Abstract:
As indicated by the extensive damage to pile foundations observed during previous earthquakes, vertical piles are weak in the horizontal direction and susceptible to failures, especially in the liquefied ground. Theoretically speaking, inclined piles are believed to have larger lateral resistance than vertical piles by transferring part of the lateral force into the axial direction. Numerous field investigations, experimental findings, and numerical simulations have reported the benefits of inclined piles. However, failures of wharves and bridge foundations supported by inclined piles resulted in the discouragement of inclined piles in the engineering design. The beneficial or detrimental effects of inclined piles in the liquefiable ground are still not well understood.
This research investigates the seismic performance of inclined piles in liquefiable soils through numerical approaches. Firstly, a comprehensive three-dimensional (3D) Finite Element Method (FEM) model of the soil-pile interaction system is established in OpenSees. Special attentions have been given to the liquefaction behavior of soil, pile geometry simulation, and the slippage and separation mechanisms at the soil-pile interface. By simulating several experiments in the literature, the proposed modeling method has been validated to be suitable to predict the behavior of single piles and pile groups under either static or dynamic loading patterns.
Secondly, based on the validated 3D FEM model, the performance of inclined piles is investigated considering various influencing factors, including pile inclination, soil liquefaction, pile group configuration (e.g., pile spacing, symmetrically and asymmetrically inclined pile groups), superstructure height, soil profile, and ground slope. With appropriate design of inclined pile groups, significant advantages of inclined piles have been observed even in the occurrence of soil liquefaction and lateral spreading.
To promote the use of inclined piles in practice, a simple design approach (i.e., the pseudo-static method) is then implemented to account for the effect of pile inclination and soil liquefaction on the pile responses. Modifications of the soil springs (i.e., p–y, t–z, and q–z springs) are integrated by using the factors obtained from 3D FEM analyses for inclined piles under axial and shear loading patterns. Three case studies are conducted and the results of the
pseudo-static analysis are compared with 3D FEM results, experimental data, as well as field observations. The proposed pseudo-static method is found to be efficient to estimate the maximum response of inclined piles embedded in liquefiable and non-liquefiable sands with reasonable accuracy.