Sinn und Berechtigung von Modellversuchen in der Geomechanik-Forschung

ZusammenfassungSinn und Berechtigung von Modellversuchen in der Geomechanik-Forschung Modellstudien nehmen im Rahmen der geomechanischen Forschung, aber auch in der Praxis (z. B. des Talsperrenbaues), einen bedeutenden Platz ein. Dennoch gibt es ebensoviele Fachleute, welche den Wert von Modellversuchen als methodisch berechtigtes Mittel zur Untersuchung geomechanischer Aufgaben verneinen, wie es überzeugte Verfechter des geomechanischen Versuchswesens gibt.Diese Verschiedenheit der Ansichten scheint zum Teil dadurch bedingt, daß über Sinn und Verwendungszweck, aber auch über die Aussagekraft von Modellversuchen mitunter sehr unklare Vorstellungen herrschen und daß — nicht zuletzt unter dem Einfluß englischer Sprachunschärfe, wo alles unter dem weit gefaßten Terminus model test zusammengeworfen wird — auf diesem Gebiet sehr Verschiedenartiges über einen Kamm geschoren wird. Deshalb wird in der gegenständlichen Darstellung zunächst der Versuch unternommen, einen logisch gegliederten Überblick über die mannigfachen Arten und den verschiedenartigen Gebrauch geomechanischer Modellversuche zu geben. Daran anschließend werden Überlegungen über den jeweils spezifischen Aussagewert und die spezifische Eignung der verschiedenen Modellarten angestellt und, um einen Wertmaßstab zu erhalten, werden diese mit den übrigen methodischen Möglichkeiten verglichen, welche der Forschung und Praxis der Geomechanik abseits von der Modellversuchstechnik zur Verfügung stehen.

---

SummaryPurpose and Justification of Model Tests in Geomechanics Research In the scope of geomechanical research, but also in practice (e. g. in dam construction), model studies play an essential rôle. Nevertheless there are many experts who deny the value of model tests as methodically justified means for investigating geomechanical problems, just as there are ardent defenders for geomechanical experiments.This difference of opinions seems to be conditioned by the fact that very indistinct ideas are existing on purpose and use, but also on the asserting power of model tests, and that — not least under the influence of a certain vagueness of the English linguistic usage, where many different things are being mixed up under the ambiguous term model test — very different notions are treated alike. Therefore the paper tries to give first a logically articulated survey on the manifold kinds and the different use of geomechanical model tests. Then, considerations are made on the pertinent specific value of statement and on the specific suitability of various kinds of models, and — in order to obtain a scale of value — the model tests are compared with the other methodic possibilities, which are at disposal for research and practice in geomechanics, aloof from the technique of model tests.

---

RésuméRaison et justification d'études sur modèle dans les recherches géomécaniques Des études sur modèle reduit jouent un grand rôle dans le cadre de la recherche géomécanique, mais aussi dans la pratique (p. e.: pour la construction des barrages). Cependant beaucoup d'experts n'apprecient pas les essais sur modèle comme outil précieux pour resoudre des problèmes géomécaniques.L'article donne un aperçu sur les différentes méthodes concernant les essais géomécaniques et sur le champ de leur application.La valeur des renseignements obtenus par des essais est comparée avec des résultats par d'autres méthodes utilisées dans la recherche et la pratique de la géomécanique.

---

---

Vortrag, gehalten im Sonderforschungsbereich 77 Felsmechanik der Universität Karlsruhe.     

A history of violence: magma incubation,timing and tephra distribution of the Los Chocoyos supereruption (Atitlán Caldera,Guatemala)

The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization ²³⁸U–²³⁰Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W-Fall (130 ⁺¹⁶/₋₁₄ ka) and I-Fall eruptions (56 ^+8.2/_−7.7 ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for >80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km³ is obtained (volcanic explosivity index VEI > 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America.     

Kinetic biomineralization through microfluidic chip tests

A homogeneous microfluidic chip was used to investigate the pore-scale characteristics during the process of microbially induced calcium carbonate precipitation (MICP). An image-processing scheme was developed to measure the projecting areas of the precipitated calcium carbonate. Calcium carbonate first precipitated on the bacterium side before spreading to the rest of the chip. The distribution of calcium carbonate was more uniform along the length of the microchip than along the width. Raman back-scattering spectroscopy was used to examine the chemical composition of the precipitate, identifying calcite and vaterite as the main mineral phases. Bacterium traces were noted on crystal surfaces in SEM images, suggesting a higher adsorptive capacity for irregular precipitates than well-shaped crystals.

     

Assessment of key transport parameters in a karst system under different dynamic conditions based on tracer experiments: the Jeita karst system,Lebanon

Artificial tracer experiments were conducted in the mature karst system of Jeita (Lebanon) under various flow conditions using surface and subsurface tracer injection points, to determine the variation of transport parameters (attenuation of peak concentration, velocity, transit times, dispersivity, and proportion of immobile and mobile regions) along fast and slow flow pathways. Tracer breakthrough curves (TBCs) observed at the karst spring were interpreted using a two-region nonequilibrium approach (2RNEM) to account for the skewness in the TBCs’ long tailings. The conduit test results revealed a discharge threshold in the system dynamics, beyond which the transport parameters vary significantly. The polynomial relationship between transport velocity and discharge can be related to the variation of the conduit’s cross-sectional area. Longitudinal dispersivity in the conduit system is not a constant value (α?=?7–10 m) and decreases linearly with increasing flow rate because of dilution effects. Additionally, the proportion of immobile regions (arising from conduit irregularities) increases with decreasing water level in the conduit system. From tracer tests with injection at the surface, longitudinal dispersivity values are found to be large (8–27 m). The tailing observed in some TBCs is generated in the unsaturated zone before the tracer actually arrives at the major subsurface conduit draining the system. This work allows the estimation and prediction of the key transport parameters in karst aquifers. It shows that these parameters vary with time and flow dynamics, and they reflect the geometry of the flow pathway and the origin of infiltrating (potentially contaminated) recharge.     

Economic,institutional and technological uncertainties of emissions trading—a system dynamics modeling approach

System dynamics models are employed for analyzing the impact of different uncertainties on carbon emission trading–both on national and business levels. Economic, institutional and technological uncertainties significantly influence any country's benefits from emission permit trading. If a country participates in trading on the international market then the possible price range becomes the source of additional uncertainty. In the case of business investment decisions for implementing resource‐saving technology, our system dynamics model shows that the first‐mover investor will get significantly fewer advantages than his followers, which leads to delay in primary investment to the sector.     

An improved fast level set method initialized with a combination of k-means clustering and Otsu thresholding for unsupervised change detection from SAR images

Detection of changes in synthetic aperture radar (SAR) images is an important challenge due to the effects of speckle noise on these images. In recent years, appropriate methods for SAR-based-change detection have been developed based on the level set methods (LSM). These methods need to set parameters for defining a proper initial contour. Moreover, the gradient information is only employed in the total energy of these methods for segmentation of the difference image. In this study, a novel method has been proposed for unsupervised change detection of multitemporal SAR images based on the improved fast level set method (IFLSM) initialized with a combination of k-means and Otsu techniques. The proposed method utilizes the discrete wavelet transform (DWT) fusion strategy and edge enhancement to achieve a noise-resistant difference image from the mean-ratio and log-ratio images. Afterward, the generated binary change map (CM) by applying a combination of k-means and Otsu techniques on the difference image is used as the initial contour to achieve a final CM on difference image using the IFLSM. To check advantages of the proposed method, experiments are applied on two sets of multitemporal SAR images corresponding to artificial Chitgar Lake (under reconstruction) in Tehran (Iran) taken by TerraSAR-X satellite in 2011 and 2012, and corresponding to San Pablo and Briones reservoirs in California (USA) acquired by ERS-2 satellite in 2003 and 2004. Results of proposed method were compared with results of some well-known unsupervised change detection methods. Experimental results prove the sufficiency of the proposed method in unsupervised change detection in terms of accuracy, implementation time, and computational complexity.