Compaction localization and anisotropic permeability evolution

The oedometric compaction of materials with collapsible structure is investigated from a numerical point of view. Such materials form planar zones of localized volumetric deformation that may or may not be accompanied by grain crushing. The purpose of the present work is to investigate the evolution of the permeability and its anisotropy as the result of the formation of compaction bands. The finite element method is used for the simulations with the commercial software ABAQUS. The mechanical response is calibrated on experimental results from the literature. Due to the localization of the deformation, the problem is not numerically stable and shows mesh dependence when a simple material model is used. To resolve the issue a nonlocal formulation is implemented. Drained oedometric tests are simulated. For the permeability different formulations are used, either ignoring the anisotropic evolution of the pore network or accounting for it. The results show that permeability anisotropy at the microscale needs to be considered, because otherwise the predicted reduction in permeability is qualitatively not in agreement with experimental results. On the whole, it is concluded that the permeability reduction following the formation of compaction bands can be highly anisotropic both at the micro and the macro scale

Effect of Compaction Banding on the Hydraulic Properties of Porous Rock - Part II: Constitutive Description and Numerical Simulations

In this paper the performance of a constitutive model for the description of the hydro mechanical behaviour of soft rock is evaluated with respect to the experimentally observed behaviour of Maastricht Calcarenite under different stress states that is presented in the companion paper. The mechanical model is elasto-plastic and consists of an associated yield surface, internal variables for the description of the hardening and softening behaviour and a non-local extension for the simulation of strain localization in form of shear bands and compaction bands. The model is implemented in the software ABAQUS and the laboratory results from the tests under dry condition with Maastricht Calcarenite are used for the calibration. The good agreement of the numerical results with the laboratory results is shown and the suitability of the model is discussed. To describe the effect of compaction bands on the permeability of soft rocks a simple analytical model based on the Kozeny–Carman equation is proposed and calibrated with the experimental results from drained tests under different stress states for Maastricht Calcarenite rock material. As the results are in good accordance with the experimental results, the model is implemented in the software ABAQUS and the numerical results are presented and discussed. Finally the performance of the model is evaluated and possible improvements are suggested

Effect of Compaction Banding on the Hydraulic Properties of Porous Rock: Part I—Experimental Investigation

The mechanical behavior and the influence of compaction banding on the hydraulic properties in soft porous rocks were studied. The tested rock was Calcarenite Tuffeau de Maastricht. In the frame of experimental investigations, triaxial and oedometric tests were conducted under dry and drained conditions. The results demonstrated that the rock is forming discrete compaction bands under high confining stresses and steep angle shear bands under low confining stresses. Permeability measurements during the oedometric and triaxial compression tests under drained conditions demonstrated that the axial permeability decreases with increasing axial strain. The maximum permeability decrease was three orders of magnitude for 40% of axial strain

Kognitiv aktivierende Methoden zur Förderung des Theorie-Praxis-Transfers in der Lehrerbildung: Theorie-Praxis-Transfers in der Lehrerbildung: Werkstattbericht

Das Ziel des Projekts ist die Förderung des Theorie-Praxis-Transfers und eines vertieften Lernverständnisses bei Lehramtsstudierenden an zwei Universitäten in Sachsen. Konkret bedeutet dies, dass theoretische und empirische Erkenntnisse psychologischer und didaktischer Forschung in einer Weise elaboriert werden, dass vor dem Hintergrund persönlicher pädagogischer Überzeugungen handlungsleitende Schlussfolgerungen für die künftige Lehrtätigkeit gezogen werden können. Ein vertieftes Verständnis von Lernen meint in diesem Zusammenhang die explizite Bewusstmachung eigener Lernprozesse mit dem Ziel, diese Erfahrungen ebenfalls in die zukünftige Lehrpraxis zu übertragen. Erreicht werden soll dies durch ein innovatives Seminarkonzept, welches den Schwerpunkt auf kognitiv aktivierende Methoden legt und insbesondere durch den Einsatz von Workshops und Lerntagebüchern realisiert wird. Der Beitrag umfasst eine kurze Darstellung des Seminarkonzeptes sowie die Präsentation der drei durchgeführten Teilprojekte und der wesentlichen Ergebnisse aus der Evaluation

Effect of Compaction Banding on the Hydraulic Properties of Porous Rock - Part II: Constitutive Description and Numerical Simulations

In this paper the performance of a constitutive model for the description of the hydro mechanical behaviour of soft rock is evaluated with respect to the experimentally observed behaviour of Maastricht Calcarenite under different stress states that is presented in the companion paper. The mechanical model is elasto-plastic and consists of an associated yield surface, internal variables for the description of the hardening and softening behaviour and a non-local extension for the simulation of strain localization in form of shear bands and compaction bands. The model is implemented in the software ABAQUS and the laboratory results from the tests under dry condition with Maastricht Calcarenite are used for the calibration. The good agreement of the numerical results with the laboratory results is shown and the suitability of the model is discussed. To describe the effect of compaction bands on the permeability of soft rocks a simple analytical model based on the Kozeny–Carman equation is proposed and calibrated with the experimental results from drained tests under different stress states for Maastricht Calcarenite rock material. As the results are in good accordance with the experimental results, the model is implemented in the software ABAQUS and the numerical results are presented and discussed. Finally the performance of the model is evaluated and possible improvements are suggested.Karlsruher Institut für Technologie (KIT) (4220

Effect of Compaction Banding on the Hydraulic Properties of Porous Rock: Part I—Experimental Investigation

The mechanical behavior and the influence of compaction banding on the hydraulic properties in soft porous rocks were studied. The tested rock was Calcarenite Tuffeau de Maastricht. In the frame of experimental investigations, triaxial and oedometric tests were conducted under dry and drained conditions. The results demonstrated that the rock is forming discrete compaction bands under high confining stresses and steep angle shear bands under low confining stresses. Permeability measurements during the oedometric and triaxial compression tests under drained conditions demonstrated that the axial permeability decreases with increasing axial strain. The maximum permeability decrease was three orders of magnitude for 40% of axial strain.Karlsruher Institut für Technologie (KIT) (4220

Experimental Investigations on Hydro-mechanical Processes in Reconstituted Clay Shale and Their Significance for Constitutive Modelling

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

Politische Instrumente zur Gewährleistung der Nachhaltigkeit von Wasserstoffimporten : eine Kurzstudie im Auftrag von Brot für die Welt und der Heinrich-Böll-Stiftung

Für Deutschland und viele Industrieländer weltweit wird der Import von grünem Wasserstoff ein zentraler Baustein auf dem Weg zur Klimaneutralität sein. Dabei muss einerseits gewährleistet sein, dass grüner Wasserstoff auch wirklich "grün" im Sinne von klimaneutral ist. Zugleich gibt es immer mehr Forderungen, dass auch andere Nachhaltigkeitskriterien - soziale, ökonomische und ökologische - bei der Produktion und dem Transport von Wasserstoff eingehalten werden. Der politisch getriebene Aufbau einer globalen Wasserstoffwirtschaft bietet von Anfang an die Möglichkeit, diesen Sektor in Einklang mit den bestehenden politischen Zielen zu bringen. Dazu zählen beispielsweise die Pariser Klimaziele oder die Agenda 2030. Die Industrienation Deutschland, die auch in Zukunft auf Energieimporte angewiesen sein wird, kann hier als führende Industrienation als Vorreiter Einfluss nehmen. Damit kann nicht nur sichergestellt werden, dass der nach Deutschland importierte Wasserstoff "grün und nachhaltig" ist, sondern auch die Nachhaltigkeit des globalen Wasserstoffmarktes insgesamt beeinflusst werden. Diese Kurzstudie untersucht, welche bereits existierenden Politikinstrumente geeignet sind, Nachhaltigkeitskriterien für Wasserstoffimporte zu verankern und im Zusammenspiel den Weg zu einem nachhaltigen globalen Wasserstoffmarkt zu unterstützen. Dabei werden ausschließlich Nachhaltigkeitsziele und -kriterien jenseits der Klimawirkung von Wasserstoff analysiert. Es ist unbestritten, dass das zentrale Ziel der Wasserstoffwirtschaft die Reduktion von Treibhausgasen bis hin zur Klimaneutralität ist, was bereits in einer Vielzahl von Studien und Stellungnahmen diskutiert wurde. Daher wird in dieser Studie von der Klimaneutralität des grünen Wasserstoffs ausgegangen, um den Fokus auf die anderen wesentlichen Nachhaltigkeitsaspekte zu lenken, die für den Import von grünem und nachhaltigen Wasserstoff aus dem Globalen Süden von entscheidender Bedeutung sind