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By Ronald F. Ayers

The study upon which this paper is based was completed by Battelle's Columbus Laboratories for the U.S. Army Corps of Engineers in 1974. It is but part of an overall effort by the Corps to evaluate the costs and benefits to the nation of waterway improvements. This study is primarily concerned with future coal markets for production from those counties near the Wabash River in the heart of the Eastern Interior Province. An objective here is to consider a most pessimistic energy (and hence, coal) demand for planning purposes.

Jan 1, 1976

By Jean-Michel Rendu

Accurate modeling of the semivariogram is an extremely important step in the geostatistical analysis of mineral deposits. Automatic fitting of a mathematical model is often possible but not necessarily desirable. Significant geologic and statistical information must be taken into account in the fitting process, which is not always available to the computer. Manual fitting of the model is, on the other hand, extremely time consuming. Interactive graphics are best suited to optimize the process. A number of interactive methods are described, which are adapted to the modeling of semivariograms in one-, two-, or three-dimensional environments.

Jan 1, 1982

From the massive equipment that moves the earth, to the parts that keep the equipment moving, it was all on display for more than 35,000 people who at-tended MinExpo 2008 at the Las Vegas Convention Center Sept. 22-24. In the largest show in the illustrious history of MinExpo, the success of the recent commodity boom was reflected in the more than 55,700 hm2 (600,000 sq ft) of floor space that was jam-packed with nearly 1,300 vendors. Among them, the makers of the industry?s largest machines, displaying their latest and greatest trucks, shovels, excavators, drills and other mining equipment. During the nearly decade-long commodities boom, equipment makers have worked hard to keep up with demand while also investing heavily in research and development. The beneficiaries of this R&D is the end user who saw first-hand at MinExpo 2008 the many advances that have already been made in safety, comfort and productivity from all the manufacturers. R&D has also helped spark more talk of automation, which is being used already at some of the world?s largest mines. Caterpillar and Komatsu have worked with the technology in surface mining and Bucyrus and Sandvik are among the industry leaders applying the science of automation to underground mines. Technology has in-creased greatly since the idea of moving massive equipment remotely was first knocked around and the idea of entire fleets operating around the clock seems to be getting closer to reality. But, until that happens, MinExpo attendees were treated to a show that featured some of the most impressive current machines the industry has to offer. In the largest booth space of the convention, Caterpillar (www.cat.com) displayed the culmination of an ambitious $280-million dollar investment, with the introduction of its new mining fleet of four new trucks. The F-series was un-veiled with common features in safety, cabs, engines, frames and bodies and Tier 2 compliant engines. The F series also features a return to the electric drive option. ?When our customers asked us for improvements to our mining trucks, we responded by making a record investment in every single truck in our line, as well as the increased capacity to produce more of them,? said Cater-pillar group president Stu Levenick. ?New technologies have allowed us to make trucks more reliable, easier to maintain and more friendly to the operator and to the environment.? The 793-series is in the 218- to 227-t (240- to 250-st) class that will be available in both mechanical (793F) and electric (793F ac) versions. The electric drive-only 313- t (345-st) 795F was also introduced, while the flagship 797B truck is in the process of being replaced by the new 797F mechanical drive, maintaining its 345- to 363-t (380- to 400-st) target payload. Completing Caterpillar?s new mining truck line will be new versions of the 785 and 789 mechanical drive trucks. The next generation of trucks will be phased into production during the next two years, with the Cat ac drive models expected to go into production in late 2010. The $280-million in-vestment is Caterpillar?s largest commitment ever to the mining industry

Jan 1, 2008

By E. J. Meets, C. F. Meyer

Bord and pillar mining at shallow depth (400 m approx. maximum) is widely used in South African coal mines. One of the problems encountered in extracting coal in this manner is the ventilation of advancing bord and pillar headings. The traditional ventilation methods of force, exhaust and overlap (force/exhaust) are reasonably effective but tend to be both cost and labour intensive. Ducting often restricts the available free area of roadways thus impeding the transport of coal and other materials inbye the coal production section. Due to the above facts, ductless fans are currently being used to minimize the amount of ducting required in advancing sections. Two different types of fans are used, namely, vortex fans and the so-called `jet' fans. Vortex fans were developed from the fan blade design used for vertical take-off aircraft. The fans have the capability of delivering air over distances of about 30 m in the underground situation without any ducting attached to it. Jet fans are standard axial flow fans fitted with outlet reduction pieces which increase the velocity pressure at the discharge to such an extent that the air delivery distance is improved to almost match that of vortex fans. The paper describes some applications of both these fan types in advancing bord and pillar sections.

Jan 1, 1993

By H. Beecher (Original by) Charmbury

Water is a most remarkable substance, essential for life of all kinds. As well as needing water to survive, man has always used it for agriculture, transportation, recreation, and many other things. When our country was young and inhabited by few people, the streams, rivers, and lakes were able to provide all the clean water needed by man and take away all the wastes created. However, with our growing population and an ever-increasing demand for goods and services, the public, industry, and government at all levels have become acutely aware of the need to manage the nation's water resources more efficiently. Abundant energy from many sources has helped this nation to become the greatest industrial nation in the world. Coal has contributed a major portion of this energy, generating electricity, running railroads, and maintaining national security during wartime. The result has been the highest standard of living in the world and a time of widespread economic prosperity. The use of water in coal mining is somewhat different from its use in most industries. With the exception of water used in cleaning plants, for underground dust control, and for fire protection, most of the water en- countered in coal mining operations serves no useful purpose. In other words, it is an undesirable element and must be removed, otherwise it will interfere with operations, cause potential water quality problems, and may even stop operations by flooding. In the past, removing water from working areas of most mines was usually a fairly simple matter. Pumps with piping were installed at sumps or low spots in the mine and the water was pumped to the surface or to drainage control facilities constructed for the operation. Ditches were often used to collect and drain the water by gravity to the outside or to main sumps for pump discharge. In either case, the water was allowed to flow into the nearest stream or river. The concept of "water is water' was generally accepted without too much concern for what was in the water since low-cost products and services, rather than clean water, were the public demand.

Jan 1, 1981

By Robert W. Greene

Next month, American Commercial Barge Line Company will begin moving coal from mines on the old Camp Breckinridge property in Western Kentucky to TVA's new 2600 MW steam plant at Cumberland City, Tennessee. By April of 1973, this movement will reach a level of 7,000,000 tons per year. TVA bought the coal rights to this property from the General Services Administration in 1965 for approximately $7 million. The reserve contains about 120 million tons of recoverable No.9 coal, and about the same recover-able amount of No. 11 coal. TVA then contracted through competitive bidding with Peabody Coal Company to mine the No.9 seam through two slope shafts. The mines are about 300 feet deep and are separated by the one major fault on this property. The mine portals are approximately 3-1/2 miles apart, with the northern portal being over nine miles distant from the Ohio River (see Figure No.1). In 1969 TV A took bids on alternate methods for transporting 120 million tons of coal to Cumberland City at seven million tons per year. These alter-natives included overland transportation to the Ohio River by rail or conveyor, water transportation from Union County, Kentucky to Cumberland City, and total transportation packages from Camp Breckinridge to Cumberland City. The latter could be a joint land/water package, or all land (rail). Ultimately American Commercial Barge Line was awarded an $88 million package transportation contract to convey the coal from Camp Breckinridge to Uniontown, Kentucky; to store it at Uniontown in a quantity sufficient to allow ratable delivery to the steam plant; and to barge from Uniontown to Cumberland City via the Ohio and Cumberland Rivers.

Jan 1, 1971

By Rodney R. Krause

In attempting to tell the general public about the coal industry's land reclamation efforts, we have often said, "We're not doing things by the book, because we're still writing it." Like any good catchphrase, the statement is not only striking but true. It is particularly true in the mountains of Appalachia, where the problems of mining; and of reclamation are made more intense by the nature of the terrain. Mining and reclaiming the land "by the book' --which is to say by the methods of contour mining traditionally used in hill country--hasn't worked too well. So a lot of conscientious coal operators and associations are trying new methods--new ways of mining, new machines for seeding and planting, and new species to seed. Not all their experience can be transplanted to other areas, and of course I don't believe that Appalachia is the only place where new methods are being developed. Nevertheless, there's enough action in Appalachia to make a detailed examination rewarding, so let's focus on the hills to see what's new.

Jan 1, 1970

By Eugie Kabwe

Rock bolts are components of tunnel support structures and their efficacy in reinforcement requires the appropriate estimation of the bolt pre-tension. However, cases of ineffective rock bolt application due to loosening are common which leads to the potential failure of the support structures, thus negatively affecting the tunnel stability. The effective employment of pre-tensioned bolt within support structures requires an appropriate installation tension as a result of sufficient bolt head/nut pre-load. Henceforth, this paper presents a load indicator washer (LIW) capable of withstanding assigned static loading as well as provides an appropriate pre-tension. The different LIW breadths are numerically analysed in the finite element code (ABAQUS) to estimate deformation when a designated 60-kN pre-load is applied. The numerical simulation employs a bi-linear isotropic hardening constitutive law governed by the von Mises yield criterion. The simulation also considers the nominal temperature of the nutLIW-rock bolt connection. Therefore, a long-term relaxation effect on bolt pre-tension as a result of stress relaxation is neglected. The compressive force required to achieve the LIW-predetermined deformation is the bolt pre-tension. It is drawn from the simulation results that the 1.5-, 2.0-, 3.0-, 3.5-, and 4.0-mm-thick LIWs are completely flattened when subjected to 28-, 42.5-, 65-, 76-, and 88-kN pre-load respectively.

By Dale A. Shay, Roy R. Cellan

The Santa Fe Mine, located in west central Nevada, began leaching ore in 1988 and completed ore processing in 1995. Homestake Mining Company has completed final reclamation of the site, including remediation of bare surface soils resulting from the oxidation of sulfide minerals and migration of acidity in the mine waste repositories. The need to remediate oxidized sulfides and mitigate resultant acidity at the Santa Fe Mine emphasizes the economic, reclamation, and environmental advantages for understanding and pre-planning for management of potential sulfide wastes during mine planning phases. The lack of pre-planning by mining companies for sulfide waste management was common in the 1980's due primarily to mining of reserves characterized largely as oxide deposits and to the common opinion that low moisture regimes in arid or semi- arid climates would not allow for significant acid generation. Since the 1980's, operational experience has shown that sulfide wastes, deposited randomly in waste dumps and without adequate planning for final reclamation success, can create final reclamation problems that are very costly to remediate. While mine waste characterization, waste management plan compilation, and in-pit selective waste handling procedures add operational costs, the reclamation experiences at the Santa Fe Mine are indicative that pre-planning and management is worthwhile both in actual overall cost efficiency and in successful reclamation of the mine site. The reclamation program at the Santa Fe Mine shows Homestake's continued commitment to the successful management and reclamation of their mine sites.

Jan 1, 2000

By Mortimer J. Richardson, Earl H. Malmstrom

INTRODUCTION The art of placer gold mine evaluation and mining has had an interesting evolution beginning in earliest times. DE RE METALLICA (c.1556), documents the use of rockers, circular sieves(jigs) and riff lest for classifying, concentrating and recovering placer gold, respectively. During the late 1800's in the heat of the international gold rush, a bucket ladder mining dredge containing its own processing plant was developed that enabled digging of placers to bedrock that were inaccessible to the hand miner. The power driven churn drill was developed at about the same tie that facilitated more rapid and larger scale sampling of placers to bedrock. The mineral jig was applied in the early part of the 1900,s to begin the replacement of riffles on placer dredges. Mining dredges proliferated in California and New Zealand to mine the deeper placers and spread throughout the world. The companies that were leaders in dredge mining technology conducted experimental work that advanced the state of the art by processing of gravels with jigs and amalgam systems to recover gold on board dredges in a continuous process. This paper will synthesize the technology of placer gold exploration, mine development and operation into guidelines for evaluation and development of small-scale prospects. Prospect Reconnaissance The location of a prospect usual1 y results from some physical evidence of the presence of gold and/or past mining activity. Any earlier activity that may have produced gold from the prospect, should be investigated before making the trip. The initial reconnaissance should attempt to verify a near-surface presence and then make observations concerning the geomorphic characteristics that relate to placer gold accumulation. Estimates of the probable depth, breadth and length of mineable gravels can be made from the surf ace by the experienced placer mining engineer. With this information, he can speculate on whether there is a viable prospect to be pursued. The placer mining engineer should be experienced in panning samples found in shallow diggings or from existing pits. This will give him immediate indications of gold presence without fear of "salting" by an over-ambitious promoter of the project. The same capability of panning is important during the other sampling phases. A thorough knowledge of logging and calculating the results is essential to proper evaluation of the deposit' s tenor. Evaluation Methods Depending upon the character of the prospect such as river, benches, terraces, jungle, the type of equipment to conduct sampling of the deposit must be determined. In most cases, the drill has replaced bulk sampling. The churn drill has had the greatest amount of accumulated experience but is slow. The reverse circulation drill (RC), is limited by its lack of verification in subsequent mining in order to prove its reliability. However, in the hands of knowledgeable placer mining engineers experienced with its use and calibration, it may be used. The RC Hammer drill (such as the Becker), can be as much as ten times faster than the churn drill and compress the time necessary to prove a prospect, or, to disprove it. All costs in balance, it is often cost effective over the churn drill.

Jan 1, 1987

By D. A. Robbins

The application of remote sensing for environmental measurements is already being utilized. Aircraft mounted imaging spectroscopy has been utilized to evaluate areas of historical mining operations as well as active mine sites. To the extent that remote sensing can provide more sensitive, cost effective, and timely monitoring potential, the technology is of interest to the industry. Questions remain about the application and validation of the data and the availability of the technology in the private sector. This presentation will discuss some of the potential uses, benefits, and concerns related to remote sensing and efforts to monitor the technology's development.

Jan 1, 1999

By Nick Barton

A recent analysis of 145 TBM tunnels of more than 1000km total length has helped to quantify the time dependence of utilization (U). In fact U = Tm, where T is time in hours and m is a negative gradient of deceleration. In poor quality ground, gradient m has a strong dependence on rock mass quality Q, for example m ˜ -0.5when Q = 0.1. Good investigation is critical for ensuring faster TBM tunneling then drill-and-blasting, which tends not to slow down (in m/hr) as the tunnel length increases. Anew design model called QTBM allows more reliable prognoses be made, and occasionally will disqualify the TBM solution.

Jan 1, 2001

By Oscar M. Wicken

Iran was a lodestone for the attention of industrial countries and companies wanting to share in its industrial development during the last two decades and particularly after 1972. Prior to 1972, most industrial projects in the private sector were on a relatively small scale and could be carried out in reasonably orderly fashion in spite of limitations of a primitive infrastructure and meager indigenous supply of managerial and technical skills. People with these skills could be found but not in abundance, and many of them were total¬ly engaged in various government ministries and projects. Thus it was that nearly all private sector industries, even long-established ones, required one or more foreigners to give guidance. A barite mine and processing facility was brought on line by Dresser Industries in 1960 without serious operational problems. A few expatriate experts were able to select and train a stable group of staff and production people and establish sound management principles for continued growth. The huge and increasing oil revenues after 1973 gave superficial credence to ideas of the Iranian government that the country could easily finance the jump into the industrial 20th century. All necessary skills and equipment not available in Iran would be imported, and intensive training programs would prepare Iranians for operating the new facilities. Large projects for steel production, copper production, oil refining, petrochemical production, cement production, and others were started or expanded. These are basic industries that consume substantial quantities of refractories. Studies made in 1972 indicated that the existing industries plus expanded and new projects scheduled to come into production would lead to a market sufficiently large to justify a refractory producing plant. Concurrent studies of raw material sources showed that clay, the largest tonnage item, would be locally available; the other raw materials would be imported. Iran Refractories Company (IREFCO) was founded in 1973 and started production in 1976.

Jan 1, 1981

By Roland W. Merwin

The Bureau of Mines has studied the possibility of using the heap leaching process for treating the gold ores in the sedimentary beds of northeastern Nevada. This paper summarizes all available information on the technical and economic feasibility of heap leaching oxidized ores from these beds, past industry application of vat leaching, results of recent Bureau of Mines and industry tests on heap leaching ores from this region, and requirements for planning the proper application of heap leaching. Preliminary tests on representative samples of ores from the region show that a satisfactory recovery of gold can be obtained by heap leaching the ores with cyanide at a relatively coarse size. Significant deposits of gold ore occur in sedimentary beds of various locations over an extended area 40 miles wide and 200 miles long in northeastern Nevada. The area is centered 40 miles west of and runs parallel to the leading edge of the Roberts Mountain thrust fault system, a prominent geologic feature in the area. The general locations of past and present gold mining operations are shown in figure 1. (slide 1)

Jan 1, 1969

By W. M. Kidd

INTRODUCTION Uranium mine inspection in Canada forms one element of the enforcement of the Atomic Energy Control Act; it is under this Act that all Canadian uranium mines and mills are licensed to operate. Inspection duties are carried out by a small core staff of federal government inspectors (working for the Atomic Energy Control Board (AECB)) largely supplemented by provincial mine inspectors working on behalf of the AECB. Unlike most resource extraction in Canada, uranium mining is under federal jurisdiction and consequently it was the AECB who decided in 1975 that changes in the Canadian uranium mining industry, particularly its expansion and the expanding role of the mine inspector in the limiting of exposures, warranted the offering of a special radiation protection training course. The Uranium Mine Inspector Training Course (UMITC) was first conducted in 1976 at the Elliot Lake Centre in Elliot Lake, Ontario. Subscription for the course was not limited to mine inspectors to enable union stewards, management personnel and provincial/federal labour inspectors to attend. This paper will present an outline of the course content, the format of its presentation and non-curriculum aspects of running a course of this type in uranium-producing community. The core lecturers for UMITC are drawn from the Radiation Protection and Uranium Mine Divisions of the AECB. In addition, guest lecturers are invited from universities and medical research centres together with industry professionals and government researchers. In all some twenty-four plus presentations are made over the first five days of lectures. The program topic areas, hazards, controls, measurements, record-keeping and health effects are preceded by an intensive half-day session on radiation fundamentals. TOPICS Hazards [Dust] A review of the dynamics of airborne particles including the effects of particle size, gravity and wake-turbulence on the behaviour of dust clouds. Associated topics are migrational aspects of dust particles and specific dust-generating mine operations. [Radiation] Canadian uranium mines are increasingly diverse in nature ranging from large scale low-grade underground operations in Elliot Lake to smaller high-grade open pits in Saskatchewan. Papers are presented on assessments of internal and external exposure, the metabolic pathways of ingested or inhaled radiation and the specifics of mine and mill hazards. Radiation hazards are further broken down into gamma surveys of uranium mines, radon daughter concentrations and problem areas. Controls The relationship between mining methods and the operating environment is critically important to ensuring safe working conditions. This refers to both the selection of machinery/devices, etc., and to engineering controls which are instituted to remedy problems created by new technology. UMITC examines a number of possible mining techniques, their criteria for selection and impact on the working environment. Control measures, ventilation practices and design, the need for continuous water misting and special open-pit precautions are presented. These lectures frequently conclude with suggestions for better operating guidelines for mine ventilation systems and the need for greater co-operation between the ventilation department and the underground crews. Measurements Uranium mining regulations stress the need for a high standard of exposure monitoring, statistical planning and record-keeping. [Statistics] Although many course participants are well versed in statistics, certain fundamentals are repeated and include, the concepts of mean, variance, standard deviation and standard deviation of the mean. Confidence levels, decision-making based on sample statistics and statistical records are also discussed. [Dust Measurement] Dust measurement is particularly critical in the mines where the high silica content of the ore body, such as those at Elliot Lake, results in the continuous generation of dust. Sampling practices, filtration, impaction, thermal impaction and electrostatic precipitation are explained together with the methods of counting samples to determine free silica. Konimetric and gravimetric techniques for dust sampling are compared and contrasted. [Radiation Measurements] Both collective and personal dosimetry systems are used in the Canadian uranium mining industry and lectures are presented on each. Techniques and possible sources of error are discussed for a variety of radon and radon daughter measurement methods - Lucas method, Tsivoglou and modified Tsivoglou, Kusnetz, Rolle. Instant working level meters and personal alpha dosimeters are explained in terms of calibration, maintenance, readout and estimation of accuracy. A lecture outlining dose estimation by means of bio-assay, whole-body counting and the use of TLD's concludes the topic. Record-Keeping An overview of the problems of changing limits,

Jan 1, 1981

By L. B. Phelps

Many coal mining companies have potential surface mine reserves which either are known or suspected to have had prior drift mining activity on them. In many cases, there is no documentation on these mines or at best, very fragmented records. These undocumented abandoned underground mines are creating engineering, financial, and environmental difficulties and concerns for both surface coal mine operators and regulatory personnel. This paper examines the use of resistivity techniques in detecting entries of abandoned drift coal mines. The detection of such a drift mine entry would confirm the presence and orientation of an abandoned underground coal mine.

Jan 1, 1985

By Charles E. Michener

This paper deals with the occurrence of basic and ultrabasic rocks and their relationship in space and time to major structures of the earth. In order to introduce the paper properly, I must go back a little and try to put the subject in perspective. In the brief time that geology has been a scientific occupation, ore deposits have been grouped and classified in various ways depending on the theories that happened to be popular at the time. Some of the early scientists said that ore came from fire, other schools argued that ore originated from water. Then came the lateral secretionists and in later years the hydrothermalists led by the Lindgren school and the latter has largely been accepted as the modern concept of ore deposits. It now seems apparent that the hydrothermal school is being seriously challenged by other schools of thought. It also seems that we have reached the point where we should be willing to admit that we do not really know in most cases how the ore got to its present position. However, for practical purposes, we can classify ore deposits as to the environment in which they do occur. This is not difficult and gives the field geologist and the mining engineer something to work with and to believe in, and it gives them a basis for carrying out their field work. On the screen, Figure 1, there is a classification of ore deposits based on the environment. Under each classification is listed the more prominent metals which are characteristic of that

Jan 1, 1971

By Juan L. Yarmuch, Gonzalo Sepulveda

This article presents a novel approach to address the mining width-constrained open pit mine production scheduling problem in the context of medium-term planning. A mathematical formulation is proposed to incorporate mining width constraints into the production scheduling process, aiming to maximize the NPV of the schedule while ensuring enough room for the operation of mining equipment. To tackle the computational challenges posed by large-scale instances of the problem, we propose a method based on variable fixing and horizontal precedence generation. In this study, we apply the developed model to real-world scenarios from Radomiro Tomic short-term mine planning problems such as optimizing the timing of major truck maintenance and the impact of external factors, like the delay in the production of the Chuquicamata underground project. Remarkable improvements are observed with the mining width-constrained model. Specifically, the mining width satisfiability is enhanced from 2 to 60% compared to the traditional open pit mine production scheduling model, underscoring the significance of incorporating these constraints. The proposed method showed good results reaching optimality gaps within 5%.

Mar 28, 2024

By C. I. Walker

"Understanding the influence of slurry particle size on wear is essential to maximising the life of centrifugal pumps operating in mineral processing plants and for hydrotransport duties. Particle size influences not only the wear rate but also the wear pattern in pumps. Complicating the situation is the different relative wear rate for different pump parts depending on particle size. A simple Slurry Wear Type (SWT) number based on particle size and size distribution is proposed as a means for categorising slurry pump wear patterns and optimising pump application and material selection. INTRODUCTION The wear of centrifugal slurry pumps in mineral processing and hydrotransport can be quite severe and is one of the major cost concerns of plant operators. Some typical worn slurry pump parts made from high chrome white iron are shown in Figure 1. Erosion wear rates of up to 2 mm/day are not uncommon [1].Centrifugal slurry pumps are required to handle solid-liquid mixtures with a very wide range of particles extending from sub-micron size clay through to 200mm and larger cobbles. Particle size distribution can also vary widely from uniform and narrow (such as graded sand) through to very broad (such as grinding circuit slurries). Slurry particles may also undergo size change due to attrition during the pumping process. The major wearing parts in a slurry pump are the impeller, side liners and casing liner. These are shown with reference to a Warman® MC centrifugal pump in Figure 2. While many particle properties (including size, shape, hardness, density and concentration) influence pump wear, this work will consider only the effect of particle size as it is the major determinant of wear characteristics. Particle size influences the wear pattern, material performance and relative component wear rate in centrifugal slurry pumps. SLURRY WEAR TYPE (SWT) BASED ON PARTICLE SIZE Soil and grain size classification systems abound. Many have different limits to the ranges for a particular classification, albeit not too"

Jan 1, 2018

By Yoshinori Iwasaki, Shosei Serata, Yutaka Mochida

A new comprehensive insitu instrumentation technique named this RCC Method has been developed for rapid assessment and improvement of the structural stability of underground openings. When applied to tunnel construction, the degree of present and prospective safety of underground openings can be determined in quantitative terms within 10 to 20 minutes of microcreep observation. When applied to mining, roofs and floors can be stabilized by controlling the stress conditions. This stress control method has eliminated the need for intensive roof bolting and extensive floor renewal in all cases where it was applied. Use of this technique is illustrated by field examples from the Seikan Undersea Tunnel of Japan and deep potash mining in Canada. NEW INSTRUMENTATION TECHNIQUE: THE RCC METHOD Failure problems in underground excavation usually arise in weak non-elastic grounds where conventional rock mechanics theories of elasticity are not only useless but also misleading. Presently, discontinuity planes in the ground are being considered a factor in assessing these failure problems, and while this development is interesting academically, it is not of much use in actual excavation work, where it is nearly impossible to identify and quantize all existing planes of discontinuity. Even if such an extraordinary task could be accomplished at an underground excavation site, effective use of the data would be difficult and impractical for rapid excavation work, with the possible exception of rare cases of ideally elastic ground.

Jan 1, 1976