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By M. E. Poad, Donald Ross, G. G. Wadell

Because of the "energy crisis" emphasis has been placed on bringing coal mines into full production faster. To accomplish this, more is involved than a rapid excavation system. Mine design should have the freedom within the law to customize as mining conditions dictate as long as the maximum safety of the miner is insured. A year ago, safety was the most prominent "social-human factor"--now, safety and energy self-sufficiency are primary to our national policy. The Single Entry research program as designed satisfies both. It investigates the hypothesis that a single-entry system, for longwall development, supported in the center by open cribs and divided by a fire-resistant partition, can be regarded as being equivalent to or better than a multi-entry system. This paper provides an explanation for the use and advantages of a single entry system in development for longwall mining, explains the problems anticipated with single entries and presents the research approach needed to evaluate and solve the problems. Under study are ground control, ventilation, fire and explosions, emergency procedures, and industrial hazards. Described are measurements data on crib and roof bolt loads as entry heading advances and longwall abutment load is superimposed, stress field determinations and preliminary structural analysis of the double and single entry, and methane liberation and ventilation records as entry advances. Some of the mine operation problems and waivers of mining laws will be discussed. This project is a complete system study having progressed approximately two years in a five-year program.

Jan 1, 1974

By A. Unal

Barbaro et al. (1990) implemented a tedious study aimed at delineating the short-scale spatial variability of sulfur in a coal seam. It is not possible, however, to extend their conclusions to any other coal seam or use theirs in any other fashion, because the background geology was not presented. Nor were the conclusions accompanied by geological interpretations in the paper. In addition, an unfortunate printing error occurred where the total sulfur (determined by High Temperature Combustion) variogram in Fig.3 was duplicated in Fig. 2 instead of the seam height variogram. A more serious error, however, has been committed in the definition of the variable, seam height. What is defined as seam height by Barbaro et al. (1990) is, in essence, mining height, and is not a regionalized variable that should be studied by geostatistical methods directly. Despite the fact that the variable, seam height, is not defined in the paper explicitly, the following quotation discloses the fallacy: "All roof rock that exceeded 1.8 m (6 ft) from the floor was not taken because the longwall was operated to not mine more than 1.8 m (6 ft) unless the coal seam height exceeded 1.8 m (6 ft)." From this definition, the seam height, and therefore the sampling height, is equal to the actual coal thickness, if the coal thickness is greater than 1.8 m (6 ft). Otherwise, it is equal to the sum of the coal thickness plus the thickness of the roof rock that complements the thickness to 1.8 m (6 ft). In the latter case, the seam height is constant and equal to 1.8 m (6 ft). It is possible to conduct a variogram study on a pool of samples that are realizations of two different variables. But the conclusions derived would not belong to any one of the two variables uniquely and, therefore, do not possess any significance. Geostatistical analysis is irrelevant for the sum of multiple regionalized variables formed by arbitrary selections. In a two¬seam setting, for example, the mining height, as defined by the thickness of one seam at one location and the thickness of both seams at another location (due to quality and/or minimum thickness considerations perhaps), should not be used in the calculation of one common variogram. The two seams should be modeled separately. They can then be combined according to the specific purposes of the study. On the other hand, if a constant is added to a regionalized variable (to incorporate dilution perhaps), the variogram of the new variable will not change. Barbaro et al.( 1990), surprisingly, does not give any geologi¬cal interpretation of their results despite the fact that most of them can be explained by the origins of sulfur in a coal seam. The presentation of the results of a geostatistical study with no reference to the geology of the deposit is uninformative. It may also be misleading for the potential users of geostatistics. It is not unusual to find nuggets of pyrite in coal seams. In such cases, pyritic sulfur will probably display a spatial structure for only a very small distance that will appear in the experimen-

Jan 1, 1991

By Wei Wu

A computer-aided method for optimization of bench blast design in surface mines is presented. The design procedures basically consist of two steps. Firstly, a series of normalized, full- scale bench crater tests must be carried out in the field to find the optimum burden that produces the largest amount of acceptable fragments and other parameters that defines the effective fracture zone. Next, the locations and initiation sequence of blast-holes will be determined in such a way that each hole, at its time of firing, will be responsible for same amount of burden rock and will be in a position favorable to effective fracture of burden rock. A computer software "B.B." which can assist the second step of the design is fully introduced and its application is illustrated by an example.

Jan 1, 1992

By V. Rastogi

Surfactant-based bactericides are able to control acid formation in sulfidic materials such as pyrite and sulfidic ores, thereby helping to abate acid rock drainage. Bactericides are used in the following two ways: as periodic or continuous spray treatments for the prevention of acidification of material actively handled and moved and in controlled-release form for reclamation. Site-specific bactericide treatments are designed for active sites and reclamation. Results from two active coal refuse sites show that acid production can be reduced by 88% or more. Results from reclaimed sites show that bactericide treatment can be more effective than the addition of alkaline materials such as limestone and can reduce acid production from 3,500 to <30 ppm. The controlled-release-pellets treatment outlasts the life of the pellets, as shown by a study of a site now 10 years old A single treatment sets up a change in site microbiology to replace acid-producing Thiobacillus ferrooxidans bacteria with heterotrophic bacteria and creates a stable site without the need for further treatments. A secondary beneficial effect of bactericides is on revegetation, and biomass from treated areas is almost 10 times that from areas not treated with bactericide. Depending on the application, bactericide treatment can be cost effective upfront and certainly long-term, compared to the perpetual water treatment that could be required, even after productive use of the site is completed

Jan 1, 1997

By M. G. Ayat, J. Dasher

Having an interest in coal slurry pipelines from a decade of arguments with Ed Wasp and crew at Bechtel about pumping thicker slurries slower, I immediately read this article and found nothing in it pertinant to the title. Ayat and Scott pumped five unidentified coals at 9% solids (50%-60% is the area of interest) in a 25-mm (1-in.) pipe around two square elbows through a 76-mm (3-in.) cyclone for up to 60 minutes and sized a large number of samples of unstated size on an unidentified wet screening device. They did not measure power consumption, discharge pressure, flow rate, or give pump tip speed or impeller diameter. They siad the cyclone had a "high" pressure drop (unmeasured) and did much of the degradation (measured) but more or less per unit of energy expended? Hargrove was not measured, so there are no data as to whether it would correlate with degradation. The authors conclude, with no attempt, correlation is "hard to establish." Please experiment before concluding. I am at a loss to know what "increasingly smaller size" means, much less what theory says such particles take "exponentially larger quantities of energy," which the authors neglected to measure. If such experiments without pertinent data or justified conclusions must be published, please attach a pertinant title.

Jan 1, 1990

By A. John R. Hart

INTRODUCTION The use of precast concrete tunnel liners as the initial and final tunnel lining for transit systems has been a major consideration of designers for over three decades. The obvious benefit of building a tunnel that requires only a single pass in constructing the structural lining can provide the opportunity of saving both time and cost. This technique has had worldwide application in transit systems in London, Munich, Hong Kong, Toronto to name a few. In the United States precast liners were evaluated for use on the BART System in San Francisco in the early 1960&apos;s but did not provide sufficient confidence in the sealing capabilities available at that time. In 1976 it was decided to call for bids on the Lexington Market Tunnels in Baltimore with a precast concrete liner alternative for one of the tunnel drives. This option was selected by the owner and UMTA to provide a study evaluation for the benefit of the industry. HISTORY In 1983 Washington Metropolitan Area Transit Authority began calling for a series of bids on soft ground tunnels on the Green Line, which included the option of using precast concrete tunnel liners first as an alternative to fabricated steel tunnel liners. Over the years following, the precast concrete tunnel liners have become known as the conventional tunnelling system and, in the last year,

Jan 1, 1989

By S. Behl, Pradip

Selective-flocculation process development generally involves single-mineral flocculation tests to identify the appropriate polymer experimental conditions for achieving the desired selectivity. Invariably the selectivity predicted on the basis of such tests is not realized when mixed-mineral tests are conducted. A systematic experimental investigation revealed that adsorption of the polymer on various substrates is critical to selecting the suitable flocculant. Simultaneously, a mathematical model was developed to predict the overall process of efficiency with a given polymer. In this paper, the results of these efforts to scientifically design a suitable selective flocculation process are presented.

Jan 1, 1994

By M. Prasad, G. M. Rao, A. K. Majumder, T. C. Rao

Froth flotation was employed to beneficiate a lean-grade siliceous rock-phosphate ore containing fluorapatite, the phosphate-bearing mineral. The main gangue minerals were quartz, iron oxides and aluminum oxides. After the rougher stage, four cleaning stages were required to upgrade the ore. The liberation size of the phosphate mineral was below 200 mesh, The reagent scheme consisted of commercial-grade sodium silicate and sodium oleate. The effect of reagent dosages, number of cleaning stages and pulp density on the efficiences of separation were studied systematically. A flowsheet was proposed for the processing of low-grade siliceous phosphate ore containing 12.1% P2O5, 55.36% SiO2 and 15.45% CaO. The flowsheet provided a useable phosphate concentrate containing 34.18% P2O5 and 14.20% SiO2 with a P2O5 recovery of 70.4% (the weight yield was 25.0%).

Jan 1, 1999

By John E. Auten

The computer program "Spike" is an "expert-rule based system" designed to fulfill two requirements. 1) acquaint unfamiliar personnel with big hole drilling techniques and 2) to stimulate the "old hands" in solving drilling problems. "Spike" will not make anyone a drilling expert The best way to understand a computer program is by example, but first some explanation of an? "expert-rule based system", As the name implies, the program tries to imitate a human expert. Unlike a normal computer program which uses a list of instructions to follow in a set order, a rule-base program has a collection of independent rules without an explicit list of things to do, one after the other. This type of program was mandatory to accommodate the ever changing situations and corrective actions that more accurately duplicate actual drilling operations and the advise of an experienced drilling expert.

Jan 1, 1988

By Bruce E. Holbein, Dennis K. Kidby, Ann L. Huber

World gold production figures and the processes used for gold production indicate a high dependence on both cyanide leaching and carbon adsorption metallurgies. Problems associated with the use of carbon in the treatment of refractory ores as well as economic and environmental considerations associated with the use of cyanide point to the advantages that can be realized through the use of more efficient gold adsorption media and with cyanide recovery. We have developed a process termed AurosaveTM-1 which provides a number of advantages through the use of a new synthetic robust gold adsorption medium, termed Vitrokele TM V-911. This process allows further recovery of gold from a variety of ores and allows for a simplified process for use not involving thermal regeneration or high pressure elution. We have also developed a cyanide recovery process termed Cyanosave ™ which uses Vitrokele TM V-911 and allows efficient recovery of cyanides from decants or tailings and re-use of recovered cyanide. This obviates the high chemical expenses for cyanide destruction where environmental issues require such water and tailings management.

Jan 1, 1998

By Howard L. Hartman

To concede that I am the most surprised - not to mention the least likely - recipient of the Daniel C. Jackling Award is a true confession I must share with you. Quite honestly, I&apos;ve asked myself, "Why me?" The Jackling Award has a well-deserved reputation of being a practitioner&apos;s, a doer&apos;s, a CEO&apos;s award - not kudos for a retired school teacher! While at least five of the previous recipients have taught in universities, to my knowledge I am the first to earn the award for "alleged" academic accomplishments. It is humbling enough to keep me livable for a long time. If you glance over the roster of Jackling Award lecture topics, you will spot another anomaly: The lectures last year and this deal with the subject of education - the only two in the 37-year history of the award. The two complement one another rather well, too, C. Allen Bom of Amax addressing critical needs of public education, while I am going to look at the post-high-school years. But I want to focus on more than engineering education. The training role of industry - the principal consumer of our product-also warrants examination. As I hope to establish, there is something unique about mining engineering - education and practice - that is both strength and weakness. We need to recognize that, if we are to cope with the weaknesses in order to capitalize on the strengths. We look at five premises that relate to the uniqueness of the mining engineer and his or her preparation for a professional career.

Jan 1, 1991

By M. A. S. Martins, H. Medeiros, B. Y. B. Dos Santos

This paper contains the geometallurgical studies, performed for Mineração Rio do Norte bauxites, applied to a selected area belonging to Plateau Saracá III, referring to an exploitation period of one year and three months, approximately. It is worth mentioning that Mineração Rio do Norte has the biggest bauxite operation in Brazil producing 8,500,000 tons of concentrate per year. The studies included wide investigations directed to the final objective of establishing a precise mining and production planning, based on the different behavior of the distinct bauxite ores, when submitted to industrial processes. Geometallurgy can be defined as the study of the regionalization (space distribution) of the metallurgical variables of a mineral deposit. This study involves and integrates all process engineering, geology, geostatistics and mining planning, among others. The development and application of the geometallugical studies to Mineração Rio do Norte were motivated by several reasons and necessities, among them: 1. Improving the forecast of the amount of concentrate (metallurgical mass yield) produced; 2. Improving the equipment operational efficiency, providing a more homogeneous feed; 3. Conducting a more precise material balance that permits a better daily, monthly and yearly production control; 4. Improving the forecasts for the final products generated by each ore type; 5. Obtaining better knowledge of the behavior of several ore types, submitted to the different process unit operations; 6. Promoting adequate ore blending, producing an homogeneous feed during mining operation.

Jan 1, 1998

This paper reviews the technical advice available to support companies in the delivery of social aspects of sustainable development. It will draw on diverse experience from the sparsely populated plains of the Central African Republic, one of the poorest countries in the world, to the densely populated villages of the Carpathian Mountains in Slovakia. It will review basic requirements for the consideration of social issues, as well as guidance on international best practice. It will review: the legal basis; coverage; consideration of alternatives; scope; inclusive decision-making; indicator development; impact monitoring and evaluation. The paper will discuss the breadth and depth of social issues for consideration, including the realms of responsibility of a company in terms of social development in different operating environments. The extractive industries invest substantial amounts of money which typically dwarfs local development, health or education budgets. Capacity building for local authorities is not directly the role of the company, but when understood as a strategy for risk management, it can play a vital part of sustainable development that benefits the local community and reduces the risk of social problems impacting profits. The paper will argue that social impact assessment is most effective when the outcomes are in line with a company?s principles and support core business practices. It is important that social impact assessment is viewed as an integral part of project decision-making and moves away from mistrusted PR and unsustainable philanthropy toward partnership, which finds suitable and appropriate solutions delivering ?win-win? outcomes. While development should not be seen as a direct company objective, engaging with development actors to better understand the operating context can ensure that social investment complements existing initiatives. The paper will also present different mechanisms for engaging with local actors, as well as developing successful social programmes.

Jan 1, 2007

By S. L. Patil, D. E. Walsh

A novel form of calibration of on-line analyzers was implemented. Rather than simple equations, a neural network was used to model the relationship between the scintillation counts (Am and Cs) of an analyzer, and the measured ash for improved on-line analysis of run-of-mine (r.o.m.) coal. Also, a new approach was followed to better evaluate neural network performance. Samples were first divided into various statistically different groups using a Kohonen network. Data was then selected for the training, calibration and prediction subsets, using criteria developed in this paper for sparse data, with representation from each group. A backpropagation based neural network architecture was used in conjunction with quick stop training. Due to noise in the data, the predictions were very good on average, but not individually.

Jan 1, 2003

By Shulin Xu, Moreno Pescara, Nicola Avagnina, Piergiorgio Grasso

The Roreto Tunnel is a shallow, twin-bore, road tunnel on the connection between the A6 and the A21 motorway in NW Italy. The challenges faced the design and construction of this tunnel derive from 1) the presence of groundwater, both phreatic and artesian; 2) excavation in loose and/or little cohesive materials; 3) excavation in cohesive materials containing water-saturated, sand lenses; and 4) surface constraints due to the urban environment. In this paper, these problems are examined and the rationale led to the optimum design choices and construction solutions explained. The experience should be useful to others when tunneling in similar situations.

Jan 1, 2003

By J. M. Mutmansky, A. Wang

This paper defines the elements of a basic economic model for decision making when considering a methane drainage system for an underground coal mine. A drainage system entails significant capital and operating expense; hence the decision to utilize drainage must be made carefully. The model outlines the basic structure of decision making and considers the costs and benefits when the methane is marketed and when the methane is vented to the atmosphere. The effects on mine safety and the dust levels in the mine are also considered, both in a general format and as economic variables. Sources of information for executing this decision making are provided for an actual mine decision.

Jan 1, 1999

By Mark L. Mott

The Pittsburgh Safety and Health Technology Center of the Mine Safety and Health Administration (MSHA) has developed the Mine Emergency Responsiveness Development (MERD) program to improve the reaction and re¬sponse of mine personnel in mine emergency situations. The MERD program simulates problems that may occur in underground mine fires and explosions or surface mine accidents. Since its inception in 1982, the MERD program has been presented to MSHA, industry, labor and state government personnel. This versatile program is easily adapted to suit various training requirements. In 1992, a Mine Simulation Laboratory was built at the Natinal Mine Health and Safety Academy, Beckley, WV, to improve training for mine emergencies and prevention and fighting of mine fires. This facility is capability of simulating a coal mine and metal-non-metal mine for training purposes. It has been included in the MERD program to provide realistic and practical training for mine rescue teams and MERD partici¬pants in advanced mine emergency operations. The objectives of the MERD program are to improve the organizational and management skills of the participants in a rescue and recovery operation and provide a better understanding of the importance that various roles have on the overall organization and the importance of their interaction. The MERD program is not intended to provide the participants with all of the abilities and knowledge required to respond effectively to a mine emergency. Rather, it is intended to give the participant an opportunity to experience the emotions, frustrations and successes of a mine emergency without having to actually be involved in one. The participants are expected to return to their regular jobs with a greater appreciation of the environment in which emergency operations take place. Experience in mine emergencies is extremely limited in the industry today. The participants are encouraged to use the knowledge gained during a MERD program to develop or enhance a mine emergency plan suitable to their needs.

Jan 1, 1993

By Gaither H. Kitchell

Introduction Fire assaying is an ancient method of determining the amount of gold and silver in geological materials. Today&apos;s commercial, mining, school, and private fire assaying laboratories still use this basic assaying method. One of the primary reagents used to collect gold and silver from the ore is litharge (PbO), or lead oxide. The Federal Occupational Safety and Health Administration&apos;s (OSHA) and the Nevada Division of Occupational Safety and Health&apos;s (OSH) have a lead standard. It states that a person exposed to airborne lead at concentrations greater than 50 µg/m3 (1.4 µg per cu ft) of air over an eight-hour period has gone beyond the permissible limit for health safety. It is not uncommon to get airborne lead concentrations of 1400 µg/m3 (40 µg per cu ft) in the flux/sampling area or 900 µg/m3 (25 µg per cu ft) around the gas/ electric furnaces during the fusion and cupelling phases. Therefore, any individual working in these areas for more than 30 days per year without proper protection is a likely candidate for lead poisoning. Lead In A Human Lead enters the body as a toxic substance by breathing it into the lungs and upper respiratory tract and by getting lead particles into the digestive system through ingestion. Smoking, eating, drinking, chewing tobacco and gum, or wiping a lead-contaminated hand across the mouth are all potential ways forgetting lead into the body. Lead taken in large quantities can actually kill a person in a matter of days. This is rare, however. The real hazard of lead overexposure is for the unsuspecting person who works in an unsafe lead environment for months or years. This individual can slowly receive damage, sometimes permanent, to the central nervous system, gastrointestinal tract, kidneys, blood, gums, and reproductive system. Safe Blood-Lead Level The Lead Standard states that the maximum safe blood-lead level is 40 µg/100 g (40 µg per 3.5 oz) of whole blood. It recommends 30 µg/100 g (30 µg per 3.5 oz) if a person is of child-bearing age. People not working around lead products normally have a blood level of less than 10 µg/100 g (10 µg per 3.5 oz). A person not adequately protected can exceed 40 µg/100 g (40 µg per 3.5 oz) in a few weeks by fire assaying only 100 samples per day per week. Studies show that some individuals have developed lead-related diseases with blood-lead levels less than 80 µg/m3 (2.3 µg per cu ft). Lead Poisoning Symptoms There is a long list of symptoms associated with lead poisoning. The most common are: a prolonged, sweet, metallic taste in the mouth; loss of appetite; anxiety and irritability; weakness and dizziness; nausea and tremors; and insomnia. Preventive Measures Based on the lead standard, a number of preventive measures can be taken to ensure that fire assay laboratory personnel frequently exposed to lead are protected against overexposure. First, the actual lead concentration within the assaying area should be determined. In Nevada, one can contact the Department of Industrial Relations, Division of Occupational Safety and Health for assistance in monitoring any laboratory. The agency will also recommend ways to protect against lead. This agency does the monitoring and provides an educational class on lead safety. This type of agency can be found in other states. Commercial consulting firms are also available, but they are expensive. Regardless of the technique used to determine lead concentrations, it is most likely that the average fire assay area exceeds the 50 µg/m3 (1.4 µg per cu ft) lead concentration limit. This is considered unsafe.

Jan 8, 1985

By Dale R. Ralston, Roy E. Williams, Gerry V. Winter, George L. Bloomsburg

Ground water inflow into a mine and the re¬sultant impact on district hydrology can be pre¬dicted on a site specific basis once the ground water flow systems at the site are sufficiently well under¬stood so that a valid conceptual model can be de¬veloped. Ground water flow systems are controlled by the hydrogeologic properties of the materials at the, site, including hydraulic continuity along flow paths, and boundary conditions. Preliminary delin¬eation of hydrostratigraphic units for conceptual models frequently can be based on surface water data; specifically, spring locations and the gain-loss reaches of streams. Quantitative predictions of mine water inflow and its impact on regional hydrology require col¬lection and analysis of numerous types of data. Hydraulic conductivity must be defined quantita¬tively both parallel and perpendicular to bedding as well as areally for each hydrostratigraphic unit. The characteristics of the Davis shale in case his¬tory number 2 illustrate this concept very well. The storage characteristics also must be determined for each hydrostratigraphic unit and the potential or hydrostatic head should be quantified vertically and areally for each unit. The potentiometric measure¬ments in the Bonneterre Formation as discussed in case history number 2 illustrate this point. The data collection and data analysis techniques constitute the weak link in the analysis of mine inflow and district impact. The technology for char¬acterizing a mine site in the field has lagged behind the technology for mathematical simulation; we at¬tribute this development to the fact that computer modeling is relatively inexpensive compared to field data collection and analysis. On-site tests provide the best means of quan¬tifying hydraulic conductivity parallel to bedding and the storage characteristics of the unit. Pump tests with multiple observation wells provide the best information from on site tests. Hydrogeologie boundaries can be located from such multiple well tests. Multiport piezometers provide a means for determining the vertical potential in a single borehole. Borehole geophysics can facilitate the def¬inition of hydrostratigraphic units. Vertical hy¬draulic conductivity is difficult but not impossible to quantify with existing field test methods; labo¬ratory tests of cores fail to give a value represent¬ative of the field situation. The storage characteristics of a confined (artesian) hydro¬stratigraphic unit can be difficult to quantify when pumping changes the confined unit to an uncon¬fined (water table) case after depressurization and dewatering. Transmissivity and storage coefficient can be approximated to some extent for given field con¬ditions by computer modeling if enough is known about hydrogeologic boundaries. Modeling can be used in a trial-and-error approach to match transmissivity and storage coefficients to existing water level data corresponding to estimated discharge rates. A solution can also be obtained using a tech¬nique referred to as the inverse method. Unfortu¬nately, such a solution is seldom unique. Fracture flow models exist but practicality usu¬ally necessitates reversion to a basic Darcy flow model. Data requirements for fracture flow models could be difficult to fulfill where fracture aperture, spacing, orientation, and length are required. Ob¬taining such data at depth prior to mining would be impossible for any mine simulation in fractured media. We are of the opinion that most fractured media simulations can be accomplished using con¬ventional Darcy flow models by viewing the field problem on a macroscopic scale. The real challenge is to delineate hydrostratigraphic units properly in the field. The question of whether a broken-up fault zone is an aquifer or a barrier boundary is seldom simple. The fractures usually can be treated as an equivalent porous medium in either case. Only a few techniques exist for predicting un¬derground mine water inflow. These techniques fre¬quently are designed to evaluate shaft or tunnel inflow under steady-state head conditions in a sin¬gle layer rather than in multiple hydrostratigraphic units. Few computer programs exist that have the

Jan 1, 1986

By A. Fiszer

One of the major problems with deep Polish hard coal mines are deformations of close-to-wall galleries since they are necessary and must he kept open for emergency situations and are largely responsible for work disturbances. In order to ensure safe and effective working operations, it is necessary to often rebuild galleries which, apart from the inevitable stoppage of operations, is greatly disadvantageous for the operation of a mine. The largest problems with maintaining the galleries open occur in Lower Silesian Coal Field mines where sometimes it is necessary to reconstruct the galleries several times [(Fig. 1)]. In light of what has been said above, the aim of this article is to present the reader with methods and ways of determining deformations occurring in close-to-wall galleries. Squeezing or convergence of headings is only a portion of the entire process of ground movement caused by ground disturbance due to workings. The term "squeezing of headings" is to be understood as a shortening of the distance between a point set on the roof of a heading and the corresponding one on the floor. It is very important to know the rules governing the process of squeezing in a particular mining system since it affords possibilities to define changes of the process and its parameters at any moment for a given system. This is of utmost importance because convergence of a heading is one of the most significant manifestations of ground pressure which has already been proved by studies performed by Everling (1). On the basis of those studies it has been observed that there exists an almost linear relation between the rate of convergence and loading [(Fig. 2)]. This, in turn, means that the deformations of the already exploited portion of heading are proportional to the pressure changes.

Jan 1, 1982