A visco-plastic constitutive model for soft clays: implementation and validation

In the present paper the main aspects of the problem of modelling the viscous behaviour of cohesive soils are discussed. The first part of the paper deals with the experimental evidence for viscods behaviour of soils and reviews the available approaches to theoretical modelling. In the second part an elastic-visco-plastic model is proposed. This is based on the assumption that the inelastic components of deformation can be divided into a time independent plastic component and a time dependent viscous component. Other characteristics of the model are the assumption of the similarity of the plastic and viscous potentials and the use of an equivalent time that governs the rate of creep within the state boundary surface. ln the third part of the paper single element predictions of the model for typical laboratory tests are illustrated. Given the high difficulty of distinguishing the viscous behaviour from the elasto-plastic behaviour in both laboratory and field experimental investigations a certain amount of numerical experimentation may be act as a guideline for the planning of laboratory tests. Finally, in the last part of the paper, two boundary value problems relevant. to geotechnical engineering, two-dimensional consolidation in axisymmetric and plane strain condition, were analysed following implementation of the model in a finite element code. ln particular, the solution of problems having complex sets of boundary conditions is dealt with in detail using the finite element technique.