Formulation
The Critical State concept is an idealization of the observed behavior of saturated remoulded clays in triaxial compression tests, and it is assumed to apply to undisturbed soils. It states that soils and other granular materials, if continuously distorted (sheared) until they flow as a frictional fluid, will come into a well-defined critical state. At the onset of the critical state, shear distortions occur without any further changes in mean effective stress, deviatoric stress (or yield stress, in uniaxial tension according to the von Mises yielding criterion), or specific volume :
where,
However, for triaxial conditions . Thus,
All critical states, for a given soil, form a unique line called the Critical State Line (CSL) defined by the following equations in the space :
where, and are soil constants. The first equation determines the magnitude of the deviatoric stress needed to keep the soil flowing continuously as the product of a frictional constant (capital ) and the mean effective stress . The second equation states that the specific volume occupied by unit volume of flowing particles will decrease as the logarithm of the mean effective stress increases.
Read more about this topic: Critical State Soil Mechanics
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