Pushover Analysis of Piles in Stratified Soil

Pile foundations have been the subject of interest for earthquake engineers since last several decades. The devastations caused in major earthquakes of the world can be the reason enough to carry out the research on the topic of seismic behavior of piles. One definite concern is liquefaction induced ground movement after the shaking in an earthquake, causing extra lateral loads acting on piles. Several numerical models have been proposed so far to obtain the response of piles in such situations. These include the Beam on Nonlinear Winkler Foundation (BNWF) model, Finite Element models, etc. On the other hand, strength and deformation demands of multi-degree of freedom systems have been obtained by methods like Response History Analysis (RHA), nonlinear static procedures (NSP) and modal pushover analysis. But the solution for pile capacity under earthquake loading with pile in a generalized multilayer soil profile is still scarce. The monotonic pushover method (force based) has been employed to study the responses of pile foundations in liquefiable soil for a single layer and for multilayered systems to study the effect of change in pile head deflections. A worldwide available robust 3D finite element tool, OpenSEES PL is used to model the soil and pile properties using 8-noded brick elements. The pile is discretized using nonlinear beam elements and extended up to the depth of last soil layer. Results for different stratified cases are presented in terms of pile head deflections. They are also compared for different positions of liquefiable layers with respect to non-liquefiable layers.