7.2 Linear Elastic Perfectly Plastic Model（Mohr⁃Co...
Soils behave rather non⁃linearly when subjected to changes of stress or strain.In reality，the stiffness of soil depends at least on the stress level，the stress path and the strain level.Some such features are included in the advanced soil models.The Mohr⁃Coulomb model，however，is a simple and well⁃known linear elastic perfectly plastic model，which can be used as a first approximation of soil behavior.The linear elastic part of the Mohr⁃Coulomb model is based on Hooke's law of isotropic elasticity.The perfectly plastic part is based on the Mohr⁃Coulomb failure criterion，formulated in a non⁃associated plasticity framework.
Plasticity involves the development of irreversible strains.In order to evaluate whether or not plasticity occurs in a calculation，a yield function，f is introduced as a function of stress and strain.Plastic yielding is related with the condition f＝0.This condition can often be presented as a surface in principal stress space.A perfectly⁃plastic model is a constitutive model with a fixed yield surface，i.e.a yield surface that is fully defined by model parameters and not affected by（plastic）straining.For stress states represented by points within the yield surface，the behavior is purely elastic and all strains are reversible.