Geomaterial Models and Numerical Analysis of Softening

摘要

Since 1960, researchers have been working on constitutive models forgeomaterials, i.e. soil and rock. In later years such models have been applied in finite element codes, in particular the simple elastoplastic Mohr-Coulomb model. More refined models exist, but they are not easily applied in practical geotechnical engineering. Even well-known Cam-Clay type models are, as yet, not generally applied for clays, and are subject to criticism. From a practical point of view, the criticism concerns among other things the prediction of lateral stresses in soil layers. From a theoretical point of view, the quite general use of non-conservative elasticity laws is not justified. In fact, a proper potential for the elastic strain-energy is missing. This study is among other things aimed at improving this situation, and some improvements of existing constitutive models are proposed. Another quite different part of this study concerns a new topic of geomechanics, namely non-local material softening. Dense clays and rock show material softening, i.e. negativeness of the second-order work, but classical softening models lead to ill-posed formulations. Numerical calculations with such models produce unreliable results. Recently, some researchers have put forward new ideas for arriving at well-posedness of boundary value problems. Stimulated by some poineering work in this field, a so-called non-local approach is put into operation.