2.5

What is the Steady State Line?

2.5.1 Introduction to the Steady State Line

It might be a bit of a stretch, but I’m leaning toward the opinion that understanding of the steady state line is the doorway to advanced geotechnical understanding and advanced geotechnical practice. To predict soil response to a change in stresses you have to understand the interaction of several variables, including stress-history-induced soil fabric, changes in normal stresses, changes in shearing stresses, and changes in soil volume. The steady state line helps you start to understand these interactions (Altaee and Fellenius, 1994).

Let me say right now that one line is not going to solve the problem of characterizing soil performance. By definition a function drawn on an x–y plot can only consider two variables. A three dimensional x–y–z plot can be drawn, but it only considers three variables. If four or five variables are involved, you can’t use a single simple black and white plot, although I’m aware that computer visualization experts use colors, textures, and vector arrows to enhance three-dimensional plots. I am a fan of the Peacock diagram, which is a three-dimensional state diagram shown in Holtz and Kovacs (1981, 2011), but it has been my experience working with students and practicing engineers that a series of two-dimensional plots works better than three-dimensional plots when developing an understanding of soil performance concepts. Use of two-dimensional plots better fits the graded ...