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By Joe Roby

Rolling disc cutters are the business end of hard-rock and mixed-face tunnel boring machines (TBMs). Since their first successful employment on a TBM more than 50 years ago, disc cutter technology has constantly evolved, allowing modern TBMs to excavate very hard and abrasive rock efficiently. Disc cutters have also been employed successfully on earth pressure balance (EPB) and slurry machines, cutting rock under water and ground pressure. The range of materials excavated by machines today is broader, excavation rates are higher and cutter costs are lower than ever before, proving the value of investment in cutter development. Disc cutters are used on a range of tunneling equipment, from pipe jacked slurry micro-TBMs less than 1 m (3.3 ft) in diameter to 15 m (49 ft) in diameter, hard-rock boring TBMs. The geological conditions under which they are employed range from sands and gravels, with several bar of water pressure, to extremely hard, massive rock with UCS up to 420 MPa. Regardless of the type of machine or geology, one thing remains constant: changing worn out cutters is costly. When cutters must be changed in the middle of a tunnel, the contractor incurs the cost of downtime as well as the cost of refurbishing or replacing the cutters. In the case of catastrophic cutter failures, the project can be stopped completely for long periods, and the costs mount up rapidly while tunnel production is at a stand still. Catastrophic cutter failures include the occasion when hard-rock disc cutters are failed in groups (called a ?wipeout? phenomenon) and the operator fails to stop the machine, which results in severe damage to the cutterhead. The cause of this can be either an undetected failed cutter propagating damage to surrounding cutters or operator error in steering. Regardless of the cause, the resulting damage can take days or even weeks to repair. When cutters fail prematurely on EPB or slurry machines in certain geological conditions, it is impossible to evacuate the chamber and, therefore, impossible to get [ ] into the chamber to change the cutters. The solution is frequently an unplanned intervention shaft that must be sunk at great cost. The importance of being able to predict cutter life accurately, and in all geological conditions, cannot be overemphasized. For these reasons, cutters have been developed for specific machine types and sizes, as well as for specific geological operating conditions. Different size cutters are required for different size machines. For example, while 483- and 508-mm (19- and 20-in.) cutters are used on large diameter TBMs, it is impossible to employ cutters so large on a small micro-TBM. Also, the cutter must be designed for the specific geological conditions under which it will be operating. The disc cutter rings required to bore extremely hard rock are the most expensive of cutter rings. However, they provide little advantage in weaker rock formations where less expensive rings will do the job as well. It is important to choose the correct cutter for the machine and the geological conditions in order to get the best balance of cost and risk.

Jan 1, 2009

The National Institute for Occupational Safety and Health conducted laboratory and field tests to evaluate the effectiveness of dust collector bags for reducing dust liberation and operator exposure from a roof bolter?s dust collection system. The laboratory tests evaluated the bag?s effectiveness to contain dust and the effect on canister filter loading in both a bag and bagless condition. The dust emissions from the collector?s exhaust were also measured in each condition during laboratory testing. Laboratory results show that nearly 100 percent of the test dust fed into the collector was captured by the dust bags. Loading and pressure drop on the dust collector?s canister filter is greatly decreased when using the bags, enabling longer periods of drilling without filter removal/cleaning. The field results showed that, even though dust standards were met, respirable dust in exhausted emissions was reduced around the bolter. Laboratory and field results show that benefits from use of the bags are realized in all areas of operator exposure.

Jan 1, 2008

By Peter Klaver

Deep tunnels have been used for decades for the temporary storage of large volumes of urban runoff, both storm water and combined sewer overflow (CSO). Tunnels are attractive because they reduce surface disruption and do double duty as storage and conveyance systems, collecting overflows from multiple locations and transporting them for treatment to various facilities. Like any hydraulic system, however, there are dynamic effects that must be fully understood during the design phase so that the final constructed product does not have unintended negative consequences. Preliminary sizing of storage tunnels is typically based on the total volume required. For example, if studies have determined that a volume of 56.8 ML (15 million gal) will provide the intended level of control, then that figure can be used, along with a preliminary idea of the desired tunnel length, to compute the required diameter. Of course, filling a long tube with water from various points along the way is not at all the same as pouring water into a bucket, and these dynamic effects require additional attention from design engineers. The rapid filling of storage tunnels can lead to the formation of bores, which are essentially moving walls of water. An open channel bore can build in height until it reaches the crown of the tunnel, at which point it becomes a pipe-filling bore. Figure 1 depicts both kinds of bores moving upwards in a rapidly filling tunnel. Bores can strike the ends of tun-nels with tremendous force, driving water and entrained air upwards into dropshafts and creating strong pressure surges in portions of the tunnel that are already filled. If the hydraulic surges are high enough to reach grade, they can cause overflows and/or damage structures at the surface. Trapped air pockets can occur through several phenomena, including the reflection of bores off dropshaft structures and the occurrence of ?premature pressurization.? The latter refers to the situation where the inflow to a tunnel is increasing more rapidly than the tunnel can convey it, such that the pipe becomes surcharged at an upstream point while points downstream are still flowing as an open channel. These air pockets are a great nuisance as they migrate toward points in the tunnel where they can rise to the surface, which are often shafts that are already filled with water (Fig. 2). The ?geyersing? that results can be hazardous and costly.

Jan 3, 2010

By Justyna Swolkień, Nikodem Szlązak, Dariusz Obracaj

Polish coal mines are characterized by severe geological conditions and the co-occurrence of natural hazards. These hazards are associated with methane and dust emissions during mining processes which can provide methane, dust or methane-dust explosions. Besides, there are such natural hazards as gas and rock outbursts, rock bursts, spontaneous combustion of coal and environmental heat load. The mutual influences of various geological conditions, as well as the natural hazards, intensify the increase of the methane explosion hazard. The occurrence of methane explosions in the Polish mining industry between 2013 and 2108 are analyzed. Fatal accidents are compared with similar events in the global mining industry. The methods of preventing the explosion hazard as well as methane emission control in the Polish coal mining sector are presented. Methane hazard prevention should be adapted to levels and other natural hazards, especially those related to ventilation of underground mine. The methods of preventing methane emissions into mine excavations are often contrary to the means of preventing other ventilation-related hazards in the underground mine, e.g. the prevention of spontaneous combustion of coal in the goaf of longwall panel. Therefore, the design of longwall panels should be preceded by a detailed analysis of the results of both methane emission prediction and forecast of other ventilation-related hazards.

By Justyna Swolkień, Nikodem Szlązak, Dariusz Obracaj

Polish coal mines are characterized by severe geological conditions and the co-occurrence of natural hazards. These hazards are associated with methane and dust emissions during mining processes which can provide methane, dust or methane-dust explosions. Besides, there are such natural hazards as gas and rock outbursts, rock bursts, spontaneous combustion of coal and environmental heat load. The mutual influences of various geological conditions, as well as the natural hazards, intensify the increase of the methane explosion hazard. The occurrence of methane explosions in the Polish mining industry between 2013 and 2108 are analyzed. Fatal accidents are compared with similar events in the global mining industry. The methods of preventing the explosion hazard as well as methane emission control in the Polish coal mining sector are presented. Methane hazard prevention should be adapted to levels and other natural hazards, especially those related to ventilation of underground mine. The methods of preventing methane emissions into mine excavations are often contrary to the means of preventing other ventilation-related hazards in the underground mine, e.g. the prevention of spontaneous combustion of coal in the goaf of longwall panel. Therefore, the design of longwall panels should be preceded by a detailed analysis of the results of both methane emission prediction and forecast of other ventilation-related hazards.

By J. F. Brune

This paper analyzes the explosion hazard resulting from the formation of methane-air mixtures in the mined-out gobs of underground longwall coal mines. Although direct examinations of the gob atmosphere are difficult due to the inaccessibility of these gobs, evidence from methane drainage practices and investigations of numerous mine explosions suggests that explosive methane zones can form within longwall gobs. Explosions and fires resulting from these methane accumulations have led to severe and fatal injuries to the miners. Most recently, this was demonstrated in the explosion of the Upper Big Branch Mine in West Virginia, where 29 miners lost their lives.The paper also reviews current research on numerical modeling of gas flows in longwall gobs and outlines how targeted injection of nitrogen into gobs can effectively reduce the volume of such explosive methane zones. The paper concludes that comprehensive monitoring of gas compositions, along the accessible fringes of the gobs along with inertization, improved ventilation schemes and further research are necessary to control this explosion hazard and make mining operations safe.

Jan 1, 2013

By M. T. Ansari

"This article explains the ways in which investment on mining infrastructure is a geopolitical issue. It discusses the effect of installing sufficient infra structure to get the product to the world market, and argues that there is a risk involved in depending on traditional suppliers who wish to invest in the infrastructure. It explains how to make a distinction between dedicated purpose infrastructure and general use infrastructure by examining the positions of the main actors in mining projects. It argues that these positions can not be understood as analogous to projects in developed countries. To conclude, infrastructure is a crucial link in the supply chain to market but the relative size of such projects in relation to the economy means that investors decisions in developing countries have quite different implications from those in developed countries."

Jan 1, 2011

By W. O. Kerr

As in other industries, companies engaged in mining and extraction use and develop intellectual property (?IP?) in the form of new technologies or production processes. The development of IP assets in mining may occur as a byproduct of ongoing operations, or result from investment in dedicated R&D efforts. New technology may lower costs, increase quality of output, and/or increase operational efficiency or safety. Key business questions with respect to any new technology are how best to use IP assets, how to protect them and how to derive value from them. IP assets can provide a competitive advantage to a developing firm that uses the technology to improve its operating results. The developing firm can preclude others from using the technology if it believes that is the best way to exploit the technology?s value. Or, it can be shared with others taking care to ensure rights are maintained, thereby generating royalty income or strategic value through cross licensing or other business relationships. Either way, in order to fully realize the maximum economic benefit, innovators must protect the IP assets and control their dissemination.

Jan 1, 2012

By Phil Rice, Mohammed Nasim, Richard Flanagan

"The Gateway Trans-Hudson Partnership (GTHP), a joint venture of WSP USA, Inc., AECOM USA, Inc, and STV Incorporated, is providing preliminary engineering services to Amtrak for the Hudson Tunnel project as well as supporting the NEPA process for getting the record of decision (ROD). This preliminary engineering design effort by GTHP includes geotechnical exploration and laboratory testing, design of structures, tunnel contract packaging and procurement planning.The Hudson Tunnel Project includes the construction of a new Hudson River Tunnel system and rehabilitation of the existing North River Tunnel. The new tunnel system will be constructed south of the existing North River Tunnel, from North Bergen under the Palisades to Hoboken in New Jersey, below the Hudson River, and connecting directly to Penn Station in New York (Fig. 1). The tunnel system is configured as two single-track tubes, intermediate ventilation shafts and cross passages in compliance with NFPA- 130 requirements. The adjacent surface alignment west of the Palisades will be constructed on viaducts, embankment and retained fills. The existing North River Tunnel (Fig. 2) consists of two single-track, electrified rail tunnels extending from tunnel portals in North Bergen, New Jersey to Penn Station in New York. Completed in 1910 by the Pennsylvania Railroad, the tunnel opened at the same time as Penn Station and the four, single-track, East River tunnels that connect Penn Station to Queens and onto Long Island and New England, respectively. Both tunnels in the existing North River Tunnel were inundated with brackish river water during Superstorm Sandy (Fig. 3), resulting in the cancellation of all Amtrak and NJ Transit service into New York City for five days. After the brackish water was removed from the tunnels, the residual chlorides and sulfates have had on-going detrimental impacts on the interior concrete and rail systems."

Sep 1, 2019

By Larry R. Powell

The Bureau of Mines, in cooperation with the Illinois Mine Subsidence Insurance Fund, is monitoring the response of two foundations to ground movements induced by subsidence from high extraction mining in southern Illinois. The objectives of the monitoring program are to study the inter- action between the ground surface and a foundation during a subsidence event and to determine the capability of the tiltmeter to detect and monitor subsidence movements. Tiltmeter data were obtained on two foundations constructed near Sesser, IL. One of the 30-by 40- ft foundations was constructed with a typical poured concrete footing, the other with a rein- forced-concrete footing poured on top of pol yethylene sheeting placed over a compacted layer of sand. Soil-filled bins were placed on the perimeters of both foundations to simulate superstructure loads. Monitoring pins and tiltplates were installed on the corners and midpoints of the footing. Additional survey points were established on the five-acre site to track the mining advance. This paper describes the monitoring instrumentation and techniques as they relate to the mining and site conditions. The capability of a tilt- meter to detect and follow the tilt of the foundations is demonstrated.

Jan 1, 1986

By S. G. Britton

Thin seam mining presents unique challenges when management or economic conditions require significant productivity increases. These challenges are increased depending upon the presence of various external factors such as labor unions, Federal and state regulations, and market characteristics. This paper explores the turn-around situation occurring at Tanoma Mining Company (TMC), a medium-sized underground coal mining company in central Pennsylvania, USA. Using a systematic approach of improving management controls and direction, labor relations, and communications, coupled with an intensive upgrade/rebuild/replacement program for equipment and systems used at the mine, TMC has begun reversing its' cashflow position from negative to positive within two years.

Jan 1, 1991

Perhaps the most significant development in China's base metal sector is the discovery of major copper porphyries in northern Jiangxi Province and the adjacent southern Anhui Province. At the center of the new exciting district is the proposed Dexing copper complex, located some 350 km east of Nanchang, the provincial capital of Jiangxi. This project represents China's first attempt to put together a major large-scale open-pit operation, comparable in magnitude to Arizona porphyry operations. With the aid of Fluor Mining and Metals, the Chinese plan to develop a 135-175 kt/d open-pit mine, a matching large-scale mill, and the infrastructure needed to accommodate the big operations. An operation of this magnitude would significantly reduce China's import requirements by some 75%. China imports of the red metal are running around 200 kt/a. Under the direction of the Ministry of Metallurgical Industry, the Chinese are currently operating a 10-kt/d mine and mill with equipment primarily of Chinese origin. Dexing engineers told ME that they are considering a possible scale-up to 20 kt/d. How this effort will ultimately jell with the major expansion program is largely a matter of conjecture. Fluor Mining and Metals received a $10-million contract in December 1978 to develop a preliminary engineering and design program. While the original plans called for a 175-kt/d capacity complex, the Chinese subsequently decided to scale it down somewhat. The current proposal is around a 135 kt/d, which would in- elude the existing operation, according to Dexing engineers. Completion of the engineering and design phase is expected by March 1980 and a go-ahead decision will likely be made at that time. The value of the engineering and construction contract is estimated between $800 million and $1 billion. At right, mined ore is dumped 150 m down the mountain to a holding pocket below for rail haulage to the processing plant. Below, a Chinese miner tackles the universal problem of hard toes in the pit with a jack leg. Reserves and Early History The Dexing mineralization consists of three principal ore bodies, including the Chushahung on the north mountain, and the Tungchang and Fuchiawu on the south mountain. Combined ore reserves are estimated by mine geologists at 1.7 Gt of 0.4-0.5% copper. As is characteristic of porphyries, the ore contains important associated values of molybdenum, rhenium, pyrite, gold, and silver. There is also some secondary calcocite and bornite with an oxidized capping. Historically, copper was recovered with iron from the pregnant solutions emanating from the Tungchang deposit as early as the Tang Dynasty (700 AD). Modern day exploration was conducted by the Bureau of Geology in 1956 and reserve figures were es-

Jan 3, 1980

By Jacob Carr, Christopher C. Jobes, Chenming Zhou, LaTasha R. Swanson, Jennica Bellanca, Jingcheng Li

Magnetic proximity detection systems (PDSs) are used with continuous mining machines (CMMs) to protect miners from striking and pinning accidents. Generators are used in a PDS to create magnetic fields covering the space around a CMM. The PDS determines the proximity of a miner relative to the CMM based on the magnetic flux density detected by a miner-wearable component (MWC) and simultaneously alerts the miner and stops the motion of the CMM if the miner is within a proximity that creates a striking hazard. A stable magnetic field is essential to the accuracy of the proximity calculations performed by the PDS. This paper presents the results of a systematic study of the magnetic influence of two types of steel structures found near a CMM— the body of the CMM itself and the wire mesh used for roof and rib control. The results show that the steel of the CMM body can change the magnetic field distribution and also alter electrical parameters of a PDS by changing its generator current. The study also shows that, depending on the distance between the wire mesh and a generator, the magnetic field can also be altered.

By Jacob Carr, Christopher C. Jobes, Chenming Zhou, LaTasha R. Swanson, Jennica Bellanca, Jingcheng Li

Magnetic proximity detection systems (PDSs) are used with continuous mining machines (CMMs) to protect miners from striking and pinning accidents. Generators are used in a PDS to create magnetic fields covering the space around a CMM. The PDS determines the proximity of a miner relative to the CMM based on the magnetic flux density detected by a miner-wearable component (MWC) and simultaneously alerts the miner and stops the motion of the CMM if the miner is within a proximity that creates a striking hazard. A stable magnetic field is essential to the accuracy of the proximity calculations performed by the PDS. This paper presents the results of a systematic study of the magnetic influence of two types of steel structures found near a CMM— the body of the CMM itself and the wire mesh used for roof and rib control. The results show that the steel of the CMM body can change the magnetic field distribution and also alter electrical parameters of a PDS by changing its generator current. The study also shows that, depending on the distance between the wire mesh and a generator, the magnetic field can also be altered.

By K. Norrena

Grade control in open pit mining requires the specification of dig limits that account for mineral grades, economic costs, and selectivity of mining equipment. Visual identification of ore rock types is ideal, but this is not always possible in lower grade disseminated deposits where ore/waste contacts are not visually discernible. In this case, conventional grade control practice consists of a two-step procedure (1) create a map of mineral grades at some selective mining unit scale, and (2) determine practical ore-waste boundaries or dig limits on the basis of the gridded block grades or assay information. This procedure is laborious, depends on a subjective assessment of where the boundary should be, and may be economically sub-optimal. We pose the determination of dig limits as an optimization problem and solve that problem with the technique of simulated annealing. Simulated annealing has the unique advantage of being able to combine multiple non-linear constraints into a single objective function. We use maximum profitability and the ability of the equipment to mine the proposed dig limits as constraints in the determination of optimal dig limits. We require a map of expected profit for eah block. Geostatistical techniques are recommended, for mapping expected profit but not necessary. Geostatistics will provide a quantification of the uncertainty in the grades within rock types using all available blasthole samples and exploration drilling. Some variant of L-optimal estimation or kriging can be used to determine the block-by-block classification that is economically optimum. We also need the expected profit for each block. It is unrealistic to assume free selection, that is, each block cannot be extracted independently of its neighbors. The optimal balance of ''accepting dilution'' and ''wasting ore'' is achieved to maximize profit subject to equipment constraints.

Jan 1, 2001

By Patrizia Pereyra, M. Guzman, C. Toledo, J. A. Rau, A. Ruiz

The use of mining tailings-based geopolymer binder as a substitute for cement can be an interesting alternative to the problem of final disposing of large volumes of them. Indeed, mining tailings have a high silica content, which makes them suitable for geopolymerization. The tailings samples contain Cu, Pb, Zn, As, Sb, Cd and Bi, mainly. X-ray diffraction results show that the tailings are composed of quartz, SiO2 (81%). Geopolymerized tailing samples (GTPS) were obtained by varying the ratio of SiO2/ Al2O3 and SiO2/NaOH. The compressive strength of the GTPS varied between 2 MPa and 8 MPa. The electrical conductivity in the leaching tests varies between 13.91– 16.11 mS/cm2 indicating that ions are present in the solution. However, the pH = 10.5 indicates that acidity is not being generated. The element that mostly leaches is iron. The highest percentage of leaching is observed for cadmium (69%) and chromium (93%). The concentrations of elements are under the maximum permissible limits for water according to the Peruvian legislation. However, mass transfer leach tests and immersion leach tests must be realized.

Feb 1, 2024

By L. K. Marshall

The importance of high quality underground mine ventilation is readily apparent. The principles of primary and auxiliary mine ventilation, however, are sometimes less readily apparent. The first article in this two-part series discusses some general aspects of primary and auxiliary ventilation. Next month's article will detail considerations involved with auxiliary mine ventilation.

Jan 1, 1982

By Louis W. Cope

Since its discovery, Cuba has been called the “Pearl of the Antilles.” The country remains that, albeit a little tarnished these days. In Havana, many of the buildings are being refurbished, while some new ones are under construction. Since 1991, the laws have been relaxed so that Cuba is developing a mixed economy of central control with free market. Joint venture agreements have been signed with businesses from many countries. This does not include the United States due to its embargo. But even these regulations have been relaxed some.

Jan 1, 2003

By Matthew E. Fowler

The Central Subway will extend the recently completed 8.2-km long Third Street Light Rail line another 2.7 km north through the Union Square shopping district to Chinatown with a concourse-to-concourse connection to the Powell Street BART Station. One mined and two cut-and-cover subway stations are planned. Particular challenges include: tunneling under existing tunnels; variable ground conditions ranging from saturated alluvium to fractured bedrock; a congested urban setting and large-span caverns. This paper gives an overview of the project as it stands midway through the preliminary engineering stage along with a discussion of the rationale and design approaches that are being used to address the construction challenges of restoring light rail service in the most densely developed areas of San Francisco.

Jan 1, 2008

By F. S. Knoll

Electrostatic separation is one of the most misunderstood physical processes used to beneficiate minerals. Nonetheless, millions of tons of titanium ores, iron ores and other minerals are processed every year economically, efficiently and safely. Over the past ten years major advances in electrostatic separation and its application have occurred. New processes include dewatering clay slurries, separating halite and sylvite, and shape separation of vermiculite and gangue minerals. Electrostatic separation techniques are based on one of two methods, electrophoresis or dieleccrophoresis -- processes involving charged and uncharged particles respectively. In some cases, the combination of these two techniques has proven quite useful. The purpose of this paper is to provide a basic understanding of the physical processes collectively called "electro- static separation" in order to enhance one's ability to define and consider new possibilities in mineral processing and other fields.

Jan 1, 1984