The Soft Soil model is a Cam-Clay type model especially meant for primary compression of near normally consolidated clay-type soils.
For full details, please refer to the PLAXIS Material Models manual.
Geomaterial Models and Numerical Analysis of Softening
UDSM - Anisotropic Clay Models: S-CLAY1 and S-CLAY1S
UDSM - Creep-SCLAY1S
UDSM - Mixed Isotropic-kinematic Hardening Elastoplastic Models for Structured Clay