PLAXIS LIQUEFACTION MODEL UBC3D-PLM - Knowledge Base

Referred to as the apex term, c cot φ p defines the point where the yieldsurface intersects the mean effective stress axis (p) (see Figure 1.3). Usually,in granular soils, the cohesion is zero, so the intersection would be locatedat the origin of the coordinate system (0,0).Figure 1.3: Systematization of the yield surfaces in p-q stress space. AfterTsegaye (2010).When the stress state is inside the space defined by the yield surfaceselastic behaviour is assumed. However, once the stress path touches theyield surface plasticity starts to occur. After the reformulation made bythe authors the latest version of the UBC3D-PLM has two yield surfaces inorder to distinguish between the primary and the secondary loading and toensure a smooth transition to the liquefied state. This mechanism is betterexplained in Section 1.5. The elasto-plastic behaviour of the model will beanalytically presented in the next paragraph.1.2 Elasto-plastic Behaviour and Hardening RuleThe elastic behaviour which occurs within the yield surface is governed by anon-linear rule. Two parameters control this non-linear behaviour; the elasticbulk modulus K and the elastic shear modulus G. These two moduli arestress dependent and the relationships are given in the following equations:6