In a short term undrained calculation for a 20m excavation in soft marine clay, I have chosen to use undrained poisson ratio of 0.45 in the view that this is a middle value for this kind of soil. The Plaxis manual recommended value is 0.495(non-compressible). By doing so, d-wall displacement, moment and shear are all smaller than those using v=0.495 and I am comfortable with the out come.
Can anyone familiar with FEM method using /not using 0.495 in total stress analysis advise on this?
Note: soil cluster-drained, water level: at bottom. I set the model this way to avoid excess pore pressure being generate in the calculation and only C=Su is used, phi is set to zero, Eu/Su=250
The misleading term in Plaxis is the "undrained" and "drained" options. Actually they are both effective stress analysis options and effect of porewater will be considered. Under these conditions, all soil parameters are effective ones for the soil skeleton itself. If total stress analysis is to be used, the non-porous option should be used.