Critical state soil mechanics

Critical state soil mechanics is the area of soil mechanics that encompasses the conceptual models representing the mechanical behavior of saturated remoulded soils based on the critical state concept. At the critical state, the relationship between forces applied in the soil (stress), and the resulting deformation resulting from this stress (strain) becomes constant. The soil will continue to deform, but the stress will no longer increase.

Forces are applied to soils in a number of ways, for example when they are loaded by foundations, or unloaded by excavations. The critical state concept is used to predict the behaviour of soils under various loading conditions, and geotechnical engineers use the critical state model to estimate how soil will behave under different stresses.

The basic concept is that soil and other granular materials, if continuously distorted until they flow as a frictional fluid, will come into a well-defined critical state. In practical terms, the critical state can be considered a failure condition for the soil. It's the point at which the soil cannot sustain any additional load without undergoing continuous deformation, in a manner similar to the behaviour of fluids.

Certain properties of the soil, like porosity, shear strength, and volume, reach characteristic values. These properties are intrinsic to the type of soil and its initial conditions.^[1]