The primary focus of this research is to evaluate the time-dependent crack growth in rocks using lab tests and numerical modeling and its application to geologic hazard problems. This research utilized Coconino sandstone and Columbia granite as the study materials and produced the subcritical crack growth parameters in both mode I and II loadings using the rock materials. The mode I loading test employs three different types of fracture mechanics tests: the Double Torsion (DT), the Wedge Splitting (WS), and the Double Cantilever Beam (DCB) test. Each test measured the mode I crack velocity. The DT test indirectly measured the crack velocity using the load relaxation method. The WS and DCB tests directly measured the crack velocity by monitoring using a video recording. The different mode I subcritical crack growth parameters obtained from the three tests are discussed. For the mode II loading test, this study developed a new shear fracture toughness test called the modified Punch-Through Shear (MPTS). The MPTS test conducted at different loading rates produced the mode II subcritical crack growth parameters. These fracture mechanics tests were calibrated and simulated using the distinct element method (DEM) and the finite element method (FEM). DEM analysis employed the particle flow code (PFC) to simulate the mixed mode crack growth and to match with the failure strength envelop of the triaxial compressive tests. FEM analysis employed the Phase2 program to analyze the crack tip stress distribution and the FRANC2D program to calculate the modes I and II stress intensity factors. The fracture mechanics tests and numerical modeling showed well the dependency of the mode II subcritical crack growth parameters according to confining pressure, loading rate, and the mode II fracture toughness. Finally, the UDEC modeling based on DEM is utilized in this study to forecast the long-term stability of the Coconino rock slope, as one of geologic hazards. The fracture mechanics approach is implemented in the program using the modes I and II subcritical crack growth parameters obtained from the lab tests and numerical modeling. Considering the progressive failure of rock bridges due to subcritical crack growth, the UDEC results predicted the stable condition of the Coconino rock cliff over 10,000 years. This result was validated by comparing it with the previous planar failure case.

Methane gas hydrates have attracted significant international interest as a potential future energy resource, but also as a geotechnical hazard for offshore operations related to hydrocarbon recovery. In this context, the abilities to detect the presence of hydrate in marine sediments and to quantify the amount of hydrate contained therein, have become increasingly important over the years. Detection and quantification of hydrates are done on the basis of seismic surveys, which measure indirectly the bulk dynamic properties of large volumes of sediment in situ. Seismic data are then interpreted using an effective medium model, which employs theoretical assumptions to relate wave velocities to gas hydrate content of the sediment. Wave velocity can then be used to infer hydrate concentration levels. A host of such effective medium models exists in the literature. Many of these models have been calibrated on and tested on specific sites, and are not readily transferable to other settings. In addition, many models ignore the existence of heterogeneities of the host sediment, or the inhomogeneous distribution of hydrate within it. These, however, are factors that may have a significant impact on the seismic signature of the sediment-hydrate system, and thus on the predicted quantity of hydrate. This paper presents a review of existing effective medium models and identifies general areas for improvement. A new numerical modelling method is outlined that enhances existing effective medium approaches, by taking explicitly into account different hydrate morphologies within the host sediment.

This thesis concerns the computation of bed adjustments of equilibrium in alluvial meandering streams. It is assumed that the channel centerlines follow sine-generated curves, the banks are rigid, and the steady-state flow is turbulent and sub-critical. The flow width is assumed to remain constant in the streamwise direction, and the flow width-to-depth ratio is large (>=15, say). The bed material is cohesionless and homogeneous. The purpose of the thesis is to develop and test a numerical model for the computation of bed development, given the aforementioned idealized conditions. The model comprises: 1- an initial bed topography generator, to generate the bed at time t = 0 of the calculations; 2- the vertically-averaged hydrodynamic model of Zhang (2007) to calculate the flow fields; and 3- a sediment transport model to relate the bed deformation to the flow. Both the initial bed topography generator (expression of the deformed bed surface) and the numerical sediment transport model based on the sediment transport continuity equation are original and developed entirely by the author. The resulting model is computationally very efficient. In contrast to previous works on the theoretical determination of bed deformation, the beds at the beginning of the calculations may represent any stage of the development process, and not necessarily the initial flat bed. The bed deformation was tested for several test cases, devised on the basis of laboratory runs available in the literature. These include Run ME-2 by Hasegawa (1983) in a 30-degree-channel, Run 3 by Binns (2006) in a 70-degree-channel and the run by Termini (1996) in a 110-degree-channel. The erosion/deposition patterns of the computed equilibrium bed topographies were found to be in reasonable agreement with their measured counterparts. However, as evidenced by the difference plots included in this thesis, in detail there are substantial differences between the computed and measured equilibrium beds, especially in the regions near the banks. As a by-product of the present thesis, the functions representing the parameters required by the hydrodynamic model of Zhang (2007) were also evaluated. In particular, the present results suggest that the coefficient Alpha-q appearing in the expression of the local friction factor (used in the flow model of Zhang 2007) depends on the flow width-to-depth ratio and bed roughness to a much larger extent than previously thought. Considering this, a generalization of the expression of Alpha-q due to El-Tahawy (2004) (and adopted by Zhang 2007 in her model) is proposed. Future work should be carried out to address the application of the present model to real river conditions, including generalizations to irregular meandering plan shapes, unsteady-state flows and non-homogenous bed materials. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2008-12-19 21:32:06.645

Groundwater is an important resource that is relied on by approximately half of the world’s population for drinking water supply. Source water protection efforts rely on an understanding of flow and contaminant transport processes in aquifers. Bedrock aquifers are considered to be particularly vulnerable to contamination if the overburden cover is thin or inadequate. The objective of this study is to further the understanding of modeling, sampling, and the potential for anthropogenic contamination in fractured bedrock aquifers. Two numerical modeling studies were conducted to examine geochemical groundwater sampling using multi-level piezometers and the role of discretization in a discrete fracture radial transport scenario. Additionally, two field investigations were performed to study the variability of bacterial counts in pumped groundwater samples and the potential for anthropogenic contamination in a bedrock aquifer having variable overburden cover in a semi-urban setting. Results from the numerical modeling showed that choosing sand pack and screen materials similar in hydraulic conductivity to each other and the fractures intersecting the borehole can significantly reduce the required purge volume. Spatiotemporal discretization was found to be a crucial component of the numerical modeling of solute transport and verification of the solution domain using an analytical or semi-analytical solution is needed. Results from the field investigations showed fecal indicator bacterial concentrations typically decrease on the order of one to two orders of magnitude from the onset of pumping. A multi-sample approach that includes collection at early-time during the purging is recommended when sampling fecal indicator bacteria for the purpose of assessing drinking water quality. Surface contaminants in areas with thin or inadequate overburden cover can migrate quickly and deeply into the bedrock aquifer via complex fracture networks that act as preferential pathways. While the presence of fecal indicator bacteria in groundwater samples signifies a possible health risk through human consumption, it was the suite of pharmaceuticals and personal care products that allowed the identification of septic systems and agriculture as the dominant sources of contamination. Land-use planning and source water protection initiatives need to recognize the sensitivity of fractured bedrock aquifers to contamination. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-02-28 17:27:54.806

Water resource infrastructure in cold regions of the world can be significantly impacted by the existence of river ice. Major engineering concerns related to river ice include ice jam flooding, the design and operation of hydropower facilities and other hydraulic structures, water supplies, as well as ecological, environmental, and morphological effects. The use of numerical simulation models has been identified as one of the most efficient means by which river ice processes can be studied and the effects of river ice be evaluated. The continued advancement of these simulation models will help to develop new theories and evaluate potential mitigation alternatives for these ice issues. In this thesis, a literature review of existing river ice numerical models, of anchor ice formation and modeling studies, and of aufeis formation and modeling studies is conducted. A high level summary of the two-dimensional CRISSP numerical model is presented as well as the developed freeze-up model with a focus specifically on the anchor ice and aufeis growth processes. This model includes development in the detailed heat transfer calculations, an improved surface ice mass exchange model which includes the rapids entrainment process, and an improved dry bed treatment model along with the expanded anchor ice and aufeis growth model. The developed sub-models are tested in an ideal channel setting as somewhat of a model confirmation. A case study of significant anchor ice and aufeis growth on the Nelson River in northern Manitoba, Canada, will be the primary field test case for the anchor ice and aufeis model. A second case study on the same river will be used to evaluate the surface ice components of the model in a field setting. The results from these cases studies will be used to highlight the capabilities and deficiencies in the numerical model and to identify areas of further research and model development.

The Alpha Magnetic Spectrometer is an International Space Station Experiment that features a unique nonlinear support system with no previous flight heritage. The experiment consists of multiple straps with piecewise-linear stiffness curves that support a cryogenic magnet in three-dimensional space inside of a vacuum chamber. The stiffness curves for each strap are essentially bilinear and switch between two distinct slopes at a specified displacement. This highly nonlinear support system poses many questions in regards to feasible computational methods of analysis and possible response behavior. This thesis develops a numerical model for a multi-bilinear-spring support system motivated by the Alpha Magnetic Spectrometer design. Methods of analysis applied to the single bilinear oscillator served as the foundation of the model developed in this thesis. The model is developed using MATLAB and proves to be more computationally efficient than ANSYS finite element software. Numerical simulations contained herein demonstrate the variety of response behaviors possible in a multi-bilinear-spring support system, thus aiding future endeavors which may use a support system similar to the Alpha Magnetic Spectrometer. Classic nonlinear responses, such as subharmonic and chaotic, were found to exist.

There is a growing need to better understand the relationship between time, strain rate, and temperature on the load-deformation behaviour of clay soils in engineering applications. These applications may include: infrastructure constructed in northern regions where climate change is a growing concern; disposal of nuclear waste; and, industrial structures, such as furnaces, foundries, and refrigeration plants. Temperature variations may induce changes in internal pressure in the soil, swelling and shrinkage, and affect the mechanical properties of the soil. This thesis presents thermal numerical modeling for two instrumented field sites in northern Manitoba. Thermal conductivity testing on samples from these sites and field data are used to calibrate these thermal numerical models. Various boundary conditions are examined. The capabilities of the models are evaluated to determine if the models adequately simulate and predict changes in temperature in geotechnical structures. A discussion is presented on the strengths and weaknesses in the models and the predictive capabilities of the models. The thesis then shifts into understanding the concepts of thermoplasticity and viscoplasticity and the mathematics relating these concepts. Mathematical models that describe these concepts are examined and compared with traditional soil mechanics approaches. The concepts of thermoplasticity and viscoplasticity are combined in an encompassing elastic thermo-viscoplastic (ETVP) model using a semi-empirical framework. A sensitivity analysis is used to evaluate quantitatively the response of the model. The model is then validated qualitatively against published laboratory data. Applications of the ETVP model are discussed.

Water resource infrastructure in cold regions of the world can be significantly impacted by the existence of river ice. Major engineering concerns related to river ice include ice jam flooding, the design and operation of hydropower facilities and other hydraulic structures, water supplies, as well as ecological, environmental, and morphological effects. The use of numerical simulation models has been identified as one of the most efficient means by which river ice processes can be studied and the effects of river ice be evaluated. The continued advancement of these simulation models will help to develop new theories and evaluate potential mitigation alternatives for these ice issues. In this thesis, a literature review of existing river ice numerical models, of anchor ice formation and modeling studies, and of aufeis formation and modeling studies is conducted. A high level summary of the two-dimensional CRISSP numerical model is presented as well as the developed freeze-up model with a focus specifically on the anchor ice and aufeis growth processes. This model includes development in the detailed heat transfer calculations, an improved surface ice mass exchange model which includes the rapids entrainment process, and an improved dry bed treatment model along with the expanded anchor ice and aufeis growth model. The developed sub-models are tested in an ideal channel setting as somewhat of a model confirmation. A case study of significant anchor ice and aufeis growth on the Nelson River in northern Manitoba, Canada, will be the primary field test case for the anchor ice and aufeis model. A second case study on the same river will be used to evaluate the surface ice components of the model in a field setting. The results from these cases studies will be used to highlight the capabilities and deficiencies in the numerical model and to identify areas of further research and model development.

The magnetic properties and crystal texture of micron-sized, lithographically patterned ferromagnetic/antiferromagnetic (FM/AF) exchange-coupled elements supporting vortex remanent magnetization states were characterized using experimental and numerical modeling techniques. 10umx10um square elements consisting of Ni80Fe20/Ir20Mn80 bilayers prepared on silicon and glass substrates using e-beam lithography and magnetron sputtering were thermomagnetically annealed under various in-plane cooling fields to induce exchange bias. Longitudinal and time-resolved Kerr effect microscopy were employed to measure the quasi-static hysteresis and dynamic response, while X-ray diffraction analysis was used to probe their crystal texture under different deposition and substrate conditions. The FM layer was found to be critical for the development of the necessary texture and spin alignment in the AF for creating interfacial exchange-bias. The exchange-bias field was found to significantly alter the magnetic behavior of the samples, leading to the stabilization of the vortex structure and asymmetric hysteresis loop shift in the quasi-static regime, as well as precessional frequency reduction of the bottom domain in the dynamic regime. Numerical simulations showed good qualitative agreement with both experimental observations and existing literature, and revealed the origin of the precessional frequency reduction as the different spin-wave eigenmodes excited by different remanent magnetization states. / Graduate

Die vorliegende Arbeit umfasst im ersten Teil eine Literaturrecherche zu Aquifer Storage and Recovery (ASR) im Allgemeinen und den Einfluss physikalisch-chemischer Prozesse auf ASR. Aus dieser konnte abgeleitet werden, dass durch standortbedingte Untergrundeigenschaften stark unterschiedliche physikalische und chemische Prozesse ablaufen und eine eindeutige Vorhersage zum Verhalten und zur Effizienz von ASR an einem neuen oder bereits genutzten Standort ohne spezifische Informationen nicht möglich ist. Des Weiteren wurde eine Literaturstudie zum Einfluss der transversalen Dispersivität, als Maß für die Vermischung von transportierten Stoffen quer zu einer (natürlichen) Fließrichtung, auf den (reaktiven) Transport durchgeführt. Letztlich wurde im Rahmen einer betreuten Masterarbeit (M. Sc. Chang Liu) eine Bewertung aus der Literatur entnommener transversaler Dispersivitäten durchgeführt. In den weiteren Teilen der Arbeit wurden Fallstudien mit unterschiedlichen Fragestellungen für die Planung und den Betrieb von künstlichen Grundwasseranreicherungen und speziell ASR numerisch modelliert und bewertet. Zuerst wurden numerische Simulationen zum konservativen Transport am Testfeld „Lauswiesen“, Tübingen, Baden-Württemberg durchgeführt. Diese beinhalteten über Direct-Push(DP)-Erkundungsmethoden gewonnene Informationen zur Untergrundstruktur. Die Ergebnisse zeigen, dass zur Vorhersage des standortspezifischen Transports in den „Lauswiesen“ und für vergleichbare hydraulische Situationen, auch in Hinsicht auf ASR, deterministische hydrogeologische Einheiten und ihre situationsgerechte Berücksichtigung in numerischen Modellen höchst relevant sind. Aufbauend auf den genannten Ergebnissen wurde eine Masterarbeit durch Herrn M. Sc. Tsegaye Abera Sereche durchgeführt. Diese Masterarbeit zeigte für diesen Fall erneut die hohe Relevanz deterministischer Strukturen gegenüber kleinskaligen, dreidimensionalen Heterogenitäten für ASR. Weiterführende numerische Simulationen zu einem möglichen ASR-Feldtest am Standort „Lauswiesen“ ergaben, dass dieser unter den gegebenen Untergrundbedingungen nur bei Abweichungen von einem vertretbaren Konzept für einen Ein-Brunnen-Test, z. B. bei sehr großen Infiltrationsmengen, oder durch Umwandlung in einen Zwei-Brunnen-Test durchführbar ist. Während dieser Arbeit wurden gemeinsame Forschungsarbeiten mit dem Kansas Geological Survey, Kansas, USA durchgeführt, welche die Bewertung der Verwendbarkeit von DP-Brunnen als alternative Infiltrationsmethode zu Oberflächenmethoden beinhalteten. Als Teil der gemeinsamen Arbeiten wurde im Rahmen der vorliegenden Arbeit eine synthetisierte, numerische Bewertung der neuen DP-Infiltrationsbrunnen sowie einen Vergleich mit einer herkömmlichen Oberflächeninfiltrationsmethode übernommen. Im Einklang mit der Zielstellung der Arbeit wurde ebenfalls eine numerische Bewertung natürlicher und anthropogener Heterogenitäten auf die Infiltration durchgeführt. Aus den Ergebnissen konnten für die neue Infiltrationsmethode signifikante Vorteile abgeleitet werden. Weitere numerische Modellierungen wurden durchgeführt, um die wesentlichen Ergebnisse auf einen Feldstandort in der Südlichen Steiermark, Österreich, anzuwenden, welcher: a) bereits ein horizontales Versickerungssystem besitzt, b) weitere Systeme erhalten soll und c) letztlich eine besondere Herausforderung für vertikale Versickerungssysteme darstellt. Die Modellierung des vorhandenen Systems zeigt die hohe Komplexität der Infiltrationsprozesse. Jedoch konnten hydraulische Parameter bestätigt und in weitere planerische Simulationen zu Verwendung von DP-basierten Infiltrationsbrunnen eingefügt werden. Diese zeigen, dass ein Brunnenfeld am Standort auf relativ geringem Raum installiert werden kann. Zusätzlich zeigt ein Feldversuch an einem weiteren Standort (Pirna, Sachsen), dass hohe Infiltrationsraten unter Nutzung von DP-Brunnen möglich sind. / The works presented in the thesis include in the first part a literature research on Aquifer Storage and Recovery (ASR) in general and the impacts of different physico-chemical processes on ASR. This research concludes that site-specific subsurface conditions lead to varying physical and chemical processes and that a conclusive prediction of function and efficiency of ASR at any site, in-operation or new site design, is not possible without site-specific information. Additionally, a literature study was conducted that focused on the impacts of transverse dispersivity, as a measure for mixing of transported species perpendicular to the (natural) flow direction, on (reactive) transport. Finally, evaluation of transverse dispersivity data available in the literature was performed, which included a supervision of a master thesis (of M. Sc. Chang Liu). Numerical simulations of case studies for different questions of planning and operation of artificial recharge systems and more specifically ASR were realized for the other parts of the thesis. The first evaluated case was the “Lauswiesen” test site, Tübingen, Baden-Wuerttemberg. This study used new insights into the subsurface structure gained by Direct-Push(DP) exploration methods. The results obtained show that for further works at the site and for comparable hydraulic conditions, also in the view of ASR, deterministic hydrogeological subunits and their consideration in numerical models are critical for prediction of site-specific transport. Based on the previous findings, a master thesis was conducted by M. Sc. Tsegaye Abera Sereche. The master thesis yet again revealed for this case the high relevance of deterministic subunits compared to small-scale, three-dimensional heterogeneities for ASR. Further, numerical simulations of a possible ASR field test at “Lauswiesen” site showed that under the prevailing subsurface conditions, a field test can only be realized when the set-up of a single-well-test is impracticably changed, by e.g. very high infiltration volumes, or by transformation into a two-well-test. During the thesis joint research works were performed with the Kansas Geological Survey, Kansas, USA, which contained the evaluation of the applicability of DP wells as an alternative to surface infiltration methods. As part of the joint work, this thesis presents a synthesized numerical evaluation of the new DP well infiltration as well as a comparison to a common surface infiltration system. Furthermore, in accordance with the main objective of the work, numerical evaluation of natural and anthropogenic heterogeneities was performed. The results concluded the advantages for the DP wells for infiltration process. Further numerical models were implemented to convey the important results to a field site at Southern Styria, Austria, where: a) an existing infiltration system is already in operation, b) further infiltration systems are planned and c) the subsurface conditions are rather challenging for vertical infiltration systems. Modeling of the existent system revealed the high complexity of the infiltration processes. However, hydraulic parameters could be verified and included into planning simulations for DP-based infiltration wells. The findings show, that a well field can be installed at a comparably small land. Additionally, a field test at a further test site (Pirna, Sachsen) indicates that high infiltrations rates are possible when DP wells are used.