A new model for Lateral Pile Behavior in Sands under Earthquake Excitation

Piled foundations are used where the superstructure load cannot be carried by conventional raft foundations. Especially in mid-rise or high-rise buildings founded on soft-loose soils, the use of piles beneath the raft is inevitable in most cases. The design of those foundation piles is commonly handled by considering the following two conditions: Static loading due to weight of structure and dynamic (or earthquake) behavior. While the static conditions can be taken into account without considering the superstructure by using some empirical relations, the behavior under seismic excitation cannot be solved by isolating the piles from the superstructure. Since the pile motion affects both the soil and superstructure and the behavior of pile is affected by the behavior of those two, the problem is called as pile-soil-structure interaction problem.

There are two common approaches for analyzing the pile-soil-structure interaction problem: Direct method and substructure method. Direct method approach takes into consideration the pile, soil and structure behavior directly by analyzing them in a single model. However, it is not preferred because analyses are highly time consuming. Instead, more efficient method called substructure approach is used in design stage. This method commonly known as beam on nonlinear winkler foundation (BNWF) method and it has three stages: Ground response analysis, non-linear lateral load-displacement relation and use of damping. In this approach, soil-pile interaction is represented using non-linear spring elements and these springs are known as p-y curves. There are some suggestions for those curves in the literature, but most of them are either for static lateral loads or includes many parameters which is not applicable in practice.

The aim of the thesis is to develop new non-linear relations for pile-soil interaction under seismic excitation. For this purpose, a finite element based soil structure interaction software will be used. The first step is to calibrate the numerical model with the results of a well-known centrifuge experiment study. After the validation of numerical model, parametrical study will be performed to show the effects of dynamic load frequency, relative density of soil, amplitude of load (maximum acceleration) and natural frequency of superstructure on the lateral response of the pile in terms of p-y behavior. The third step is to develop a relation which includes the mentioned parameters. The last step is to test the method by analyzing some well-known pile-soil-structure interaction studies by using suggested relation.