Critical State Soil Mechanics - Modified Cam-Clay Model

Modified Cam-Clay Model

Professor John Burland of Imperial College who worked with Professor Roscoe is credited with the development of the modified version of the original model. The difference between the Cam Clay and the Modified Cam Clay (MCC) is that the yield surface of the MCC is described by an ellipse and therefore the plastic strain increment vector (which is perpendicular to the yield surface) for the largest value of the mean effective stress is horizontal, and hence no incremental deviatoric plastic strain takes place for a change in mean effective stress (for purely hydrostatic states of stress). This is very convenient for constitutive modelling in numerical analysis, especially finite element analysis, where numerical stability issues are important (as a curve needs to be continuous in order to be differentiable).

The yield surface of the modified Cam-clay model has the form

 f(p,q,p_c) = \left^2 + p\,(p - p_c) \le 0

where is the pressure, is the equivalent stress, is the pre-consolidation pressure, and is the slope of the critical state line.

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