@misc{GrandasTaveraCudmaniCsuka, author = {Grandas Tavera, Carlos Eduardo and Cudmani, Roberto and Csuka, Antal}, title = {Numerical investigations of the influence of initial static shear stress on the bi-directional loading of dense sand}, series = {10th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE2023)}, journal = {10th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE2023)}, editor = {Zdravkovic, Lidija and Kontoe, Stavroula and Tsiampousi, Aikaterini and Taborda, David}, doi = {10.53243/NUMGE2023-45}, pages = {6}, abstract = {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.}, language = {en} } @misc{GrandasTaveraWichtmannMachačeketal., author = {Grandas Tavera, Carlos Eduardo and Wichtmann, Torsten and Machaček, Jan and Nitsch, Antonia}, title = {An extended theory of porous media for expansive soils}, series = {10th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE2023)}, journal = {10th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE2023)}, editor = {Zdravkovic, Lidija and Kontoe, Stavroula and Tsiampousi, Aikaterini and Taborda, David}, doi = {10.53243/NUMGE2023-379}, pages = {6}, abstract = {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.}, language = {en} } @misc{KnittelTafiliGrandasTaveraetal., author = {Knittel, Lukas and Tafili, Merita and Grandas Tavera, Carlos Eduardo and Triantafyllidis, Theodoros}, title = {New perspectives on preshearing history in granular soils}, series = {Scientific reports}, volume = {13}, journal = {Scientific reports}, issn = {2045-2322}, doi = {10.1038/s41598-023-31419-9}, abstract = {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.}, language = {en} } @misc{NitschLeutholdMachačeketal., author = {Nitsch, Antonia and Leuthold, Julia and Machaček, Jan and Grandas Tavera, Carlos Eduardo}, title = {Experimental investigations on hydro‑mechanical processes in reconstituted clay shale and their significance for constitutive modelling}, series = {Rock Mechanics and Rock Engineering}, volume = {56}, journal = {Rock Mechanics and Rock Engineering}, number = {4}, issn = {1434-453X}, doi = {10.1007/s00603-022-03202-1}, pages = {2457 -- 2478}, abstract = {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.}, language = {en} } @misc{NitschMachačekWichtmannetal., author = {Nitsch, Antonia and Machaček, Jan and Wichtmann, Torsten and Grandas Tavera, Carlos Eduardo}, title = {Validierung und Kalibrierung eines hypoplastischen Stoffmodells f{\"u}r expansive B{\"o}den}, series = {Bautechnik}, volume = {100}, journal = {Bautechnik}, number = {11}, issn = {0932-8351}, doi = {10.1002/bate.202300062}, pages = {689 -- 698}, abstract = {Einige B{\"o}den neigen aufgrund ihrer tonmineralogischen Zusammensetzung bei Kontakt mit Wasser zur Volumen{\"a}nderung, welche sich ph{\"a}nomenologisch entweder als Expansion oder durch eine Quelldruckentwicklung {\"a}ußert. In der Baupraxis m{\"u}ssen sowohl die Quellph{\"a}nomene als auch das hydromechanisch gekoppelte Materialverhalten allgemein z.B. bei der Bemessung von Tunnelbauwerken oder Abdichtungen ber{\"u}cksichtigt werden. Existierende empirische Modelle sind f{\"u}r komplexe Randbedingungen oft unzureichend, doch die Anwendung h{\"o}herwertiger mechanischer Stoffmodelle stellt aufgrund komplexer Modellformulierungen und meist aufwendiger Bestimmung der ben{\"o}tigten Materialparameter eine große H{\"u}rde dar. In diesem Aufsatz wird ein von den Autor:innen k{\"u}rzlich vorgestelltes neuartiges hypoplastisches Stoffmodell f{\"u}r expansive B{\"o}den durch die Anwendung auf weitere experimentelle Studien validiert. Zur Erleichterung der Anwendung des Stoffmodells in der Praxis wird eine vereinfachte Parameterkalibrierung erl{\"a}utert, die keine aufwendige experimentelle Untersuchung erfordert.}, language = {de} }