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By Yohan Cha, Eun-soo Hong, Gye-Chun Cho

"Rapid population growth and scarcity of space have led many developed cities to bury supply facilities. In line with this, utility tunnels have been employed in Korea since the 1970s. However, approximately 70% of structures were installed more than 20 years ago, in response to the issue of ageing, tunnel enlargement has been proposed. The aim of this study is to investigate geo-mechanical behavior due to tunnel enlargement. Tunnel enlargement methods have been researched to suggest a optimal method. A finite element analysis is conducted to evaluate ground behavior by the expansion of internal space. Vertical displacement and settlement trough width are investigated according to ground stiffness and different enlargement size. It was determined that displacement is affected by the enlargement size and ground stiffness. Based on the deformation results obtained from the numerical analysis, it is possible to predict ground behavior and stability upon tunnel enlargement. INTRODUCTION Various infrastructures such as electric lines, communication lines, gas pipes, and water pipes are jointly accommodated by utility tunnels. These utility tunnels improve the aesthetics of urban areas and help ensure stable supply. The first utility tunnel in Korea was adopted in 1978 and new tunnels are still being installed with the development of new suburb cities. Nevertheless, about 70% of the utility tunnels were installed over 20 years ago and they are still being used through ongoing repair. Moreover, 90% of utility tunnels were installed before 1995. With aging of the nation’s utility tunnels various problems such as concrete deterioration and scarcity of capacity have arisen. As solution, reconstruction has been considered. Reconstruction can enlarge space and improve the performance by replacing existing structures. For reconstruction, two routes have been proposed: underground excavation and cut and cover. In order to avoid traffic problems caused by road occupation and civil appeals during construction projects, underground excavation is the more attractive option. Tunnel enlargement methods have been classified (Seo et al., 2008; An et al 2013) and major considerations during tunnel enlargement have been outlined (Beak et al., 2007). Enlargement construction cases on road tunnels around the world were introduced (Kim et al., 2012) and the deformation curve during tunnel expansion was proposed to investigate the range of protection that should be offered (Kim et al., 2008; Beak et al., 2011). However, tunnel enlargement technology is limited to road tunnels and railway tunnels. Hence, a study on shallow box tunnel enlargement is required for practical application."

Jan 1, 2016

By Adriana Amaro Diacenco

Neste trabalho, os procedimentos para modelagem de estruturas de compósitos do tipo sanduíche que incorporam materiais viscoelásticos são apresentados. A análise numérica foi desenvolvida utilizando a Teoria de Deformação Cisalhante de Primeira Ordem (FSDT), que é implementada em um elemento Serendipity retangular contendo oito nós e cinco graus de liberdade. A incorporação do amortecimento para os modelos de elementos finitos em compósitos de placas laminadas é feita usando a abordagem de módulo complexo e a resolução numérica das equações resultantes do movimento são aspectos particularmente relevantes dos procedimentos de modelagem. Após as discussões de vários aspectos teóricos, as funções de resposta em frequências (FRF's) são calculadas para placas laminadas de compósitos com camada viscoelástica.

Aug 17, 2017

By K. -H. Lux, Z. Hou

ABSTRACT: It is well known in underground mining and waste disposal that the development of excavation damaged zones (EDZ), and thus, hydraulic pathways, is closely related to the excess in the corresponding damage boundary (= long-term strength) of the rock mass and the resulting damage. By integrating short-term and long-term strength, dilatancy, damage and healing into the newly extended Hou/Lux constitutive model for rock salt, it is possible to treat the tertiary creep, to identify the EDZ around underground facilities and to predict the time-dependent development of the EDZ in rock salt. Under in-situ conditions, the EDZ of a 37-year-old drift at the Sondershausen salt mine and the EDZ around a drift dam in rock salt are numerically examined. The numerical analysis gives satisfactory results. RÉSUMÉ: Dans les exploitations minières et le stockage souterrain des déchets, le développement des zones endommagées et fracturées (EDZ – excavation damaged zone), créant des chemins préférentiels pour écoulement, est étroitement lié au contexte géotechnique et à la méthode d’excavation. En intégrant la résistance court et long terme, la dilatance, l’endommagement et le colmatage, le nouveau modèle rhéologique Hou/Lux pour le sel gemme est capable de traiter le fluage tertiaire, d’évaluer l’extension de l’EDZ et de prédire l’évolution de EDZ dans temps autour des ouvrages creusés dans le sel gemme. L’EDZ d’une galerie datée de 37 ans dans la mine de sel de Sondershausen et les EDZ autour de barrage des galeries dans un sel gemme ont été modélisées. Les résultats numériques fournissent des résultats satisfaisants. ZUSAMENFASSUNG: Bekanntlich ist die Entstehung von Auflockerungszonen und damit hydraulischen Wegsamkeiten in der unmittelbaren Umgebung um bergmännische Hohlräume mit der Überschreitung der entsprechenden Schädigungsgrenze eng verbunden. Unter Berücksichtigung der Bruchfestigkeit, Schädigungsgrenze, Dilatanz, Schädigung und Verheilung kann das Stoffmodell Hou/Lux das Verhalten des tertiären Kriechens beschreiben, die Auflockerungszone im Salzgebirge ermitteln und ihre zeitabhängige Ausdehnung vorausberechnen. Mit diesem Stoffmodell werden die Auflockerungszonen einer 37jährigen Strecke in der Salzgrube Sondershausen und die Auflockerungszonen um ein exemplarisches Abdichtungsbauwerk im Salzgebirge numerisch untersucht. Dabei werden zufriedenstellende Berechnungsergebnisse erzielt.

Jan 1, 2003

By Keivan PakIman, Maziar Pasdarpour

Transportation tunnels are highly sensitive to ground movements and are required to be stable and secure for safe operation. In urban areas, the interaction between tunnels and adjacent piles, which are widely used to support buildings and other structures, requires careful consideration. The seismic response of tunnels may vary depending on the lateral stiffness and strength of the tunnel walls, while the axial loading and seismic impact of adjacent piles may cause soil displacement and stress changes that can damage the tunnel lining. As a result, tunnel owners often impose strict limits on the design of new piles lying close to existing tunnels including maximum allowable tunnel deformation, stress change limits, and minimum tunnel to pile separation distances. This paper describes a numerical analysis of the inuence of the axial loading and seismic impact of bored pile foundations on subway tunnels, undertaen using the nite element software laxis D. ased on the results of the numerical analysis, the paper suggests a more realistic and less conservative approach for designing piles in close proximity to transportation tunnels. INTRODUCTION The interaction between tunnels and adjacent piles can cause stress changes and displacements in the soil and structures which may adversely impact structural performance and tunnel safety. It is therefore important to take account of relative load transfer and piling conguration when designing new piles in

Jun 23, 2024

By W. Swidzinski

"Zelazny Most" post-flotation copper mine tailings pond is the only place to of storeing wastes for KGHM POLSKA MI EDZ S.A. The flotation tailings is are the main waste stream in copper mining in Poland. Sufficient storage capacity for tailings is crucial for , thus uninterrupted production of copper is crucially related to the possibility of storing wastes in the pond. The pond covers a Its over 14 km2 arca, almost 50 m high dams making this dame this construction one of the largest in the world. The risk assessment of potential damage due to un stable ility loss of dams or environmental contamination, as well as safely constructing damsincrease of dams within the design criteriaprocess, require quick access to a large amount of the monitoring data , which in vast amount have to be monitored, that needs to be analyzed and processed and reported, every day. This In the paper describes the numerical information system "SyZeM" , used for designated to the "Zelazny Most" pond, baseding on the Oracle database and Geographical Information System , to manage the graphical and descriptive data in coherent way., is presented. The main structure of the system, as well as the methodology of storing, processing and reporting the geological, geotechnical, hydrogeological, geophysical, chemical and survey data are shown. The aspects of Optimizing optimal and risk mitigation and safe management of copper wastes and risk mitigation with the help of "SyZeM" are discussed.

Jan 1, 2007

By Avula Rajashekar Yadav, Sreenivasa Rao Islavath

Barrier pillars and gateroads play a vital role for the safe exploitation of coal from the panel in the longwall workings. The barrier pillars and gateroads are subjected to the front abutment and side abutment loads during the retreat of the panel. These structures may fail if the developed load on them is higher than their strength. The stability of the longwall structures such as barrier, gateroads and face is paramount in extracting the coal from the panel safely. For this, a deep longwall mine in India is chosen for the study using a 3D numerical modelling technique. In this paper, three critical conditions such as scenario 1 (no side goaved-out panel), scenario 2 (with side goaved-out panel) and scenario 3 (with two side goaved-out panels) are taken. For each scenario, five retreat distances such as 100, 125, 150, 175 and 200 m are considered for detailed investigation. The development of vertical displacement in gateroads, vertical stresses on barriers, vertical stress concentration factor, abutment zone and yield zone for longwall face are extracted and analyzed. Also, the safety factor of the barrier and longwall face is estimated considering the Hoek–Brown rock mass failure criterion. From the study, it is observed that the maximum vertical displacement of 121 mm in TG3 at scenario 3 for a retreat distance of 200 m and a minimum vertical displacement of 33 mm in TG2 for a retreat distance of 100 m at scenario 2. The development of vertical stress on the barrier is found to be between 8.78 and 13.40 MPa, and the safety factor of the barrier lies in between 1.56 and 1.80. The study also revealed that the yield zone at the longwall face lies within 2 to 3 m.

Dec 29, 2023

By A. Mainza, A. Mabentsela

A finite element model of a 5 m radius DC arc ilmenite furnace in idling mode was used to test the notion that the slag solidifies when it comes in to contact with colder pig iron, thus constituting the initial step in the formation of solid slag at the slag-pig iron interface. It was found that a slag that is 150°C hotter than the pig iron does not solidify at the interface. The 150°C temperature difference between the slag and pig iron is a result of solid slag at the slag-pig iron interface, not the other way around as suggested in the literature. Calculations show that the thickness of the frozen slag at the slag-pig iron interface is 1.7 cm for the furnace used. It is proposed that slag solidification begins with the slow co-current flow of molten slag and pig iron in the outer parts of the furnace. This provides enough time for molten slag to interact with molten pig iron without solidifying. As the reduction products form due to reduction of the slag by carbon in the pig iron, the slag solidifies. This approach negates the need for the slag to solidify by merely coming into contact with an inherently colder pig iron. Making use of a low thermal contact conductance between the slag and pig iron was found to be sufficient to numerically capture the presence of solid slag at the slag-pig iron interface and to preserve the 150C difference between the slag and pig iron phase.

Mar 30, 2023

By Bo-Hyun Kim, Mark K. Larson

"Bumps remain a critical safety concern in underground coal mining, despite significant advancements in engineering controls. These events occur when relatively high stresses in a coal pillar in conjunction with low confinement exceed the pillar’s critical capacity, causing the pillar to rupture without warning. Floor failure often occurs and can be an indicator of bump risk, as it is strongly associated with brittle failure known as spalling under a lower confinement. Significant floor heave at a western U.S. coal mine has been observed where the pillar width in a three-entry gate road system was 53 m, while no significant floor heave was observed where the pillar width in another gate road system was 22 m. This phenomenon was widely reported in the region and at another mine in another western coal field it has been reported that larger pillars are always associated with floor heave. In this study, a spalling model based on the S-Shaped brittle failure criterion and associated with the anisotropic characteristics of the materials was used in FLAC3D. The observed floor heave phenomenon associated with the larger pillars was demonstrated using this modeling approach.INTRODUCTIONFloor failure in a coal mines often inhibits longwall mining operation, as large displacement of floor strata, known as floor heave, interferes with travel, access, ventilation, and equipment operation. Aggson (USBM 1978) investigated floor heave in West Virginia where underclay is relatively strong and high horizontal stress is present. It was reported that the failure mode is mainly by buckling rather than by plastic flow.This study was developed as part of an effort by the National Institute for Occupational Safety and Health (NIOSH) to better understand rock mass behavior in longwall coal mines in highly stressed, bump-prone ground. More specifically, this study attempts to explain through numerical models small energy releases in the form of floor heave. The authors believe that brittle rock failure is associated with both floor heave and some bump mechanisms, if not directly involved in their cause."

Jan 1, 2019

By Jim Hazzard

A numerical investigation is presented to examine fluid flow in fractured rock slopes. In mining geomechanics, different numerical modelling approaches are used to estimate fluid pressures in open pit mines. The most common technique is the Equivalent Porous Medium (EPM) approach in which the fractured rock is assumed to behave as a porous continuum. Depending on the geometry and properties of the problem, this may not always be the best approach. The paper presents a parametric study to examine the effect of fracture spacing, fracture and matrix diffusivity and excavation rate on the fluid behaviour in rock slopes. Based on the model results, guidelines are provided as to when EPM models can be used and when different modelling approaches (e.g., discrete fracture flow) may be necessary.

Jun 1, 2012

By C. Yi, D. Johansson, C. San Miguel, M. Wimmer

Sublevel caving (SLC) is a mass mining method based upon the utilization of gravity flow of blasted ore and caved waste rock. Production blasting has significant impact on the efficiency and productivity of SLC output, affecting material fragmentation, flow and recovery. Misfires could occur during blasting in SLC, which results in the loss of explosives and poor fragmentation. Usually, the blastholes are top-initiated with redundant lower primers set at + 25 ms as a precaution. If the top primers fail, the lower primers may initiate the explosive, which will induce out-of-sequence delays that can influence fragmentation and gravity flow. This work investigated the impact of misfires and out-ofsequence delays on fragmentation and gravity flow through numerical simulations using a coupled finite element and discrete element method. Different scenarios of misfires and out-of-sequence delays were studied, and the fragment size distribution was obtained to evaluate the blasting performance. The material flow behaviour was investigated to assess the gravity flow process. The results indicated that misfires significantly affect the fragmentation and the gravity flow process while the effects of out-of-sequence delays are not so significant for the investigated cases

Jan 1, 2024

By M. B. Dusseault, A. Pirayehgar

"There is concern that hydraulic fracturing (HF) near an existing critically stressed fault could trigger slip and generate a seismic event of significance. To this end, a mathematical discontinuum model representing a naturally fractured rock (NFR) mass containing a fault is created, and fault slip response to fluid injection is studied. UDECTM is used as a Discrete Element Method (DEM) approach to define the seismic moment, and also to assess the influence of injection and slip on further shear slip propagation. In most of the simulations, slip and dilation take place along a number of oriented fracture surfaces, so it is reasonable to assume that in a real case, microseimic emissions would accompany each slip “event”. The moment magnitude scale (Mw) is used to measure the size of the microseismic event in terms of the energy released. Seismic moment is a measure of the total energy (work) released during a seismic event and is used to measure its size. From another aspect, the injection energy is calculated as the total energy required for achieving the hydraulic fracturing; this is viewed as energy to open fractures against the ambient stress field and much of it is potential stored energy that can be released and create discontinuities (work of fracture), deformations (W=F·d), heat and radiated seismic energy. A small amount of the total released energy is transformed to radiated seismic energy and another small amount results in tensile fractures. Fracture energy is used to calculate the work required to create fracture surfaces. Comparing the energy release by fracturing or seismic events indicates their contribution to the total amount of released energy or total work. The amount of energy associated with the stick-slip event is small compared with the overall work done to generate the distortions (i.e. increases in aperture by forcing them open) in the rock mass, and much of the energy in slip is lost as heat from the plastic deformation, rather than as radiated seismic energy.Microseismic monitoring shows the spatial distribution and magnitude of seismicity associated with slip of bedding planes and natural and incipient fractures. Work calculations have been undertaken to look at the various sources of energy storage (elastic strain energy) or dissipation (slip), and likely the energy losses from viscous dissipation could be addressed as well, helping to clarify HF processes in NFRs."

Jan 1, 2015

By U. Caliskan, S. Miskovic

Gravity separation is a technique that depends on the difference in density of minerals for their separation. Although this method is one of the oldest separation techniques, it is still preferred in the industry because of its low capital and operating cost while it is environmental-friendly. In this paper, we present a new numerical methodology that can be used to investigate dynamics of dense slurry flows in gravity separation systems. A simple channel with a set of riffles is selected as a test platform in order to observe the effect of the riffle shape on segregation profile of particles with different densities. It is believed that the riffle shape would affect the slurry flow and possibly cause one class of particles to segregate within the riffle zone. The turbulence, as a disturbance effect within the riffle zone, causes heavy particles to displace the light, that is, the heavy particles will be trapped in riffles, while the lighter particles are carried by water to the end of the channel, which is an example to uninterrupted suspension. MP-PIC model in OpenFOAM is used to study the effect of riffle shape and slurry percentage of solids in this simple gravity separator on particle segregation profile of four discrete mineral density classes, which are Quartz/Clay (SG 2.6), Pyrite (SG 4.2), Chalcopyrite (SG 5.1), and Gold (SG 19.32). Gold particles are found to be readily captured and retained in the riffles because of their high density, while particles with the intermediate densities are more influenced by the flow. The developed model framework has been proven robust and capable of providing physical results even for the flows with a very high percentage of solids, characteristic for mineral processing operations. INTRODUCTION Gravity-based ore concentration techniques make use of differences in density of minerals within an ore to enable separation of valuables from the gangue. As some of the oldest techniques used for ore beneficiation, they are known to offer a range of benefits such as low specific energy consumption and low capital and operating costs (Burt, 1999; Falconer, 2003; Holland-Batt, 1998), however, they suffer from low selectivity, poor separation efficiency, and low capacity. Gravity separation techniques are common practices in the mining industry and are employed widely for the precious mineral concentration, iron ore recovery and coal preparation (Kroll-Rabotin, Bourgeois, & Climent, 2013; Laplante & Spiller, 2002; Williams, 1997). For example, gravity separation systems are highly applicable for precious metal enrichment operations by being included in primary grinding circuits, shaking table tailing separation, pre-concentration of leach feed and flotation concentrate enrichment for both flash and conventional flotation purposes (Burt, 1999; Falconer, 2003; Holland-Batt, 1998; Laplante & Spiller, 2002; McAlister, 1992). Gravity separation can be employed in the copper processing circuits by being integrated into the pre-flotation circuit to capture the gravity recoverable gold (GRG) and any free copper aiming to enhance the gold and copper recovery of the plant. When native copper and GRGs are present in the deposit, this integration not only facilitates plant overall performance via removal of the valuables early in the circuit, but it also reduces downstream operational expenditures due to less retention time of coarser copper particles in the system.

Jan 1, 2019

By Thomas Novak, Sampurna Arya

Controlling dust generation and keeping it below permissible limits to meet federal dust standards at the working face of a room-and-pillar coal mine is a challenge for a mine operator. With the recent changes in federal dust regulations requiring lower worker exposure, maintaining compliance has become increasingly difficult. The current most effective practice of dust control at a continuous miner face in an underground mine is the use of a flooded-bed scrubber. A study carried out by the U.S National Institute for Occupational Safety and Health (NIOSH) indicated that a flooded-bed scrubber could achieve cleaning efficiencies between 58 and 90 percent. But the operation of such a system is maintenance intensive. The flooded-bed scrubber screen becomes clogged with dust particles and requires frequent cleaning to maintain performance. However, the dust control issue is not solely a mining-industry problem. Other industries face similar issues. The University of Kentucky collaborated with Toyota Motor Manufacturing on the development of a novel wet scrubber, called the vortecone scrubber, for capturing over-sprayed paint particles in automotive paint booths. The vortecone scrubber achieved a cleaning efficiency of 99 percent and required minimal maintenance. This study aims to assess the ability of this vortecone scrubber to capture respirable dust in an underground coal mine. The paper presents the results of computational fluid dynamics (CFD) modeling of this vortecone scrubber. It discusses the effects of air quantity and dust particle size on the performance of the scrubber. 

By Thomas Novak, Sampurna Arya

Controlling dust generation and keeping it below permissible limits to meet federal dust standards at the working face of a roomand-pillar coal mine is a challenge for a mine operator. With the recent changes in federal dust regulations requiring lower worker exposure, maintaining compliance has become increasingly difficult. The current most effective practice of dust control at a continuous miner face in an underground mine is the use of a flooded-bed scrubber. A study carried out by the National Institute for Occupational Safety and Health (NIOSH) indicated that a flooded-bed scrubber could achieve cleaning efficiencies between 58 and 90%. But, the operation of such a system is maintenance intensive. The flooded-bed scrubber screen becomes clogged with dust particles and requires frequent cleaning to maintain performance. However, the dust control issue is not solely a mining industry problem. Other industries face similar issues. The University of Kentucky collaborated with Toyota Motor Manufacturing on the development of a novel wet scrubber, called the vortecone scrubber, for capturing oversprayed paint particles in automotive paint booths. The vortecone scrubber achieved a cleaning efficiency of 99% and required minimal maintenance. This study aims to assess the ability of this vortecone scrubber to capture respirable dust in an underground coal mine. The paper presents the results of computational fluid dynamics (CFD) modeling of this vortecone scrubber. It discusses the effects of air quantity and dust particle size on the performance of the scrubber.

By Thomas Novak, Sampurna Arya

Controlling dust generation and keeping it below permissible limits to meet federal dust standards at the working face of a roomand-pillar coal mine is a challenge for a mine operator. With the recent changes in federal dust regulations requiring lower worker exposure, maintaining compliance has become increasingly difficult. The current most effective practice of dust control at a continuous miner face in an underground mine is the use of a flooded-bed scrubber. A study carried out by the National Institute for Occupational Safety and Health (NIOSH) indicated that a flooded-bed scrubber could achieve cleaning efficiencies between 58 and 90%. But, the operation of such a system is maintenance intensive. The flooded-bed scrubber screen becomes clogged with dust particles and requires frequent cleaning to maintain performance. However, the dust control issue is not solely a mining industry problem. Other industries face similar issues. The University of Kentucky collaborated with Toyota Motor Manufacturing on the development of a novel wet scrubber, called the vortecone scrubber, for capturing oversprayed paint particles in automotive paint booths. The vortecone scrubber achieved a cleaning efficiency of 99% and required minimal maintenance. This study aims to assess the ability of this vortecone scrubber to capture respirable dust in an underground coal mine. The paper presents the results of computational fluid dynamics (CFD) modeling of this vortecone scrubber. It discusses the effects of air quantity and dust particle size on the performance of the scrubber.

By B. Mishra, Q. Shi, Y. Zhao, G. Zhao

Shale is anisotropic due to the presence of bedding planes. The anisotropic strength of shale has been extensively studied. However, little attention has been paid to the size effect on shale strength considering the anisotropy. This research uses the discrete element method to study the size effect on the strength of shale under the uniaxial stress state. It is assumed that the anisotropy is caused by bedding planes, while the size effect is caused by randomly distributed flaws. The numerical model of shale comprises three components: shale matrix modeled by bonded particles (2) bedding planes modeled by smooth joints (3) flaws modeled by discrete fractures. The developed model is scaled to different sizes and tested in the uniaxial compression and the direct tension tests. The test result show that the uniaxial compressive strength decreases as the specimen size increases when the loading direction is perpendicular or parallel to bedding planes. The uniaxial compressive strength is determined by the flaws while the bedding planes only play a limited role. However, the size effect on the direct tensile strength depends on the direction of bedding planes. When the loading is perpendicular to bedding planes, the size effect is not prominent. The direct tensile strength is determined by the bedding planes while the flaws have little effect. When the loading direction is parallel to bedding planes, the direct tensile strength decreases when the specimen size increases. The direct tensile strength is determined by the flaws while the bedding planes have little effect.

Mar 2, 2022

By D. K. Weatherley, T. P. Oladele, L. B. Bbosa

Comminution is a critical stage of mineral processing which aims to reduce the size of ore particles through breakage, consequently increasing the likelihood of liberation of valuable minerals. Several factors, such as pre-existing cracks, mineralogical composition and particle size, are known to affect ore breakage behaviour. While investigating the contributing role of each factor is essential to improve understanding of breakage, isolating individual factors by experiment is typically impractical. Numerical techniques such as the Bonded Particle Model-Discrete Element Method (BPM-DEM) have been developed as a means of studying closely controlled breakage conditions. This study evaluates this technique in modelling the effect of pre-existing cracks breakage behaviour for synthetic ore specimens during impact breakage in a short impact load cell (SILC). Synthetic ore was modelled as a collection of discrete entities connected by brittle-elastic beams. Model parameters were calibrated against macroscopic material properties of a conventional homogenous synthetic ore. The extent of pre-existing cracks within specimens was prescribed by varying discontinuities between the connecting entities. An approach with the insertion of seed points was used to model the mineralogy of the specimens. Results showed that pre-existing cracks resulted in a decrease in the fracture force as the crack density increased. Additionally, the irregularity of fracture patterns within rock specimens after impact became more apparent as the crack density increased. The findings were used to emphasise some of the attributable causes of the variation observed between ore hardness characterisation tests and in situ ore behaviour. Keywords: Element Method; Bonded Particle Model, synthetic rock sample; rock fracture, preexisting cracks

Jan 1, 2020

By Mogens Henriksen

In the past decade, numerous urge scale drilling projects have made use of reverse circulation air lift methods. Reverse air lift pumping can be established by injecting gas into a column of liquid; the subsequently decreased density of the gas-liquid mixture allows atmospheric pressure outside the lift conduit to establish flow. The rate of flow can be controlled by varying the gas to liquid ratio. A typical reverse circulation air lift system is depicted in Figure 1. Allen1 has described a number of reverse air lift drilling projects. Although cited examples are generally related to large diameter holes, the method has seen use in other applications such as sand dredging, chemical pumping, water well pumping and continuous coring. One particular benefit obtained with enclosed reverse circulation drilling is elimination of lost circulation. The required air/water ratio for pumping at a given submergence and lift has been established experimentally by Gibbs2. His data, however, do not reflect sensitivity of flowrate to air/water ratio. Further, in Gibbs' work, air apparently is injected continuously along the column of water. This configuration differs from that used in reverse air lift drilling where air is injected at discrete points only. Gas lift theory has received considerable attention over the past decades. Orldszewski3 defined flow regimes in two phase flow. Griffith and Wallis4 determined relative velocities of gas to liquid. Two-phase flow has been studied extensively for oil transport in inclined and vertical pipes by Chierici et a15, Beggs and Brill6, and Gould, Tek and Katz.7

Jan 1, 1977

By Essie Esterhuizen, Michael M. Murphy, Chris Mark

"The design of underground coal mines requires a clear understanding of the overburden response, the loading of pillars, the loading of the gob, the pillar failure process, and the ultimate load carried by partly or fully yielding pillars. Very few highquality stress measurements of yielding pillars and gob loading have been made in full extraction mining. Well-calibrated numerical models can assist in providing a better understanding of the load and failure processes, provided the coal, the overburden, and the gob are all modeled with sufficient realism. A program of numerical model calibration and validation was carried out using FLAC3D.1 The models were calibrated against observed and measured performance of coal pillars and the overburden in operating mines to provide a basic set of input parameters that can be used to provide a realistic first estimate of expected ground response and pillar loading. Input parameters for modeling coal pillar response were based on data from triaxial testing on coal samples, combined with both matching the depth of failure in the coal ribs to observations as well as matching the peak pillar resistance to an empirical equation. The models were calibrated against strong roof and floor case histories in which the pillar strength is governed by failure and yielding of the coal within the pillar and the surrounding strata only had a limited impact on pillar strength. Input parameters for the overburden were determined from a large database of laboratory tests and model calibration against maximum subsidence and subsidence curvature. Further overburden calibration was carried out by matching stresses in the mining horizon to field measurements. Three examples of the application of the calibrated dataset and modeling methodology to field measurements are presented. The results show that a reasopable estimate of the in-seam stress distribution and overburden response can be obtained for both strong and weak overburden scenarios at various depths of cover.INTRODUCTIONThe planning and design of coal mine excavations requires reliable estimates of the expected strength and loading of the mine structures to achieve global stability. Empirical methods are widely used to estimate the strength and loading of coal pillars and have been incorporated into pillar design procedures, such as Analysis of Longwall Pillar Stability (ALPS) (Mark, 1987) and Analysis of Retreat Mining Pillar Stability (ARMPS) (Mark and Chase, 1997), that are widely used in the United States. ~umerical models are finding increasing application as a tool for underground mine design because of their. versatility and the ever increasing computational power available to mine designers. A prerequisite for the application of numerical models is the calibration of the models against observed rock mass response (Hoek et al., 1990; Skiles and Stricklin, 2009). The calibration process may include comparison of model results to measured stress and deformation and modifying the input parameters in a systematic manner to achieve a satisfactory agreement between the model results and measurements. Once models have been calibrated, they can be applied to evaluating similar mining layouts in similar geological conditions."

Jan 1, 2010

By K. M. Mohamed, I. B. Tulu

"Failures of coal ribs are major hazards in underground coal mines. For the period of 2010 to 2014, rib falls were the leading cause of groundfall fatalities and accounted for 35% of all groundfall-related fatalities. Currently, the National Institute for Occupational Safety and Health (NIOSH) is conducting a research project to develop an engineering-based design methodology for rib control in coal mines to reduce rib fall accidents and fatalities in underground coal mines. Numerical models can be used as part of the design methodology provided the models are appropriately calibrated and verified. The paper presents a coal rib model to simulate the mechanism of the coal deformation and fracturing that can lead to stress-driven rib falls. The proposed coal rib model was calibrated against published data from an instrumented rib site at the West Cliff mine in Australia. Fracturing of the coal rib was defined by critical values of shear strain of the coal material and rib displacement. A critical plastic shear strain of 2.8% and a sudden increase of rib displacement of 30 to 45 mm were sufficient to develop a fracture plane in the rib model. Accordingly, a discontinuous rib deformation was achieved and it compared favorably against field monitoring data. INTRODUCTION Coal ribs are the vertical walls of coal formed when entries are developed in a coal bed. Failures of coal ribs are a major hazard in underground coal mines. Furthermore, failing ribs can contribute indirectly to roof and floor instability by increasing opening widths across intersections and entryways. Over the last 18 years, there has been a continual occurrence of injuries and fatalities in underground coal mines due to rib falls. For the period of 2010 to 2014, rib falls (excluding longwall face and bursts) were the leading cause of ground fall fatalities and accounted for 35% of all groundfall-related fatalities [1]. Despite the threat of rib falls, the amount of rib falls and rib support research conducted in the U.S. is limited compared with what has been done in pillar and roof support design. Currently, the National Institute for Occupational Safety and Health (NIOSH) is conducting a research project to develop an engineering-based design methodology for rib control in coal mines to minimize the number of rib fall accidents and fatalities in underground coal mines."

Jan 1, 2016