On the other hand, it may also warn you about the limitations of the Mohr-Coulomb model, since it clearly demonstrates its linear or bi-linear behavior under various loading conditions.įigure 2: Triaxial test simulation with the HSsmall model using the PLAXIS Soil Test facility Are you convinced? Using this tool will really make you appreciate the Hardening Soil and HSsmall model for its authentic representation of real soil behavior. It enables students and young engineers to understand various features of soil behavior, and it will show the capabilities and limitations of your soil model. There is even a parameter optimization tool available.īesides calibration of model parameters, the Soil Test facility is a very nice ‘learning tool’. If you have real lab test data available, you can do a further calibration and validation of your model parameters. This is a very convenient tool in which you can quickly check the model’s response under loading conditions similar to real soil lab tests. Once you have determined your set of model parameters for the Hardening Soil or HSsmall model, you can test your ‘digital soil’ in the PLAXIS 2D/3D Ultimate Soil Test facility. Hence, the ‘fear’ for the Hardening Soil model and its numerous parameters to be determined, is simply not justified.įigure 1: Hardening Soil model - Yield contour in principal stress space Soil Test Facility It generally provides more accurate results than using a simple model, based on the same limited data. This can be very useful in an early stage of a project, when only limited soil data are available. published a paper with correlations providing a first estimate of all HSsmall model parameters for sandy soils, just based on Relative Density (Brinkgreve et al., 2010). You can build a database of parameter sets for different soils, irrespective of the loading conditions something that does not make sense when using simple models like the linear elastic perfectly plastic Mohr-Coulomb model, because for such models, changing loading conditions require different parameter values. The model itself will take care of stress-and-strain-dependency of stiffness and strength without changing the parameters. For the HS(small) model this is probably true. Model ParametersĪ constitutive model, together with its set of model parameters, is supposed to be representative of a particular soil. And there are typical ratios between the various stiffness parameters for different types of soil, so once you have determined a single stiffness parameter, you can usually have a good estimate of the others. Stiffness can also be obtained from field test data ( CPT, SPT) by means of correlations. “Do I need to perform all those tests to be able to use the Hardening Soil model?” They can be obtained from different soil lab tests. Therefore, the Hardening Soil model has different stiffness parameters for different loading directions. Different loading directions ( compression, shear, unloading) will cause a different stiffness response. In contrast to other engineering materials, soil stiffness cannot simply be defined by a single Young’s modulus ( E). More accurate pore pressure development in undrained loading.Realistic non-linear behavior instead of bi-linear stress-strain response.Distinction between primary loading and unloading or reloading stiffness.Strain-dependency of stiffness (modulus reduction).Stress-dependency of stiffness and strength.The Hardening Soil (HS) model (Schanz et al., 1999), or even better, the HS model with small-strain stiffness (HSsmall) (Benz, 2007) includes several features of soil behavior that are relevant for many practical applications, such as: Features of Soil BehaviorĪs mentioned in the blog on The Importance of an Appropriate Soil Model, simple models lack some important features of soil behavior. In this article, some practical details of the Hardening Soil model will be further presented, with the purpose to take away some fear and encourage engineers to use this model in their geotechnical applications. The Hardening Soil model is a model that captures several features of real soil behavior both for sandy soils as well as for clays and silts. In a previous blog, the importance of using advanced soil models for geotechnical finite element calculations, was discussed. Brinkgreve, and first presented by Virtuosity.
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