The Lumberjack, September 07, 2011

The student newspaper of Humboldt State Universityhttps://digitalcommons.humboldt.edu/studentnewspaper2011/1000/thumbnail.jp

Investigating the Hydrogeotechnical and Microstructural Properties of Cemented Paste Backfill Using the CUAPS Apparatus

Dans l'industrie minière et des minéraux, un grand volume et une large variété de résidus miniers qui se composent de fractions grossières et fines et pouvant être soit réactifs (production d'acide) ou non réactifs sont produits à travers le monde chaque jour. La plupart des opérations minières utilise la fraction grossière des résidus miniers pour le remblayage souterrain alors que les fines sont généralement déposées en surface dans des parcs à résidus ou derrière des digues de retenue. Il est toutefois bien connu que les digues de retenue sont à risque de rupture dû à une fuite, l'instabilité, la liquéfaction et d'un défaut de conception. En outre, les rejets générateurs d‘acidité peuvent causer des dommages importants à l'environnement sous la forme de drainage minier acide en libérant des métaux lourds, s'ils ne sont pas correctement gérés. Pour résoudre ces problèmes, la solution de gestion des résidus miniers est d'adopter une approche qui est techniquement appropriée, économiquement viable, écologiquement durable et socialement responsable. Le remblai cimenté en pâte (RCP) est l'une des plus récentes méthodes novatrices de gestion des résidus et se compose généralement d'un mélange des résidus miniers tout-venant sans deslamage (70-85% solides), un liant hydraulique (3-7% en poids) pour répondre aux critères de stabilité requise et d'eau de mélange (20-25% d'eau). La plupart des travaux de recherche a été jusqu'à présent effectuée en focalisant sur les propriétés physico-chimiques, minéralogiques, mécaniques et microstructurales des RCP. La plupart du temps, des moules en plastique conventionnels non drainés sont généralement utilisés pour déterminer les paramètres de conception du remblai minier en pâte qui dépendent du pourcentage solides, de la granularité des résidus, du type de liant et de sa teneur, et du temps de cure. Toutefois, des études récentes ont montré que pour une même recette de remblai utilisée au laboratoire et in situ après un temps de cure donné, la performance mécanique du remblai préparé au laboratoire était toujours inférieure à celle du remblai in situ. La raison principale derrière ce phénomène est que la cure du remblai en pâte in situ se serait faite sous l'action des contraintes effectives qui se seraient progressivement développées dans le chantier remblayé en raison de leur consolidation (sous poids propre ou par surcharge) et ainsi, entraîne l'amélioration du taux de d‘acquisition de la résistance mécanique finale. La mise en place et les propriétés des remblais in situ ne peuvent être reproduits à l'aide des moules classiques. Par conséquent, il existe un besoin évident de développer de nouveaux équipements et de nouvelles procédures d'essais capables de reproduire de façon réaliste les conditions de cure in situ des remblais cimentés en pâte dans un environnement de laboratoire contrôlé. Dans ce cas le but étant d'être en mesure d'atteindre des résistances mécaniques les plus élevées possibles et/ou au moins équivalentes pour une meilleure conception de remblai. Cette thèse est composée principalement de quatre articles/manuscrits de journaux avec comité de révision par les pairs. Le premier article essaye d'investiguer les différences dans les propriétés hydromécaniques des RCP observées entre les échantillons qui curent dans les conditions de laboratoire et in situ par le biais de la première version d'un nouvel appareil d‘essais en laboratoire appelé CUAPS (système de cure sous pression appliquée). Il aborde substantiellement les propriétés physiques, hydrotechniques et géochimiques d‘échantillons de RCP préparés avec des résidus catégorisés comme grossiers (15 wt% ­< grains de moins de 20 μm < 35 wt%) provenant d'une mine polymétallique européenne. Le deuxième article présente davantage l'évaluation de l'appareil CUAPS modifié qui permet d‘estimer certaines propriétés hydromécaniques des RCP incluant la compression anisotrope (consolidation 1-D) et la perméabilité. L'appareil CUAPS modifié capture bien la déformation axiale qui se produit dans le remblai pendant sa compression (soit par surcharge ou par son poids propre) et cela permet de réaliser des essais de consolidation unidimensionnelle, mais aussi des essais de dissipation de la pression interstitielle, de perméabilité (mesure de la conductivité hydraulique saturée), de cure sous contrainte effective appliquée et de cure sous différents taux de compression. Les résultats préliminaires illustrent bien l'efficacité, l'utilité et la capacité de cet appareil CUAPS modifié dans l'optique de l'optimisation réaliste des recettes de RCP à être utilisées pour le remblayage souterrain. Le troisième article focalise particulièrement sur les propriétés de consolidation unidimensionnelle à l'aide de l'appareil CUAPS modifié. Les échantillons de remblai en pâte ont été préparés avec des résidus catégorisés comme fins (35 wt% ­< grains de moins de 20 μm < 60 wt%). Le quatrième et dernier article présente les résultats de l'étude sur les effets des conditions de cure (consolidée et non consolidée) sur les propriétés microstructurales du RCP au moyen de la porosimétrie par intrusion de mercure (PIM) et la détermination de la surface spécifique. Quelques modèles empiriques de prédiction de la résistance en compression uniaxiale (UCS) en fonction de certains paramètres de la microstructure des RCP ont été proposés. Cette thèse de doctorat a non seulement permis une meilleure compréhension des propriétés des remblais en pâtes préparés en laboratoire, mais il a également permis d'évaluer avec succès l'appareil CUAPS modifié qui peut être un outil précieux pour la collecte de données équivalentes à celles du remblai in situ mais à l'échelle du laboratoire. Ce travail est considéré comme une étude originale qui a investigué le comportement en consolidation unidimensionnelle des échantillons de RCP à différents temps de cure et aussi le comportement d'échantillons de RCP curés sous une série d'incréments de pressions en permettant le développement graduel de la contrainte effective dû au drainage (simulant les chantiers souterrains remblayés). Cette recherche a donc contribué à une meilleure compréhension du comportement de ce matériau relativement complexe qu'est le RCP et a mis au point une procédure d‘essai pour évaluer la performance mécanique qui pourrait être considérée lors du processus de conception de tout remblai cimenté en pâte. Enfin, l'appareil CUAPS modifié aidera les chercheurs et les opérateurs des remblais à mieux comprendre les propriétés de consolidation des CPB frais ou durcis qui devraient être préparés en laboratoire. In the mining and mineral industry worldwide, large volumes and many varieties of mine tailings consisting of coarse and fine fractions that are either reactive (acid generating) or non-reactive are produced every day. Most mining operations use the coarse fraction of the tailings for underground backfill, while the fines are usually deposited on the surface into tailings impoundments or dams. However, it is well known that these dams are at risk of failure due to leakage, instability, liquefaction and inadequate design. Moreover, unless they are properly managed, acid-generating tailings can cause significant environmental damage by generating acid mine drainage that releases heavy metals. Overcoming such problems requires tailings management approaches that are technically suitable, economically viable, environmentally sustainable and socially responsible. Cemented paste backfill (CPB), an engineering material, is used in a recent, innovative tailings management method. Typically, CPB is a mixture of total mill tailings without removing the fines, or desliming (70–85 wt% solids), and single, binary and ternary hydraulic binders (3–7 wt%) in order to meet stability requirements and combined with mixing water (20–25 wt%). Most studies to date have focused on the physicochemical, mineralogical, mechanical and microstructural properties of CPB. Conventional undrained plastic moulds (non-perforated) are usually used to determine mine backfill design parameters, depending on the solid mass concentration, grain size grading, binder type and content, and curing time. However, recent studies have shown that for identical backfill recipes used in the laboratory and in situ after a given curing time, the performance (i.e., mechanical strength) of laboratory-prepared CPB samples is consistently lower than that obtained from in situ CPB samples. The primary reason is that in situ backfill material is cured under effective stresses that develop gradually in a stope due to self-weight and/or time-dependent consolidation loads, which accelerate the rate of final strength development. In situ CPB placement and properties cannot be replicated using conventional moulds. Therefore, innovative equipment and test procedures that allow realistic reproduction of in situ curing conditions of CPB materials in a controlled laboratory setting are needed. The aim is to obtain higher or at least equivalent mechanical strength, and consequently a better backfill design

Community, society and adaptation: Assessing the institutional factors behind long-run growth in the local and regional economy.

The purpose of this thesis is to develop and test a framework on the role and dynamic interaction of group life (community) and societal rules (society) as one of the factors shaping patterns of economic growth and adaptation. Cross-country regression analysis is undertaken to determine the significance of the relationships between community and society (individually and jointly) and various institutional factors. Following this, two pairs of comparative city-region case studies explore how these dynamics play out in specific geographical and institutional contexts. The findings confirm the importance of the interaction between community and society in shaping individual incentives and territorial responses to change. In general, 'bridging' forms of community and strong societal rules facilitate positive outcomes, whilst 'bonding' forms of community have broadly negative impacts on growth and adaptation. Critically, the significance and impact of community appears to be dependent on the societal environment in which it operates. Community matters most when society is weakest, but community is not simply a substitute for rules; indeed community and society appear to potentiate positive outcomes in important cases, for example near the technology frontier. Diversity - of sectors, groups, and institutions - appears to be particularly important in facilitating positive forms of community and society interaction, and in promoting adaptive economies. Overall, there is strong recursivity in the relationships, suggesting path dependency (lock-in or evolution) may be the norm. The study contributes to understanding the 'black box' of institutions, particularly within the context of regional economies, and underlines the importance of the role of community- level forces and political economy in processes of economic growth and adjustment. It suggests there is value in pursuing the role of institutions still further, and exploring in more detail the agenda of an evolutionary economic geography

System of Terrain Analysis, Energy Estimation and Path Planning for Planetary Exploration by Robot Teams

NASA’s long term plans involve a return to manned moon missions, and eventually sending humans to mars. The focus of this project is the use of autonomous mobile robotics to enhance these endeavors. This research details the creation of a system of terrain classification, energy of traversal estimation and low cost path planning for teams of inexpensive and potentially expendable robots. The first stage of this project was the creation of a model which estimates the energy requirements of the traversal of varying terrain types for a six wheel rocker-bogie rover. The wheel/soil interaction model uses Shibly’s modified Bekker equations and incorporates a new simplified rocker-bogie model for estimating wheel loads. In all but a single trial the relative energy requirements for each soil type were correctly predicted by the model. A path planner for complete coverage intended to minimize energy consumption was designed and tested. It accepts as input terrain maps detailing the energy consumption required to move to each adjacent location. Exploration is performed via a cost function which determines the robot’s next move. This system was successfully tested for multiple robots by means of a shared exploration map. At peak efficiency, the energy consumed by our path planner was only 56% that used by the best case back and forth coverage pattern. After performing a sensitivity analysis of Shibly’s equations to determine which soil parameters most affected energy consumption, a neural network terrain classifier was designed and tested. The terrain classifier defines all traversable terrain as one of three soil types and then assigns an assumed set of soil parameters. The classifier performed well over all, but had some difficulty distinguishing large rocks from sand. This work presents a system which successfully classifies terrain imagery into one of three soil types, assesses the energy requirements of terrain traversal for these soil types and plans efficient paths of complete coverage for the imaged area. While there are further efforts that can be made in all areas, the work achieves its stated goals

LHUFT Bibliography January 2020

Subject headings have been updated to reflect current Library of Congress standards

Analysis of a Three-Dimensional Railway Vehicle-Track System and Development of a Smart Wheelset

Wheel flats are the sources of high magnitude impact forces at the wheel-rail interface, which can induce high levels of local stresses leading to fatigue damage, and failure of various vehicle and track components. With demands for increased load and speed, the issue of wheel flats and a strategy for effective maintenance and in-time replacement of defective wheels has become an important concern for heavy haul operators. A comprehensive coupled vehicle-track model is thus required in order to predict the impact forces and the resulting component stresses in the presence of wheel flats. This study presents the dynamic response of an Euler- Bernoulli beam supported on two-parameter Pasternak foundation subjected to moving load as well as moving mass. Dynamic responses of the beam in terms of normalized deflection and bending moment have been investigated for different velocity ratios under moving load and moving mass conditions. The effect of moving load velocity on dynamic deflection and bending moment responses of the beam have been investigated. The effect of foundation parameters such as, stiffness and shear modulus on dynamic deflection and bending moment responses have also been investigated for both moving load and moving mass at constant speeds. This dissertation research concerns about modeling of a three-dimensional railway vehicle- track model that can accurately predict the wheel-rail interactions in the presence of wheel defects. This study presents a three-dimensional track system model using two Timoshenko beams supported on discrete elastic supports, where the sleepers are considered as rigid masses, and the rail pad and ballast as spring-damper elements. The vehicle system is modeled as a three-dimensional 17- DOF lumped mass model comprising a full car body, two bogies and four wheelsets. The railway track is modeled as a pair of three-dimensional flexible beams that considers two parallel Timoshenko beams periodically supported by lumped masses representing the sleepers. The wheel-rail contact is modeled using nonlinear Hertzian contact theory. The developed model is validated with the existing measured data and analytical solutions available in literature. The nonlinear model is then employed to investigate the wheel-rail impact forces that arise in the wheel-rail interface due to the presence of single as well as multiple wheel flats. The effects of single and multiple wheel flats on the responses of vehicle and track components in terms of displacements and acceleration responses are investigated for both defective wheel and the flat-free wheel. The characteristics of the bounce, pitch and roll motions of the bogie due to a single wheel flat are also investigated. The study shows that nonlinear railpad and ballast model gives better prediction of the wheel-rail impact force than that of the linear model when compared with the experimental data. The results clearly show that presence of wheel flat within the same wheelset has significant effect on the impact force, displacement and acceleration responses of that wheelset. This study further presents the modeling of a MEMS based accelerometer in order to detect the presence of a wheel flat in the railway vehicle. The proposed accelerometer can survive in a dynamic shock environment with acceleration up to ±150g. Simulations of the accelerometer are performed under various operating conditions in order to determine the optimum configuration

Integrating Socially Assistive Robots into Language Tutoring Systems. A Computational Model for Scaffolding Young Children's Foreign Language Learning

Schodde T. Integrating Socially Assistive Robots into Language Tutoring Systems. A Computational Model for Scaffolding Young Children's Foreign Language Learning. Bielefeld: Universität Bielefeld; 2019.Language education is a global and important issue nowadays, especially for young children since their later educational success build on it. But learning a language is a complex task that is known to work best in a social interaction and, thus, personalized sessions tailored to the individual knowledge and needs of each child are needed to allow for teachers to optimally support them. However, this is often costly regarding time and personnel resources, which is one reasons why research of the past decades investigated the benefits of Intelligent Tutoring Systems (ITSs). But although ITSs can help out to provide individualized one-on-one tutoring interactions, they often lack of social support. This dissertation provides new insights on how a Socially Assistive Robot (SAR) can be employed as a part of an ITS, building a so-called "Socially Assistive Robot Tutoring System" (SARTS), to provide social support as well as to personalize and scaffold foreign language learning for young children in the age of 4-6 years. As basis for the SARTS a novel approach called A-BKT is presented, which allows to autonomously adapt the tutoring interaction to the children's individual knowledge and needs. The corresponding evaluation studies show that the A-BKT model can significantly increase student's learning gains and maintain a higher engagement during the tutoring interaction. This is partly due to the models ability to simulate the influences of potential actions on all dimensions of the learning interaction, i.e., the children's learning progress (cognitive learning), affective state, engagement (affective learning) and believed knowledge acquisition (perceived learning). This is particularly important since all dimensions are strongly interconnected and influence each other, for example, a low engagement can cause bad learning results although the learner is already quite proficient. However, this also yields the necessity to not only focus on the learner's cognitive learning but to equally support all dimensions with appropriate scaffolding actions. Therefore an extensive literature review, observational video recordings and expert interviews were conducted to find appropriate actions applicable for a SARTS to support each learning dimension. The subsequent evaluation study confirms that the developed scaffolding techniques are able to support young children’s learning process either by re-engaging them or by providing transparency to support their perception of the learning process and to reduce uncertainty. Finally, based on educated guesses derived from the previous studies, all identified strategies are integrated into the A-BKT model. The resulting model called ProTM is evaluated by simulating different learner types, which highlight its ability to autonomously adapt the tutoring interactions based on the learner's answers and provided dis-engagement cues. Summarized, this dissertation yields new insights into the field of SARTS to provide personalized foreign language learning interactions for young children, while also rising new important questions to be studied in the future