The SHANSEP NGI-ADP model is an advanced constitutive model developed to enable the analysis of dikes and embankments according to the new design requirements (based upon undrained Critical State calculations) within a FEM environment. It overcomes limitations of the traditional NGI-ADP model with respect to the varying undrained shear strength of soils due to load history. Three additional input parameters are needed for this model, namely α, m and s^A_u,min. They are used to calculate (update) the undrained shear strength s^A_u dependent on the effective stress history by using the SHANSEP concept. The effect of parameters α and m was investigated and the results show that the effect of α is more dominant. However, the range of variation of these two parameters is short.

Undrained behaviour of real soft soil (a) and SHANSEP NGI-ADP model (b)

The SHANSEP NGI-ADP model in combination with other constitutive models

Apart from using the SHANSEP NGI-ADP model merely as an NGI-ADP model and then switching to the SHANSEP concept as described in the attached document, it is possible to use it as an 'extension' of any other constitutive model implemented in PLAXIS.
The process to switch from another soil model to the SHANSEP NGI-ADP model is described in the document as well, by using the Special option parameter to activate the SHANSEP concept and by changing the material of the soil cluster to the SHANSEP NGI-ADP model.

---

With the release of PLAXIS 2D/3D CONNECT Edition V20 Update 1 (January 2020), the PLAXIS User Defined Soil models are delivered with the PLAXIS installation. When enabling the Geotechnical SELECT Entitlement [GSE] when starting the PLAXIS application, this model becomes available in the Parameters tab when selecting "User defined" for the Material model.