TY - GEN A1 - Grandas Tavera, Carlos Eduardo A1 - Cudmani, Roberto A1 - Csuka, Antal ED - Zdravkovic, Lidija ED - Kontoe, Stavroula ED - Tsiampousi, Aikaterini ED - Taborda, David T1 - Numerical investigations of the influence of initial static shear stress on the bi-directional loading of dense sand T2 - 10th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE2023) N2 - Advanced constitutive models are required for realistic prediction of the seismic behavior of geotechnical structures, such as dams and embankments, under undrained alternating loading conditions. The constitutive models should be able to capture accurately two important aspects related to the boundary value problem: the influence of a non-zero initial static shear stress and the multi-directional nature of the earthquake loading. Experimental studies show that the deformation characteristics of granular materials under undrained cyclic loading conditions depend on the initial static shear stress, initial void ratio and loading direction. In this paper, two advanced constitutive models from the hypoplasticity family are compared with each other and with experiments regarding to their ability to account for the influence of the initial static shear stress on liquefaction. Y1 - 2023 U6 - https://doi.org/10.53243/NUMGE2023-45 ER - TY - GEN A1 - Grandas Tavera, Carlos Eduardo A1 - Wichtmann, Torsten A1 - Machaček, Jan A1 - Nitsch, Antonia ED - Zdravkovic, Lidija ED - Kontoe, Stavroula ED - Tsiampousi, Aikaterini ED - Taborda, David T1 - An extended theory of porous media for expansive soils T2 - 10th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE2023) N2 - The successful simulation of the behaviour of expansive soils using FEM strongly depends on the acting hydromechanical processes and their proper consideration. During swelling processes, part of the pore water is bound to the solid. However, the associated change of volume fractions in the porous medium and its contribution to the overall material behaviour is not accounted for in most numerical frameworks. A numerical framework based on the theory of porous media and a novel constitutive model is proposed. The theory of porous media includes a distinct swelling water phase that does not participate in the flow through the pore space. A bidirectional mass transport enables the transition from free to swelling water during change in water content. The reduction of the effective pore space is considered at the finite element level. By consistent balancing in the governing equations, the swelling induced reduction of hydraulic conductivity is directly accounted for. The performance of the proposed framework is demonstrated by back calculation of laboratory tests on different materials. Its capabilities to simulate complex loading paths in (un)saturated conditions with a single set of parameters are shown. KW - Swelling; Expansive soils; Partial saturation; Hydro-mechanical coupling; Porous Media Y1 - 2023 U6 - https://doi.org/10.53243/NUMGE2023-379 ER - TY - GEN A1 - Machazek, Jan A1 - Nitsch, Antonia A1 - Wichtmann, Torsten A1 - Grandas Tavera, Carlos Eduardo T1 - Numerical modelling of expansive geomaterials: Finite element formulation and constitutive models T2 - Computers and Geotechnics N2 - The successful simulation of the behaviour of expansive soils using FEM strongly depends on the acting hydromechanical processes and their proper consideration. During swelling processes, part of the pore water is bound to the solid. However, the associated change of volume fractions in the porous medium and its contribution to the overall material behaviour is not accounted for in most numerical frameworks. In this paper, a numerical framework based on the Theory of Porous Media (TPM) and a three-dimensional hydro-mechanically coupled hypoplastic constitutive model for expansive soils are proposed. The TPM includes a distinct swelling water phase that does not participate in the flow through the pore space. A bidirectional mass transport enables the transition from free to swelling water during change in water content. By consistent balancing in the governing equations, the swelling induced reduction of hydraulic conductivity is directly accounted for. The performance of the proposed framework is demonstrated by back calculation of laboratory tests on different materials. Its capabilities to simulate complex loading paths in (un)saturated conditions with a single set of parameters are shown. KW - Expansive soils Hypoplasticity Swelling pressure Swelling strain Theory of porous media Y1 - 2024 U6 - https://doi.org/10.1016/j.compgeo.2024.106739 SN - 1873-7633 SN - 0266-352X VL - 176 ER - TY - GEN A1 - Knittel, Lukas A1 - Tafili, Merita A1 - Grandas Tavera, Carlos Eduardo A1 - Triantafyllidis, Theodoros T1 - New perspectives on preshearing history in granular soils T2 - Scientific reports N2 - The design of deep dump slopes for opencast mines usually requires information about the soil resistance to liquefaction during earthquakes. This resistance depends not only on the initial stress, the initial density, and the amplitude of the cyclic loading, but also on the preshearing, that is, the deviatoric stress path applied to the soil before the cyclic loading. To explore the influence of preshearing on the subsequent soil behaviour, a set of triaxial tests with a combination of undrained preshearing and drained stress cycles using two sample preparation methods is presented. It is shown that the preshearing as well as the preparation method have a major influence on the strain accumulation upon cyclic loading. Simulations of the experiments with four advanced constitutive models reveal that neither the long-lasting effect of preshearing nor the preparation method can adequately be captured by all of the models. This deficiency of the constitutive models can lead to unsafe designs due to the overestimation of the cyclic resistance to liquefaction and to the underestimation of long term settlements. Y1 - 2023 U6 - https://doi.org/10.1038/s41598-023-31419-9 SN - 2045-2322 VL - 13 ER - TY - GEN A1 - Nitsch, Antonia A1 - Leuthold, Julia A1 - Machaček, Jan A1 - Grandas Tavera, Carlos Eduardo T1 - Experimental investigations on hydro‑mechanical processes in reconstituted clay shale and their significance for constitutive modelling T2 - Rock Mechanics and Rock Engineering N2 - The hydro-mechanical processes of a reconstituted clay shale (Opalinus Clay) were studied and implications for constitutive modelling of swellable clay shales derived. The study aims to provide further insights into these coupled processes. For that, oedometric swelling tests with varying boundary conditions and loading paths, oedometric compression tests under dry and saturated conditions, and permeability tests were performed. The results showed a unique preloading line for the dry state when plotting the void ratio against the vertical stress. For saturated states, this line was shifted to the left (to smaller stresses) which revealed a severe reduction of preloading stress due to saturation. All loading paths converged in a normal compression line (NCL) regardless of the mechanical boundary conditions during saturation. A trend line affine to the NCL was established for swelling pressures at different initial void ratios. The influence of saturation on the mechanical properties became further evident, as the un-/reloading stiffness was significantly reduced. A linear relationship between volumetric deformation and saturation was found. A severe swelling induced reduction of permeability in the saturated state was demonstrated and confirmed by the analysis of consolidation processes during oedometric loading. The experimental findings were used to derive fundamental assumptions for constitutive modelling and were discussed within a numerical framework for expansive soils. KW - Hydro-mechanical behaviour KW - Swelling KW - Oedometric compression KW - Permeability KW - Constitutive modelling Y1 - 2023 U6 - https://doi.org/10.1007/s00603-022-03202-1 SN - 1434-453X SN - 0723-2632 VL - 56 IS - 4 SP - 2457 EP - 2478 ER - TY - GEN A1 - Grandas Tavera, Carlos Eduardo A1 - Nitsch, Antonia A1 - Machaček, Jan T1 - A 1D Hypoplastic constitutive model for expansive soils T2 - Acta Geotechnica N2 - This paper presents a simple hypoplastic constitutive model that describes the essential features of the material behaviour of partially saturated clayey soils observed in oedometric compression tests. The model is formulated in terms of net stress and degree of saturation. The total strain rate is decomposed into a portion related to the changes in saturation and a portion for the evolution of net stress. However, no distinction is made between plastic and elastic strains. With this strain rate decomposition, the maximum swelling strain/stress are obtained by simulating wetting processes under constant stress/strain conditions. In addition to the void ratio, the model includes two scalar variables to track the loading history (preloading). The calibration of the model constants using common laboratory tests is discussed. Confined and unconfined swelling tests under oedometric conditions with subsequent loading and unloading phases carried out on three different materials were satisfactorily simulated by the model. Its promising results call for an extension to a 3D formulation. Y1 - 2022 U6 - https://doi.org/10.1007/s11440-022-01548-y SN - 1861-1133 SN - 1861-1125 VL - 17 SP - 4313 EP - 4331 ER - TY - GEN A1 - Grandas Tavera, Carlos Eduardo A1 - Vogelsang, Jakob A1 - Triantafyllidis, Theodoros T1 - Simplified simulation of the installation of vibro-piles in water saturated soil T2 - Soil Dynamics and Earthquake Engineering N2 - This paper presents a novel and simplified approach to simulate the effects of the vibro-pile installation on the deformation of deep excavation shoring walls at high ground water levels. Although commonly-used finite element simulations provide acceptable predictions of the wall displacements caused by underwater excavations, anchor installation, or pit dewatering processes, they could not explain the unexpected large wall movements measured in different excavations during the vibro-pile installation stage. Previous dynamic finite element … Y1 - 2019 UR - https://www.sciencedirect.com/science/article/pii/S0267726118306754 SN - 1879-341X SN - 0267-7261 IS - 121 SP - 491 EP - 498 ER - TY - GEN A1 - Gerolymatou, Eleni A1 - Grandas Tavera, Carlos Eduardo A1 - Triantafyllidis, Theodoros T1 - Modelling Localization on Varying Scales T2 - Bifurcation and Degradation of Geomaterials with Engineering Applications : Proceedings of the 11th International Workshop on Bifurcation and Degradation in Geomaterials dedicated to Hans Muhlhaus, Limassol, Cyprus, 21-25 May 2017 N2 - Localization, both in the form of compaction bands and of shear bands, poses special challenges to finite element simulations, as the results tend to vary with the used discretization. As a rule, so called non simple continua in the sense of Noll are used to resolve the problem. In this way an internal length is introduced, which controls the size of the domain in which strain localizes. Such an approach requires an element length that is significantly smaller than the internal length, making it thus unsuitable for practical applications in the large scale. An alternative was suggested by Pietruszczak and Mróz, as far as shear bands are concerned. In this approach the shear band thickness is assumed to be a material parameter, with an element size that is significantly larger. In the present work this approach is extended to compaction bands and the discretizations required for the two approaches are compared. Y1 - 2017 SN - 978-3-319-56396-1 SN - 978-3-319-85905-7 SN - 978-3-319-56397-8 U6 - https://doi.org/10.1007/978-3-319-56397-8_49 SN - 1866-8755 SP - 399 EP - 405 PB - Springer CY - Cham ER - TY - GEN A1 - Niemunis, Andrzej A1 - Grandas Tavera, Carlos Eduardo A1 - Fitz, Jan-Erik ED - Manzanal, Diego ED - Sfriso, Alejo O. T1 - High-Cycle Accumulation Model with EAS Elements T2 - From fundamentals to applications in geotechnics : proceedings of the 15th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 15–18 November 2015, Buenos Aires, Argentina N2 - A FE implementation in the commercial program ABAQUS® of the high cycle accumulation model for sand is discussed. Due to the large gradients of the predicted accumulation, elements with enhanced assumed strains are used. Application of EAS to constitutive models formulated in rates (incrementally non-linear and path dependent) requires, apart from return mapping and equilibrium iterations, an additional iterative process for determination of the enhanced strain. It is demonstrated that EAS elements can cope well with difficult accumulation fields and with the strong material nonlinearity as required by the HCA model. Y1 - 2015 SN - 978-1-61499-602-6 SN - 978-1-61499-603-3 U6 - https://doi.org/10.3233/978-1-61499-603-3-1301 SP - 1301 EP - 1308 PB - IOS Press CY - Amsterdam ER - TY - GEN A1 - Machaček, Jan A1 - Staubach, Patrick A1 - Grandas Tavera, Carlos Eduardo A1 - Wichtmann, Torsten A1 - Zachert, Hauke T1 - On the automatic parameter calibration of a hypoplastic soil model T2 - Acta Geotechnica N2 - This paper presents an approach for the automatic parameter calibration (AC) of a hypoplastic constitutive soil model. The calibration software developed in this work simplifies the parameter calibration, reduces the subjective “human” factor on the calibration result and lowers the entry hurdle for the use of the hypoplastic constitutive model. The performance of the software was demonstrated by comparing automatically calibrated parameter sets for two sands and their related simulations of the underlying experimental data with simulations using two reference parameter sets. The first reference parameter set was calibrated the classical way, "by hand", and the second was calibrated using the AC tool ExCalibre. Two different optimization methods were used, namely the Differential Evolution (DE) and the Particle Swarm Optimization (PSO). The simulations performed with the parameters obtained from the AC agree well with the experimental data and show improvements over the reference parameter sets. With respect to the optimization method, the performance of the DE proved superior to that of the PSO. Various measures of comparison were examined to quantify the discrepancy between experiment and simulation. By repeating 500 calibration runs, the dispersion of parameters was determined and correlations between different parameters of the hypoplastic model were found. Y1 - 2022 U6 - https://doi.org/10.1007/s11440-022-01669-4 SN - 1861-1125 VL - 17 IS - 11 SP - 5253 EP - 5273 ER - TY - GEN A1 - Tafili, Merita A1 - Grandas Tavera, Carlos Eduardo A1 - Triantafyllidis, Theodoros A1 - Wichtmann, Torsten T1 - Constitutive anamnesis model (CAM) for fine‐grained soils T2 - International Journal for Numerical and Analytical Methods in Geomechanics N2 - Mainly, two divisions are encountered in the literature regarding constitutive models: elasto‐plasticity and hypoplasticity. In addition, barodesy and the framework of generalized plasticity are used. The main disadvantage of nearly all models is the failure to reproduce the mechanical behaviour under cyclic loading without restrictions. A model which deals neither with the true hypoplastic nor the true elasto‐plastic approach will be proposed herein. Moreover, it combines and establishes the unification of both frameworks and it can be assigned to both of them. It introduces a so called historiotropic surface, responsible for the memory of the soil, but no consistency condition. It also introduces a hypoplastic strain rate, but incorporating the distance to the new surface for its intensity and the back stress tensor. Hence, both the intergranular strain as well as the fabric‐dilatancy tensor are omitted, even though the eight‐shaped stress hysteresis at cyclic mobility is well reproduced Y1 - 2022 U6 - https://doi.org/10.1002/nag.3428 SN - 0363-9061 VL - 46 IS - 15 SP - 2817 EP - 2848 ER -