Mining candidate causal relationships in movement patterns

This is an Accepted Manuscript of an article published by Taylor & Francis in the International Journal of Geographical Information Science on 01 October 2013, available online: http://wwww.tandfonline.com/10.1080/13658816.2013.841167In many applications, the environmental context for, and drivers of movement patterns are just as important as the patterns themselves. This paper adapts standard data mining techniques, combined with a foundational ontology of causation, with the objective of helping domain experts identify candidate causal relationships between movement patterns and their environmental context. In addition to data about movement and its dynamic environmental context, our approach requires as input definitions of the states and events of interest. The technique outputs causal and causal-like relationships of potential interest, along with associated measures of support and confidence. As a validation of our approach, the analysis is applied to real data about fish movement in the Murray River in Australia. The results demonstrate the technique is capable of identifying statistically significant patterns of movement indicative of causal and causal-like relationships. 1365-8816Australian Research Council Discovery Projec

NUMERICAL MODELING OF ROCK CUTTING AND ITS ASSOCIATED FRAGMENTATION PROCESS USING THE FINITE ELEMENT METHOD

As the need for reaching fuel reserves at greater depths increases, over the past 30 years scientists have been exploring and developing the technology required to efficiently drill rock at highly pressured environments; yet, there are still gaps in the understanding of the physical phenomena involved. One of the basic problems has to do with the cutter-to-rock interaction during the cutting process. This study employs the Finite Element Method (FEM) to investigate the mechanics of rock cutting because of its flexibility in handling material heterogeneity, nonlinearity and boundary conditions. Using the FEM to model fracturing of a brittle material like rock –and consequently treating its discontinuous chips– is a challenging undertaking that requires the tackling of a sequence of complex problems: As the cutter advances and touches the rock material, a contact problem first arises. This is followed by nonlinear deformation and the determination as to when and whether the rock would fail. Subsequently, the question of how to initiate the fragmentation process has to be resolved if the rock fails. The cycle repeats starting with a new contact problem after new surfaces are generated due to fracture. At present, few researchers have focused on crack initiation and subsequent crack propagation, but even fewer have accounted for actual chip formation, and none has considered the dynamic interaction amongst chips, newly formed surfaces, and the cutter. One important goal of this study is to advance the modeling such that it is possible to follow the cutter in a complete cutting process in a credible manner. A framework of three-dimensional FEM modeling was developed so that the fragmentation process observed in laboratory rock scratching tests could be properly simulated. A thorough calibration of the rock material model was carried out, together with extensive sensitivity analyses of contact models, damage based failure and its associated fracture modeling using the commercial software LS-DYNA. This study was able to obtain ductile failure mode for shallow cuts, and brittle failure for deep cuts as observed in the laboratory, all without a priori setting on the failure modes. Also, cutting force magnitudes and tendencies obtained from the study correlated well with published results of the physical experiments. Moreover, in a limited scope, this study also investigated the effects of applying external hydrostatic pressure on rock cutting. Preliminary numerical results indicate a good comparison with few published data. Lastly, theoretical models for obtaining cutting forces were assessed, providing a better understanding of their limitations and usability

Assessment of Populations with Spatially Explicit Dynamics and the Consequences for Marine Protected Areas

Spatial processes can have important consequences in the population dynamics of fishes and marine invertebrates. Therefore fisheries management should consider space in the techniques used to understand population dynamics. The purpose of this thesis was to investigate spatial dynamics of fish populations in Maryland's coastal bays (Chapter 2) and evaluate effects of spatial management (in the form of marine protected areas (MPAs)) on accuracy of abundance estimates (Chapter 3). In Chapter 2, I examined trawl survey data from Maryland's coastal bays to estimate trends in relative abundance of four commonly caught fish species using a generalized linear model that allowed region specific estimates. Species showed different responses in the two regions, but trends over time were not related to local habitat variables. In chapter 3, I examined the effects of an MPA on the accuracy and bias of estimates from spatially aggregate and explicit surplus production models (SPMs) using a simulation experiment. I found that spatially-explicit SPMs produced more accurate estimates of biomass than spatially-aggregate SPMs, and that larger MPAs produced more accurate estimates than smaller MPAs

Minimum soil disturbance planting for rice-based rotations in northwest Bangladesh: Effects on plough pan and water balance

Soil degradation in the rice-based cropping system of Bangladesh has prompted research to switch from conventional tillage (CT) to minimum soil disturbance crop establishment, featuring strip planting (SP) and increased crop residue retention. However, the new residue retention levels and crop establishment methods need to be tested for their water use efficiency. Therefore, two field trials were initiated to evaluate the effects of SP and bed planting (BP) with increased crop residue retention on soil physical properties, components of the water balance and water productivity in two rice-based crop rotations. Field trials were conducted during 2015-2017 in two long-term conservation agriculture (CA) experimental fields established since 2010 in two regions of northwest Bangladesh, namely 1) Alipur, the alluvial soil region, and 2) Digram, the High Barind Tract (HBT) region. The trials consisted of three tillage treatments in the main plots - SP, BP and CT. The subplots comprised of two levels of residue retention - high residue (HR) and low residue (LR). High residue and LR treatment involved the retention of respectively 50 % and 20 % by the height of the previous crop, either anchored or loose. Strip planting and BP were done with a Versatile Multi-crop Planter mounted on a two-wheel tractor (2-WT). Seven years of continuous CA practices have provided evidence that minimum soil disturbance and increased residue retention have altered the soil physical properties in both silty loam soil at Alipur and silty clay loam soil at Digram. The physical changes were reflected in the reduction of soil BD, enhancement of total porosity (TP) and reduction of penetration resistance (PR) in the 0-20 cm soil depth. High residue treatment reduced BD from 1.37 to 1.33 g cm-3 at Alipur and 1.27 to 1.24 g cm-3 at Digram soil in the 0-10 cm soil depth compared to the LR treatment. High residue retention increased macroporosity by an average of 55 % over LR treatment. Irrespective of residue retention, the average (two soils) decrease in BD was 4.5 % and 2.6 % in 0-10 cm depth for SP and BP treatment, respectively, compared to CT. The highest BD of 1.65 g cm-3 was achieved at 10-20 cm soil depth in the CT plot, which clearly indicates a massive plough pan at this depth. However, BD of the plough pan was reduced by 3.8 % in the SP and 4.6 % in the BP treatment indicating the amelioration of subsoil compaction due to the absence of puddling over seven years. Penetration resistance in the plough pan was also decreased from 2.15 MPa (CT) to 1.93 MPa (SP) at Alipur and 2.55 MPa (CT) to 2.32 MPa (SP) at Digram. In the silty loam soil, saturated hydraulic conductivity (Ksat) at 0-10 cm under CT was 1.00 cm hr-1 which was increased to 1.39 cm hr-1 by SP and to 1.52 cm hr-1 by BP. In the silty clay loam soil, Ksat at 0-10 cm was increased from 0.32 cm hr-1 under CT to 0.66 cm hr-1 by SP and to 0.81 cm hr-1 by BP. In 10-20 cm soil depth, Ksat increased from 0.22 cm hr-1 under CT to 0.48 cm hr-1 by SP and to 0.43 cm hr-1 by BP. Soil compaction by a 2-WT with a single wheel-pass, two wheel-passes, and four wheel-passes with and without extra loading was also tested in non-CA fields adjacent to the two long-term trials. At 0-5 cm depth, soil BD with a single wheel pass was 1.37 g cm-3, which increased to 1.40 g cm-3 after two passes, and further increased to 1.47 g cm-3 with four passes. The BD of 0-5 cm depth with no extra loading was 1.37 g cm-3 which was increased to 1.39 g cm-3 with 100 kg extra loading and further increased to 1.43 g cm-3 with 200 kg extra loading. At 5-10 cm depth, compaction by CT involving four passes indicated that a 2-WT, when frequently trafficked at this depth for many years, creates a dense soil layer that is reasonably related to the formation of the plough pan. The least limiting water range (LLWR) range could be a good indicator of soil quality in soil compaction studies since the LLWR concept includes the effects of several growth-limiting factors such as matric potential, aeration and penetration resistance that are integrated into a single parameter. Conventional tillage had a larger LLWR which is also comparable to the LLWR of strip tillage single wheel pass treatment. Conservation agriculture practice facilitates tillage, fertilizer and seeding operation in a single pass. Thus, single wheel pass traffic by a low weight 2-WT may not create measurable compaction in the surface soil and the subsurface soil. High rice residue retention treatment increased wheat yield by 7-18 % in the whole study period (2015-2017) compared to low residue retention. Strip planting increased wheat yield by 18-25 % compared to CT in the three years. By contrast, BP increased wheat yield by 16 % compared to CT in 2015 but not in 2016 or 2017. Strip planting saved 15-36 % irrigation water for wheat growth compared to CT in three years. In contrast to SP, BP saved only 8-25 % irrigation water than CT. Irrigation water productivity of wheat was higher under SP (2.2 kg m-3) than that under BP (1.7 kg m-3) and CT (1.3 kg m-3). The results suggest that SP performed better than BP in terms of crop productivity and irrigation water productivity. Total water losses under SP continuous flooding irrigation were 80.0-125.0 cm, while the values were 82.0-123.0 cm for BP and 66.0-86.0 cm for CT. Deep drainage during the rice crop for SP, BP and CT accounted for about 41 %, 44 %, and 39 % of the total loss, respectively. Alternate wetting and drying irrigation reduced the drainage losses by 35 %, 26 % and 48 % for SP, BP and CT, respectively. The yield of rice ranged from 6.1-6.9 t ha-1, 6.1-6.6 t ha-1 and 6.5-6.7 t ha-1 for SP, BP and CT, respectively. Irrigation water productivity for rice was higher under CT (0.88 kg m-3) compared to SP (0.66 kg m-3) and BP (0.60 kg m-3). Improved crop yield under SP with residue retention should encourage smallholder farmers to adopt minimum soil disturbance planting in the rice-based rotation. However, altered water balance in the non-puddled minimum soil disturbance plot may require more irrigation for rice while allowing greater infiltration to groundwater. In contrast, for wheat, SP and HR had positive effects on water use and water productivity. Since water lost by deep percolation returns to the groundwater and is potentially available for reuse, non-puddled rice can beneficially increase groundwater recharge when practised in a large command area. Hence, CA practices appear to decrease the requirement for groundwater for irrigation of dry season wheat while increasing the potential for groundwater recharge, but this needs further investigation. Keywords: Barind area (Bangladesh); bed planting; conservation agriculture; conventional tillage; deep drainage; least limiting water range; minimum soil disturbance; number of wheel passes; soil compaction; strip planting; water balance

Development and validation of a wheelchair caster testing protocol

The majority of wheelchairs delivered in less-resourced settings fail prematurely. This issue has been recognized by the WHO Guidelines that recommend product testing based on field conditions to evaluate and improve wheelchair quality. This work is motivated from WHO’s recommendation and this is first scientific study investigating inclusion of environmental conditions in wheelchair testing. The goals of this work were to develop a testing protocol for wheelchair casters based on field conditions, evaluate the impact of environmental testing factors on quality and make appropriate recommendations for wheelchair testing based on study outcomes. In this study, an evidence-based approach was followed in which wheelchair testing evidence, expert advice, and field evidence were continually triangulated to inform the testing protocol development. A literature review (Chapter 1) was carried out and expert advice was sought to generate a list of testing methods with environmental factors based on outdoor failures. Caster system failure was identified as a key testing gap that poses significant safety risks to the wheelchair users. Development of a caster testing equipment (Chapter 2) and a caster failure checklist (Chapter 3) was carried out through an iterative design and review approach. The checklist was distributed for collecting failure data following psychometric evaluation and revisions. Testing factors of shock, corrosion and abrasion were validated to respective field exposures and caster testing was conducted (Chapter 4). Environmental factors impacted the durability of 25% caster models and altered failure modes for 75% models. Two-thirds of the altered failure modes have significant risk of causing injuries to users and wheelchair failures. About 73% of the testing failures matched with the most common failure modes experienced in the field. Based on study findings, environmental factors strongly influence both the time-to-failure and failure mode for caster models. We recommend that environmental exposure need to be considered as part of wheelchair testing protocols to help improve the external validity of the testing, which will ultimately improve the safety and reliability of the device. These recommendations are discussed along with caster design recommendations and suggestions for future work in Chapter 5

Mechanical design of hybrid moulds: mechanical and thermal performance implications

Tese de doutoramento em Ciência e Engenharia de PolímerosThe design and manufacture of injection moulds are the most time-consuming phases in the development of new plastics products. In the last two decades the advances in rapid prototyping and manufacturing technologies made possible the use of materials alternative to steel in some mould components. The integration of these components with conventional mould structures originated to the concept of hybrid mould. This alternative design solution aimed at satisfying the need for deployment of short series of new products more quickly and at competitive prices. This research work investigates the influence of materials used in moulding blocks of hybrid moulds in the mould performance, namely, reproducibility, operation regimes, thermal and mechanical issues. Furthermore it was analysed the effect on the definition of the more adequate processing conditions and the moulding properties. The study was based on tri-dimensional objects: a tubular cylindrical part and a more geometrically complex support box. The tube was produced in an existing simple instrumented hybrid mould and the support box was produced in a reusable and flexible hybrid mould. The latter was designed and manufactured in the context of this research work. The performance of the hybrid moulds was evaluated by comparing various combinations of moulding blocks (cavity and core) produced in alternative materials with the standard steel solution when injection moulding polypropylene. The comparison was based on the observation of the morphology structure of the mouldings, the thermal performance, the moulding shrinkage and the structural performance of the mould. The moulds were instrumented with pressure and temperature sensors and a load cell for monitoring the ejection force needed on a moulding pin incorporated in the lateral movement of the support box. The prediction of the moulding performance of the moulds was done using the injection moulding software Moldex3D. The mechanical performance of the components in alternative materials was done with the structural analysis software ANSYS Workbench. The results show the importance of predicting the mould regime temperature when establishing the appropriate processing conditions when softer materials are used in the moulding blocks. It was concluded that in the design of hybrid moulds it is necessary to consider the deformation of the moulding blocks that are caused by the pressure field during injection. This is critical to predict the shrinkage and the final dimensions of the mouldings.O projecto e o fabrico de moldes de injecção para plásticos ocupam um longo período de tempo no desenvolvimento de novos produtos. Nas duas últimas décadas os avanços das tecnologias de prototipagem e de fabrico rápido tornaram possível o uso de materiais metálicos alternativos e de resinas sintéticas em alguns componentes do molde. A inserção destes em estruturas convencionais deu origem ao conceito de molde híbrido. Esta solução alternativa procurou satisfazer a necessidade de colocar pequenas séries de novos produtos no mercado mais rapidamente e com preços competitivos. Este trabalho de investigação explora, essencialmente, a influência dos materiais usados nos blocos moldantes de moldes híbridos no desempenho do molde (ex. reprodutibilidade, regimes de funcionamento, aspectos térmicos e mecânicos). Também se estudou a sua influência no estabelecimento das condições processamento mais adequadas e nas propriedades das peças moldadas. Estudaram-se duas peças de geometria tridimensional: uma peça tubular e uma caixa-suporte com detalhes complexos. O tubo circular foi produzido num molde híbrido simples e já existente e a caixa-suporte num molde híbrido flexível e reutilizável. O segundo molde foi especificamente projectado e fabricado no âmbito deste trabalho de investigação. O desempenho dos moldes híbridos foi avaliado comparando o efeito de várias combinações de materiais alternativos nos blocos moldantes (bucha e cavidade) com a sua versão convencional em aço, na moldação de polipropileno. A comparação contemplou a observação da estrutura morfológica, o desempenho térmico, a contracção das moldações e o desempenho estrutural do molde. Os moldes foram instrumentados com sensores de pressão e temperatura e com uma célula de carga para medir a força de extracção de um pino moldante incorporado num movimento lateral da caixa-suporte. Utilizaram-se softwares de simulação do processo de moldação por injecção (Moldex3D) e estrutural (ANSYS Workbench) na previsão do desempenho dos componentes moldantes dos moldes híbridos. Os resultados mostram a importância da previsão do regime de temperatura de funcionamento do molde híbrido no estabelecimento das condições apropriadas ao processamento quando são utilizados materiais menos rígidos nos elementos moldantes. Foi constatado, ainda, que no projecto de moldes híbridos se devem considerar as deformações dos blocos moldantes causadas pelas pressões durante o ciclo para prever a contracção e as dimensões finais das peças moldadas.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/28113/200

Mechanical performance and sustainability assessment of reinforced soil walls

Soil reinforced retaining wall structures are materiallymore efficientthan competing construction solutions such as gravity and cantilever walls. Nevertheless, the behaviour and interactions between the com ponent materials are com plex and not fully understood. Current design methods are typically limited to simple cases with respect to material properties, geometry, and boundary conditions. Advanced numerical models using finite element and/or finite difference methods offer the possibilityto extend the understanding ofthese systems and to predictwall performance under operational conditions. In this Thesis, numerical models were developed and shown to give satisfactory predictions ofwall behavior when compared with results of instrumented physical structures. The verified models were useful for sensitivity analyses using a range ofwall geometries and boundaryconditions, material parameters and different constitutive models. As examples ofthe obtained results, the compressibility ofthe precast panel bearing pads significantly modified the axial vertical facing load but has no significant effect on the tension developed in the soil reinforcement layers. Also, the stiffness ofthe foundation soil has greater effect on the tension developed in soil steel reinforcing elements than for polymeric reinforcement layers.lt has been possible to perform sensitivity analysis using parameters that define soil-structure interactions. Such interactions have been analyzed using different commercial software programs and bydefining them with elements from the continuum media using 2D and 3D models. Laboratory reinforcement pullout tests using steelladder and polymeric strips were performed as part of the Thesis. Those parameters that have the greatest influence on soil-reinforcement interaction are identified, quantified, and compared to default-design wlues anda range ofvalues used to calibrate numerical models. From the results of2D and 3D numerical models suitable correlations have been obtained to allow 2D models to be used in plane strain reinforced soil walls with discontinuous soil reinforcement elements in the running walllength ofthese structures. With a proper sustainability assessment it has been possible to make quantitative comparisons between reinforced soil wall structures and other alternativés performing the same function (such as gravity and cantilever walls) construcfed to different heights. Using a modelbased on the multi-attributeutilitytheoryand wlue analysis decision-making, the best solutions with least negative impact were identified in an example set of alternative earth retaining wall options from a sustainable perspective. The results include possible scenarios based on the relative importance ofthe three pillars ofsustainability(i.e., environmental, economic, and sociallfunctional) as judged bydifferentstakeholders. Reinforced soil walls turned outto be the best choice in most cases analyzed, based on a quantitative end score. The models and analysis methodologies developed as part ofthis Thesis work have improved understanding ofthe behavior ofthese structures, and offered possibilities to improve and optimize designs in the future.Els murs de contenció amb sòl reforçat són estructures materialment més eficients que altres solucions constructives alternatives, com ara els murs de gravetat o en voladís. No obstant això, el seu comportament i les interaccions entre els materials que componen aquestes estructures són complexos i no entesos completament. Els mètodes de disseny actuals solen estar limitats a casos senzills respecte a les propietats dels materials, la geometria i les condicions de contorn. Models numèrics avançats utilitzant elements finits i/o diferències finites ofereixen la possibilitat d'ampliar la comprensió d’aquests sistemes estructurals i de predir el comportament de l'estructura en condicions de servei. En aquesta Tesi s'han desenvolupat models numèrics que han demostrat donar prediccions satisfactòries del comportament d’aquest tipus de murs quan es comparen amb resultats obtinguts d'estructures físiques instrumentades. Aquests models verificats han estat útils per a poder fer anàlisis de sensibilitat segons diferents geometries del parament i condicions de contorn, paràmetres dels materials i diferents models constitutius. Com a exemple dels resultats obtinguts, s’ha determinat que la capacitat de compressió de les peces de recolzament dels panells prefabricats modifica de manera significativa la càrrega desenvolupada vertical axial en el parament, però no té un efecte significatiu en la tensió desenvolupada a les capes de reforç del sòl. O també, que la rigidesa del sòl de fonamentació té un efecte més gran sobre la tensió desenvolupada en elements de reforç metàl·lics que en polimèrics. Ha estat possible dur a terme anàlisis de sensibilitat utilitzant els paràmetres que defineixen les interaccions sòl-estructura. Aquestes interaccions han estat analitzades utilitzant diferents programes comercials numèrics i definint-les amb elements del medi continu tant en models 2D com en 3D. Com a part de la Tesi, s'han de dut a terme assaigs de laboratori d'extracció de reforços tipus malla metàl·lica i banda polimèrica. Els paràmetres que tenen una influència principal en la interacció sòl-reforç han sigut identificats, quantificats i comparats tant amb els valors per defecte de disseny com amb valors reportats a la literatura utilitzats per a calibrar models analítics, permetent el calibratge dels models numèrics generats. Dels resultats dels models 2D i 3D s’han obtingut correlacions que permeten concloure que els models 2D en deformació plana són adequats per a representar el funcionament de les estructures de sòl reforçat amb elements de reforç discontinus a la direcció del parament. Mitjançant una avaluació adequada de la sostenibilitat ha estat possible fer comparacions quantitatives entre estructures de sòl reforçat i altres alternatives constructives que compleixen la mateixa funció (com els murs de gravetat o en voladís) construïdes a diferents altures. Mitjançant un model basat en la teoria de la utilitat multiatribut i d’anàlisi de valor per a la presa de decisions, es van identificar els processos més representatius i de major impacte des d’un punt de vista sostenible. Els resultats obtinguts inclouen un ajust basat en possibles escenaris de presa de decisió per la importància relativa dels tres pilars de la sostenibilitat (ambiental, econòmic, i social/funcional). L'alternativa de sòl reforçat va resultar ser la millor, obtenint una puntuació més alta en gran part dels escenaris de presa de decisió considerats. En base a una puntuació quantitativa final, els murs de sòl reforçat van resultar ser la millor opció en la majoria dels casos analitzats. Els models i metodologies d'anàlisi desenvolupades com a part de aquest treball de Tesi han millorat la comprensió del comportament d’aquestes estructures, i ofereixen possibilitats per a millorar i optimitzar els seus dissenys en el futurLos muros de contención con suelo reforzado son estructuras materialmente más eficientes que otras soluciones constructivas alternativas, tales como los muros de gravedad o en voladizo. Sin embargo, su comportamiento y las interacciones entre los materiales que componen estas estructuras son complejos y no completamente comprendidos. Los métodos de diseño actuales suelen estar limitados a casos sencillos con respecto a las propiedades de los materiales, la geometría y las condiciones de contorno. Modelos numéricos avanzados utilizando elementos finitos y/o diferencias finitas ofrecen la posibilidad de ampliar la comprensión de estos sistemas y de predecir el comportamiento de la estructura en condiciones de servicio. En esta Tesis se han desarrollado modelos numéricos que han demostrado dar predicciones satisfactorias del comportamiento de este tipo de muros cuando se comparan con resultados obtenidos de estructuras físicas instrumentadas. Estos modelos verificados han sido útiles para análisis de sensibilidad según diferentes geometrías del paramento y condiciones de contorno, parámetros de los materiales y diferentes modelos constitutivos. Como ejemplo de los resultados obtenidos, la capacidad de compresión de las piezas de apoyo de los paneles prefabricados modifica de manera significativa la carga vertical axial desarrollada en el paramento, pero no tiene un efecto significativo en la tensión desarrollada en las capas de refuerzo del suelo. O también, que la rigidez del suelo de cimentación tiene un mayor efecto sobre la tensión desarrollada en elementos de refuerzo metálicos que en poliméricos. Ha sido posible llevar a cabo análisis de sensibilidad utilizando los parámetros que definen las interacciones suelo-estructura. Tales interacciones han sido analizadas utilizando diferentes programas numéricos comerciales y definiéndolas con elementos del medio continuo tanto en modelos 2D como 3D. Como parte de la Tesis, se han llevado a cabo ensayos de laboratorio de extracción de refuerzos tipo malla metálica y banda polimérica. Los parámetros que tienen una mayor influencia en la interacción suelo-refuerzo han sido identificados, cuantificados y comparados tanto con los valores por defecto de diseño como con valores reportados en la literatura usados para calibrar modelos analíticos, permitiendo la calibración numérica de los modelos generados. De los resultados de los modelos 2D y 3D se han obtenido correlaciones que permiten concluir que los modelos 2D en deformación plana son adecuados para representar el funcionamiento de las estructuras de suelo reforzado con elementos de refuerzo discontinuos en la dirección del paramento. Con una evaluación adecuada sostenibilidad ha sido posible hacer comparaciones cuantitativas entre estructuras de suelo reforzado y otras alternativas constructivas que cumplen la misma función (tales como los muros de gravedad o en voladizo) construidas a diferentes alturas. Mediante un modelo basado en la teoría de la utilidad multiatributo y análisis de valor para la toma de decisiones, se identificaron los procesos más representativos y de mayor impacto desde un punto de vista sostenible. Los resultados obtenidos incluyen un ajuste basado en posibles escenarios de toma de decisión por la importancia relativa de los tres pilares de la sostenibilidad (ambiental, económico, y social/funcional). La alternativa de suelo reforzado resultó ser la mejor, obteniendo una mayor puntuación en gran parte de los escenarios de toma de decisión considerados. En base a una puntuación final cuantitativa, los muros de suelo reforzado resultaron ser la mejor opción en la mayoría de los casos analizados. Los modelos y metodologías de análisis desarrolladas como parte de este trabajo de Tesis han mejorado la comprensión del comportamiento de estas estructuras, y ofrecen posibilidades para mejorar y optimizar sus diseños en el futuroPostprint (published version

Geomechanical behaviour of laminated, weak roof strata and development of an appropriate reinforcement strategy

The work presented in this thesis has been concerned with investigation of the geomechanical behaviour of laminated weak roof strata along longwall roadways in underground coal mines and the mechanisms for effective reinforcement. Field investigations have been particularly associated with underground conditions at Angus Place Colliery, New South Wales, Australia. The principal objectives of this investigation are to understand the deformation behaviour of the laminated weak roof strata and the roof reinforcement problems which have plagued longwall roadway support and underground mining in West Coalfield of New South Wales. Based on the comprehensive engineering understanding of the geomechanical behaviour of laminated weak roof strata, an appropriate reinforcement strategy is developed. The thesis consists of four major parts associated with different approaches adopted in conducting the investigation, including: 1. Laboratory investigation: Conventional deformation and strength parameters of major roof rocks, such as, coal, mudstone and sandstone, including modulus of elasticity, uniaxial compressive strength, (UCS), uniaxial tensile strength, cohesion and angle of internal friction, along with shear strength, triaxial compressive strength with different confinements, have been conducted, in order to determine the mechanical properties of roof rock masses. On the other hand, a series of tests has been conducted to investigate the water sensitivity of mechanical properties of roof rocks, in order to evaluate the effect of water on mechanical properties of roof rocks and to determine the deterioration mechanism of roof rock. According to the results, the intact roof rocks can be classified from medium strong to weak rock mass subjected to the 0% water content. When the water content and discontinuity have been taken into consideration, the roof and floor strata in maingate 22, Angus Place Colliery can be classified as a weak strata. In general, the mechanical properties of surrounding rock masses, the integrity of roof and floor structures are significantly influenced by discontinuity and water. 2. Mine site investigation: The major purposes of this work are to determine the detailed roof deformation behaviour and roof layer separation in the roof strata and the performance of rock bolting reinforcement system used in longwall roadway by using the wire and sonic extensometers and instrumented bolts. According to this work, the roof deformation is differentiated into three different stages associated with different mining activities, that is: a) stage of development, b) stage of time dependent deformation (after development and before extraction) and c) stage of extraction. On the other hand, the deformation behaviour at different horizons associated with different roof geological settings is also determined. Correspondingly, the rock bolting performance is monitored including the maximum axial load, the distribution of load along the length of bolt, the bending moment of bolts as well as the load variation with different stages during the mining. 3. Parametric study: The parametric study is conducted by two and three dimensional computer modelling using Map3D and Phase2. Three dimensional modelling determines the stress redistribution and deformation around opening after roadway development and during the longwall extraction, which provides basic stress parameters as reference for the two dimensional modelling. In two dimensional modelling, the comprehensive parametric study on rock bolting reinforcement system and grouting reinforcement has been conducted. It is noted that the roof stability can be improved through three different ways, which are: a) optimising combination of rock bolting parameters, such as, bolt length, pretension, inclination, stiffness, distribution, etc, b)using combined reinforcement methods, such as, rock bolting and grouting reinforcements, c) altering geometry of opening, particularly for the rectangular shape of opening. 4. Theoretical analyses: The principles of material and structural mechanics have been used and based on these mechanical theories, the roof deformation mechanisms have been developed associated with different stages of mining activities. Based on the outcomes of the study, the reinforcement strategy has been developed using three approaches, including, a) the features of underground geological and geomechanical conditions and deformation behaviour of opening, b) the reinforcement methods and parameters, and c) Principles of New Austrian Tunnelling Method (NATM). Also, the procedure for development of reinforcement strategy has been proposed which can be used as a guide for evaluating the deformation behaviour and developing the reinforcement strategy under different adverse ground conditions

Inferred Weak Rock Mass Classification for Stope Design

Empirical design methods are commonly used for rock mechanics evaluations. An appropriate method of rock mass classification is required to use these empirical methods. There are limitations for rock mass classification methods when access to the ore zone is restricted. The Cameco Corporation Eagle Point Mine in northern Saskatchewan, Canada, uses the longhole open stope mining method for the recovery of uranium ore. The Modified Dilution graph is used for the prediction of stope hanging wall dilution. The mine currently uses a rock mass classification based on an estimate of the alteration and strength of a rock mass from geological drift mapping. Since this method is highly subjective, point load testing of diamond drill hole core was completed to attempt to correlate the alteration and strength of different rock types to remove the user subjectivity. The results of the testing indicated a general trend of decreasing rock strength with increasing alteration, albeit with considerable scatter. A repeatable, standardized method of evaluating the stope geometry and inferred rock mass classification for reconciliation purposes was developed. The standardized stope evaluation method removes significant subjectivity currently involved in estimates of stope geometries and the magnitude of dilution. A new lithology based method for interpreting the mine specific geological alteration and strength classification system was developed based on several sources of rock mass classification observations. This resulted in a correlation linking individual rock mass property descriptions between different classification systems for an improved estimate of the Q’ classification value. This improved method of estimating the rock classification Q’ value, as well as conventional techniques for linking classification systems, was used in a stope reconciliation process to predict open stope dilution. Twenty-seven stope reconciliation case histories were documented and used to compare predicted and measured dilution, based on three different approaches for estimating rock mass classification values. The results showed a minor improvement in dilution prediction using the approach developed in this study. The systematic stope reconciliation and rock mass classification approach did highlight areas in the weak pegmatoidal rocks where improved rock classification estimates should be investigated

Model development for efficient simulation of CO2 storage

Carbon capture and storage (CCS) is an important component of several initiatives to reduce global greenhouse gas emissions by injecting and storing CO2 in underground reservoirs. Simulation technology plays an important role in providing storage capacity estimates and analyzing long-term safety and risk factors of leakage to the surface. Two of several important questions that need to be answered before a storage project may be approved is how fast and how much CO2 can be injected without compromising the integrity of the sealing caprock, which stops it from migrating to the surface. To evaluate the integrity we rely on mathematical models, but due to the large extent of the area that needs to be considered and the many processes that are involved the calculations can quickly become large and complicated and very time consuming to solve. For screening purposes of potential storage sites, or investigation of potential storage sites when little data is available, many model realizations are needed, thus fast and robust yet accurate numerical techniques are not only tractable but also essential. To understand what happens to the CO2, formation water and rock during injection and storage, we have thoroughly reviewed the main processes that are relevant to the integrity of the reservoir and sealing formations. These main processes are fluid flow, stress change and temperature change and they are all coupled where for instance a change in pore pressure and temperature due to CO2 injection causes deformations and stress alterations that can affect the integrity of the injection reservoir and caprock. Considering the low solubility of CO2 in formation water under typical storage con- ditions (depth, temperature, pressure and salinity) we have illustrated that it is a good approximation to treat the injected CO2 and formation water as two separate fluids. Miscibility is therefore not an important process to consider in relation to long-term mechanical integrity and this simplifies the mathematical description of fluid flow. Whether the thermo-hydro-mechanical coupling, where the temperature change is also considered, is important to evaluate is less obvious. Through examples we show that the in situ temperature is important to consider when estimating material proper- ties, but the effect of the cold (CO2) injection, relative to the storage formation, is very local and mainly affects the near-field of the injector. The cooling effect reduces the spreading of the CO2, but has little effect on the pore pressure. In general, cold injec- tion (relative to formation temperature) lowers the fracture pressure of the rock and the limit for maximum sustainable injection rate, and therefore, ignoring non-isothermal effects can underestimate the risk of failure, and vice versa for hot injection. A risk analysis of reactivation of faults in the sealing formation in the CO2 storage project at In Salah, Algeria, revealed that the thermal effect can make the difference between safe and risky storage. To achieve a procedure for faster numerical evaluation, the layering structure and high aspect ratio of typical storage reservoirs can be used to simplify the mathematical description of the internal physical processes using a method of dimensional reduction. This has previously been found particularly attractive in simulating the migration of CO2 in the context of CCS. Since hydro-mechanical coupling is particularly essential to consider when evaluating the integrity of the caprock, we have extended this concept to also include the geomechanical processes. The underlying assumptions of negligible vertical flow compared to horizontal flow (Vertical Equilibrium, VE, assumption) and linearly varying displacement across the thickness of the reservoir (Linear Vertical Deflection, LVD, assumption) has proved promising in providing significant savings in computational time and effort with up to more than ten times faster calculations compared to a full-dimensional model. It has also been demonstrated that such models can retain a high accuracy when applied to realistic field data, such as the conditions at the CO2 storage plant at In Salah, Algeria. Also, the range of applicability of the dimensionally reduced model is to a leading order the thickness of the reduced domain and accurate solutions in the order of 0.1 % and less difference in solution compared to a full-dimensional formulation for aquifers up to 100 meters thick has been achieved