From Theory to Practice in Pile DesignE.H. Davis Memorial Lecture

The procedures used for pile design are classified into three categories: empirical, simplified but theory-based, and site-specific advanced theory-based methods. The various aspects of pile behaviour which may need to be considered are reviewed and design procedures in each category are reviewed for each aspect. In many cases involving conventional loadings, the second category of design procedure is often quite adequate, but for problems involving special loading conditions, such as cyclic loading or loading arising from soil movements, the use of more sophisticated methods of analysis may be necessary to obtain an economical and safe design.

Examples are presented to illustrate the use of each category of design in actual field cases.

Introduction

The design of pile foundations has long relied on empericism but over the past three decades, substantial progress has been made in the development of improved methods of pile design based on sound theoretical principles. The motivation for such development has included the wider use of piling, a greater recognition of the need to limit deformations, and the need to resist increasingly large loads. The offshore oil industry has provided a particular stimulus to research in pile analysis and design, as the size and nature of the loads on such foundations has made simple extrapolation of previous onshore experience either extremely hazardous or very uneconomical. It is worthy of note that Australia has been prominent in applying theoretical analyses to pile design and that many of these methods of analysis are contained in the Australian Piling Code (AS 2159-1978). The widespread acceptance of this Code suggests that there has been a recognition by engineers of the need for more soundly-based pile design procedures.

The aim of this paper is to show how theoretical analyses can be translated into practical design procedures and applied to the design of pile foundations subjected to both “conventional” loadings and to “special” loadings such as those induced by externally generated soil movements. The approaches to pile des ign are class ified into three categories, depending on the level of sophistication of the analysis and the nature of the geotechnical data involved. The applicability to practice of the more soundly-based design approaches is demonstrated by comparing observed and theoretical pile behaviour. Finally, some examples are described of pile design and analysis involving each of the three categories of design procedures.