In general, they form an advanced treatment of the constitutive models. They lead to finer prediction of soil behavior. Improvement in the prediction of shear strains have resulted from the use of multiple nested yield loci within the yield surface and the development of bounding surface models which incorporate a smooth transition from elastic to plastic behavior.

Generally, if one loop lying inside a loop contains another loop is called nested hysteresis loops. And regarding its use in earthquake engineering, I agree Rajib Biswas .

Hi,

why nested?! Cam clay is unable to provide realistic results as there is a abrupt loss of strength on the dry side (for compacted dense samples as they would undergo softening rather than hardening) of the critical state. when you are loading a sample (sands) sometimes your yield surface (the oval) would not stay fixed in the stress space and keep changing its position without volume change. As you reach the yield point somewhere on the moving oval, this specific oval become fix in the coordinate system....