TY - GEN A1 - Niemunis, Andrzej A1 - Prada-Sarmiento, L. F. A1 - Grandas Tavera, Carlos Eduardo T1 - Paraelasticity T2 - Acta Geotechnica N2 - A 3D hysteretic, fully reversible constitutive model with rate-independent damping and with variable secant stiffness is proposed. A reversible dilatancy–contractancy effect is an optional feature as described in the companion paper (Niemunis et al. in Acta Geotech, 2011). The present paper describes the basic aspects of the model only. A strain path reversal is defined, and a treatment of the past reversals using a stack structure is proposed. Y1 - 2011 U6 - https://doi.org/10.1007/s11440-011-0137-4 SN - 1861-1125 SN - 1861-1133 VL - 6 IS - 2 SP - 67 EP - 80 ER - TY - GEN A1 - Niemunis, Andrzej A1 - Grandas Tavera, Carlos Eduardo A1 - Prada-Sarmiento, L. F. T1 - Anisotropic visco-hypoplasticity T2 - Acta Geotechnica N2 - Apart from time-driven creep or relaxation, most viscoplastic models (without plastic and viscous strain separation) generate no or a very limited accumulation of strain or stress due to cyclic loading. Such pseudo-relaxation (or pseudo-creep) is either absent or dwindles too fast with increasing OCR. For example, the accumulation of the pore water pressure and eventual liquefaction due to cyclic loading cannot be adequately reproduced. The proposed combination of a viscous model and a hypoplastic model can circumvent this problem. The novel visco-hypoplasticity model presented in the paper is based on an anisotropic preconsolidation surface. It can distinguish between the undrained strength upon triaxial vertical loading and horizontal loading. The strain-induced anisotropy is described using a second-order structure tensor. The implicit time integration with the consistent Jacobian matrix is presented. For the tensorial manipulation including numerous Fréchet derivatives, a special package has been developed within the algebra program MATHEMATICA (registered trade mark of Wolfram Research Inc.). The results can be conveniently coded using a special FORTRAN 90 module for tensorial operations. Simulations of element tests from biaxial apparatus and FE calculations are also shown. Y1 - 2009 U6 - https://doi.org/10.1007/s11440-009-0106-3 SN - 1861-1133 SN - 1861-1125 VL - 4 IS - 4 SP - 293 EP - 314 ER - TY - CHAP A1 - Grandas Tavera, Carlos Eduardo A1 - Triantafyllidis, Theodoros A1 - Knittel, Lukas ED - Triantafyllidis, Theodoros T1 - A Constitutive Model with a Historiotropic Yield Surface for Sands T2 - Recent developments of soil mechanics and geotechnics in theory and practice N2 - A simple, yet versatile yield surface in the stress space is combined with a hypoplastic equation to simulate the influence of recent deformation history on the mechanical behaviour of sand. This yield surface is used to describe the intensity of anelastic flow. In the model, the state is fully described by the current stress, the void ratio and a novel back stress-like tensor. This new state variable determines the shape and size of the yield surface and accounts for recent deformation/stress history. The direction of the anelastic flow upon shearing is obtained from a generalization of the Taylor’s dilatancy rule. As a distinctive feature of the model, this dilatancy is able to reproduce the strong contractancy upon reversals observed in experiments without the need of additional state variables. The model corrects some known shortcomings of previous hypoplastic models like overshooting and the excessive accumulation of stress/strain upon strain/stress cycles of small amplitude (ratcheting). Laboratory tests are simulated to show the capabilities of the model to reproduce the soil behaviour under monotonic and cyclic loading conditions after different deformation histories. Y1 - 2020 SN - 978-3-030-28515-9 SN - 978-3-030-28516-6 SP - 13 EP - 43 PB - Springer CY - Cham ER - TY - CHAP A1 - Machaček, Jan A1 - Grandas Tavera, Carlos Eduardo A1 - Triantafyllidis, Theodoros ED - Triantafyllidis, Theodoros T1 - Coupled Numerical Simulations for Seismic Hazard Assessment of Large Opencast Slopes T2 - Recent developments of soil mechanics and geotechnics in theory and practic N2 - Earthquake stability assessments of large opencast mine slopes (dimensions exceeding several hundred meters) are complex and non-linear problems, often addressed using pseudo-static approaches that neglect material-induced failures and the role of pore-fluids. In this study, a numerical approach is used to understand the dynamic response of saturated and unsaturated soils. Since the requirements for such simulations are often not yet met by commercial software packages, user-defined finite elements and user-defined material models have been implemented in Abaqus/Standard. To account for the large depth of the finite element model, a scaling procedure of the system of equations is proposed to purge the influence of initial stress. The constitutive model parameters are calibrated based on laboratory tests and by back calculation of downhole measurements. Large-scale fully coupled finite element simulations are performed to study the response of a flooded opencast mine under earthquake loading. The present work illustrates the importance of the pore-fluids treated as independent phases in the context of seismic analysis of slopes. The simulations show strong wave diffraction effects for inhomogeneous dump structures, resulting in smaller displacements in near-surface areas of the slope. Furthermore, it was found that large areas of the dump show a (significant) temporary decrease of effective mean pressure. Y1 - 2020 SN - 978-3-030-28515-9 SN - 978-3-030-28516-6 SP - 266 PB - Springer CY - Cham ER - TY - CHAP A1 - Niemunis, Andrzej A1 - Grandas Tavera, Carlos Eduardo ED - Wu, Wei T1 - Essential Concepts of Neohypoplasticity T2 - Desiderata Geotechnica N2 - The neohypoplastic model [12] eliminates several shortcomings of the hypoplastic vW-HP model [17]. The most important improvements are presented here. The general form of the constitutive equation is slightly modified by two additional terms in brackets. The functions and are completely reformulated in order to deal with numerous problems of the old model: perpetuum mobile of the second kind, too small dilatancy during triaxial tension paths, poor predictions of peak stress and inconsistent behaviour of the model at the upper density limit. A new state variable similar to the one from the Sanisand model [3] is introduced. The hitherto used state variables: the stress and the void ratio are preserved, of course. Moreover, a new kind of nonlinearity is proposed: the rotation of the deviatoric stress response. The problems connected to the extension intergranular-strain extension are not discussed here. Y1 - 2019 UR - https://link.springer.com/chapter/10.1007/978-3-030-14987-1_16 SN - 978-3-030-14986-4 SN - 978-3-030-14987-1 U6 - https://doi.org/10.1007/978-3-030-14987-1 SP - 132 EP - 142 PB - Springer CY - Cham ER - TY - CHAP A1 - Niemunis, Andrzej A1 - Grandas Tavera, Carlos Eduardo T1 - Computer Aided Calibration, Benchmarking and Check-Up of Constitutive Models for Soils. Some Con� clusions for Neohypoplasticity T2 - Holistic Simulation of Geotechnical Installation Processes N2 - A computer aided calibration, benchmarking and testing of constitutive models is presented. A large collection of test data for Karlsruhe sand is used together with the neohypoplastic model as an example. The essential feature of the procedure is an automatic evaluation of the discrepancies between a test and its simulation. They can be minimized by modifications of material constants or used as a benchmark for different models. Apart from the curve-fitting part one may check whether a constitutive model violates the Second Law. For this purpose several specially designed stress loops are tried out. A shake down of all state variables is established. The neohypoplasticity and the barotropic hypoelasticity are used as examples in the thermodynamic tests. In conclusion several modification to neohypoplastic models are presented. Y1 - 2017 U6 - https://doi.org/10.1007/978-3-319-52590-7_7 SP - 168 EP - 192 PB - Springer International Publishing CY - Karlsruhe ER - TY - CHAP A1 - Niemunis, Andrzej A1 - Grandas Tavera, Carlos Eduardo A1 - Wichtmann, Torsten T1 - Peak Stress Obliquity in Drained and Undrained Sands. Simulations with Neohypoplasticity T2 - Holistic Simulation of Geotechnical Installation Processes N2 - The difference between undrained and drained peak friction angle is considerable (up tp 10^ ∘ 10∘), despite identical densities and pressures (at peak). This cannot be explained using the elastoplastic formalism. An attempt is made to describe this effect with neohypoplasticity. For this purpose two types of nonlinearity are used, the well-known term Y m_ ij ‖ ̇ ϵ ‖ Y mij‖ ϵ˙‖ and the novel skew-symmetric correction tensor which is added to the elastic stiffness. Y1 - 2016 U6 - https://doi.org/10.1007/978-3-319-23159-4_5 SP - 5 EP - 114 PB - Springer International Publishing CY - Karlsruhe ER - TY - CHAP A1 - Osinov, V. A. A1 - Chrisopoulos, S. A1 - Grandas Tavera, Carlos Eduardo T1 - Vibration-induced stress changes in saturated soil: a high-cycle problem T2 - Holistic Simulation of Geotechnical Installation Processes N2 - Numerical modelling of the cyclic deformation of soil can be performed with the use of two types of constitutive models: incremental plasticity models and so-called explicit cyclic models. The present study deals with the application of a model of the second type—the high-cycle accumulation model for sand—to the analysis of vibration-induced stress changes in saturated soil. The application of the model requires the concurrent solution of two coupled boundary value problems: a dynamic problem for the determination of strain amplitude and a quasi-static problem for the calculation of stress evolution. The coupling of the two problems has been implemented in a two-dimensional axisymmetric formulation with the finite-element program Abaqus. The model is applied to the analysis of stress changes near a concrete wall caused by a vibrating pile. The numerical results show that a large-amplitude vibration, e.g. during the installation of vibratory driven piles, may substantially reduce both the effective and the total stresses in front of the wall. The effective stress may be reduced to zero resulting in soil liquefaction. Y1 - 2016 U6 - https://doi.org/10.1007/978-3-319-23159-4_4 SP - 69 EP - 84 PB - Springer International Publishing CY - Karlsruhe ER - TY - CHAP A1 - Osinov, V. A. A1 - Grandas Tavera, Carlos Eduardo T1 - A Numerical Approach to the Solution of Dynamic Boundary Value Problems for Fluid-Saturated Solids T2 - Holistic Simulation of Geotechnical Installation Processes N2 - A dynamic boundary value problem for a fluid-saturated solid can be represented as two coupled boundary value problems for one-phase media. This allows us to solve the problem with a commercial computer program without a built-in procedure for the solution of dynamic problems with non-zero permeability, provided that the user is able to establish the required coupling between the two problems. This approach has been implemented in the present paper with the computer program Abaqus/Standard using the dynamic analysis for one-phase media as a built-in procedure without the need to construct a user-defined finite element. Y1 - 2015 U6 - https://doi.org/10.1007/978-3-319-18170-7_8 SP - 149 EP - 162 PB - Springer International Publishing CY - Karlsruhe ER - TY - RPRT A1 - Grandas Tavera, Carlos Eduardo T1 - Einfluss der Anisotropie von weichem Ton beim Grenzzustand von Baugrubenecken und der Gebrauchstauglichkeit von Verbauwänden N2 - Die Standsicherheit von nicht-ebenen Schlitzwand-Ecklamellen in weichem, normalkonsolidiertem bindigen Boden und die Setzungen von benachbarten Fundamenten infolge des Herstellungsvorgangs einer Schlitzwand wurden mit Hilfe der FE-Methode numerisch untersucht. Um das K0−anisotrope Verhalten des Bodens besser simulieren zu können, wurde eine Erweiterung der Visko-Hypoplastizität entwickelt und in einer FE-kompatiblen Subroutine implizit implementiert. Die neue anisotrope Visko-Hypoplastizität ist in der Lage, die Ratenabhängigkeit, das Kriechen, die Relaxation, die Anisotropie, und die Akkumulation des Porenwasserdruckes infolge undrainierter Deformationszyklen wiederzugeben. Bezüglich der Standsicherheit wurde der unter Suspension gestützte Aushub des Eckschlitzes und das Verhalten des Schlitzes bis zum Bruchzustand simuliert. Der dadurch entstandene Bruchkörper hat die Form eines vertikalen Viertelzylinders, der von seiner Unterseite her von einer geneigten Ebene begrenzt wird. Im Vergleich mit den in Deutschland üblichen verwendeten analytischen Verfahren zur Berechnung der Standsicherheit, die normalerweise von einem Erdkeilmodell ausgehen, ist der Mechanismus für den Eckschlitz mit dem Viertelzylinder kritischer. Dieses Ergebnis spricht für die Entwicklung eines analytischen Verfahrens, das auf diesem Mechanismus basiert. Die Simulationen der Gebrauchstauglichkeit von benachbarten Fundamenten infolge der Herstellung von Eckschlitzwänden zeigen, dass die Setzungen stark von der Abwicklungslänge des Eckschlitzes abhängen und wenig vom Verhältnis der Schenkellängen L1 /L2 . Zusätzlich nehmen die Setzungen mit der Gebrauchslast des Fundamentes zu. Für die gleiche Gebrauchslast nimmt die Setzung mit dem Abstand des Fundamentes zum Schlitz stark ab. Sowohl die Standsicherheit des offenen Schlitzes als auch die Setzungen des benachbarten Fundamentes hängen stark von der Zeit ab. Ein schnellerer Aushub des Schlitzes und eine schnellere Betonierung der Wand führen zu größeren Standsicherheiten und kleineren Setzungen des Fundamentes, als eine langsamere Vorgehensweise. Y1 - 2011 UR - https://gepris.dfg.de/gepris/projekt/5285688/ergebnisse?context=projekt&task=showDetail&id=5285688&selectedSubTab=2& ER - TY - GEN A1 - Nitsch, Antonia A1 - Machaček, Jan A1 - Wichtmann, Torsten A1 - Grandas Tavera, Carlos Eduardo T1 - Validierung und Kalibrierung eines hypoplastischen Stoffmodells für expansive Böden T2 - Bautechnik N2 - Einige Böden neigen aufgrund ihrer tonmineralogischen Zusammensetzung bei Kontakt mit Wasser zur Volumenänderung, welche sich phänomenologisch entweder als Expansion oder durch eine Quelldruckentwicklung äußert. In der Baupraxis müssen sowohl die Quellphänomene als auch das hydromechanisch gekoppelte Materialverhalten allgemein z.B. bei der Bemessung von Tunnelbauwerken oder Abdichtungen berücksichtigt werden. Existierende empirische Modelle sind für komplexe Randbedingungen oft unzureichend, doch die Anwendung höherwertiger mechanischer Stoffmodelle stellt aufgrund komplexer Modellformulierungen und meist aufwendiger Bestimmung der benötigten Materialparameter eine große Hürde dar. In diesem Aufsatz wird ein von den Autor:innen kürzlich vorgestelltes neuartiges hypoplastisches Stoffmodell für expansive Böden durch die Anwendung auf weitere experimentelle Studien validiert. Zur Erleichterung der Anwendung des Stoffmodells in der Praxis wird eine vereinfachte Parameterkalibrierung erläutert, die keine aufwendige experimentelle Untersuchung erfordert. Y1 - 2023 U6 - https://doi.org/10.1002/bate.202300062 SN - 0932-8351 VL - 100 IS - 11 SP - 689 EP - 698 ER -