ABSTRACT
The finite element program Plaxis has – especially after development of version 7.0 – become a versatile tool not only for research purposes but also for many practical applications. The particular problem of modelling excavations in soft clays requires an anisotropic model for the mobilisation of the undrained shear strength during different construction sequences. The existing soft clay model does not entirely cover the need of such modelling and consequently a new anisotropic, multi-yield surfaces model is proposed. The model is based on observed small-strain yield behaviour of Norwegian marine clays. The anisotropic (double) bounding surface (for active and passive conditions) is defined by a modified Tresca yield criterion. Upon unloading / reloading due to alternating removal of soil volumes and bracing / anchor pre-stressing of the retaining structure a series of inner yield surfaces exhibiting kinematic strain hardening are generated until the past generated bounding surface is reached. The theoretical background of the model is presented and simple examples are used to illustrate the model capabilities.
