Behaviour of soil before failure - The Mechanics of Soils and Foundations - page 175

Table 11.2 Yield and critical states in drained tests - Example 11.2

Sample Initial state Yield point Critical state

p 0 q y p y q f p f v 0 v y v f

(kPa) (kPa) (kPa) (kPa) (kPa)

D 600 1.97 0 600 1.97 588 600 1.83

E 400 1.97 280 400 1.97 392 400 1.90

F 150 1.97 260 150 1.97 147 150 2.10

swelling, at their yield points and at failure at their critical states, shown in Table 11.2,
were found by scaling from the diagram.

Example 11.3: Calculation of undrained stress path A soil has the parameters M =

0.98, 3.25, but the shape of the state boundary surface

is unknown. A sample is isotropically normally compressed in a triaxial apparatus
to p 0

λ = 0.20, κ = 0.05 and N =

600 kPa and tested undrained by increasing the axial stress with the total
mean stress p held constant. It is observed that the change of pore pressure can be
approximated by

=

q /300.
The test result are given in Table 11.3 for equal increments of q . An undrained
stress path defining a constant volume section of the state boundary surface or the wet
side of critical is shown in Fig. 11.15.

u =

Table 11.3 Results of undrained test - Example 11.3
q (kPa) p (kPa) p (kPa) u (kPa)

0 600 0 600

50 600 8 592

100 600 33 567

150 600 75 525

200 600 133 467

250 600 208 392

300 600 300 300

Figure 11.15 Undrained stress path - Example 11.3.