ABSTRACT

A phenomenological model is a model that describes observed behavior (phenomena), without trying to model the underlying physical processes that cause or drive such behavior. This chapter describes the initial work modeling the observed behavior of a soil sample when sheared. When sheared, a soil starts from an initial condition and ultimately reaches the steady-state condition. The steady-state of deformation occurs in a particulate mass for any loading and drainage condition where the shear stress breaks down the original structure and puts it into a new "flow" structure. Soil particles move and reorient continuously during shearing and even in the steady-state flow-structure, for elongated particles, there can be small, continual, random movements, while for bulky grains, there can be grain rotations. Critical state soil mechanics (CSSM) models that assume zero shear strain and shear stresses for pure hydrostatic compression are making an unconservative, incorrect assumption.