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By G. Bräuner

The methods of burst control treated in the authors' very informative paper have been applied in the Ruhr Coalfield, Germany, for more than 20 years and have proved to be highly effective. It might be interesting here to mention a few experiences: The symptoms of critical stresses when drilling with small diameters ("test drilling") are essentially the same as described. However, we consider the situation safe if these symptoms occur beyond a certain distance ahead of the face. That safety distance equals three times the seam thickness plus the daily advance. It is the total seam thickness that counts, not merely the mined portion. Critical stresses within the safety distance are dissolved by so-called destressing measures: drilling with heavier equipment, blasting, or water infusion. To avoid bump initiation, the destressing operations should begin at the sides of the stressed zone rather than in the middle. As to water injection, there are two different principles. If the situation is critical already, high pressures are applied for hydraulic fracturing. If the stresses still allow to drill deep holes, the fluid pressure is kept low and acts for a longer time. This is to make the coal break successively instead of violently - a long-term precaution. When the stresses are very high, destressing is the most appropriate means. We mostly drill with 95 mm-diam (3.7 in.- diam). The techniques in detail are somewhat complex and subject to modifications. But the general idea is to accomplish burst prevention by controlling the potential burst situations.

Jan 1, 1990

By C. M. Walck

The Rosebud district is located in the Kamma Mountains, southeast of the townsite of Sulphur, Nevada. Since discovery in 1989, LAC Minerals, in joint venture with Equinox Resources, has delineated a resource containing approximately 570,000 ounces of gold and 5,500,000 ounces of silver. The deposit is of the volcanic-hosted epithermal quartz-sericite type. Mineralization occurs in tabular zones in and along the hanging wall of the South Ridge fault, and in cross-cutting high-angle structures. Multiple stages of discontinuous stockwork gold-and silver-bearing quartz-calcite-clay veins cut variably clay-altered, silicified, and sericitized rhyolitic Miocene volcanic rocks.

Jan 1, 1993

By P. Ritsopoulos, A. J. Dentsoras

The objective of this paper is the development of a reliable simulation model for the operation and production capacity of an aggregates quarry. Based on this model, a computer program is introduced that provides the final production outputs according to the defined material gradation and machinery characteristics. The program takes into consideration all operational parameters that may be introduced by the user through the whole machinery network. As a result, all production parameters are properly updated. The structured simulation program can help detect production inefficiencies that result from design ineffectiveness. Additionally, the program can be used for the generation of alternative scenarios for future modifications of a plant's configuration. Finally, a designer can use it as a tool for obtaining optimum solutions concerning newly designed quarries. As a case study, a quarry operating at Heraklion, Crete, was examined. The application of the program to the plant produced a complete image of the quarry's input/output characteristics, along with some suggestions for improvements on certain production processes.

Jan 1, 1998

By G. Bräuner

The methods of burst control treated in the authors' very informative paper have been applied in the Ruhr Coalfield, Germany, for more than 20 years and have proved to be highly effective. It might be interesting here to mention a few experiences: • The symptoms of critical stresses when drilling with small diameters ("test drilling") are essentially the same as described. However, we consider the situation safe if these symptoms occur beyond a certain distance ahead of the face. • That safety distance equals three times the seam thickness plus the daily advance. It is the total seam thickness that counts, not merely the mined portion. • Critical stresses within the safety distance are dissolved by so-called destressing measures: drilling with heavier equip¬ment, blasting, or water infusion. • To avoid bump initiation, the destressing operations should begin at the sides of the stressed zone rather than in the middle. • As to water injection, there are two different principles. If the situation is critical already, high pressures are applied for hydraulic fracturing. If the stresses still allow to drill deep holes, the fluid pressure is kept low and acts for a longer time. This is to make the coal break successively instead of violently - a long-term precaution. • When the stresses are very high, destressing is the most appropriate means. We mostly drill with 95 mm-diam (3.7 in. - diam). The techniques in detail are somewhat complex and sub¬ject to modifications. But the general idea is to accomplish burst prevention by controlling the potential burst situations.

Jan 1, 1989

By Mary Nelima Ondiaka, Oladunni Oyelola Alabi, Fatai Olufemi Aramide, Francis Gitau, Talabi Henry Kayode

Iron ore is essential in steelmaking but high-grade ores have diminished, making it necessary to turn to low-grade ores, which need further beneficiation to upgrade the iron content. Biobeneficiation techniques such as bioleaching, bioflotation and bioflocculation have proven successful in iron ore processing. Consequently, these methods have emerged as sustainable alternatives to conventional beneficiation. The biobeneficiation processes occur in mild conditions using bioreagents and biosurfactants derived from microbes, and offer a reduction of chemicals used in processing. This potentially offers methods that are relatively energy efficient, cost effective and environmentally friendly while tackling the constraints of dwindling high-grade iron ore resources.

Sep 1, 2024

Acid mine drainage (AMD) forms when sulfide minerals are exposed to oxidizing conditions in coal and metal mining, highway construction, and other large-scale excavations. Iron sulfides common in coal regions are predominately pyrite and marcasite (FeS2), but other metals may be complexed with sulfides forming chalcopyrite (CuFeS2), covellite (CuS), galena (PbS), and sphalerite (ZnS). Pyrite commonly occurs with these other metal sulfides thereby causing AMD where Cu, Pb, and Zn are mined. Upon exposure to water and oxygen, sulfide minerals oxidize to form acidic, sulfate-rich drainage. Metal concentrations in AMD depend on the type and quantity of sulfide minerals present. The drainage quality emanating from underground mines or backfills of surface mines is dependent on the acid-producing (sulfide) and alkaline (carbonate) minerals contained in the disturbed rock. In general, sulfide-rich and carbonate-poor materials produce acidic drainage. In contrast, alkaline-rich materials, even with significant sulfide concentrations, often produce alkaline conditions in water. Approximately 20,000 km of streams and rivers in the United States are degraded by AMD. About 90% of the AMD reaching streams originates in abandoned surface and deep mines. Since no company or individual claims responsibility for reclaiming abandoned mine lands (AML), no treatment of the AMD occurs and continual contamination of surface and groundwater resources results. The oxidation of iron disulfides and the generation of acidity occur through several reactions (Stumm and Morgan, 1970). The chemical equations can be found in Caruccio and Geidel (2000). If any of the processes represented by the equations were slowed or altogether stopped, the generation of AMD would also slow or cease. The equations show that 1000 Mg of rock containing 1% sulfur, all as pyrite, would yield upon complete reaction 31.25 Mg of acidity. Therefore, 31.25 Mg of 100% CaCO3 would be required to neutralize the acidity. The alkaline content of overburden determines whether there is enough neutralization potential (NP) to counteract the acid produced from pyrite oxidation. Of the many types of alkaline compounds present in rocks, only carbonates and clays occur in sufficient quantity to effectively neutalize AMD. A balance between the acid-producing potential and neutralizing capacity of an overburden sample will indicate the ultimate acidity or alkalinity that might be expected in the material upon complete weathering. Accurate prediction and control of AMD before surface mining require an understanding of three important factors: 1) overburden geochemistry, 2) method and precision of overburden handling and placement in the backfill during reclamation, and 3) the postmining hydrology of the site.

Jan 1, 2002

By J. N. Philbrook

As with most industries, mining must now include in its plan of operation mechanisms to address a project's environmental impact. New regulations have focused attention on the potential environmental impacts of industry, particularly the handling of wastes. Modifications are currently being proposed to the Bevill Amendment. And development is ongoing of Resource Conservation and Recovery Act (RCRA) Subtitle D regulations specific to mining wastes. The result is a growing concern on the part of lenders, developers, buyers and owners regarding acquisition and ownership of mining properties. One of the most effective tools in managing the regulatory requirements is an environmental audit. An environmental audit can be a literature review to determine regulatory requirements. The audit can also take on the form of a phase-one site assessment. This is a limited investigation to determine whether there are specific

Jan 1, 1991

By O. R. Swendseid

The Mountain Con mine is a relatively old, deep mine located in Butte, Montana. Operations at this property through the present shaft were started before the turn of the century. As mining progressed to depth, increasing demand for ventilation facilities and changing mining conditions made it convenient to convert some nearby shafts to airways. The fact that these openings had not been originally planned for use as airways made it necessary in some instances to utilize long and inefficient already-estab¬lished entries to service working areas. This situation existed in the Lexington fresh air system. The Lexington system consists of a vertical, 3-compartment shaft extending from surface to the 3200 level and a series of 2-compartment air raises and old horizontal-haulage openings extending into a mining area several thousand feet west of the Lexington shaft between the 3900 level and the 4200 level. Because of restrictions and high resistance in the portion of the system between the bottom of the Lexington shaft on the 3200 and the mining area on the 3900, the capacity of this system is only 85,000 cubic feet of air per minute. It was calculated that the capacity of the system could be in¬creased to meet the demands of the current mining program in this section of the mine by utilizing a single, straight, horizontal air course on the 3200 and by driving an inclined air raise 740 feet long between the 3900 and the 3200.

Jan 1, 1967

By Kelly F. Bailey

The issue of regulating non-asbestiform varieties of the amphiboles actinolite, tremo1ite, and anthophyllite to the same degree as asbestos has been studied in detail by the National Stone Association. The ramifications of such a regulation, and the over simplistic regulatory definition of a fiber, are enormous not only for the aggregate industry and its users, but also for the nation. Evaluation of the health, geological, mineralogical, technical, economic and legal issues do not support an "asbestos-like" regulation of non-asbestiform minerals. The adverse consequences of regulating non-asbestiform varieties of actinolite, tremolite and anthophyllite like asbestos would be magnified many times if a similar standard for generic mineral fibers were promulgated.

Jan 1, 1988

By Jerome F. Machamer

Ninety percent of manganese is used as an alloying element in steel. Smaller amounts are used in dry-cell batteries, in aluminum and bronze alloys, and many other uses. The element has several oxidation states, and oxidation-reduction reactions control its chemical behavior. Manganese, in primary minerals such as rhodochrosite, rhodonite, and braunite, is in a divalent oxidation state, and manganese in secondary minerals, such as pyrolusite and cryptomelane, is in a quadrivalent state. Virtually all manganese ore production comes from three types of sedimentary manganese deposits. First, lenticular beds of manganese carbonate or carbonate-silicate rock in Early Precambrian volcano-sedimentary complexes in South America and Africa have been major sources of manganese ore. Second, laterally extensive beds of mangano-silicate and manganiferous carbonate minerals in certain banded iron formations are major sources of commercial ore and constitute the largest resource of manganese. Finally, manganese accumulations deposited in marginal to epicontinental basins are the largest source of current manganese ore production. Residual deposits resulting from the destructive weathering of rocks with a low manganese content have been, but are no longer, important sources of manganese ore. Most deposits have been altered to some extent by super- gene oxidative processes, and are economic because of that alteration. Outcrops of manganese ores are invariably oxidized and can be very deceiving as to the character of the underlying material. Nearshore facies of epicontinental basins, and nearshore age-equivalents of metalliferous black shales are among the targets for new manganese exploration. Very high-grade manganese occurs in sedimentary deposits altered by metamorphic and metasomatic processes.

Jan 1, 2001

By R. Bruce Thorndycraft

Heap leaching should not be chosen for development of a property solely on the basis of paper studies. Management should be made to understand where the risks are in heap leaching, and management should be alerted to the variability of costs in heap leaching, many of which are based upon company philosophy. These concepts are complex, but easily illustrated with guided tours of existing heap leach facilities.

Jan 1, 1998

By M. García-Vásquez

In Peru, the third destination in worldwide exploration based on expenditure, mining conflicts have spread dramatically over the last decade. Mining companies need to create new initiatives to avoid social conflicts and strengthen the social capital needed to keep mining in a country with proven mineralogical riches. This document provides information about a research project that explored the opinions and experiences of a resource many times overlooked by companies: the human resource. Over 30 surveys were conducted among professionals working at mines in the Peruvian mining industry, in different departments and from different organizational levels. Mining employees acknowledged that they play an important role in the development of company-community relationships and gave their impressions about initiatives implemented by international mining companies in Peru. Mining employees also provided their recommendations to succeed in a location where cultural differences have not been properly considered.

Jan 1, 2011

By Ted D. Maki, Joseph B. Taylor

INTRODUCTION FMC's Paradise Peak mine, located 13 Ian (8 miles) south of Gabbs, Nevada, became opera¬tional in April of 1986 (Figure 1). It was designed and built by Davy McKee, who was instrumental in equipment design and selection. It is the 7th largest gold deposit in the United States with defined reserves of 10.9 mt (12 million st) containing 34 million gms (1.1 million tr oz) of recoverable gold and 933 million gms (30 million tr oz) of recoverable silver. The mine extracts ore by the open-pit method, taking advantage of a 1.5:1 stripping ratio. The mill operates at a 3600 mt/day (4000 st/d) capacity. Crushing is done in three stages to achieve an ore size of minus 0.635 cm (0.25 inches). Grinding further reduces the ore to 85% minus 100 mesh. The ground ore is treated with cyanide in agitated leach tanks and then washed in the counter-current decantation (OCD) thickeners. Zinc is added to the clarified, deaerated pregnant solution to precipitate the precious metals. The precipitate is acid digested to eliminate excess zinc, filtered and retorted to drive off contained mercury. The retorted precipitate is then fluxed, melted and poured through cascade molds. Dore bars are cleaned for shipment and the slag is sent to an in-house slag treatment system. ELECTROSTATIC SEPARATION The dry electrostatic slag treatment system at Paradise Peak is the first installation of its kind. Electrostatic separation has been widely used in mineral processing since the early 1950's. A brief discussion of the theory behind the process is helpful to those not familiar to electrostatic separation. Charging and sepa¬rating slags, dry minerals or other materials by ion bombardment is the most common form of electrostatic separation. Millions of tonnes of minerals are processed each year by this method. In an ion bombardment separation, granular material is fed onto a grounded metal cylinder (or roll) and charged by a corona-producing electrode placed above the roll's surface (Figure 2). While both conductors and non¬conductors become charged, only the conductor is able to lose its charge. The charged non¬conductor, as it rests on the roll's surface, "sees" an oppositely charged image of itself in the metal surface. It is attracted to the image charge, becomes electrostatically pinned to, and moves with the roll's surface. The conductive particle also sees an image and is attracted to it. But upon touching the roll's surface, it discharges rapidly to the grounded surface and is thrown free from the roll's surface with a projectile motion. In the case of precious metal slags, the con¬ductive particles would be metallic prills of dore metal; and the nonconductive particles would be the slag, free of metal. Middling grains, generally, are in the form of a metallic prill encased in or incompletely liberated from slag. LABORATORY TESTING A number of precious metal slag samples have been tested in the laboratory. It has been found that the composition of slags vary widely from one refinery operation to another. Typical laboratory procedure is to crush and size the slag followed by two-stage lab-scale electro¬static separation. The conductor fractions from the first and second pass are then combined as a prill concentrate; middlings fraction and clean slag tailings from the second pass are held separate. Selected results from laboratory testing are shown in Table 1. It is important to note in Table 1 that the assays represent overall silver and gold, not metallic values. From experience, the laboratory results are typically lower in grade and recovery than the industrial installations. This is largely due to the hydroscopic nature of precious metal slags coupled with the high local humidity in Carpco's Jacksonville, Florida, location. Relative humidity in Jacksonville can range form 60-95%, while most mining locations in the

Jan 1, 1987

By Mining Engineering

The 43rd Annual American Mining Hall of Fame Awards Banquet and Fundraiser, sponsored by the Mining and Minerals Education Foundation (MMEF), will be held Dec. 6 in Tucson, AZ. Each year, the MMEF honors a slate of individuals and companies who have made notable contributions to the advancement of the mining industry. This year’s distinguished nominees are: Kathleen L. Quirk, president and chief executive officer and a member of the board of directors of Freeport-McMoRan Inc. is the 2025 Hall of Fame Inductee. Quirk joined Freeport in 1989 and had responsibility for a broad range of corporate functions, including tax, investor relations, corporate development and treasury before being named chief financial officer in 2003. She was named president of Freeport in 2021 and became a member of the board of directors in 2023. As a senior member of the company’s executive team for more than 20 years, she has been instrumental in Freeport’s strategic planning and execution of company goals. During that period, Quirk was named Best CFO in Metals and Mining by Institutional Investor Research magazine on numerous occasions. She holds a bachelor of science in accounting from Louisiana State University.

Aug 1, 2025

By A. F. McKown, P. E. Sperry, W. L. Fourney, D. E. Thompson

INTRODUCTION Underground drill and blast excavation is usually accomplished with small diameter holes loaded with high energy explosives. The detonation pressures are extremely high and an extensive amount of energy is dissipated in the process; however, very little of this energy is used to create the specified fracture planes required for excavation. The available energy is expended in producing radially outgoing stress waves, in crushing the adjacent rock, and in producing a dense, randomly oriented radial crack pattern about the holes. This causes several undesirable effects: 1. Overbreak at the perimeter, which results in more muck to remove and extra concrete or shotcrete to fill the voids. 2. Damage to or loosening of the remaining rock at the perimeter which may result in the need for additional support measures. 3. Ground vibrations and/or airblast, which could result in damage to nearby structures and complaints by people living or working in the area. Several steps may be taken to minimize these effects. Where control of the perimeter is desired, smooth blasting techniques are generally employed in which the spacing and burden of perimeter holes are reduced and lighter, decoupled charges are used. Where vibration damage to structures is feared, control is generally exercised by limiting the charge weight per delay period so that the ground vibrations at the nearest structure do not exceed a peak particle velocity of two inches per second. Where blasting complaints may be a problem, con-

Jan 1, 1979

By B. D. Hansen

Newmont has been on a focused path of improving operations for many years. After the merger of Newmont and Santa Fe Pacific Gold, Newmont created significant synergies of over $50million per year in Nevada, primarily through optimal ore movements and consolidation of various functions. During the current period of low gold and copper prices, Newmont has refocused its efforts on efficient operations worldwide. This paper will describe the methods and programs that continue to be implemented at Newmont's many mine facilities in Nevada. Newmont has used a combination of computer technology, optimal use of infrastructures, procurement strategies, functional consolidation, enhanced mine planning and a variety of available metallurgical processing options to decrease the cost of operations and increase profitability.

Jan 1, 1999

By B. D. Hansen

Newmont has been on a focused path of improving operations for many years. After the merger of Newmont and Santa Fe Pacific Gold, Newmont created significant synergies of over $50 million per year in Nevada, primarily through optimal ore movements and consolidation of various functions. During the current period of low gold and copper prices, Newmont has refocused its efforts on efficient operations worldwide. This paper will describe the methods and programs that continue to be implemented at Newmont's many mine facilities in Nevada. Newmont has used a combination of computer technology, optimal use of infrastructures, procurement strategies, functional consolidation, enhanced mine planning and a variety of available metallurgical processing options to decrease the cost of operations and increase profitability.

Jan 1, 1999

By Lewis L. Oriard

INTRODUCTION In recent years, there has been a trend in the direction of larger drilling equipment and larger diameter blastholes. Although this change has improved the efficiencies and reduced the costs in many operations, it has increased the potential for damage to underground openings. In addition, in many instances one now finds more sophisticated delicate instruments, automated control facilities, and a large variety of structures in proximity to blasting activity. The combined effect of larger-scale blasting activity and its proximity to various features of interest is such that there is an increased need for a more refined analysis of blasting effects and their control. BLASTING EFFECTS ON ROCK SURFACES The Breakage Mechanism In order to develop techniques for controlled blasting, one must first understand the features of the mechanisms by which blasting causes rock breakage to occur. These features have not been easy to demonstrate, mostly due to the difficulty in making tests and observations at the high stress levels and short time durations involved. When an explosive charge is detonated, the material surrounding the charge is subjected to a nearly instantaneous, very high pressure [on the order of 1.4 to 13.8 GPa (0.2 to 2.0 X 106 psi), depending on the explosive]. If the charge is coupled to "average" rock, this pressure will pulverize the surrounding rock for a distance on the order of 1 to 3 charge radii in hard rock, and to a greater distance in softer rock (this is also dependent on the type of explosive). As the pressure wave passes into the rock, high tangential stresses cause radial cracks to appear, and the nearly discontinuous radial stress zones gen¬erated by the shock front may cause tangential cracks to appear. The extent of these cracks depends on the energy available in the explosive, how quickly the energy is transmitted to the rock, and the strength properties of the rock. The discontinuous shock front is quickly dis¬sipated, but the expanding gases generate a longer-acting pressure. A compressive pulse travels to the nearest face or internal rock boundary where it is reflected in tension. The tensile strengths of most rocks are roughly 40 to %o of their compressive strengths, so the rock may now fail in tension whereas it may have been able to support the diminished compressive phase without failure. The ten¬sile deflection typically produces a failure described as tensile slabbing or scabbing. Laboratory experiments and field experience have pretty well established that several mechanisms are involved. These include (1) the classical case of tensile parallel slabbing when the pressure pulse is reflected at a free surface; (2) failure under quasi-static compressive loading (the shape is normally irregular due to discontinuities in the rock); (3) radial cracking under the action of tangential stresses at the periphery of the expanding pressure pulse; (4) peripheral cracking at the discontinuous shock front which is quickly dissipated; and (5) additional mass shifting due to the venting of the explosive gases. The first three items have received much attention in the laboratory and the literature. The complex effects of gas venting are difficult to test in the laboratory because of the difficulty in reproducing the many weak planes and discontinuities typical of most field conditions, which play such a prominent role in determining the behavior of the rock mass subjected to blasting. Unfortunately, gas venting effects can be pro¬jected to significant distances under certain field conditions, and are sometimes difficult to control. It is not unusual for gas venting to be the overriding factor in determining the final geometric shape and physical condition of the finished excavation. Sources of Damage For the purposes of this discussion, damage includes not only the breaking and rupturing of rock beyond the desired limits of excavation but also an unwanted loosening, dislocation, and disturbance of the rock mass the integrity of which one wishes to preserve (such as mine pillars, underground openings, etc.). The sources of damage include, of course, all those physical features of the rock breakage mechanism. Each of these effects must be limited to the desired zone of breakage and excavation if the integrity of the remaining rock mass is to remain undiminished. The primary zone of rock breakage usually can be controlled in the normal process of field experimentation to determine proper charge sizes and location for primary excavation. However, it frequently happens that there is damage from sources which are more difficult to account for in the design process, which are often overlooked. These are (1) the overbreak due to poor drilling control, (2) dislocation of rock (mass shifting) due to venting of explosive gases, and (3) loosening or dislocation due to the influence of seismic waves (ground vibrations). CONTROL OF ROCK BREAKAGE Importance of Geometry In studying the rock mass and blasting design con¬siderations, it is important to keep in mind the geometric relationships among charge size, shape, and position, and the physical features of the rock mass to be preserved. The features of principal interest are the external shape and position of the rock mass relative to blasting, and the position and attitude of any weak planes in the rock mass. The Sequence of Blasting and Excavation Events Unfortunately, there are too many times when the task of preserving delicate rock is considered hopeless, and because of this attitude, no further effort is ex¬pended towards caution or control. In such cases there is often a failure to recognize the importance of the se¬quence of the procedures. Attention to this can greatly reduce unwanted effects at minimum cost. Perimeter Control The requirements for perimeter control are highly dependent on the special needs of each particular proj¬ect. The desirable degree of control is a highly variable

Jan 1, 1982

By Gary L. Simmons

Many large (refractory) sulfide gold resources exist in Nevada and other parts of the world that are not amenable to conventional flotation concentration using air as the flotation gas medium. Over the past five years Santa Fe Pacific Gold Corporation (SFPG) has investigated flotation process options to economically treat refractory ores and resources of this type at its Lone Tree and Twin Creeks mines. Conventional flotation technology applied to the original high-grade gold resources at Lone Tree and Twin Creeks was initially unsuccessful. Review and analysis of auriferous (gold-bearing) iron sulfide mineralogical characteristics and flotation ..:hemistry provided a fundamental understanding that led to the development of a new flotation process that SFPG refers to as N2 TEC. This paper discusses the development of this technology and compares N TEC results with conventional flotation practice.

Jan 1, 1997

"When boring a tunnel, homogeneous hard rock is the exception rather than the rule. While contractors can set goals such as meters per month and performance incentives, it is also prudent to plan for difficult ground. A properly designed tunnel boring machine (TBM) can tackle fault zones, water inflows, squeezing ground, or whatever the risk may be. The alternative is not a good one: modifying the machine in the tunnel after bad ground is encountered. Not only does this result in increased downtime, but it also needlessly exposes the crew to the tunnel conditions. In the worst case scenario, the entire operation grinds to a halt.However, an accurate GBR cannot always be obtained, particularly for mountainous, high cover tunnels in remote locations. And even with a thorough GBR, unforeseen geological events can occur. What can be done in these situations? Difficult Ground Solutions (DGS) is ground investigation system with a suite of options that can be added to a shielded hard rock machine or dual-mode, Crossover machine to better enable advance when conditions are unknown or difficult conditions are anticipated.DGS consists of a set of integrated features tailored to a specific project’s geology. The main components of the system allow for ground investigation ahead of the TBM, increased monitoring and methods to keep a machine shield from becoming stuck.In fault zones and squeezing groundIf fault zones or squeezing ground are known or suspected, or if there is even a possibility of encountering them, this can greatly affect the TBM operation. Shielded machines protect the crew from the surrounding rock, and they can bore and line a tunnel efficiently, but in fault zones and converging material their shields can be their downfall. Avoiding a stuck machine is paramount to project success. DGS employs several features to avoid the problem of a machine becoming stuck. The first of these is multi-speed cutterhead drives. These drives effectively give the machine multiple modes of operation—high speed, low torque for hard rock, and low speed, high torque for difficult ground. Designing a machine with high-torque, continuous boring capabilities allows that machine’s cutterhead to restart with break-out torque in difficult ground. The net effect is that the machine can keep boring in the event of a face collapse and can bore through fault zones and running ground where the potential for cutterhead jamming exists. Going one step further, multi-speed gearboxes give the machine the ideal earth pressure balance- (EPB-) type torque if larger sections of soft ground are anticipated.Secondly, TBMs can get through squeezing ground and faults using Continuous Shield Advance. This design utilizes a stepped shield configuration — where each successive shield is slightly smaller in diameter — to avoid becoming stuck in converging ground. External shield lubrication is an added insurance against becoming stuck, using a series of radial ports that can pump Bentonite into the annular space to act as a lubricant in squeezing material.As a last effort, if a machine has already become stuck the TBM can utilize augmented, or “super” thrust. Additional thrust jacks can be added to supply an extra boost in a short stroke, generating enough force to break loose a trapped shield."

Jan 12, 2017