Introduction: purpose of models

Models of the mechanical behaviour of soils have served two purposes in this book: they have been used primarily to illustrate facets of the observed behaviour of soils which might at first sight be considered extraordinary but which, with even a simple model of soil behaviour, can in fact be anticipated; however, Section 11.3 has shown how such models can be used in finite element analyses of geotechnical problems of practical importance. There are different requirements for models used for purely illustrative purposes and for models used for predicting the response of geotechnical structures. The illustrative model is expected to give a simplified but overall picture of soil behaviour, but the predictive model must be able to match rather closely the behaviour of the elements of real soil which are being deformed in a particular prototype. Some of the simplifying assumptions of the illustrative model are inappropriate for the predictive model if the predictions are to be useful. Many implicit or explicit assumptions have been made in this book in presenting the simple models; the effects of relaxing some of these assumptions are discussed briefly in this chapter.

Effects of time

Loading of a soil with no drainage, or with restricted drainage, in general leads to the generation of excess pore pressures as a result of prevented volume change in the soil. With time, these excess pore pressures tend to dissipate to equilibrium values.