@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{MachazekNitschWichtmannetal., author = {Machazek, Jan and Nitsch, Antonia and Wichtmann, Torsten and Grandas Tavera, Carlos Eduardo}, title = {Numerical modelling of expansive geomaterials: Finite element formulation and constitutive models}, series = {Computers and Geotechnics}, volume = {176}, journal = {Computers and Geotechnics}, issn = {1873-7633}, doi = {10.1016/j.compgeo.2024.106739}, pages = {14}, 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. 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.}, 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{GrandasTaveraNitschMachaček, author = {Grandas Tavera, Carlos Eduardo and Nitsch, Antonia and Machaček, Jan}, title = {A 1D Hypoplastic constitutive model for expansive soils}, series = {Acta Geotechnica}, volume = {17}, journal = {Acta Geotechnica}, issn = {1861-1133}, doi = {10.1007/s11440-022-01548-y}, pages = {4313 -- 4331}, abstract = {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.}, language = {en} } @misc{NitschLeutholdMachačeketal., author = {Nitsch, Antonia and Leuthold, Jan and Machaček, Jan and Wichtmann, Torsten and Grandas Tavera, Carlos Eduardo}, title = {Experimental investigations of the stress-dependent swelling behavior of reconstituted claystone}, series = {Fachsektionstage Geotechnik 2021: 24. Symposium Felsmechanik und Tunnelbau}, journal = {Fachsektionstage Geotechnik 2021: 24. Symposium Felsmechanik und Tunnelbau}, pages = {8}, abstract = {An experimental campaign giving a holistic overview on the hydro-mechanically coupled behavior of Opalinus Clay shale is presented. Oedometric swelling tests show a pronounced stress pathdependent swelling behavior that is governed by the local permeability and the mechanical preloading stress. A linear coupling between deformation and volumetric water content can be established during initial saturation that causes a swelling-induced reduction of the hydraulic permeability. Swelling deformation and pressure result in the mechanical degradation of the material with a reduction of preloading stress and elastic stiffness. Based on the experimental results, fundamental characteristics of the material behavior are derived and form the basis for the future development of a new constitutive model that is able to predict the hydro-mechanically coupled material response}, 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} }