Under natural conditions, soil consists of three phases: soil particles (e.g. sand grains), water and air. Above the groundwater level, the soils are usually in an unsaturated state, in which the individual soil particles are connected to one another via capillary bridges. In unsaturated soils, the cohesion of the grain structure is significantly influenced by what is known as "capillary cohesion". The surface forces of the pore water create suction stresses which additionally press the individual soil grains against one another and in this way lead, among other things, to an increased shear strength of the soil. The size of the suction depends on the degree of saturation of the soil, which is why the capillary pressure-saturation relationship (Water Retention Curve, WRC) is an important key function for characterizing the hydraulic and mechanical behaviour of unsaturated soils. The capillary cohesion disappears both in the dry and in the saturated state and is therefore also referred to as "apparent cohesion". As a result of natural fluctuations in the water content or the degree of saturation of the soil, for example due to precipitation or a rising groundwater level, there is a risk of saturation due to the increasing dissolution of the capillary bridges and the cohesion of the grain structure. The resulting sudden rearrangement of the grain structure is also referred to as capillary collapse and, under certain conditions, can lead to sometimes very large subsidence of a soil. Loosely deposited, fine-grained soils with a metastable structure are particularly at risk in this context. When extracting lignite, large amounts of overburden are produced in opencast mines, which are then stored on dumps. Depending on the extraction and transport technology used for the debris, different types of dump are created. However, what all tilted floors have in common is that, in contrast to naturally grown floors, they are often characterized by a particularly loose storage and represent a special case due to the associated high deformation potential. During the open mining operation, the groundwater must also be pumped to great depths under the opencast mine, which is why, after closure, there are particularly large increases in the groundwater, which are very problematic in terms of capillary collapse. Due to the high risk of capillary collapse, which is difficult to calculate, these areas have so far remained largely unused. As part of the research project, a tilted soil from the German open-cast lignite mine is examined, which consists mainly of medium and fine sand and also contains organic components in the form of coal of different sizes.

Für das Verhalten von einigen natürlichen und technischen Partikel-Fluid-Systemen (PFS) spielt die Temperatur eine entscheidende Rolle. So kann es zur Bildung von Feststoffbindungen (Eis) kommen, wenn die Temperatur unter den Gefrierpunkt bei feuchten oder fluidgesättigten PFS sinkt. Resultierende mechanische Eigenschaften wie Steifigkeit, Fließ- oder Bruchspannungen sind von großer Bedeutung für zahlreiche Anwendungen. Die Hauptziele des Projektes sind: - Entwicklung und Validierung eines mikromechanischen Modells der Feststoffbindung - Beschreibung der mechanischen Eigenschaften von gefrorenen Materialien mit der Diskrete Elemente Methode (DEM)

Soils are natural particle-fluid systems (PFS), in which complex physical, chemical and biological processes,interfacial processes, and phase transitions occur, that are not sufficiently investigated experimentally,well-understood, and that cannot be simulated numerically with sufficient accuracy yet. In technicalPFS certain properties of particles are generated by means of controlled physical, chemical and biologicalprocesses, interfacial processes, and phase transitions (e. g. functionalized particles). Technical PFS alsorequire further research regarding understanding, modelling and process optimization. The problems innatural and technical PFS are partly analogous. Therefore, it is obvious, to investigate processes innatural and technical PFS interdisciplinary in order to reach a benefit of scientific findings. Exactly in thispoint, the originary and the potential of the planned research training group can be seen. The individualdisciplines name, model, and simulate similar processes identically or differently. Especially the lengthscales, on which PFS are investigated experimentally, modelled and simulated are different. By meansof the cooperation with strategical partners and the facilities at TUHH, e. g. electron microscopy, theprocesses are visualized over several length scales. Process models and numerical simulation methods ofthe involved collegiates serve for better understanding and description of complex processes. By means ofthe cooperation and interdisciplinary methodology new findings are expected. A research training groupprovides an optimal framework to reach these objectives. Scientists of the disciplines civil engineering,mechanical engineering and process engineering will focus their research within the guiding topic ”Processesin natural and technical Particle-Fluid Systems“ (PintPFS). Existing competences and resourcesof the involved scientists regarding experimental investigations, modelling and simulation of PFS enablean interdisciplinary research approach that raises expectation of innovations in the following fields:progress in modelling of PFS, better understanding of capillary effects, modelling of erosion, transportand sedimentation processes, development of functionalized particles, as well as development of numericalexperiments for PFS. The training group is supported by visiting scientists and strategical partners,especially Deutsches Elektronen-Synchrotron (DESY) at Hamburg and Helmholtz-Zentrum Geesthacht(HZG). The proposed dissertation projects show the interdisciplinary research approach. To reach theobjectives, the research training group is accompanied by structured qualification and supervision conceptsfor the scholarship holders supporting a fast orientation within the different research topics, anacceleration of work processes, a networking with existing research structures, and the acquisition ofsocial skills.

In diesem Projekt sollen granulare Füllstoffe mittels Wirbelschichtsprühgranulation hergestellt werden. Die Füllstoffe sollen zur Schadensreduktion bei Kollisionen in Schiffsdoppelwände eingebracht werden, wodurch die auf die äußere Wand einwirkende Kraft nach innen übertragen wird und die Energiedissipation durch Bruch des Füllmaterials stattfindet. Das Füllmaterial muss einer Vielzahl von Anforderungen genügen und beispielsweise eine möglichst geringe Masse aufweisen. Zudem soll das Material nicht toxisch sein, sich sehr gut fördern und pumpen lassen und hydrophb sein. Die Herstellung der Granulate erfolgt mit der Wirbelschichtsprühgranulation. Das Grundprinzip besteht darin, dass das fluidisierte Partikelbett mit einem sehr gute Wärme-, Stoff- und Impulstransport einhergeht. Durch das Eindüsen einer Flüssigkeit (Supsension, Lösung, Schmelze) werden die Tropfen fein auf den Partikeln verteilt und ummanteln dadurch den innenliegenden Kern. Durch die Verwendung und Kombination geeigneter Materialien und die Optimierung der Betriebsparameter lassen sich so Granulate mit hoher Energiedissipationsdichte generieren.