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By J. G. Groppo

Laboratory settling and filtration testing was conducted on wet processed fly ash in order to determine the applicability of conventional dewatering techniques to reduce the moisture content prior to drying. Settling tests showed that acceptable clarity (<1.5 g/l suspended solids) could be achieved after as little as 6 minutes of settling. After settling to a consistency of 40 weight % solids, continuous laboratory vacuum filtration testing produced a cake containing below 20% moisture with throughput exceeding 150 lb/ft2/hr.

Jan 1, 1997

By W. A. Vine

Next year, in 1964, Butte will celebrate its Centennial. It was in May, 1864, that the first recorded mining activity took place. During that summer, several rich placers were found on Silver Bow Creek and its tributaries, and a gold rush followed. As placer mining proceeded in the creek beds, the quartz lodes on the hillsides were located and the veins were prospected. Mining in Butte entered its second phase when the rich silver mines, the Alice, Moulton, and Lexington, were opened. The silver boom lasted until the decline in the price of silver in the early 1890&apos;s forced the closure of many of the mines. An indication of the beginning of the copper mining era in Butte was in 1866 when it was noticed that green copper carbonate discolored some of the, lode material. It was not until ten years later, however, that the Anaconda and St. Lawrence claims were located by Michael and Ed Hickey. The claims were sold in 1880 to Marcus Daly and in 1881, Daly obtained financing and organized the Anaconda Silver Mining Company to exploit the vein The silver venture was a failure because of the predominance of copper which diluted the bullion to only 400 fine.

Jan 1, 1963

By Amy McBrayer, Andrea Brickey

Area mining is a surface mining method that allows for efficient mining and contemporaneous reclamation of tabular or bedded deposits, e.g., coal. Mine planning methods for area mines differ from those of open pit metal mines. Area mines in the Powder River Basin (PRB) use various processes for mine planning at both the strategic and tactical stages. With the ever changing commodity markets, it is becoming increasingly important for mine operators to be able to react quickly to the changing business environment. Tools that allow for the development and rapid comparison of production schedule scenarios are key to ensuring agile mine operations. A survey of mine engineers responsible for mine design and production scheduling at coal operations provides clarity on the current mine design and production scheduling processes in the PRB, as well as a discussion on potential solutions to upcoming challenges. In this article, we describe various mine planning processes used by the coal producers in the Powder River Basin. The survey identifies a clear gap in the ability to create comprehensive schedules associated with limited tools and lack of engineering labor needed to frequently conduct the mine design and scheduling process.

Jul 8, 2023

By C. D. Litton, I. E. Perera

Experiments were conducted to evaluate the response characteristics of commercially available gas, smoke and flame sensors to fires of common combustible mine materials. The experiments were conducted in the large-scale fire gallery located at the National Institute for Occupational Safety and Health (NIOSH) Lake Lynn Laboratory in Fairchance, PA, using ponderosa pine, red oak, Douglas fir, high and low volatile coals, polyvinyl chloride (PVC) and styrene butadiene rubber (SBR) conveyor belts, No. 2 diesel fuel and diesel exhaust. All the experiments (except those using No. 2 diesel fuel and the diesel exhaust tests) were conducted in a similar manner, with combustible materials heated rapidly by electrical strip heaters, producing smoldering fires that quickly transitioned into flaming fires. The sensors included a diffusion-type carbon monoxide (CO) sensor, photoelectric- and ionization-type smoke sensors, a video smoke/flame detector and an optical flame detector. Simultaneous measurements were obtained for average gas concentrations, smoke mass concentrations and smoke optical densities in order to quantify the levels of combustion products at the alert and alarm times of the sensors. Because the required sensor alarm levels are 10 ppm and 0.044 m-1 optical density for CO and smoke sensors, respectively, the different sensor alarms are compared to the time at which the CO and smoke reached these alarm levels (Litton et al., 1991). In addition, the potential impact of using smoke sensors that have met the performance standards from accredited testing laboratories is also evaluated using the response of an Underwriters’ Laboratory (UL)-approved combination photoelectric/ionization smoke detector. The results are discussed relative to fire sensor needs that can have a positive impact on mine fire safety.

Jan 1, 2014

By M. E. Rossi

This paper discusses the use of Conditional Simulation (CS) models to provide mill feed grade profiles for different time periods. The conventional approach of classifying block estimates as ore or waste generally does not adequately represent dilution, lost ore and the anticipated grade control data, including variability of mill feed from the pit and possible stockpiles. The detailed simulation of grade control practices can be done, but at the Pre- or Feasibility stage of the project may be impractical, since drawing dig limits on multiple benches is tedious and time consuming. Using the Feasibility Grade Control (FGC) method as developed by the Centre for Computational Geostatistics (CCG, University of Alberta-Edmonton), the CS models can be processed quickly to establish dilution and lost ore, and predict daily or short-term feed to the mill. The simulated nodes can be aggregated into selective mining units with adequate representation of likely geometries to be recovered from the pit, to mimic anticipated selectivity. An example from a large copper deposit is shown. The study provides an estimated stream of tonnages and grades fed to the plant by mining periods of interest and based on a specific mine design and schedule. The resulting cash flows support the economic and financial analyses of the Feasibility Study; also leads to improving mine schedules; and aids in developing blending schemes if necessary. INTRODUCTION The conventional approach of separating mineralized material into ore or waste categories does not always include a realistic amount of dilution and ore loss. Also, often it does not provide a good estimate of the grade that will be fed to the mill. If the grade control estimates are unbiased, they will over the long run represent the long-term average of grades fed to the mill; but the anticipated variability of mill feed from the pit and stockpile sources may be misrepresented. Some references on traditional grade control implementations can be found in Chunnett (1982); Davis et al. (1989); Srivastava et al. (1992); and Nowak (1992). Alternative methods based on economic variables improved significantly on the purely grade-based control methods, see Douglas et al. (1994). Further developments involved the use of geostatistical conditional simulations (CS) and profit models, which in several cases have been successfully implemented (Aguilar and Rossi, 1996; Rossi, 1997; Deutsch et al., 2000; Norrena and Deutsch, 2002; Neufeld, 2005; Jewbali and Dimitrakopoulos, 2009). But they can be impractical, mostly due to the lack of understanding of the methodology involved; even if semi-automatic dig limit drawing is implemented, there is always a need for is tedious and time consuming checking and corrections, even if using a single profit model derived from the simulated grades.

Jan 1, 2019

By Kanhaiya Mishra, Phanil. K. Mandal, S. K. Behera, P. S. Paul, Prashant Singh, C. N. Ghosh

The techno-economic and social benefits of cemented paste backfill (CPB) resulted in its wide acceptance by the mining industry. The Ordinary Portland Cement (OPC) remains the key binder but to diminish its economical constraints, suitability of alternate binders has been examined worldwide. The present study aimed to investigate the effect of partial replacement of OPC with fly ash on the CPB’s strength and to determine the most optimal mix to achieve the required strength (1 MPa at 28 days of curing) at the most cost-effective way using the Bayesian network (BN). The CPB mixes were prepared at 72 wt.% solid concentration with mill tailings (87–91%), OPC (6–13%), and fly ash (0–4%), and instantly after mixing, fresh (slump, bleeding, density) CPB properties were measured. The strength was tested at 7, 14, 28, and 56 days of curing and initially analysed through traditional model. The traditional models follow the aleatory principle and are considered not appropriate for geotechnical engineering. Hence, the BN model was developed and tested. The reliability of two classifiers in learning model structure was compared which gives Naïve Bayes as the highest reliable tool. The CPB’s strength is most sensitive to the OPC content. The most consistent mix(s) is mill tailings: 87–88%, OPC: 9–11%, fly ash: 1–4%. Adding fly ash at 89–91wt% mill tailings possesses high failure probability of the CPB. The collinearity test indicates that the fines percentage and chemical composition of CPB’s ingredients are highly correlated with its slump, bleeding, and strength development.

Jul 14, 2022

By D. R. Hanson, H. Lawson

In this study, NIOSH researchers conducted a machine learning analysis to examine whether a model could be constructed to assess the probability of dynamic failure occurrence based on geochemical and petrographic data. Random forest, cluster analysis and dimension reduction were all applied. The objective of dimensionality reduction was to explore patterns and groupings in the data and search for relations between compositional parameters. Cluster analyses were performed to determine if an algorithm could find clusters with given class memberships and to what extent misclassifications of dynamic failure status occurred. A random forest analysis performed on data from the Pennsylvania Coal Sample Databank cross-referenced with accident data from the Mine Safety and Health Administration (MSHA) determined that 7 parameters of the 18 examined exerted the most influence on results. Cluster analysis on data after dimensionality reduction resulted in a hierarchal clustering algorithm finding four clusters, with one relatively distinct dynamic failure cluster, and three clusters consisting mostly of control group members but with a small number of dynamic failure members.

Feb 1, 2023

By Warren H. Weisz

A cement, in the broad sense, is any substance which will cause various materials to adhere to each other. Clay was probably the first material to be used by man as a cement or binding agent. Water occurs in or is mixed with the clay to make it plastic, so that it can be formed in place. The sun and air remove the water from the clay and on drying strength is developed. The clays unless fired are not too resistant to water, therefore, their use is best when restricted to dry areas. Gypsum used as a cementitious material is not the subject of this paper, but its use dates back thousands of years. Gypsum mortars were used by the Egyptians in building such massive masonry structures as the pyramids. The Egyptian mortar consisted of a mixture of sand with burned gypsum (of an impure type of 81.5 per cent calcium sulphate and 9.5 per cent calcium carbonate) for the cementitious material. The burning of this type of cementitious material took place at relatively low temperature. These burning reactions will be covered later when the dehydration of gypsum is discussed. The setting of the partially dehydrated gypsum is considered to be crystallization from a supersaturated solution which deposits crystals of dihydrate (gypsum). In low water-content mixes, the interlocking of the needle-like crystals helps to produce higher strengths. Slaked lime made from limestone burned at higher temperatures (1648 F is generally considered as the calcining temperature, although under certain conditions incipient calcination will take place at 1250 F) is another early-period cementitious material. During slaking with water, a colloidal or amorphous hydrated lime is formed. When it is allowed to dry, it hardens and develops low strengths. On exposure to the carbon dioxide of air in the presence of some moisture, carbon dioxide is adsorbed and part of the calcium hydroxide is converted to calcium carbonate. Structures in which a lime mortar is used continue to grow in strength as this reaction proflesses. Hydrated lime has the disadvantage of not setting under water.

Jan 1, 1960

By J. A. G. Llerena, J. Sattarvand

Tailings dam failures have been occurring in recent years. They are considered more vulnerable than hydraulic dams due to the lack of regulations on specific design criteria, and stability requirements regarding monitoring during the construction and maintenance process. Thus, monitoring the dam is essential to know the dam's existing state and ensure its safety. One of the reasons tailings storage facilities fail is slope instability caused by moisture content. A relationship does exist between moisture content and surface strength, early detection of seepage would help to assess the physical condition of the dam. Moreover, to cover the tailings dam area in an efficient way Unmanned Aerial Vehicles (UAVs) are suitable because of their versatility and high-resolution data acquisition. Mounted with a high-resolution RGB camera, and thermal, or hyperspectral sensors UAVs can acquire good quality images that combined with image analysis and machine learning algorithms yield a good estimate of soil moisture.

Feb 1, 2023

By L. Yuan, A. Smith

"NIOSH’s mine fire simulation program, MFIRE, is widely accepted as a standard for assessing and predicting the impact of a fire on the mine ventilation system and the spread of fire contaminants in coal and metal/nonmetal mines, which has been used by U.S. and international companies to simulate fires for planning and response purposes. MFIRE is a dynamic, transient-state, mine ventilation network simulation program that performs normal planning calculations. It can also be used to analyze ventilation networks under thermal and mechanical influence such as changes in ventilation parameters, external influences such as changes in temperature, and internal influences such as a fire. The program output can be used to analyze the effects of these influences on the ventilation system. Since its original development by Michigan Technological University for the Bureau of Mines in the 1970s, several updates have been released over the years. In 2012, NIOSH completed a major redesign and restructuring of the program with the release of MFIRE 3.0. MFIRE’s outdated FORTRAN programming language was replaced with an object-oriented C++ language and packaged into a dynamic link library (DLL). However, the MFIRE 3.0 release made no attempt to change or improve the fire modeling algorithms inherited from its previous version, MFIRE 2.20. This paper reports on improvements that have been made to the fire modeling capabilities of MFIRE 3.0 since its release. These improvements include the addition of fire source models of the t-squared fire and heat release rate curve data file, the addition of a moving fire source for conveyor belt fire simulations, improvement of the fire location algorithm, and the identification and prediction of smoke rollback phenomena. All the improvements discussed in this paper will be termed as MFIRE 3.1 and released by NIOSH in the near future INTRODUCTION The MFIRE program, originally developed in the 1970s by the U.S. Bureau of Mines (now the Office of Mine Safety and Health Research (OMSHR) at the National Institute for Occupational Safety and Health (NIOSH)) and Michigan Technological University, has been a mainstay in modeling of the mutual influences between a fire and the mine ventilation system during an underground mine fire. Several update versions have been released over the years, including MFIRE 1.27, 1.29, 1.30, 2.0/2.01, 2.10, and 2.20. The MFIRE program logically comprises four parts: (1) a conventional network calculation, where it performs the basic network balancing without considering heat or mass transfer; (2) a temperature calculation to establish the reference temperature distribution before a non-steady state (transient-state) simulation; (3) a transient-state simulation that follows changes in ventilation step-by-step to produce a continuous description of the temperature distribution, smoke, and contaminant spread through the ventilation system during a fire event; and (4) a quasi-equilibrium simulation to predict the state of the ventilation system after a relatively long period of time (defaulted as 5 hours in MFIRE) as the fire reaches a quasi-steady state. In summary, MFIRE is a computer simulation program that performs normal ventilation network planning calculations and dynamic transient-state simulation of ventilation networks under a variety of conditions including the influence of natural ventilation, fans, fires, or any combination of these (Chang et al., 1990)."

Jan 1, 2016

By A. Noble

"Froth flotation circuits are widely used throughout the mineral processing industry for the concentration of fine particles. It had been estimated that nearly 2 Gt (2.2 billion st) of ores are treated globally each year using this versatile separation process (Fuerstenau, 1999). Due to the high feed tonnage, a large economic incentive exists for flotation plant operators to optimize the performance of this critical processing circuit. Prior to the 1950s, the optimization of flotation circuits primarily involved the manual adjustment of operating variables based on visual observation and sporadic sampling (Lynch, Harbort and Nelson, 2010). During the next several decades, however, the advent of improved on-line instrumentation coupled with the rapid development of high-speed microprocessors allowed the industry to develop more advanced control systems that could quickly adjust operational parameters in response to disturbances in ore characteristics and plant flows. These early online controls typically involved feedback loops designed to stabilize cell performance through the automatic manipulation of process variables such as pulp levels, gas rates and chemical dosages. The set-points for these controllers were often set by plant operators based on one or more operator objectives, such as maximizing throughput, recovery or grade. More recently, these regulatory controllers have been interfaced with high-level data display and management systems that provide operators with the ability to better optimize flotation plant performance based on mathematical models and rule-based algorithms (Greet, 2010).While tremendous strides have been made during the past several decades, even the most modern flotation plants are still faced with the long-standing question: “What are we trying to optimize?” From an operator perspective, some common responses include “Maximize tonnage of saleable concentrate” or “Maximize metals recovery at a customer-specified market grade.” These replies may or may not reflect those of management, who often focus on economic goals such as “Maximize profits for each operational unit” or “Maximize rate of return for all corporate assets.” Unfortunately, these high-level objective statements do not always translate well into practice due to the disconnect between plant operating protocols and product value. Attempts have been made by industry to overcome this issue using various types of optimization routines such as linear programming or other optimization engines. While this approach does have some merit, these blind routines require considerable input data and interpretational expertise and provide little or no fundamental insight that can be used to drive improvements in concentrator performance."

Feb 1, 2017

A group of geologists is located in a remote area of North America, without telephone lines, electricity or even running water. They have spent days accumulating data for a mining company that is eager to receive any information about the dig. But the team does not have access to a wired communications infrastructure. So the geologists must wait until they get to the nearest town to transmit their data. TMI Communications has a mobile satellite communication system that allows geologists in the field to transmit their data from remote locations. The company&apos;s satellite is the heart of its North American mobile communications network. This satellite turns all of North America, including Canada, Mexico and the Caribbean into a single digital communications cell. Traditional terrestrial communications systems, such as dedicated phone lines or cellular systems, cannot handle a remote geological exploration camp&apos;s extensive communications needs. Cellular technology, where available, has high costs and limited applications. For geologists in the isolated areas of North America, accessible and reliable phone service is vital to success. For those who have established temporary camps, TMI Communications&apos; satellite phone service has improved the speed and accuracy of their communications with home base. This wireless network is suited to meet the needs of existing data applications and the challenges of new ones. It can support any one- or two-way, fixed or mobile data transfer. TMI&apos;s network enables geologists to transmit exploration results, spreadsheet information and location co- ordinates to anywhere in the world, at any time. This is important if a team needs to relay vital data back to its headquarters to support immediate decision making on a prospect site or a find.

Jan 1, 1999

By Chen-Luh Lin, Jan D. Miller, Sindhoora Puvvada

Most of the future phosphate resources in Florida, which accounts for 70  percent of production in the United States, are contaminated with too much dolomite that is difficult to remove with existing industrial practices. The low-grade ore quality coupled with increased phosphate demand is of concern to the Florida phosphate industry. In order to resolve the dolomite issue, various beneficiation technologies were designed and evaluated, but none have been sufficiently successful [1]. 

By G. Almgren

With the exception of sublevel caving, the most common method of underground mining in Sweden is the "cut-and-fill" method. It is normally used for mining non-ferrous metals , and&apos; is used extensively in the complex sulfide ore mines of the Boliden Company in north and central Sweden as well as the mines of the STORA and Vieille Montagne Companies in central Sweden. All in all, the cut-and-fill method is used in 13 of Sweden&apos;s 45 mines. As the mines are relatively small, the volume of ore mined by this method represents only about 5 % of the total ore production in Sweden. The commercial value, however, is much large than this percentage would imply. The production volumes and grades of some typical mines are shown in Table I. As seen, when rated internationally, the grades are comparatively low. The prices are set according to ?international metal prices? as dictated by the London stock exchange, and in lieu of governmental support, rational management methods are critical in order to achieve satisfactory profit.

Jan 1, 1975

By J. Kallioinen

Theoretical considerations, experimental results and plant experience have lead to a new design concept called the unit reactor approach. It has been successfully implemented to the largest flotation cell on the market, the 4000 cu ft OK TankCell. The work has also lead to a new operating idea called size specific flotation. The paper discusses these concepts in the view of full scale field experiments. In large scale porphyry copper flotation experiments conducted in Chile the new large TankCell with its new low energy input Free Flow mechanism out-performed the more conventional designs. The recovery was substantially better, especially in the coarse fractions. In some experiments the difference in total recovery was up to 10%-units and the savings in total energy consumption at the same time over 40%.

Jan 1, 1995

By Adolf U. Honkala

Dundee Cement Company was incorporated in 1958. The equity capital for the venture was supplied by a Swiss firm called Holderbank Financier and a group of its principals. Holderbank Financier, a holding company, is a direct outgrowth of Holderbank Cement Company, a company founded in 1912 by the father of Dr Hans Gygi who is the president of Dundee Cement Company and a member of the Board of Holderbank Financier. From one plant in 1912 located in Zurich, Switzerland, Holderbank grew to its present size of 32 plants in 17 countries, having a capacity of 90 million barrels of cement per year. Dundee Cement Company constructed its first cement plant near the little town of Dundee, Michigan. This site was selected because there is an abundance of limestone and clay of the correct chemical composition for cement manufacture and the deposit was advantageously located near the large population centers of Detroit, Toledo, Cleveland, and Chicago. Construction of the 5. 5 million barrel, two kiln, plant was completed and the plant started up in the fall of 1959. After a year or two of the usual problems in a new plant and the expected difficulty of breaking into a nearly saturated market, Dundee began to prosper.

Jan 1, 1970

By Z. Sample, S. Kaushik

"INTRODUCTION Industries around the globe have been making significant advancements in recent years due to innovations in automation technology. With the implementation of modern automation technology, professionals in process automation or plant operations can expect significant and exciting change, and the mining and mineral processing industries are no exception. From 2000 to 2010, the International Council on Mining & Metals (ICMM) reported that an increased output and increased value of most metals has resulted in a rise in global metal and mineral process industries from $214 billion to $644 billion. [1] Since most productivity increases in mining and mineral process industries have been achieved through the ability to process lower grade ores with improved efficiency and larger equipment, these industries have begun to adopt advanced automation and control technologies. Despite a growth slow-down, the mining and mineral processing industries are poised for continued and sustainable growth and development due to an increasing demand for energy minerals and emerging technologies requiring minerals and metals previously not demand. However, as these industries becomes more automated, new challenges are arising on the horizon. DEMOGRAPHIC TIME BOMB John Payne from BP is credited with first using the term Demographic Time Bomb to describe the upcoming crisis in the process industry in finding experienced operations personnel. From a survey of 912 mining professionals, Stratum International found that a mere 0.4% of senior level candidates were between the ages of 25 and 34 and a similar proportion aged over 75 years. This indicates that there is both a deficiency of young skilled workers and a skilled workforce that is retiring earlier than the previous generation. Combined with data published by the US Department of Labor stating that the median age of the mining workforce is approaching 50 years old, this implies that these skilled mining and mineral process professionals are an aging population with irreplaceable knowledge and experience that are expected to retire in the next 5-10 years. While it is projected that the labor pool will be sufficient to fill open positions, the real question is if this young workforce will have necessary skill sets and experiences."

Jan 1, 2015

By S. Que

Local community acceptance is a key aspect of planning and managing mining projects, whether through sustainability assessment and reporting or corporate social responsibility programs. However, there has been very little research to understand the determinants of community acceptance. This paper seeks to identify key mine characteristics and demographic factors that influence individual acceptance of mining projects. Six demographic factors and 16 mine characteristics were selected based on literature review. Four of the six demographics factors were confirmed to be significantly (p < 0.05) correlated with people?s attitude of the importance of the mine characteristics. All sixteen mine characteristics are identified as important factors. The most important mining factors are Job opportunities, water shortage or pollution, air pollution and land pollution. Both the mining and control groups have same opinion of 12 mining characteristics and differ on four (infrastructure improvement, labor shortage for other businesses, noise pollution, and mine life). During design and management of mines, this data can be used as a reference. This result will facilitate better choice experiment (survey) design for discrete choice modeling. Such discrete choice models can provide a viable framework for data-driven community engagement and sustainable mine management.

Feb 23, 2014

By Robert E. Ennis

The somewhat misnomered "continuous" face section is in most mines today still far from perfect continuity. Achieving uninterrupted flow of coal from the mining machine to the outside has been a long sought for goal. Clearly, the largest problem to be solved in continuous mining today is one of increasing the cutting time of the miner. Full machine utilization can never be achieved with the new high capacity miners, as long as their performance is tied to that of the shuttle car. Figure No. I illustrates the point at which shuttle car haulage distance determines unit productivity rather than the productive capacity of the miner. Continuous mining is never realized. A recent development has proven, however, that truly continuous mining and haulage is possible. The Bell & Zoller Coal Company working with the Research and Development Department of Hewitt-Robins Inc. developed and perfected a new mining system which offers advantages in terms of increased productivity at reduced mining costs and enhances the safety of personnel at the face. This new system involves the use of two pieces of equipment that form a unbroken link, at all times, between the mining machine and the mine belt haulage system. These pieces are a Mobile Bridge Conveyor, and an extensible panel conveyor. The following areas of discussion will be covered during the review of this development. I. The design and operating features of the new system. 2. Its application in underground mining 3. The performance of the system to date 4. Operation and maintenance cost considerations 5. Safety features of the system

Jan 1, 1965

By W. G. Pariseau

Face and pillar bursts, bumps and bounces are violent failures that occur in underground coal mines in response to a complicated interplay of face and pillar geometry, seam depth, coal strength and moduli and interactions between roof, seam and floor strata. Additional complications arise from the presence of gas, mainly methane, and associated pressure and flow that vary with time and are further influenced by the rate of face advance. Numerical models provide a means of quantitatively accounting for the various complications of mining geometry, the stratigraphic column, mechanical properties, gas flow properties and associated interactions. A fully coupled hydromechanical finiteelement code, utAH4, serves the purpose well and allows study of the important interaction between stress concentration and gas pressure in determining safety and stability of the face during the advance of a longwall panel in a deep underground coal mine in central Utah. Face advance is relatively fast compared with gas flow and depressurization in coal seams of low gas permeability. Consequently, gas pressure is high at the face. When a longwall is stationary, depressurization occurs at the face, so effective stress and strength increase. thus, when gas flow at the face is high and requires a pause in face advance to bring gas concentration to an acceptable level, a second benefit occurs because of timely depressurization. However, quantitative analysis of a deep coal mine shows that regardless of gas pressure, high stress concentration is more likely to pose a threat to face and pillar wall stability.

Aug 1, 2013