structural elements and flat shell elements are used for the piles and pile cap in the structural model. Nonlinear soil springs are adopted for modeling the lateral and axial pile-soil interaction.; The continuum model is capable of accounting for pile-soil interaction and pile-soil-pile interaction appropriately, and these interactions are shown to have a significant effect on the stability behavior of pile groups. However, the continuum model requires significant computer resources and is not feasible for use by practitioners in firms where such resources are not available. On the other hand, the structural model is efficient and simple to implement, but does not automatically capture pile-soil-pile interactions. In order to include pile-soil-pile interaction for groups of closely spaced piles, the group-reduction factor is introduced in an approximate fashion. Both the continuum model and structural model developed in the present study are used together for some representative but simpler pile configurations to obtain the group-reduction factor.