ABSTRACT
The key concept of critical state soil mechanics (CSSM) (Schofield & Wroth 1968) is that soil, when sheared to large strain levels, will deform continuously without a change in either volume or stress state, i.e., a critical state is attained. For a given soil, when the critical-state points are plotted in both e− log(p′) and q− p′ spaces, unique loci emerge (e− void ratio, p′ - mean effective stress and q− deviator stress). Been & Jefferies (1985) proposed using the state parameter to describe the proximity of the current state to the critical state in the e−log(p′) plane.The state parameter, ψ, is defined as the difference between the current void ratio (e) and the void ratio at the critical state (ecs) at the same mean effective stress. Been and Jefferies presented correlations between the state parameter and properties including the undrained shear strength and the peak angle of shearing resistance. Subsequent research studies have confirmed the usefulness of the state parameter as a predictor of soil behavior, (e.g., Yang (2002), Jefferies & Shuttle (2002)). The state parameter also acts as a key parameter for more recently-developed constitutive models of soil (e.g., Jefferies (1993); Gajo & Wood (1999); Li & Dafalias (2000)).
