Sublevel caving is an underground mass mining method that utilizes the gravity-induced material flow for ore extraction. The granular flowbehavior is one of the main phenomena describing this mining method’s efficiency; therefore, a good understanding of the flow behavior is essential.The knowledge of the material flow behavior evolved in the late 1950:s when the mining method became more commonly used. However, due tothe complexity of the granular material flow, all parameters are not well studied, and a lack of knowledge still exists. With the increasing mining depths, higher stresses will occur inside the rock mass. How these increased stresses influence flow behavioris one of the parameters that are not well studied. Unfortunately, manipulating these is challenging in physical material models and mighteven be impossible in field experiments. However, achieving such control is possible using a discrete element method software. The model developedfor this thesis simulates pre-stressed rock mass up to 50 MPa and monitors the flow behavior in the software PFC3D. The result showed that the increased stress had the potential of causing a stable configuration of material inside the opening ring, known as a hangup.The hang-up later was destabilized when the blast continued to the next ring. For the chosen blasting geometry, the shape of the draw zone of thematerial that reached the extraction point did not seem to be affected by the stresses. / Skivrasbrytning är en gruvbrytningsmetod som nytjar flödet av material som skapas av graviationen och dess effektivitet är starkt kopplad tillbetendet hos materialflödet. Sedan gruvbrytningsmetoden blev allt vanligare i slutet av 1950-talet har ett flertal experiments konstrueratsför att utvärdera de parametrar som har antagits ha en inverkan på flödet, vilket resulterat i en effektivare gruvbrytningsmetod. På grund avkomplexiteten hos materialflödet är inte alla parametrar lika väl studerade, och brist på kunskap existerar fortfarande. Med de fortsatt ökande djupen i gruvorna, förväntas allt högre spänningar inuti berget, och hur dessa påverkar materialflödet är inte välstuderat. Dessa spänningar är svåra att kontrollera i både materialmodeller och vid fältförsök. Med distinkt elementmetodprogramvara kan däremotspänningarna i berget kontrolleras och flödesbeteendet studeras. I den modell som byggts för detta arbete utvärderas spänningar upp till 50 MPai programvaran PFC3D. Resultatet från simuleringarna utförda i PFC3D visade att de ökade spänningarna kan orsaka upphängning av materialet i öppningskransen.Flödet återupprättades när brytningen fortgick till nästa krans. Utöver detta studerades flödesbeteendet av det material som nådde uttagspunkten,där visade resultatet att omgivningstrycket inte har en inverkan på flödet för den valda sprängningsgeometrin.

This dissertation investigates contractional fault-related folding, an important mechanism of deformation in the brittle crust, using a range of kinematic and mechanical models and data from natural structures. Fault-related folds are found in a wide range of tectonic settings, including mountain belts and accretionary prisms. There are several different classes of fault-related folds, including fault-bend, fault-propagation, shear-fault-bend, and detachment folds. They are distinguished by the geometric relationships between the fold and fault shape, which are driven by differences in the nature of fault and fold growth. The proper recognition of the folding style present in a natural structure, and the mechanical conditions that lead the development of these different styles, are the focus of this research. By taking advantage of recent increases in the availability of high-quality seismic reflection data and computational power, we seek to further develop the relationship between empirical observations of fault-related fold geometries and the kinematics and mechanics of how they form. In Chapter 1, we develop an independent means of determining the fault-related folding style of a natural structure through observation of the distribution of displacement along the fault. We derive expected displacements for kinematic models of end-member fault-related folding styles, and validate this approach for natural structures imaged in seismic reflection data. We then use this tool to gain insight into the deformational history of more complex structures. In Chapter 2, we explore the mechanical and geometric conditions that lead to the transition between fault-bend and fault-propagation folds. Using the discrete element modeling (DEM) method, we investigate the relative importance of factors such as fault dip, mechanical layer strength and anisotropy, and fault friction on the style of structure that develops. We use these model results to gain insight into the development of transitional fault-related folds in the Niger Delta. In Chapter 3, we compare empirical observations of fault-propagation folds with results from mechanical models to gain insight into the factors that contribute to the wide range of structural geometries observed within this structural class. We find that mechanical layer anisotropy is an important factor in the development of different end-member fault-propagation folding styles. / Earth and Planetary Sciences

"Safety is a value, not just a Priority" Geomechanically stable underground excavations require continuous assessment of rock mass behavior for maximizing safety. Optimizing pillar design is essential for preventing hazardous incidents and improving production in room-and-pillar mines. Maintaining regional and global stability is complicated for underground carbonate or stone deposits, where extensive fracture networks and groundwater flow become leading factors for generating unsteady ground conditions including karsts. A sudden encounter with karst cavities during mine advance may lead to safety issues, including ground collapse and outflow of unconsolidated sediments and groundwater. The presence of these eroded zones in pillars may cause their failure and poses a risk to the lives of miners apart from disrupting the pre-planned mining operations. A pervasive presence of joints and fractures plays a primary role in promoting structurally controlled failures in stone mines, which accelerates upon interaction with the karst cavities. The prevalent empirical and analytical approaches for pillar design ignore the geotechnical complexities such as the spatial density of discontinuities, karst voids, and deviation from the design during short-range mine planning. With the increasing market demand for limestone products, mining organizations, as well as enforcement agencies, are investing in research for increasing the efficiency of extracting valuable resources. While economical productivity is essential, preventing risks and ensuring the safety of miners remains the cardinal objective of mining operations. According to the Mine Safety and Health Administration (MSHA), since 2000, about 31% of occupational fatalities at all underground mines in the United States are caused due to ground collapse, which rises to 39% for underground stone mines. The objective of this study is to provide a reliable and methodological approach for pillar design in underground room-and-pillar hard rock mines for safe and efficient ore recovery. The numerical modeling techniques, implemented for a case study stone mine, could provide a pragmatic framework to assess the effect of karsts on rock mass behavior, and design future pillars detected with voids. The research uses data acquired from using remote sensing techniques, such as LiDAR and Ground-penetrating Radar surveys, to map the excavation characteristics. Discontinuum modeling was valuable for analyzing the pillar strength in the presence of discontinuities and cavities, as well as estimating a safe design standard. Discrete Fracture Networks, created using statistical information from discontinuity mapping, were employed to simulate the joints pervading the rock mass. This proposed research includes the calibration of rock mass properties to translate the effect of discontinuities to continuum models. Continuum modeling proved effective in analyzing regional stability along with characterizing the redistributed stress regime by imitating the excavation sequence. The results from pillar-scale and local-scale analyses are converged to optimize pillar design on a global scale and estimate the feasibility of secondary recovery in stone mines with a dominating discontinuity network and karst terrane. Stochastic analysis using finite volume modeling helped evaluate the performance of modified pillars to assist production while maintaining safety standards. The proposed research is valuable for improving future design parameters, excavation practices, and maintaining a balance between an approach towards increased safety while enhancing production. / Doctor of Philosophy / "The most valuable resource to come back out of a mine is a miner" – Anonymous. The United States accounted for 27% of the global limestone market share which was valued at US$58.5 billion in 2020 [148]. It is projected to reach a target of US$65.3 billion in 2027, growing even in midst of the COVID-19. As surface reserves deplete, much of the mineral demand gap is supplemented by mining underground deposits. Underground mines extract minerals from deep within the earth compared to surface mines. As a result, the miners experience a greater number of accidents in a constricted environment because of roof/tunnel collapse, fewer escape routes, ventilation, explosions, or inundation. According to the Mine Safety and Health Administration (MSHA), about 15% of all underground mine injuries in the US were caused by rockfalls since 1983. The majority of underground stone deposits are mined using the room-and-pillar mining method, which resembles a chessboard design where the light squares are mined, and the dark squares are left as rock pillars to support the tunnels. Limestone, a carbonate rock, contains a lot of fractures and joints (discontinuities). Erosion of rocks due to continuous water flow through the fractures leads to the formation of cavities known as karsts. Interaction of karsts with the prevalent fracture network increases rockfall risk during mining. The collapse of voids along with an inrush of filled rock-clay-water sludge can harm miners' lives, damage machinery, and stop further operations. Literature is scarce on topics that quantify the risk and disruption posed by these cavities in underground mines. Most rock classification systems cannot classify their effect because of the unpredictability and extensive analysis required. The objective of this research is to provide a reliable and methodological approach for designing pillars in underground hard rock mines for ensuring a safe working environment and efficient mineral recovery. This research starts with analyzing the strength of pillars, in which karst cavities were discovered while mining. The safety concerns often lead the miners to not excavate around the cavities and leave valuable resources unmined. Data from ground-penetrating radar and laser scanning surveys were used to characterize the voids and map the discontinuities. Discrete-element numerical modeling was used to simulate the pillars as an assembly of blocks jointed by the discontinuities. The simulation results help us understand the instability issues in the karst-ridden pillars and ways to improve upon the existing design. The findings were used to modulate the parameters for regional-scale models using finite volume modeling for less computationally intensive analyses and simulating rock as a continuum. The continuum models were highly effective in analyzing the instability issues due to the prevalent karstic network. This helps understand any alternative scenario that could have been implemented to optimize ore recovery while preventing risks. The results from the single pillar and regional analyses are combined to optimize pillar design on a global mine scale. This dissertation focuses on improving hazard mitigation in mines with unpredicted anomalies like karsts. Although this research is based on a specific mine site, it empowers the operators to explore the presented techniques to increase safety in all underground mines. The suggested methodology will help devise better strategies for handling instability issues without jeopardizing the mine operations. The primary motivation is to keep the underground miners safe from hazardous situations while fulfilling the secondary objective of maximizing mineral production.

This research focused on three main objectives: (1) quantify coarse aggregate morphological characteristics using an improved FTI (Fourier Transform Interferometry) image analysis system, (2) evaluate the effects of morphological characteristics of coarse aggregates of various mineral compositions on the mechanical performances of stone matrix asphalt (SMA) mixtures constituted; (3) investigate the relationship between the uncompacted void content of coarse aggregates and morphological characteristics. To achieve the first research objective, a Fourier Transform Interferometry (FTI) system was adopted to capture three-dimensional high-resolution images of aggregates. Based on these digital images, the FTI system uses the two-dimensional Fast Fourier Transform (FFT2) method to rapidly measure aggregate morphological characteristics, including sphericity, flatness ratio, elongation ratio, angularity, and surface texture. The computed shape characteristics of all aggregates were in good agreement with manual measurement results, demonstrating the accuracy and reliability of this image analysis system. For the second objective, a series of simple performance laboratory tests were performed on eight types of SMA mixtures with different morphological characteristics. Test included wheel-track loading, dynamic modulus, flow number, and beam fatigue. The wheel tracking test included asphalt pavement analyzer (APA) and Model mobile load simulator (MMLS). In the APA test, samples included eight types of SMA mixtures that consisted of aggregates of 22 fractions. In the MMLS test, six types of SMA mixture samples that consist of coarse aggregate of 15 fractions were tested. Regression analyses were then conducted between weighted mean morphological characteristics and performance parameters. The fatigue performance parameters include |E*|sin φ, where |E*| is complex modulus obtained from dynamic modulus test, the number of loading cycles to failure, and the seismic modulus difference. The rutting performance parameters include |E*|/sin φ, flow number, flow number slope, rut depth and creep slope. For the third objective, different coarse aggregate fractions from different quarries in Virginia were analyzed using the improved FTI system. Regression analyses were performed to investigate the correlation between morphological characteristics and uncompacted void content of coarse aggregates at the size ranges of 4.75-9.5mm and 9.5-12.5 mm, respectively. Aggregate morphological characteristics were found to play an important role in the mechanical performance of stone matrix asphalt mixture and the uncompacted air void content of the coarse aggregates. Both the experimental results and simulation results demonstrated that using more of equi-dimensional, less flaky and elongated coarse aggregates with angular and rougher-textured aggregates is favorable to the mechanical performances of SMA mixtures. Recommended values for each morphological characteristic are provided. / Ph. D.

The behavior of the ballast particles during their interaction with tamping tines in tamping operation is studied by developing a simulation model using the Discrete Element Model (DEM), with the aim of optimizing the railroad tamping operation. A comprehensive literature review is presented showcasing the applicability of DEM techniques in modeling ballast behavior and its feasibility in studying the fundamental mechanisms that influence the outcome of railroad tamping process is analyzed. The analysis shows that DEM is an excellent tool to study tamping operation as its important and unprecedented insights into the process, help not only to optimize the current tamping practices but also in the development of novel methods for achieving sustainable improvements in the track stability after tamping. The simulation model is developed using a commercially available DEM software called PFC3D (Particle Flow Code 3D). A detailed explanation is provided about how to set up the DEM model of railway ballast considering important parameters like selection and calibration of particle shapes, ballast mechanical properties, contact model, and parameters governing the contact force models. Tamping operation is incorporated into the simulation model using a half-track layout with a highly modular code that enables a high degree of adjustability to allow control of all process parameters for achieving optimized output. A parametric study is performed to find the best values of tine motion parameters to optimize the linear tamping efficiency and a performance comparison has been made between linear and elliptical tamping. It is found that squeeze and release velocity of the tines should be lesser for better compaction of the particles and linear tamping is better compared to elliptical tamping. / Master of Science / Railway track stability is the resistance of the tracks to deformation and is affected by the rail traffic, ballast fouling (contamination of ballast) and the changing environmental conditions. The track stability depends on the normal and frictional support provided by the ballast to the sleepers. Non-uniform ballast consolidation below the railway sleeper results in erratic wheel-rail contact forces, low traffic speeds, poor ride quality, and derailments. Thus, tamping is a railway track maintenance method done periodically on the railway tracks to ensure track stability. Tamping process involves compacting the railroad ballast underneath the sleeper. The sleeper is lifted by a desired height and then vibrating tamping tools called tines are inserted into the ballast below the sleeper to fill the void created by lifting of the sleeper and the sleeper is dropped back on to the ballast. So, it is important to understand the ballast mechanics, dynamics and ballast’s behavioral response to the tamping operation. Since, large scale experiments such as this are difficult, this operation has been simulated in a commercially available software called PFC3D using a Discrete Element Model (DEM) to represent the railway ballast. It is shown through a simulation that though spherical particles provide better computational efficiency, they cannot capture the exact ballast behavior like clumps (a collection of spherical pebbles). So using clumps to represent ballast, efforts are made to optimize the linear tamping efficiency. This is done by changing the values of parameters like tine amplitude, tine frequency, insertion velocity and squeeze velocity and finding their optimum values. Linear tamping results are compared with elliptical tamping. Thus, an optimum tamping cycle would help save money spent on the track maintenance activities.

The development of Discrete Element Model (DEM) of railway ballast for the purpose of studying the behavior of ballast particles during tamping is addressed in a simulation study, with the goal of optimizing the railroad tamping operation. A comprehensive literature review of applicability of DEM techniques in modeling the behavior of railway ballast is presented and its feasibility in studying the fundamental mechanisms that influence the outcome of railroad tamping process is analyzed. A Discrete Element Model of railway ballast is also developed and implemented using a commercially available DEM package: PFC3D. Selection and calibration of ballast parameters, such as inter-particle contact force laws, ballast material properties, and selection of particle shape are represented in detail in the model. Finally, a complete tamping simulation model is constructed with high degree of adjustability to allow control of all process parameters for achieving realistic output. The analysis shows that DEM is a highly valuable tool for studying railroad tamping operation. It has the capability to provide crucial and unprecedented insights into the process, facilitating not only the optimization of current tamping practices, but also the development of novel methods for achieving sustainable improvements in track stability after tamping in the future. Different ways of modeling particle shapes have been evaluated and it has been shown that while using spheres to represent irregular ballast particles in DEM provides immense gains in computational efficiency, spheres cannot intently capture all properties of irregularly shaped particles, and therefore should not be used to model railway ballast particles. Inter-particle and wall-particle contact forces are calculated using Hertzian contact mechanics for determining ballast dynamics during tamping. The results indicate that the model is able to accurately predict properties of granular assemblies of the railway ballast in different test cases. The developed model for simulating tamping operation on a half-track layout is expected to be extended in future studies for evaluating rail track settlement and stability, optimization of tamping process, and performance of different ballast gradations. / MS

This work explains the effect of failure on permeability anisotropy and dilation in sands. Shear failure is widely observed in field operations. There is incomplete understanding of the influence of shear failure in sand formations. Shear plane orientations are dependent on the stress anisotropy and that view is confirmed in this research. The effect of shear failure on the permeability is confirmed and calculated. Description of permeability anisotropy due to shear failure has also been discussed. In this work, three-dimensional discrete element modeling is used to model the behavior of uncemented and weakly cemented sand samples. Mechanical deformation data from experiments conducted on sand samples is used to calibrate the properties of the spherical particles in the simulations. Orientation of the failure planes (due to mechanical deformation) is analyzed both in an axi-symmetric stress regime (cylindrical specimen) and a non-axi-symmetric stress regime (right cuboidal specimen). Pore network fluid flow simulations are conducted before and after mechanical deformation to observe the effect of failure and stress anisotropy on the permeability and dilation of the granular specimen. A rolling resistance strategy is applied in the simulations, incorporating the stiffness of the specimens due to particle angularity, aiding in the calibration of the simulated samples against experimental data to derive optimum granular scale elastic and friction properties. A flexible membrane algorithm is applied on the lateral boundary of the simulation samples to implement the effect of a rubber/latex jacket. The effect of particle size distribution, stress anisotropy, and confining pressure on failure, permeability and dilation is studied. Using the calibrated micro-properties, simulations are extended to non-cylindrical specimen geometries to simulate field-like anisotropic stress regimes. The shear failure plane alignment is observed to be parallel to the maximum horizontal stress plane. Pore network fluid flow simulations confirm the increase in permeability due to shear failure and show a significantly greater permeability increase in the maximum horizontal stress direction. Using the flow simulations, anisotropy in the permeability field is observed by plotting the permeability ellipsoid. Samples with a small value of inter-granular cohesion depict greater shear failure, larger permeability increase and a greater permeability anisotropy than samples with a larger value of inter-granular cohesion. This is estimated by the number of micro-cracks observed. / text

L’estimation de la durée de vie et de la rupture de structures composées par des matériaux quasi-fragiles nécessite le développement de nouveaux modèles théoriques et numériques. Dans ce travail, la modélisation de l’apparition des fissures et leur propagation en chargement monotone est d'abord étudiée. Un modèle d'effet de taille pour les structures fissurées et sa forme généralisée pour les structures présentant des défauts plus complexes qu’une fissure sont développés. Les prédictions du modèle de rupture sont comparées à des résultats expérimentaux de la littérature pour divers spécimens composés de différents matériaux et de différentes tailles. Des échantillons présentant des défauts initiaux en forme de V et en forme de trou illustrent les capacités de la formulation. Ensuite, l’endommagement et la fissuration induite par des chargements cycliques en fatigue sont discutés. Un modèle local en éléments discrets est développé, qui permet de coupler les deux mécanismes (endommagement et fissuration). Les prédictions numériques sont comparées aux résultats théoriques et expérimentaux. À la fin, les applications associées au comportement du béton bitumineux renforcé par des grilles en fibres de verres sont analysées en détail. / The prediction of the fatigue life and the rupture of structures made of quasi-brittle materials requires the development of new theoretical and numerical models. In this work, the modelling of the crack initiation and propagation under monotonic loading is firstly investigated. A size effect model for cracked structures and its generalized form for structures with defects more complex than a crack are developed. The predictions of the proposed model are compared with experimental results from the literature for various specimens of different materials and sizes. Samples with initial V-shaped and hole-shaped defects exemplify the formulation's capabilities. Then, the damage and cracking induced by cyclic fatigue loads is discussed. A local model using discrete elements is developed, that allows the coupling of two mechanisms (damage and fatigue cracking). The numerical results are compared to those of experimental bending fatigue tests. Finally, applications associated with the behavior of fiber glass reinforced asphalt concrete are analyzed in detail.

Particulate systems in practical applications such as biomass combustion, blood cellular systems and granular particles in fluidized beds, have often been computationally represented using spherical surfaces, even though the majority of particles in archetypal fluid-solid systems are non-spherical. While spherical particles are more cost-effective to simulate, notable deficiencies of these implementations are their substantial inaccuracies in predicting the dynamics of particle mixtures. Alternatively, modeling dense fluid-particulate systems using non-spherical particles involves increased complexity, with computational cost manifesting as the biggest bottleneck. However, with recent advancements in computer hardware, simulations of three-dimensional particulate systems using irregular shaped particles have garnered significant interest. In this research, a novel Discrete Element Method (DEM) model that incorporates geometry definition, collision detection, and post-collision kinematics has been developed to accurately simulate non-spherical particulate systems. Superellipsoids, which account for 80% of particles commonly found in nature, are used to represent non-spherical shapes. Collisions between these particles are processed using a distance function computation carried out with respect to their surfaces. An event - driven model and a time-driven model have been employed in the current framework to resolve collisions. The collision model's influence on non–spherical particle dynamics is verified by observing the conservation of momentum and total kinetic energy. Furthermore, the non-spherical DEM model is coupled with an in-house fluid flow solver (GenIDLEST). The combined CFD-DEM model's results are validated by comparing to experimental measurements in a fluidized bed. The parallel scalability of the non-spherical DEM model is evaluated in terms of its efficiency and speedup. Major factors affecting wall clock time of simulations are analyzed and an estimate of the model's dependency on these factors is documented. The developed framework allows for a wide range of particle geometries to be simulated in GenIDLEST. / Master of Science / CFD – DEM (Discrete Element Method) is a technique of coupling fluid flow solvers with granular solid particles. CFD – DEM simulations are beneficial in recreating pragmatic applications such as blood cellular flows, fluidized beds and pharmaceutics. Up until recently, particles in these flows have been modeled as spheres as the generation of particle geometry and collision detection algorithms are straightforward. However, in real – life occurrences, most particles are irregular in shape, and approximating them as spheres in computational works leads to a substantial loss of accuracy. On the other hand, non – spherical particles are more complex to generate. When these particles are in motion, they collide and exhibit complex trajectories. Majority of the wall clock time is spent in resolving collisions between these non – spherical particles. Hence, generic algorithms to detect and resolve collisions have to be incorporated. This primary focus of this research work is to develop collision detection and resolution algorithms for non – spherical particles. Collisions are detected using inherent geometrical properties of the class of particles used. Two popular models (event-driven and time-driven) are implemented and utilized to update the trajectories of particles. These models are coupled with an in – house fluid solver (GenIDLEST) and the functioning of the DEM model is validated with experimental results from previous research works. Also, since the computational effort required is higher in the case of non – spherical particulate simulations, an estimate of the scalability of the problem and factors influencing time to simulations are presented.

Asphalt joints are potentially weakest parts of every pavement. Despite of their importance, reliable tools for measuring their mechanical properties for design and performance assessments are still scarce. This is particularly true for cold joints when attaching a new hot pavement to a cold existing one as in case of large patches for pavement repair. In this study, three static fracture testing methods, i.e. indirect tensile test (IDT), direct tension test (DTT) and 4 point bending (4PB), were adapted and used for evaluating different laboratory made joints. The results suggested that joints with inclined interfaces and also the ones with combined interface treatments (preheated and sealed) seemed to show more promising behaviors than the vertical and untreated joints. It was also confirmed that compacting from the hot side towards the joint improved the joint properties due to imposing a different flow pattern as compared to the frequent compaction methods. The latter finding highlighted the importance of asphalt particle rearrangements and flow during the compaction phase as a very little known subject in asphalt industry. Studies on compaction are of special practical importance since they may also contribute to reducing the possibility of over-compaction and aggregate crushing. Therefore, in this study, a new test method, i.e. Flow Test (FT), was developed to simulate the material flow during compaction. Initially, asphalt materials were substituted by geometrically simple model materials to lower the level of complexity for checking the feasibility of the test method as well as modeling purposes. X-ray radiography images were also used for capturing the flow patterns during the test. Results of the FT on model materials showed the capability of the test method to clearly distinguish between specimens with different characteristics. In addition, a simple discrete element model was applied for a better understanding of the test results as a basis for further improvements when studying real mixtures. Then, real mixtures were prepared and tested under the same FT configuration and the results were found to support the findings from the feasibility tests. The test method also showed its potential for capturing flow pattern differences among different mixtures even without using the X-ray. Therefore, the FT was improved as an attempt towards developing a systematic workability test method focusing on the flow of particles at early stages of compaction and was called the Compaction Flow Test (CFT). The CFT was used for testing mixtures with different characteristics to identify the parameters with highest impact on the asphalt particle movements under compaction forces. X-ray investigations during the CFT underlined the reliability of the CFT results. In addition, simple discrete element models were successfully generated to justify some of the CFT results. / <p>QC 20151104</p>