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PREFACE:
Geotechnical engineers have to deal with complex geometrical configurations as well as enormously difficult materials which exhibit, strongly, a path-dependent mechanical behavior. In addition, geological deposits display extensive inhomogeneities which are often difficult to define quantitatively.
As a result most geotechnical engineering design problems require significant use of the engineer’s imagination, creativity, judgment, common sense and experience. To many geotechnical engineers therefore the role of any advanced analysis, particularly advanced computer based analyses, remains undefined.
The editors have therefore invited some outstanding engineers who are engaged not only in developing advanced level geotechnical analyses, but are also in consulting practice to write various chapters of this book. These chapters show that a careful blend of engineering judgment and advanced principles of engineering mechanics may be used to resolve many complex geotechnical engineering problems
It is hoped that these may inspire geotechnical engineering practice to make more extensive use of them in the future. Because of the difficulties associated with complex geometries and material behavior it is not surprising that the advanced analyses described in this book make extensive use of modern digital computers. Simplified hand calculations, although they have the attraction of being very good teaching tools, are rarely able to quantitatively reproduce the complete physical characteristics of the problem.
Chapter 1 deals with the complex interactions between fluid and solid skeletons for both static and dynamic loading. The governing equations for the solid and fluid constituents have been set out in a general manner and a nonlinear transient finite element formulation for the problem developed. A centrifuge model test of a dike is then simulated by the analysis, and the success of the developed analysis was demonstrated by the ability of the analytical model to reproduce the physical observations in the centrifuge model. Because the method of construction usedhas often significant influence on the mechanical behavior of geotechnical engineering structures, the next three chapters describe modifications to the finite element formula-tion to take account of constructioninduced events.
Chapter 2 investigates the effects of compaction-induced stresses on the behavior of retaining walls and buried flexible culverts.
Chapter 3 describes the use of an anisotropic soil model in the simulation of excavations. Such unloading problems in saturated clay, which result in a transient safety factor diminishing with time, can create dangers on many construction sites.
Chapter 4 shows the finite element analysis of either cantilever, propped or anchored retaining wallsin which effects of construction methods (excavated or backfilled) are considered. The chapter concludes with the application of the analysis to a complex embedded retaining wall. The development and the use of the finite element method in analysing a number of penetration problems involving sampling tubes and piles are described in Chapter 5.
Such analyses can not only provide quantitative information on the changes in soil state caused by the penetration but also enable one to extract characteristic soil parameters from the simulation of actual field tests such as cone penetration and pressure-meter tests. A simplified analysis of the dynamic pile driving problem by a combination of onedimensional wave equations for the pile with an approximate plan-wave propagation model for the soil has been considered in Chapter 6.
Such analyses which include soil inertia effects represent a considerable improvement on conventional analysis of pile driving problems. In many situations the soil properties do not vary in one or two spatial directions and it is then possible to use the finite layer approach described in Chapter 7.
By using an analytical representation of the field in the horizontal direction, such semianalytical methods became very efficient. The final two chapters describe both the development and use of explicit finite difference methods for analysing a wide range of geotechnical engineering problems involving both continuous as well as discontinuous jointed media. Such distinct element methods may prove to have much wider applications in the future. The editors hope that these demonstrations of advanced analysis applied to geotechnical engineering problems might encourage engineers to consider incorporating them in their strategies. Perhaps equally important, such analyses might enable them to extrapolate more effectively experience gained from one geotechnical site to another.
