Summary
The intergranular strain concept was originally developed to capture the small‐strain behaviour of the soil with hypoplastic models. A change of the deformation direction leads to an increase of the material stiffness. To obtain elastic behaviour for smallstrains, only the elastic part of the material stiffness matrix is used. Two different approaches for an application of this concept to nonhypoplastic models are presented in this article. These approaches differ in the determination of the elastic stress response, which is used for reversible deformations. The first approach determines an elastic response from the original material model, and the second one uses an additional elastic model. Both approaches are applied on barodesy. The simulations are compared with experimental results and with simulations using hypoplastic models with the original intergranular strain concept.
Die Wahl eines passenden Materialmodells, das in der Lage ist, das Bodenverhalten bei FE‐Berechnungen realistisch darzustellen, hat einen maßgeblichen Einfluss auf die dabei erhaltenen Berechnungsergebnisse. Anhand von Vergleichsrechnungen mit mehreren Materialmodellen sollen die Gemeinsamkeiten und Unterschiede bei den Ergebnissen verdeutlicht werden. Hierfür wird ein Baugrubenaushub simuliert und sowohl die auftretenden Verformungen als auch die mittels Parameterreduktion ermittelte Standsicherheit betrachtet. Dabei wird neben den bekannteren Modellen Hardening Soil und der Hypoplastizität die Barodesie als Modell für FE‐Berechnungen vorgestellt. Während sich bei allen Modellen vergleichbare Verformungen einstellen, werden bei der berechneten Standsicherheit deutliche Unterschiede festgestellt.
The intergranular strain concept (IGS) and intergranular strain anisotropy formulation (ISA) are state of the art extensions to describe small-strain effects. The main conceptional difference between ISA and IGS is the purely elastic strain range introduced by ISA. In addition, the ISA formulation used in this article includes an additional state variable in order to reduce accumulation effects for cyclic loading with a larger number of repetitive cycles. Barodesy is enhanced here with ISA to improve its small-strain predictions. The performance of this new model is compared with barodesy enhanced with IGS. It turned out that the small-strain extensions do not negatively influence predictions under monotonic loading. Differences between ISA and ISG are only remarkable for very small-strain cycles and even there they are negligible for certain parameter values.
The reloading behaviour of the soil is dominated by effects of the recent deformation history as well as by the overall stress history, indicated by overconsolidation. The stiffness of an overconsolidated soil is higher than the stiffness of normally consolidated soil. In basic hypoplastic and barodetic models, the stiffness for reloading is underestimated, and thus so‐called ratcheting effects appear. In this article, we propose a relation to improve the reloading behaviour of barodesy: we introduce an extension, which increases the stiffness in dependence of the distance to the asymptotic state boundary surface and the current dilatancy. Thus, within an intermediate strain range, the stress‐strain behaviour is improved and ratcheting effects are significantly reduced. The behaviour of the proposed extension is verified by simulation of typical element tests and validated by a comparison with experimental results.
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