Methods

Longwall Mining Method and Design

Studies estimate that 156 billion tons of coal, representing 68 pct of the minable reserves in the United States, is subject to multiple-seam mining. Historically, room-and-pillar mining has dominated coal production, and this mining method has been the focus of most multiple-seam research. Advances in Longwall Mining Method have made this system more economically attractive because of its efficiency and production potential. The high productivity being achieved by longwall mining demonstrates its potential for being a substantial segment of underground coal production. Longwall mines produce more than 30 pct of all underground coal, up from 5 pct just 15 years ago. The continued growth of longwall mining without appropriate multiple-seam planning may increase the cost and risk of mining. Optimization of the mine design factors is arguably the primary means for controlling interactions between operations. The U.S. Bureau of Mines, in an effort to improve long- wall planning, is investigating multiple-seam longwall design and systems development.

Significant advances have been made in longwall design for single seams in the areas of gate road pillar design, panel layout, powered support selection, and roof control. Multiple-seam designs are less developed, but progress is being made as more longwall operators gain experience. In research,

Wood Crib Design & Mine Roof Support

Objective: To minimize support costs and to improve ground control by improving wood-crib design and utilisation through the development of engineering methods that will match the placement and performance of the wood cribs to the load conditions imposed by the mine environment.

Background: While wood cribs are used extensively to stabilize mine openings, their utilization is often based on historical practice or trial-and-error rather than on engineering design. This has led to conservative crib utilization where more capacity than is necessary is employed or inadequate capacity is provided when mine conditions worsen. Critical design parameters, such as the stiffness of the support structure, arc often ignored. Optimum crib design and employment is becoming increasingly important as the utilization of wood cribs increase due to the growth of longwall mining, and as the cost of wood continues to rise. A single longwall operation will spend as much as a million dollars per year on the support of the gate roads.

Approach: A model has been developed that predicts wood-crib performance. The model determines the force-displacement relationship for various wood-crib designs through a mathematical equation developed from full-scale testing of several support configurations in the U.S. Bureau of Mine’s (USBM’s)

Multiple Seam Longwall Mining Design

Objective

Provide longwall operators with practical information and guidelines concerning mine design to reduce problems associated with the interaction of adjacent workings in multiple-seam longwall mines.

Background

The high productivity achieved by longwall mining demonstrates its potential to provide a substantial segment of underground coal production. Longwall mines produce more than 30 pct of underground coal, up from 5 pct just 15 years ago. However, the continued growth of this mining method without appropriate multiple-seam planning may increase the cost and risk of mining. Research by the U.S. Bureau of Mines (USBM) indicates that 25 longwall mines (32 pct of the total number in the United States) have mining in adjacent coalbeds either above or below. About half of these longwall mines report some type of interaction problem with the adjacent workings, such as caving due to subsidence.

Optimization of mine design factors is the best means for controlling interactions between operations in adjacent seams. To avoid higher mining costs, operators should focus on adopting practices and procedures that prevent and control interactions in multiple seams. The USBM, in an effort to improve longwall mine planning, has been investigating multiple-seam longwall design and development.

Approach

There are three primary design

Rock Drag Cutting

The Bureau of Mines, in its continuing efforts to improve productivity and enhance the workplace environment of hard-rock underground mines, has investigated mechanical excavation techniques and in particular drag cutting techniques to achieve these goals. Two fragmentation techniques that use drag cutters have found some success in the mining industry: the kerf-core technique and, the conventional technique.

The conventional technique is characterized by machines that use a multiplicity of cutters fixed to a rotating cutterhead that make shallow, parallel cuts spaced sufficiently close to break out the intervening material (fig. 1). This most common drag cutting excavation technique is represented in the industry by drum-type continuous miners and roadheaders. Some of these machines employ over 100 individual cutters on a single cutterhead that may rotate at speeds up to 70 rpm. These machines are generally limited in the amount of cutting force they can supply by their own weight. Because of the high cutter speeds and the low cutter forces available, continuous miners are limited by their performance to coal or very soft rock; roadheader machines can be used in rock with compressive strength up to 12,000 to 18,000 psi, depending on its abrasiveness.

In contrast, the kerf-core technique is characterized by

Tailings Backfill

This report presents a study of three typical tailings samples as potential cemented backfill in underground mines. The testing series was unique in that the pulp densities of the samples were all above 75 pct solids. Test results included dry density; slump; percent settling after 28 days of curing; tensile strength after 28, 120, and 180 days of curing; and unconfined compressive strengths after 7, 28, 120, and 180 days of curing. The physical properties of the various test mixtures were further analyzed using linear and nonlinear statistical methods to produce correlations and mathematical equations. Physical properties were used to determine the influence of mix additives and as input for numerical modeling studies of backfill. The mathematical relations were used as a predictive tool in determining the suitability of various materials as backfill.

Conventional room-and-pillar mining has been commonly used in the United States. However, the domestic mining industry has been hardpressed to maximize mineral productivity in order to compete with foreign suppliers. As a consequence, U.S. mines no longer have the luxury of leaving ore-rich pillars as ground support, and reserves tied up in highly fractured material cannot be left behind. Existing mines are also encountering greater ground stresses as

Longwall Pillar Design Method

The past decade has provided a wealth of practical experience with longwall pillar design. Design formulas developed specifically for longwalls have proven their value in numerous applications. Analytic methods, including numerical models, have also made important contributions. These advances have been based on basic research into abutment loads, coal pillar mechanics, and the interaction between pillar performance and entry stability.

The goal of this paper is to review the state of the art in longwall pillar design from the standpoint of the practitioner. Actual case histories are presented to illustrate the current capabilities and limitations of pillar design methods. The paper also discusses the advances that can be expected in the future.

Pillar design has long been a central issue for mining research. In the United States, pillar design formulas were first developed for anthracite mining in the first decades of this century (Zern, 1928). Pillar design again became the focus of attention during the mining research “renaissance” of the 1970’s and early 1980’s. Familiar pillar design formulas were updated in the light of new research (Hustrulid, 1976; Bieniawski, 1984), and powerful analytic and numerical approaches began to be brought to bear.

The rapid growth of longwall mining during the past decade brought

Mining Methods VS Underground Crusher Location

In Section 2 we dismissed those “big-room” applications not needing fundamentally new equipment, and lumped all the rest together. Now, as we examine specific mine types, it is appropriate to differentiate within these categories the manner in which portable crushers might be used, and the consequent effect on desired machine parameters. The common yardstick by which we will measure all these mining methods is the basic decentralized crusher concept, beyond which portability, or the degree thereof, will be the special and distinguishing feature. Accordingly, underground hard-rock mines are divided into three major groups, listed below with their distinguishing characteristics.

 Low Head Room Room and Pillar: Most similar to coal mines in their mining methods, this group exhibits more rapidly moving mining fronts and the greatest need for portability. Machine height is critical, but other dimensions may be more flexible due to room size and single level mine plans. Great portability also demands minimal site preparation.

High Head Room Room and Pillar: No particular height problems are encountered here.
Slow moving mining fronts (on single or multi-levels) allow less frequent crusher moves and generally create greater throughputs from a single mining unit.

Non Room and Pillar: This large group includes many different mining plans, but most are characterized

Longwall Mining

I was requested to write an article on Longwall Mining a short time ago; however, the time has been so short that I have not had time to prepare an article as I would like to have presented it to this body. In writing this article it has not been my intention in making comparison of various mines, to favor one or discredit the other. I hope it will be considered in that light.longwall-mining

The coal mining industry as I have seen it in the past, at present and in the future. In years gone by large tracts of coal land could be obtained at a very small cost, and as yet coal land may be purchased at a reasonable price in this country, but I believe the time is near at hand when the methods of mining will have to be changed greatly in this country. Many changes have taken place in the last few years, some of them have been forced by law, others by the coal operators themselves, after being convinced that the changes made were for their own benefit. During my 20 years in the mines I have seen

Diamond Drill Sampling Methods

In diamond-drill work, a true sample consists of all the material cut by the bit—both core and cuttings. As the recovery of this sample is the object of diamond drilling, the utmost care should be taken to secure it. Speed of drilling and low costs are of little value if an inaccurate sample is obtained. The engineer in charge must study his material and lay out the plan of sampling, and then see that the drill runner follows his instructions; for the runner may be more interested in obtaining a large footage than in developing accurate methods of sampling.

The foregoing is a brief description of a few of the common methods of collecting and preserving diamond-drill samples. Variations of these methods will suggest themselves on every new piece of work. The essential point to bear in mind in all diamond-drill sampling is that the sample must comprise all of the core obtainable and all of the cuttings. This involves the proper operation of the drill as well as the careful collecting of the core and sludge. The engineer must use his own judgment as to the practical methods that will give the desired results under the conditions obtaining.

Accounting for Small Mining Operation

The observations here presented are not those of an expert accountant, but of one who, while he has seen considerable service in the accounting departments of large companies, has spent more time in engineering and operating.

This paper is intended to cover, in a measure, mine accounting for small mines, as distinguished from the elaborate systems, requiring many persons in the accounting department. I shall attempt to outline a system embracing the essentials of accounting, and simple enough in form to permit one or two persons to carry it on from month to month, in sufficient detail to be able to tell quickly the grade of ore, the prices received for metals, costs per ton for mining and milling, costs per foot for development, upward or downward tendencies in costs, ore settled or in transit, cash on hand, stocks of supplies on hand, efficiency of labor, etc.

As in all accounting, there are two main divisions: that of revenue received for what is sold, and that of disbursements made for what is bought, so in mine accounting we have to consider chiefly the income derived from sales of ore or concentrates, and the expenses incurred in producing the said ore or concentrates

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