Residual and critical strength states

The stress conditions that apply at the critical state line represent the ultimate strength of the soil (i.e. its critical state strength) and this is the lowest strength that the soil will reach provided that the strains within it are reasonably uniform and not excessive in magnitude. The residual strength of a soil only operates, in the case of clays, after the soil has been subjected to considerable strains with layers of soil sliding over other layers.

It is important that the difference between these two strengths is appreciated. Skempton (1964) shows that the residual angle of friction of London clay, <j>t, can be less than 10° whereas Schofield and Wroth (1968) report that the same soil at critical state conditions has an angle of friction <pcv of 22j°

Further study

The materials in this chapter is simply an introduction to critical state soil mechanics. Readers interested in pursuing this subject further should obtain a copy of Atkinson and Bransby (1978).

Chapter 14

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