Several hydraulic loadings impose earthen levees to time-dependent variably saturated seepage conditions. The main objective of this study is to improve the analysis of levees under transient seepage with the use of unsaturated soil mechanics. An extensive set of laboratory testing, field monitoring and numerical modeling are performed to analyze a silty sand setback levee located near Seattle, WA. In-situ data obtained from field monitoring are used to monitor suction and effective stress within the levee’s embankment and foundation over the past two years. Soil samples taken from the site are used to perform index, water retention, and unsaturated multi-stage triaxial tests in the laboratory. A finite element model of transient seepage under saturated-unsaturated conditions is then developed and calibrated to reasonably match the field data. The results highlight the need to consider unsaturated soil mechanics along with climatic variables and soil-atmosphere interaction when analyzing levees under transient seepage conditions.

<p dir="ltr">Biorefineries rely on compression feed screws to transport biomass for biofuel production in chemical reactors. However, flowability issues within these feedscrews often lead to production downtime, impacting profitability. Modeling biomass flow within the feedscrews is crucial to optimize processing parameters like torque and speed, reducing downtime. Biomass is a non-uniform granular material which faces flowability issues. The problems in flowability is influenced by factors such as particle size, moisture content, material composition, and processing methods. Identifying key parameters that can influence the material behavior is vital to minimize production downtimes. Feedscrews operate under high pressures which makes obtaining accurate material parameters at these high pressures challenging. Many methods used within the pharmaceutical industry to obtain material parameters are unable to reach the larger pressures that the material experiences within the feedscrew. However, Triaxial testing can be used to test the material at the high pressure of interest. Triaxial testing has been used within the civil engineering field to test granular materials such as soils, sand, and rocks. The Finite Element Method (FEM) using a continuum model is used for modeling systems with a large number of particles. The modified Drucker-Prager Cap (mDPC) continuum model is often used to capture complex material behavior, including densification and shear yielding in granular materials. This model seems well suited to capture the behaviors of biomass material. The focus of the thesis is to obtain the shear failure properties of corn stover using triaxial testing and the Drucker-Prager Cap continuum model. Simulations and experimental data are utilized to establish a criterion for identifying shear failure. While simulations depict ideal behavior of a DPC material with frictionless and frictional platens, experimental data shows trends of real-life corn stover. Simulation results effectively predict the material’s friction angle but show larger errors in estimating cohesion, potentially due to extrapolation or cohesion’s sensitivity to volumetric plastic strain. Further simulations at smaller hydrostatic unloading pressures are recommended to reduce this error. Experimental trends for shear failure seem to align with simulation trends for shear failure identification. However, the densification trends in experiments lack the clarity observed in the trends from the simulations. More triaxial experiments should be run to determine if the trends are consistent at other hydrostatic loading and unloading pressures. More than two experiments at the same hydrostatic loading pressure should also be run to estimate the shear failure line to obtain a better estimation. Experimentally there are a number of other factors that could contribute to errors such as the estimated material diameter used to calculate Mises stress, if corrections were made for items such as the moving piston, latex membrane, and more, and how far the shear failure line is extrapolated to the vertical axis.</p>

In dieser Arbeit wird das Tragverhalten von Leichtbeton unter mehraxialer Druckbeanspruchung behandelt. Zu diesem Zweck wurden zahlreiche Versuche mit verschiedenen Hochleistungsleichtbetonen in einer Triaxial-Prüfmaschine durchgeführt. Als Leichtzuschlag wurde Blähton verwendet. Die hergestellten Betone können in Festigkeitsklassen zwischen LC 35/38 und LC 80/88 eingeordnet werden. Bei den Hauptversuchen wurden vor allem die Bruchbilder, die Bruchfestigkeiten und die Prüfkörperverformungen registriert und analysiert. Im Rahmen der Auswertung der Versuche werden die Einflüsse von Matrix und Art des Leichtzuschlages auf die Bruchwerte und auf das Ver-formungsverhalten der Leichtbetone herausgearbeitet. Parallelen und Unterschiede zu bekannten Forschungsergebnissen an Leichtbetonen und zu Beton mit Normalzuschlägen werden aufgezeigt. Für die mathematische Beschreibung der Bruchwerte werden Näherungsfunktionen für zweiaxiale und für dreiaxiale Druckspannungskombinationen vorgeschlagen. / In this research the behaviour of lightweight concrete under multiaxial compression was investigated. Therefore more than 500 single tests were performed in a triaxial testing machine. The high performance lightweight aggregate concretes can be classified in Strength classes between LC 35/38 and LC 80/88. The main focuses in the evaluation of the experiments were the crack pattern, the fracture strength and the deformations. Especially the influences of type of matrix and type of lightweight aggregate on the fracture values and on the deformation behaviour of lightweight were identified. Parallels and differences to known research on lightweight concretes and concrete with normal aggregates were identified. For the mathematical description of the ultimate loads approximations were proposed for biaxial and triaxial compressive stress combinations.

In dieser Arbeit wird das Tragverhalten von Leichtbeton unter mehraxialer Druckbeanspruchung behandelt. Zu diesem Zweck wurden zahlreiche Versuche mit verschiedenen Hochleistungsleichtbetonen in einer Triaxial-Prüfmaschine durchgeführt. Als Leichtzuschlag wurde Blähton verwendet. Die hergestellten Betone können in Festigkeitsklassen zwischen LC 35/38 und LC 80/88 eingeordnet werden. Bei den Hauptversuchen wurden vor allem die Bruchbilder, die Bruchfestigkeiten und die Prüfkörperverformungen registriert und analysiert. Im Rahmen der Auswertung der Versuche werden die Einflüsse von Matrix und Art des Leichtzuschlages auf die Bruchwerte und auf das Ver-formungsverhalten der Leichtbetone herausgearbeitet. Parallelen und Unterschiede zu bekannten Forschungsergebnissen an Leichtbetonen und zu Beton mit Normalzuschlägen werden aufgezeigt. Für die mathematische Beschreibung der Bruchwerte werden Näherungsfunktionen für zweiaxiale und für dreiaxiale Druckspannungskombinationen vorgeschlagen. / In this research the behaviour of lightweight concrete under multiaxial compression was investigated. Therefore more than 500 single tests were performed in a triaxial testing machine. The high performance lightweight aggregate concretes can be classified in Strength classes between LC 35/38 and LC 80/88. The main focuses in the evaluation of the experiments were the crack pattern, the fracture strength and the deformations. Especially the influences of type of matrix and type of lightweight aggregate on the fracture values and on the deformation behaviour of lightweight were identified. Parallels and differences to known research on lightweight concretes and concrete with normal aggregates were identified. For the mathematical description of the ultimate loads approximations were proposed for biaxial and triaxial compressive stress combinations.