Critical state strength of soil - The Mechanics of Soils and Foundations - page 140

Figure 9.18 Normalized initial and critical states of a soil - Example 9.3.

while p = 600 kPa remains constant, but in the undrained test p decreases from 600

to 284 kPa as the pore pressure increases while p c = 284 kPa remains constant because

the specific volume does not change.

Example 9.4: Critical state Mohr circles and friction angle For the four tests given in
Table 9.2 the principal stresses at the critical state can be calculated from Eqs. (3.3)
and (3.4). Rearranging:

σ a = p +

2

3 q

σ r = p −

1

3 q

σ r are given in Table 9.4 and the Mohr circles are given in Fig. 9.19.
Scaling from the diagram, the critical friction angle is

σ a and Values for

φ c = 25 ◦ .

Table 9.4 Critical states of a soil - Example 9.4

q f p f

σ af σ rf

Sample (kPa) (kPa) (kPa) (kPa)

A 588 600 992 404

B 278 284 469 191

C 147 150 248 101

D 196 200 330 134