Page 208 - Analysis and Design of Energy Geostructures

Deformation in the context of energy geostructures 181

Figure 4.22 The concept of critical state: representation of the CLS in terms of (A) mean and devia-
toric stress, and (B) mean stress and specific volume.

Figure 4.23 The critical state and normal compression lines.

The critical state concept is typically employed to address the mechanical behav-
iour of fine-grained soils (see, e.g. Roscoe and Burland, 1968), but it is also applicable
to the analysis of coarse-grained soils (see, e.g. Atkinson and Bransby, 1978). Through
the critical state theory, a unified characterisation of the mechanical behaviour of both

fine- and coarse-grained soils can be achieved. In this context, the concept of overconso-
lidation ratio allows the former materials to be distinguished, for example in overconso-
lidated or normally consolidated, while the concept of relative density allows the latter
materials to be denoted, for example as dense or loose.
The concept of critical state applied to the interpretation of the mechanical behav-
iour of geomaterials such as soils is represented in Fig. 4.24. When the material is
sheared, after some progressive yielding states, it reaches a state in which shearing can
continue without variation in volume. The corresponding void ratio to the achieved
critical state is termed critical void ratio, e c . At critical state, geomaterials exhibit lower