The solution is exact in a theoretical sense, but is still an approximation to the real problem, as assumptions about geometry, the applied boundary conditions and the constitutive behaviour have been made in idealising the real physical problem into an equivalent mathematical form. For a particular geotechnical structure, if it is possible to establish a realistic constitutive model for material behaviour, identify the boundary conditions, combine these with the equations of equilibrium and compatibility, and then perform the resulting integrations, an exact theoretical solution can be obtained.
The ability of each method to satisfy the fundamental theoretical requirements and provide design information is summarised in Tables 1 and 2 respectively.Ī closed form solution is the ultimate method of analysis. Each of these categories is now considered in turn. Likewise, if dynamic loading was involved, the equilibrium equations would have to be extended to account for inertia and damping effects.Ĭurrent methods of analysis can be conveniently grouped into the following categories: closed form, simple and numerical analysis. For example, if the flow of pore fluid is involved, then the continuity equation and boundary conditions involving prescribed flows or pore fluid pressures would also have to be accounted for. The above discussion is clearly simplified. For example, they could define a displacement constraint, a sequence of load application, excavation, construction, or a pore water pressure change. These are specific to the situation under consideration and define the nature of the boundary value problem to be investigated. The lecture concludes by presenting some views about the future.
#ELASTIC REALITY DEFINITION SERIES#
This leads the author to propose a motion for debate: ‘Numerical methods of analysis have reached the stage where they are superior to conventional approaches and can replace them in the geotechnical design process.’ Cases both for and against the motion are then presented, using a series of practical examples. The various different methods of analysis that are currently available to geotechnical engineers are then categorised and compared. This lecture begins by discussing the role of analysis in design. For such analysis to be used in a constructive manner, and to avoid future disasters, it is important that geotechnical engineers understand both the enormous potential of this type of analysis and its pitfalls.
Recent comparisons ( Gaba et al., 2002 Ravaska, 2002) indicate that the use of numerical analysis, as opposed to conventional methods, can lead to more economical design, and consequently the use of this type of analysis is likely to increase in the future.Īlthough most geotechnical engineers have had contact with numerical analysis, this has often been at arm's length, and many do not fully appreciate the complexities and subtleties involved in its use. This is a pertinent question to ask at this time as new codes of practice, for example Eurocode 7, are not as prescriptive as the older codes and allow the designer to choose an appropriate method of analysis. The title of this Rankine Lecture, ‘Numerical analysis: a virtual dream or practical reality?’, essentially poses the question: ‘Is numerical analysis just an advanced toy for academics and the privileged few, or is it in a position to provide a genuine tool for routine geotechnical analysis?’
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