Designing Piles for Seismic Events

"This paper sets out a simplified approach by which the practical foundation designer can undertake the relevant calculations to satisfy the requirements for deep foundation design in seismic areas. The following matters are dealt with:a. Design issues that should be addressed;b. Pile design for axial loading, including the possible effects of liquefaction;c. Pile design for lateral loading where liquefaction does not occur;d. Pile design for lateral loading where liquefaction does occur;e. Measures to mitigate against liquefaction effects.The paper is a modified version of a paper presented in 2013 to the 19th NZGS GeotechnicalSymposium, Queenstown, New Zealand.1. INTRODUCTIONConsideration of the effects of earthquakes and seismic loadings is an increasingly important aspect of modern foundation design, and most contemporary standards have a mandatory requirement for such consideration. For example, the Australian Piling Code, AS 2159-2009, states that “a pile shall be designed for adequate strength, stiffness and ductility under load combinations including earthquake design actions”. However, the methods by which such considerations can be undertaken are generally not set out in the standards, and many approaches have been utilized, ranging from very simplistic methods to extremely complex computer analyses. Accordingly, there appears to be scope for an approach that is soundly based but which is neither too simplistic nor too complex.Poulos (1989) has suggested that there are three categories of analysis and design, as follows:1. Category 1: empirical methods.2. Category 2: simplified but soundly-based methods.3. Category 3: more comprehensive methods that are soundly-based, and site-specific.The objective of this paper is to set out a systematic but simplified approach which falls into Category 2 above, and by which the foundation designer can undertake the relevant analyses to satisfy the foundation design requirements for seismic regions. Emphasis is placed on methods that do not require “black box” software or which employ complex soil models in which the physical meaning of the parameters is unclear."