# Critical State Soil Mechanics

The soil attains a critical state when there is a constant shear stress and no further volumetric strain occurs. However, dry soils often attain peak shear stress before attaining the critical state. Hence, the strength of the soil is based on its critical state strength and the peak strength.Critical state of soil continues to distort without further changes in void ratio or normal stress or shear stress, but the strains achieve turbulent flow. At the shearing point, soils achieve critical states, which are independent on the initial states. Hence, critical shear stress does not differ initially for both dry and wet soils since the void ratio and the effective pressure is the same (Atkinson 2007).The critical state parameters are l, M, and G. Soil sample changing states are easily indicated by the specific volume, deviatoric stress and effective mean stress. The key laboratory tests that can be used in the estimation of critical state parameters are the triaxial (axial symmetry) test and simple or direct shear test.These test samples should have a consolidation, which is related to the effective pressure at the onset of the tests (Joseph 2009). Further, the tests should have continuity to such a large extent of the strains for the samples to achieve critical states. Some samples, especially the ones that are over-consolidated tend to fail prior to the attainment of the critical state.Peak strengths indicate points that are on top of the critical state lines of the (p’, q) plot. Further, drained isotropic unloading and loading aids in the determination of l and k in the apparatus of triaxial.Stress path tests also aid in parameters determination. Hence, different tests (triaxial extension, triaxial compression) offer different M values while l varies with respect to the unloading degree or stress level. Such necessitates the reconsolidation of samples of soil to the effective stresses in the field for the application of the