In Fig. 9.4(c) the normal compression and critical state lines are parallel and both
have the same gradient, Cc. The parameter e defines the position of the critical state
line in the same way that e0 defines the position of the normal compression line.
Equation (9.2) is the friction failure criterion discussed in Sec. 3.3 and φ
c
is the critical
friction angle. The critical state line shown in Fig. 9.4(c) is directly above the critical
overconsolidation line shown in Fig. 8.7. (The height of the critical state line above the
critical overconsolidation line is τ
f given by Eq. (9.2).) Later, in Chapter 11, we will