Sand Hypoplasticity (von Wolffersdorff, 1996)


Sand hypoplasticity is an advanced incrementally non-linear constitutive model, an outcome of an extensive research at Karlsruhe University in 1990’s. It incorporates pressure- and density-dependency of soil behaviour. Its response has been validated using a number single and finite element simulations of various geotechnical problems. When combined with so-called intergranular strain concept (Niemunis and Herle, 1997), it is capable of predicting small strain stiffness degradation and cyclic loading effects.

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  1. Gerrard Steven
    Gerrard Steven 5 years ago

    When using this model,what is the value of the state variable?

  2. Piotr Kowalczyk
    Piotr Kowalczyk 5 years ago

    Dear All,

    I am using sand hypoplastic model in my research and I have encountered some problem when looking into cyclic simple shear test in the range of small strains.

    Firstly, I have tried to simulate cyclic simple shear test from Shahnazari & Towhata (2002), Fig. 5, on Toyoura Sand. It is in the range of medium strains, up to 3%, starting from medium dense state of Dr=58%, finishing in dense state Dr=84%. The simulation looks really good (unfortunately I can not attach in the comment section the pdf I have prepared to visualize the problem more explicitly). The sample contracts systematically with cycles thus the stiffness increases as per the experiment.

    Secondly, I have subjected the same sample to cyclic loading but with significantly reduced strain amplitude, i.e. 0.1%. As expected, also here the sample contracts, however, the stiffness decreases with cycles which to me does not seem physical.

    The model is calibrated as shown in Herle & Gudehus (1999) Table VII for Toyoura Sand. Intergranular strain parameters are set to also rather common values: R=0.0001, m_R=5.0, m_T=2.0, Beta=0.5, ksi=6.0. I have tried using both umats, from prof. Masin and prof. Fellin, both give the same answers. I have also tried to look how the change of the constitutive model by Wegener & Herle (2014) changes the response but did not observe an improvement regarding my problem.

    I am wondering where is it I can be wrong here. Maybe some of you encountered a similar problem. Theoretically, I think I should be able to model sand behaviour for both strain levels with a single set of calibrated parameters.

    Thank you all in advance for any comments and tips on how to approach my problem.


  3. Raffaele Ragni
    Raffaele Ragni 1 year ago

    Hello soilmodels community,
    There seems to be a bug in the Plaxis version of the hypoplastic model for sand – p’-q curve of loose samples in Plaxis-Soiltest dilate when contraction is instead expected. Both triax driver and test simulation in soilmodels give expected contractive response.
    Not sure what the best channel to discuss the issue is – whether here or directly contacting Bentley.
    Any suggestion is appreciated.

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