Find out the Mobilized Stiffness in Hardening Soil Model

Question

Hi All, 
 
 Is there a way to extract the mobilized stiffness when using the Hardening Soil Model (or HSS)? I am interested in a numeric value (and not a symbol). 
 
 Thanks

Dennis Waterman · Accepted Answer

Dear Omar, 
 The orginal publication is the PhD work of Dr. Thomas Benz. You may be still able to download it from the website of the University of Stuttgart as they used to have all PhD works available for download. 
 With kind regards, 
 Dennis Waterman

Dennis Waterman · Answer

Dear Omar, 
 It is not vague at all, the HS and HSS model follow the widely used concept of yield surfaces and plasticity that is described in many books. 
 The only stiffness matrix that exists is the elastic stiffness matrix which is made up by Eur and G0 (in case of HSS). The values of E50 and Eoed are not directly used by the model: they are only used initially to determine the shape of the yield surfaces as well as the hardening rules of the yield surfaces. The stiffness matrix determines the elastic strain in a stress point, the yield surfaces and their hardening rules determine the plastic strain in a stress point. The Material Models Manual of PLAXIS describe the formulation of both models. But we're also quite open on how it works when we explain it during courses and workshops. More fundamentally there are many books on yield surfaces and plasticity, but most of them end up being quite mathematical. Though "Soil behaviour and Critical State Soil Mechanics" from David Muir Wood is a very comprehensible book on this topic. 
 Your last reasoning I find interesting. I'm quite sure that 99% of the people that drive a car have no idea or understanding of how a car works, but they still succesfully drive them (well, ok, considering the amount of accidents we may argue on the rate of succes). 
 With kind regards, 
 Dennis Waterman

Find out the Mobilized Stiffness in Hardening Soil Model

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