Deep Cover Research Articles

Ambient noise tomography of an iron-oxide copper–gold (IOCG) deposit under thick cover

As most outcropping and shallow mineral deposits have been found, new technology is imperative to finding the hidden critical mineral deposits required for the renewable energy transition. One such seismic technique, called ambient noise tomography (ANT), has shown promise in recent years as a low cost and low environmental impact passive method of three-dimensional (3D) imaging of shear-wave velocity structure of the Earth. Over the last twenty years the method has been well-established in academia to image crustal and regional scale geological features but has seldom been used at the mineral exploration deposit-scale. In this paper we show the application of seismic ANT at an IOCG deposit in South Australia under more than 750 m of sedimentary cover. A 100-site survey in a 10 by 10 grid with site spacing of 1 km, using 3-component nodal seismometers with a natural-frequency of 5 Hz, was conducted over a two-week period. Data were inverted to generate a 3D velocity model to a depth of 2 km. When compared to drillholes in the survey area, the tomographic model delineates cover sequence lithologies and the depth of crystalline basement. A velocity anomaly in the basement has characteristics of a potential IOCG deposit and is aligned with a gravity anomaly due to brecciated haematite. The results of the paper indicate that ANT is a useful tool for deep cover mineral exploration that can potentially expedite the discovery of new deposits.

Natural source-field induced polarisation exploration of an iron-oxide copper-gold (IOCG) deposit under thick cover

Induced polarisation (IP) is a common geophysical method of exploration for disseminated sulphides. However, in areas with deep (>200 m) and conductive (10 Ωm or less) cover, the technique is less successful as it requires a significant transmitter source and large-offset dipoles. An alternative approach is to use natural-variations in Earth’s external magnetic field as the polarising source of the signal, known as natural-field IP. This paper presents a study of extracting IP information from electrical dipole observations during a broadband magnetotelluric (MT) program with a 9 km by 9 km grid of 100 sites above the Vulcan IOCG deposit beneath 750 m of cover, ∼40 km north of the Olympic Dam IOCG mine in South Australia. Inter-site transfer functions between 95 sites and five reference sites at the southeast and southwest corners of the grid were computed to determine a phase shift between horizontal electric fields in the bandwidth of 1–100 s period. Phase shifts of up to – 5 degrees were centred on a region of brecciated hematite where drill holes intersected pyrite, and an inferred fault-zone from passive seismics that marks the boundary between upper crust that is resistive (>100 Ω.m) with high magnetic susceptibility to the south of the fault, and a region of conductive crust (<10 Ω.m) which is low magnetic susceptibility. Our study suggests that the natural-field IP method can identify regions of polarizable minerals beneath deep cover where artificial power sources cannot be feasibly deployed. Such surveys are cheaper, safer, and easier to deploy as only receivers are required, and 3D coverage can be obtained as the source-field is of much larger dimension than the survey array. In addition, the natural-field IP signals are observed as part of the MT program so that both electrical resistivity and polarisation parameters can be determined.

Resisting the KGB Mythmakers: Willy Fisher, spy fiction, and the myth of Rudolf Abel

ABSTRACT The Soviet Committee for State Security (KGB) suffered a shocking setback when the head of its deep cover (illegal) agent networks in the United States Rudolf Abel, whose real name was William (Willy) Fisher, was arrested in Brooklyn in 1957. After Fisher was swapped for the downed CIA U-2 pilot Francis Gary Powers and an American PhD student Frederic Pryor in 1962, the KGB attempted to turn the setback into a public relations victory by constructing the myth of an ideal Soviet intelligence officer. However, the myth required that Fisher continue his public life under the assumed identity of Rudolf Abel until his death and beyond. Drawing on KGB archival documents, memoirs of former KGB officers, Fisher’s published personal letters, and Russian language journalistic accounts, this article chronicles and analyses both the KGB activities to make Fisher into the mythic Abel and the former officer’s seemingly hopeless but remarkably persistent struggle to preserve his personal identity and integrity. A struggle that culminated in a little-known spy fiction novella which, using allusions and metaphors, articulated his critique of the KGB.

“All I Do Is Think of You”

Research Article| June 01 2023 “All I Do Is Think of You” Michael Boyce Gillespie Michael Boyce Gillespie Michael Boyce Gillespie is an associate professor in the Department of Cinema Studies at New York University. His research interests include black visual and expressive culture, film theory, visual historiography, popular music, and contemporary art. He is the author of Film Blackness: American Cinema and the Idea of Black Film (Duke University Press, 2016) and co-editor with Lisa Uddin of Black One Shot, an art criticism series on ASAP/J. His recent writing has appeared in Regeneration: Black Cinema 1898-1971, Film Comment, Film Quarterly, liquid blackness, and Ends of Cinema. He was the consulting producer on The Criterion Collection releases of Deep Cover and Shaft. Search for other works by this author on: This Site PubMed Google Scholar Journal of Popular Music Studies (2023) 35 (2): 5. https://doi.org/10.1525/jpms.2023.35.2.5 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Michael Boyce Gillespie; “All I Do Is Think of You”. Journal of Popular Music Studies 1 June 2023; 35 (2): 5. doi: https://doi.org/10.1525/jpms.2023.35.2.5 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentJournal of Popular Music Studies Search This dossier, a gathering of five essays, is devoted to distinct concentrations on the affective registers of songs. Each paper enacts a generative sense of the politics and pleasures of music, demonstrating the work of listening to and thinking with/through this music. These essays evince critical adjacencies and crucial consequences of music by considering the resonances and textures of the sonic. What began as a panel for the 2022 Pop Conference has expanded to consider a range of inquiries that center music’s meaning-making capacities. In total, this work explores issues of historiography, gender, melancholy, culture, performativity, mnemonic relations, memorialization, and becoming. Together, Miriam Petty and Joshua Chambers-Letson share their mutual and respective identification with “Everything’s Alright” from Jesus Christ Superstar. Brittnay L. Proctor examines the black womanist abundance of Minnie Riperton’s vocal performance on Come to My Garden (1970). Julie Beth Napolin focuses on the poignancy of Barbara Lewis’s... You do not currently have access to this content.

Seven Curses

Research Article| June 01 2023 Seven Curses Michael Boyce Gillespie Michael Boyce Gillespie Michael Boyce Gillespie is an associate professor in the Department of Cinema Studies at New York University. His research interests include black visual and expressive culture, film theory, visual historiography, popular music, and contemporary art. He is the author of Film Blackness: American Cinema and the Idea of Black Film (Duke University Press, 2016) and co-editor with Lisa Uddin of Black One Shot, an art criticism series on ASAP/J. His recent writing has appeared in Regeneration: Black Cinema 1898-1971, Film Comment, Film Quarterly, liquid blackness, and Ends of Cinema. He was the consulting producer on The Criterion Collection releases of Deep Cover and Shaft. Search for other works by this author on: This Site PubMed Google Scholar Journal of Popular Music Studies (2023) 35 (2): 32–38. https://doi.org/10.1525/jpms.2023.35.2.32 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Michael Boyce Gillespie; Seven Curses. Journal of Popular Music Studies 1 June 2023; 35 (2): 32–38. doi: https://doi.org/10.1525/jpms.2023.35.2.32 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentJournal of Popular Music Studies Search They were not cowards and we are not heroes. We are mourners.Susan Sontag1The current saber-rattling is probably giving him more than a slight case of déjà vu right about now. This is where he came in, way back when, our freewheelin’ troubadour, with his “Talkin’ World War III Blues,” his “Hard Rain’s A-Gonna Fall,” his “Masters of War.” Before 9.11.01, Love and Theft was an abstract expressionist painting Dylan could never have intended to carry a topical frame. Funny what a little moonlight can do: Now poets are bringing us the news. Before that fateful Tuesday, Love and Theft could not have been so easily read as Dylan’s contribution to the literature of the apocalypse.Greg Tate2 September 11, 2001. The day Bob Dylan’s Love and Theft was released. As Greg Tate’s review of the album that ran in the Village Voice two weeks later made... You do not currently have access to this content.

Strategies for Targeting in Undercover Terrains: Modeling Multi-Source Data in Apuí Region, SW Amazon Craton, Brazil

Exploring covered terrains is a challenge that requires the integration of multiple sources of knowledge, particularly in the initial stages of mineral exploration. The Apuí region, located in the Southwestern Amazon Craton, has a small and constant gold production, despite the deep cover and limited geological knowledge. The gold is mainly hosted in quartz veins and breccias that cut Paleoproterozoic volcano-sedimentary sequences. The occurrences have similar characteristics to magmatic–hydrothermal deposits, such as a lack of regional metamorphism and intense hydrothermalization. We undertook a multi-source prospective investigation on different scales using 2D and 3D techniques to translate the footprints of the mineral system into mappable criteria. Gold prospectivity maps for the Juma District and Guida Target were produced by integrating geological, geochemical, and geophysical datasets in knowledge-driven fuzzy systems. Regional airborne magnetization vector inversion (MVI) models were utilized. The correlation between the drill cores and the magnetic susceptibility models highlighted a potential surface for gold mineralization associated with the boundary between a granitic intrusion and volcano-sedimentary rocks. The prospectivity maps reduced the search area, and the regional susceptibility models allowed for the reconnaissance of structures and bodies that may be related to gold mineralization at depth. The results present new strategies for increasing discovery performance in the Southern Amazon Craton under cover.

Digging Deep: A Journey into Southeast Asia’s Past. Charles Higham. Bangkok: River Books, 2021. 256 pp., 226 photographs. Paperback ฿850, ISBN 97886164510586.

Asian Perspectives, Vol. 62, No. 2 © 2023 by the University of Hawai‘i Press. Digging Deep: A Journey into Southeast Asia’s Past. Charles Higham. Bangkok: River Books, 2021. 256 pp., 226 photographs. Paperback ฿850, ISBN 97886164510586. Reviewed by Dougald O’REILLY, Australian National University Autobiographies penned by archaeologists are rare finds indeed and with his book Digging Deep: A Journey into Southeast Asia’s Past, Professor Charles Higham joins the august ranks of Sir Mortimer Wheeler and W. M. Flinders Petrie in penning a reckoning of his distinguished career in the field. Over 14 chapters, Higham takes us through the arc of his life, beginning with a childhood recounted in remarkable detail thanks to the author’s habit of keeping a daily journal throughout his life. The first four chapters of Digging Deep cover Higham’s formative years. Born in 1939, Higham was educated in South London. He developed a passion for archaeology at an early age, due in part to Mortimer Wheeler’s appearance on British television. Higham and his brother first volunteered in the 1955 excavations of the Bronze Age site of Snail Down in Wiltshire before broadening their horizons by working on the digs at Arcy sur Cure in France. Higham studied for two years at the Institute of Archaeology, London University, with a focus on the archaeology of the western Roman provinces. He was privileged to have the opportunity to excavate in the United Kingdom at the Roman-era site of Verulamium and in France at an Iron Age site, Camp du Charlat. In 1959, he took up an offer from Cambridge University, where he studied the European Neolithic, Bronze, and Iron ages. In Digging Deep, these early years read like a Boy’s Own adventure, including an early trip to excavate in the fabulously named Grotte de L’Hyène in France and being awoken from siesta by Mongolian bagpipes played by the excavation director. A highlight of Higham’s time at Cambridge was being selected for the university’s rugby side and playing before a crowd of nearly 70,000 spectators and later being selected as an England triallist. A rugby career was not to be and Higham embarked on a doctorate focused on the prehistoric economic history of Switzerland and Denmark. He was awarded his Ph.D. in 1966. In the late 1960s, antipodean universities were eager to attract academic talent and recruited many Cambridge graduates. Higham was offered a lecturing position at the University of Otago in New Zealand the year he completed his doctorate. He was appointed Foundation Professor of Anthropology only two years later, at the age of 29. An American graduate student, Donn Bayard, later to have a long and distinguished career himself at Otago, introduced Higham to Southeast Asian archaeology. This area of study was largely overlooked at the time, but was brought to prominence by a number of astonishing claims including what was dubbed the ‘WOST’, World’s Oldest Socketed Tool, which was dated at the time to the fourth millennium B.C. (Solheim 1968). Higham’s work with Bayard at the Thai site of Non Nok Tha led to an introduction to another fabled Southeast Asian specialist, Chet Gorman, who Higham was told “was a bit wild [and] a bit too keen on illegal stimulants;” indeed, Higham recounts being offered some “herbacious-looking stuff” that Gorman called ‘Sakhon Nakon crippler’ during one of their digs (p. 91). Gorman and Higham excavated together in remote jungle in northern Thailand chasing the origins of agriculture while listening on the radio to reports of downed B-52 bombers over the not-too-distant north Vietnam. They continued their collaboration at the famed site of Ban Chiang in Northeast Thailand. These early experiences in Thailand convinced Higham of the importance of understanding the arc of human development in Southeast Asia and he struck out on his own, as is detailed in chapter 7. Building on the relationships he had established with Thai researchers, many of whom were to study with him in New Zealand, Higham focused his attention on “a little gem of a site,” Ban Na Di, while Gorman continued research at Ban Chiang (p. 98). It was...

Rockmass Permeability Induced by Longwall Mining Under Deep Cover: Potential Gas Inflow from a Sheared Gas Well

Rockmass Permeability Induced by Longwall Mining Under Deep Cover: Potential Gas Inflow from a Sheared Gas Well

Behavior and innovative design model on soil pressure at the top of large-diameter buried steel pipes

Existing design models of soil pressure at the top of buried steel pipes are limited to small-diameter pipes. This study aims to investigate the behavior and design model on the soil pressure for large-diameter pipes considering the pipe diameter, diameter-to-thickness ratio, and cover depth. The distribution and size of soil pressure are obtained from finite element models and compared with traditional design models. Sensitivity studies of soil parameters, trench parameters, and friction coefficients are discussed. Furthermore, an innovative design model of soil pressure for large-diameter pipes is proposed. The results indicate that the basic distribution pattern of soil pressure is the “inverted basin”/parabola for large/small-diameter pipes, respectively. Peak soil pressure typically appears in the pleura of pipes with great flexibility and deep cover depth. The modulus and Poisson's ratio of backfill and soil-soil friction coefficient have an influence range of within 10% for soil pressure, while trench parameters have a more significant influence. Prism load is too large at high cover depth, and Marston load is small at low cover depth. The proposed basin model for soil pressure adopts the form of “straight line + parabola” for distribution and “Marston + pleura” load for size, with high accuracy and strong adaptability.

Maximizing drilling information in greenfields exploration: Linking the fabric and geochemical footprint of the basement to the surface in South Australia

Detection of mineral system footprints in regions under thick cover is challenging. The difficulties are enhanced in regions with low-relief landscapes that are deeply weathered. This research examines how information from a single drill hole in an underexplored region can deliver a significant amount of information to assist in greenfields exploration. This study describes the geochemical dispersion processes through >500 m of cover based on observations from drill hole CDP008, and explores the possibility of recognising landscape features that link basement features with the surface.Our study revealed that: (1) the lower fluvial sandstone package contains a geochemical footprint of the underlying basement rocks, produced by vertical and lateral geochemical dispersion; whereas (2) the overlying sediments do not record any footprint of the basement rocks; and (3) the top limestone units are a chemical barrier for vertical geochemical dispersion due to their lack of permeability.Basement features identified from magnetic data are mimicked by linear surface landscape features that lie above them, which may potentially be associated with vertical geochemical dispersion processes, linking the basement with the surface. Hence from the point of view of mineral exploration, surface geochemical sampling should target these particular neotectonic/reactivation-associated features of the landscape.We suggest that in areas of deep cover, neotectonics/reactivation surface landscape features have the highest prospectivity to detect deep basement geochemical signatures at surface. The findings from this study may therefore impact approaches to mineral exploration under cover in similar landscape contexts around the world, such as regions in West Africa, India, China and Brazil.

Geochemical exploration of ore deposits that are hidden beneath the surface. Status and prospects

The reduction in the number of deposits reaching the modern erosional surface has led to the need to develop and improve the geochemical exploration methods for searching for deposits under deep cover. They are focused on the identification of gas and lithochemical halos of indirect (CO2, H2, He, NH4+, K+ ions, etc.) and direct indicators (Au, Pb, Cu, etc.) for buried ore bodies and blind deposits. The data of experimental and methodical works for numerous deposits of different genesis suggest that the formation of superimposed halos of these two groups of indicators of ore-forming environment proceeds by a single mechanism. Their joint migration to the day surface and the subsequent unloading into the atmosphere form halos in the subsurface air, where the concentration of the indicative elements many times exceeds the geochemical background. That allows laser analytical equipment used in meteorology (lidars, correlation spectrometers, etc.) to be applied during fi ldwork to monitor the composition of the atmosphere.

Spy House

How does the performance of an actor differ from that of a spy? Is the successful spy transformed, not simply transported? Is playing a role no longer playing for the effective spy? These questions touch on the distinctions in performance theory articulated for decades by Richard Schechner as ‘transportation’ and ‘transformation’. First outlined in his 1981 essay ‘Performers and spectators transported and transformed’, Schechner’s theory of where performance can take a person makes the important distinction between that which is temporary and that which is permanent. Deceptive deep cover performances fundamentally rely on transportation being the only outcome and never transformation. If the spy transforms, the spy will no longer be deceiving the enemy; the spy will have joined the enemy, become the enemy, perhaps by default serve the enemy. On the other hand, the most successful undercover performance would be so complete that it would be not simply acting (transportation) but the real thing (transformation). This article interrogates the tension between transportation and transformation in actual and representations of deep cover.

Longwall mining, shale gas production, and underground miner safety and health

This paper presents the results of a unique study conducted by the National Institute for Occupational Safety and Health (NIOSH) from 2016 to 2019 to evaluate the effects of longwall-induced subsurface deformations on shale gas well casing integrity and underground miner safety and health. At both deep-cover and shallow-cover instrumentation sites, surface subsidence measurements, subsurface in-place inclinometer measurements, and underground pillar pressure measurements were conducted as longwall panels were mined. Comparisons of the deep-cover and shallow-cover test site results with those from a similar study under medium cover reveal an interesting longwall-induced response scenario. Under shallow and medium covers, measured horizontal displacements within the abutment pillar are one order of magnitude higher than those measured under deep cover. On the other hand, measured vertical compressions under deep cover are one order of magnitude higher than those under shallow and medium covers. However, FLAC3D simulations of the casings indicate that, in all three cases, the P-110 production casings remain intact under longwall-induced deformations and compressions, which has serious implications for future mine design in areas where shale gas wells have been drilled ahead of mining.

Re-analysis of Abutment Angle Method for Moderate and Deep Cover Retreat Room and Pillar Mines and Investigation of Loading Mechanics Using Finite Volume Modeling

Mining-induced stresses in underground coal mines play a significant role in pillar and ground support design, hence in the safety of mining operations. In the US, Analysis of Longwall Pillar Stability (ALPS) and in Australia, Analysis of Longwall Tailgate Serviceability (ALTS) software are used for designing Longwall coal mine layouts; and in the US, Analysis of Retreat Mining Pillar Stability (ARMPS) software is used to design retreat room-and-pillar mine layouts. All these software determine the adequacy of the design by comparing the estimated loads to the load-bearing capacity of the pillars and they use the “abutment angle” concept and a square decay stress distribution function to calculate the magnitude and distribution of the mining-induced loads. The abutment angle concept has been successfully applied to US longwall coal mines with the use of ALPS and ALTS in Australia. ARMPS uses the same concept for retreat room and pillar coal mine design in the US. The suggested abutment angle for coal mines in the US was derived as 21° by the back analysis of underground stress measurements from the 1990s and implemented in ALPS and ARMPS. The ALPS methodology was re-examined and calibrated for Australian conditions with additional Australian stress measurements and resulted in the original ALTS methodology which has been continually improved and expanded with additional cases. In this paper, some recent stress measurements are back-analyzed, and the abutment angles are investigated to verify the applicability of using 21° in retreat room and pillar mines with different depths and mining dimensions. For shallow mines, the derivation of the 21° abutment angle is supported by the new case histories. However, at depths greater than 200 m, the abutment angle was found to be decreasing with increasing depth. In this study, a new equation for the calculation of abutment angle for moderate and deep cover cases was constructed and tested for its applicability in retreat room and pillar mines. The differences in the mechanism of complete side abutment loads in shallow and deep cover mines are further analyzed by applying the finite volume modeling (FVM) approach to two case study mines, one shallow, and one deep cover. A 2D model of each mine is created and one-side and two-side abutment loads of consecutive panels are analyzed. Analysis of the deep cover mine indicated that the prior panel gobs provide a considerable amount of support to the overburden strata. These higher gob loads prevent a higher percentage of overburden loads from being transferred to the active panel workings, and this is in agreement with the lower abutment angles observed for deep cover mines. The findings of this study should only be used for retreat room-and-pillar mines’ production pillar loads since these are calculated geometrically using the abutment angle concept.

Pillar design and coal burst experience in Utah Book Cliffs longwall operations

Longwall mining has existed in Utah for more than half a century. Much of this mining occurred at depths of cover that significantly exceed those encountered by most other US longwall operations. Deep cover causes high ground stress, which can combine with geology to create a coal burst hazard. Nearly every longwall mine operating within the Utah’s Book Cliffs coalfield has been affected by coal bursts. Pillar design has been a key component in the burst control strategies employed by mines in the Book Cliffs. Historically, most longwall mines employed double-use two-entry yield pillar gates. Double-use signifies that the gate system serves first as the headgate, and then later serves as the tailgate for the adjacent panel. After the 1996 burst fatality at the Aberdeen Mine, the inter-panel barrier design was introduced. In this layout, a wide barrier pillar protects each longwall panel from the previously mined panel, and each gate system is used just once. This paper documents the deep cover longwall mining conducted with each type of pillar design, together with the associated coal burst experience. Each of the six longwall mining complexes in the Book Cliffs having a coal burst history is described on a panel-by-panel basis. The analysis shows that where the mining depth exceeded 450 m, each design has been employed for about 38000 total m of longwall panel extraction. The double-use yield pillar design has been used primarily at depths less than 600 m, however, while the inter-panel barrier design has been used mainly at depths exceeding 600 m. Despite its greater depth of use, the inter-panel barrier gate design has been associated with about one-third as much face region burst activity as the double-use yield pillar design.

The current perspective of the PA 1957 gas well pillar study and its implications for longwall gas well pillars

Many states rely upon the Pennsylvania 1957 Gas Well Pillar Study to evaluate the coal barrier surrounding gas wells. The study included 77 gas well failure cases that occurred in the Pittsburgh and Freeport coal seams over a 25-year span. At the time, coal was mined using the room-and-pillar mining method with full or partial pillar recovery, and square or rectangle pillars surrounding the gas wells were left to protect the wells. The study provided guidelines for pillar sizes under different overburden depths up to 213 m (700 ft). The 1957 study has also been used to determine gas well pillar sizes in longwall mines since longwall mining began in the 1970 s. The original study was developed for room-and-pillar mining and could be applied to gas wells in longwall chain pillars under shallow cover. However, under deep cover, severe deformations in gas wells have occurred in longwall chain pillars. Presently, with a better understanding of coal pillar mechanics, new insight into subsidence movements induced by retreat mining, and advances in numerical modeling, it has become both critically important and feasible to evaluate the adequacy of the 1957 study for longwall gas well pillars. In this paper, the data from the 1957 study is analyzed from a new perspective by considering various factors, including overburden depth, failure location, failure time, pillar safety factor (SF), and floor pressure. The pillar SF and floor pressure are calculated by considering abutment pressure induced by full pillar recovery. A statistical analysis is performed to find correlations between various factors and helps identify the most significant factors for the stability of gas wells influenced by retreat mining. Through analyzing the data from the 1957 study, the guidelines for gas well pillars in the 1957 study are evaluated for their adequacy for room-and-pillar mining and their applicability to longwall mining. Numerical modeling is used to model the stability of gas wells by quantifying the mining-induced stresses in gas well casings. Results of this study indicate that the guidelines in the 1957 study may be appropriate for pillars protecting conventional gas wells in both room-and-pillar mining and longwall mining under overburden depths up to 213 m (700 ft), but may not be sufficient for protective pillars under deep cover. The current evaluation of the 1957 study provides not only insights about potential gas well failures caused by retreat mining but also implications for what critical considerations should be taken into account to protect gas wells in longwall mining.

Investigating different methods used for approximating pillar loads in longwall coal mines

Accurately estimating load distributions and ground responses around underground openings play a significant role in the safety of the operations in underground mines. Adequately designing pillars and other support measures relies highly on the accurate assessment of the loads that will be carried by them, as well as the load-bearing capacities of the supports. There are various methods that can be used to approximate mining-induced loads in stratified rock masses to be used in pillar design. The empirical methods are based on equations derived from large databases of various case studies. They are implemented in government approved design tools and are widely used. There are also analytical and numerical techniques used for more detailed analysis of the induced loads. In this study, two different longwall mines with different panel width-to-depth ratios are analyzed using different methods. The empirical method used in the analysis is the square-decay stress function that uses the abutment angle concept, implemented in pillar design software developed by the National Institute for Occupational Safety and Health (NIOSH). The first numerical method used in the analysis is a displacement-discontinuity (DD) variation of the boundary element method, LaModel, which utilizes the laminated overburden model. The second numerical method used in the analysis is Fast Lagrangian Analysis of Continua (FLAC) with the numerical modeling approach recently developed at West Virginia University which is based on the approach developed by NIOSH. The model includes the 2D slice of a cross-section along the width of the panel with the chain pillar system that also includes the different stratigraphic layers of the overburden. All three methods gave similar results for the shallow mine, both in terms of load percentages and distribution where the variation was more obvious for the deep cover mine. The FLAC3D model was observed to better capture the stress changes observed during the field measurements for both the shallow and deep cover cases. This study allowed us to see the shortcomings of each of these different methods. It was concluded that a numerical model which incorporates the site-specific geology would provide the most precise estimate for complex loading conditions.

Foamed backfilling for combatting mine fires

Although mine fires and attempts to extinguish them have existed for as long as coal mining, there has so far been no reliable practical method developed for extinguishing mine fires burning for a long time under deep cover. A new ‘foamed backfilling’ method combines nitrogen-enhanced foam with non-combustible solids to create a fluid, slurry-like mixture, which is injected into the mine workings remotely through boreholes to extinguish a mine fire. When injected in the area of the fire, the foamed backfill material will smother the active fire, provide moisture, block ventilation and absorb heat. Nitrogen gas released as the bubbles decay and the foam dissipates creates an inert oxygen-deficient atmosphere to inhibit combustion. Finally, the non-combustible solid particles suspended in the foam will backfill the mine workings, rubble zones, burnt-out areas and fractures to block ventilation permanently after the foam dissipates. Thus, injection of foam-transported backfill material addresses all three legs of the fire triangle; heat is removed, oxygen is excluded and the fuel is isolated, which increases the odds of success. Economic benefits include the ability to use low-cost non-combustible materials derived from on-site sources or waste from other industries, low water consumption and wider borehole spacing.

Influence of longwall mining on the stability of gas wells in chain pillars

Longwall mining has a significant influence on gas wells located within longwall chain pillars. Subsurface subsidence and abutment pressure induced by longwall mining can cause excessive stresses and deformations in gas well casings. If the gas well casings are compromised or ruptured, natural gas could migrate into the mine workings, potentially causing a fire or explosion. By the current safety regulations, the gas wells in the chain pillars have to be either plugged or protected by adequate coal pillars. The current regulations for gas well pillar design are based on the 1957 Pennsylvania gas well pillar study. The study provided guidelines for gas well pillars by considering their support area and overburden depth as well as the location of the gas wells within the pillars. As the guidelines were developed for room-and-pillar mining under shallow cover, they are no longer applicable to modern longwall coal mining, particularly, under deep cover. Gas well casing of failures have occurred even though the chain pillars for the gas wells met the requirements by the 1957 study. This study, conducted by the National Institute for Occupational Safety and Health (NIOSH), presents seven cases of conventional gas wells penetrating through longwall chain pillars in the Pittsburgh Coal Seam. The study results indicate that overburden depth and pillar size are not the only determining factors for gas well stability. The other important factors include subsurface ground movement, overburden geology, weak floor, as well as the type of the construction of gas wells. Numerical modeling was used to model abutment pressure, subsurface deformations, and the response of gas well casings. The study demonstrated that numerical models are able to predict with reasonable accuracy the subsurface deformations in the overburden above, within, and below the chain pillars, and the potential location and modes of gas well failures, thereby providing a more quantifiable approach to assess the stability of the gas wells in longwall chain pillars.

Analysis of ARMPS2010 database with LaModel and an updated abutment angle equation

The Analysis of Retreat Mining Pillar Stability (ARMPS) program was developed by the National Institute for Occupational Safety and Health (NIOSH) to help the United States coal mining industry to design safe retreat room-and-pillar panels. ARMPS calculates the magnitude of the in-situ and mining-induced loads by using geometrical computations and empirical rules. In particular, the program uses the “abutment angle” concept in calculating the magnitude of the abutment load on pillars adjacent to a gob. In this paper, stress measurements from United States and Australian mines with different overburden geologies with varying hard rock percentages were back analyzed. The results of the analyses indicated that for depths less than 200 m, the ARMPS empirical derivation of a 21° abutment angle was supported by the case histories; however, at depths greater than 200 m, the abutment angle was found to be significantly less than 21°. In this paper, a new equation employing the panel width to overburden depth ratio is constructed for the calculation of accurate abutment angles for deeper mining cases. The new abutment angle equation was tested using both ARMPS2010 and LaModel for the entire case history database of ARMPS2010. The new abutment angle equation to estimate the magnitude of the mining-induced loads used together with the LaModel program was found to give good classification accuracies compared to ARMPS2010 for deep cover cases.