K0 as a Function of Changes in Stress and Strain Conditions during Consolidation, Unloading and Reloading
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- NGI articles 
There are several examples in the literature that describe empirical correlations for the coefficient of earth pressure at rest, K0, and undrained shear strength, su, in normally consolidated and overconsolidated clays as a function of index properties like plasticity index, overconsolidation ratio, OCR, and friction angle. However, a physical understanding of the reason why the coefficient of earth pressure at rest varies as a function of these parameters is still lacking, which causes an uncertainty in the value of K0 to use in geotechnical analyses and in design. This paper investigates the relationship between deformation and mobilization of friction. At the same time, it considers that the unloading process has to be looked at as a stability problem where a static, stabile equilibrium needs to be maintained, thus requiring that the mobilized shear strength equals the applied shear stress. The resulting values of coefficient of earth pressure at rest, K0, interpreted from effective stress paths alone, give realistic results, also in agreement with recent statistical evaluations on the K0-value in Norwegian clays. The new interpretation contributes to explain the widely used empirical correlations presented in the literature.