Geoscience Reference
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Multiscale Geomechanics
0.009
(a)
(b)
Figure 9.8. Variation in void ratio as a function of effective stress at critical state:
a) for clays [BIA 72]; and b) for sands [SAI 97]
9.4.2.3.1. Clay
According to experimental results provided by several authors, the friction angle at
critical state decreases with the plasticity index ( I p ). As can be noted in Figure 9.10,
for the same value of I p , a difference of 10 degrees may exist. However, though this
error may have important consequences for applications, where the deformations can be
relatively great, for current applications, its impact is minor. Biarez and Favre [BIA 72]
suggest a relation between φ pp and w L . The friction angle varies from 32 to 20 degrees
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