9.9 State and state parameters
In Chapter 8 I introduced the concept of the state of a soil as the combination of
its current voids ratio or water content, normal effective stress and overconsolidation
ratio. It is important to understand that it is the state which controls many aspects of the strength and stiffness of soil and it is necessary to determine both voids ratio
or water content and normal effective stress; water content or stress alone are not
sufficient.
In Sec. 8.4 I considered the relationship between the current state and a critical line,
which is below the critical state line, and introduced the ideas of states on the wet side
of critical and on the dry side of critical, as shown in Fig. 8.7. While this qualitative
description is important it is necessary to quantify state as the distance of current state
from the critical state line.
Earlier in this Chapter I described procedures for normalizing test results for shear
and triaxial tests and these are illustrated in Figs. 9.6 and 9.9. What I am going to do
now is combine the ideas of state and normalizing to define state parameters.
Figure 9.13(a), which is like Fig. 9.6, shows a state at A with voids ratio ea and
normal effective stress σ
a
together with a critical state line. The vertical and horizontal
distances of the point A from the critical state line are