“Who Needs Constitutive Models?”

Professor John Carter, Pro-Vice Chancellor, Faculty of Engineering and the Built Environment. University of Newcastle.

Constitutive models are essential in any rational theoretical modelling in geotechnics. How the stress-strain response of soil or rock is represented in these models is usually the key to successful prediction of the behaviour of geotechnical structures. However, the important details of these models, particularly the idealizations that are made, are often poorly understood or ignored, sometimes at significant cost to the unwary analyst. Indeed, the capabilities and the shortcomings of these models, especially the more advanced models, are not always easy to ascertain. In some cases determination of the input parameters is not straightforward. Consequently, it may be difficult to determine which model to select for a particular task.

The lecture will chart the development of constitutive models used to represent the mechanical behaviour of soils and provide an overview of the principles and the main features and components of existing, widely used constitutive models for soil. The clear intention is to emphasise the physical basis theses models, rather than their mathematical complexity. While the focus is on saturated soil mechanics, the behaviour of unsaturated soils will also be mentioned. Some of the constitutive models encoded in the software packages used routinely in geotechnical practice are reviewed, and discussion is also provided on their specific limitations. Examples of practical applications, including problems involving soil-structure interaction, will be used to illustrate both the advantages and some of the pitfalls of the commonly used models. A brief description of recent developments in this area of geotechnical research will also be included.

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