ABSTRACT
It is well known that the behavior of soil, in particular cohesive soil, is affected by the loading time and the strain rate (e.g., Adachi et al. 1996). Hence, it is necessary to include the viscous effect in the derivation of the constitutive equations. Studies on the effect of the viscosity of soil have been performed with viscoelastic or viscoplastic models. Over the last 30 years, viscoplastic models have been proposed following the development of elastoplastic models. In this chapter, we will discuss both the viscous nature and the plastic nature of soil.
