Peak states - The Mechanics of Soils and Foundations - page 155

Figure 10.17 Peak states of soils with different states.

10.7 Relationship between peak strength and
state parameter
Figure 10.16(a) shows the relationship between the peak strength and the normalizing
parameters e λ or v λ . Instead of using these normalizing parameters we could use the
volume state parameter S v defined in Fig. 9.13 and by Eqs. (9.19) and (9.23).
Figure 10.18(b) shows stress-strain curves for two samples of the same soil in shear
tests. The samples had different initial voids ratios, as shown in Fig. 10.15. They have
the same critical state strength but different peak strengths. Figure 10.18(a) shows the
voids ratios at the peak states and the corresponding state parameters S v . Sample 2
has the larger peak strength and the larger state parameter because its state is furthest
from the critical state line.
Figure 10.18(c) shows the relationship between the peak stress ratio and the state
parameter at the peak. When S v = 0 the peak strength and the critical state strength

are the same and the peak strength increases steadily with increasing values of the state
parameter. There will be a similar increase in peak strength with state parameter for
triaxial tests.
Figure 10.18(c) shows a linear relationship between peak stress ratio and state
parameter but the relationship may not be linear for all soils. This will be discussed
further in Sec. 11.6.