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Virtually all mineable Appalachian coal seams exist in a multi-seam environment. This makes it inevitable that most seams will eventually experience interaction induced ground control and mining problems. Indeed, it has been estimated that every working face will experience interaction effects from previous or current workings at least once during its lifetime (1), and that these problems are considerably exaggerated when seams are in close proximity -- a distance of less than 110 feet. The continued increase in multi-seam problems has resulted in considerable research activities over many years (2,3,4,1). Theoretical analysis, numerical and physical model studies, statistical and empirical analysis of numerous interaction related field data have been applied to multi-seam mining situations and have identified many useful trends and design criteria (4,5,6,7). To fully utilize research results and transfer multi-seam mining technology to field engineers, a design model -- USEAM was constructed (8). This model, designed for close seam under-mining situations, was computerized to facilitate utilization. In the current research, a new computer program "MSEAM" was developed to produce a model for both under- and overmining close seam situations. It is hoped that both of these software packages will aid field engineers in using important interactive design criteria to gain a better understanding of interaction mechanisms. Through advance planning with these programs, detrimental interaction may be avoided and minimized, and occasionally a design can be selected which will allow interaction effects to be utilized to the benefit of mining operations.

Jan 1, 1987

By Takashi Sasaoka

Chain Conveyor Cutter (CCC) is a chainsaw-type machine and originally developed for the construction of underground walls and/or ground improvements. CCC was developed from the accumulated technology of coal mining, combining the cutting technology of a shearer and the fuctions of chain conveyor. The CCC can cut harder soils and soft rocks, and vertically mixes the cut soils/rocks with cementing material selected through the discharging port installed at the bottom of the machine. In Indonesia, highwall mining trials have already been conducted in several coal mines. However, full-scale and regular operations have not been done yet due to the ground and machine control issues from their geological conditions. In order to overcome these problems, the application of CCC to highwall mining systems was proposed, and its applicability and technical issues to be solved were investigated in this research. This paper discribes the characteristics of CCC system and discusses the application of CCC to highwall mining systems.

Jan 1, 2012

By Leigh J. Wardle

This paper describes a numerical method for calculating the three¬-dimensional stresses and displacements induced by tabular excavations in a rock mass consisting of parallel layers of distinct material properties. The method is based on the superposition of numerical solutions for elementary displacement discontinuities in a parallel layered rock mass. The method can be used to analyse complicated excavation layouts such as those encountered in room-and-pillar or longwall mining. The method can automatically take into account the effect of the earth's surface. The method offers an economic and efficient solution to stress analysis problems which cannot be adequately modelled using two¬-dimensional methods and for which the expense of three-dimensional finite element or general boundary element analysis cannot be justified.

Jan 1, 1984

By David Conover

The El Boleo Copper Project is currently in the final design stages for development of a 3-MM-tonne/yr underground copper mine located in Baja California, Mexico. The nearly horizontal mineralized zones are amenable to exploitation by conventional mechanized coal mining technology using continuous miners, shuttle cars, and belt haulage. The mine design resembles a typical full-extraction coal mining operation utilizing a sequence of mains, sub-mains and production panels. Due to numerous faults, mining will be conducted as several small adjacent mines accessed through adits from large arroyos cutting through the mine area. Up to four seams may be mined in some areas with a maximum overburden depth of about 250 m. The ore zone is relatively weak and plastic, subject to extensive creep over time. The mine workings will pass through areas of historical shortwall mining panels where the ground has flowed into old entries and gob areas, and then reconsolidated. A small test mine was developed to evaluate mechanical cutting performance, roof-bolt anchorage capacities, roof and pillar stability and caving behavior. In-mine measurements were combined with two- and three-dimensional FLAC models to evaluate alternative development and production pillar designs. The paper will discuss the various factors influencing ground stability at the El Boleo project and the strategies employed in developing a suitable ground control design.

Jan 1, 2009

By R. Kanniganti

The primary problems of pillar design in seams subject to interaction are due not only to difficulties in predicting loading, but also to the often unsymmetrical nature of the stress fields. The effects of uneven stress fields on failure patterns within a pillar were studied wing a two dimensional finite element method. Lower seams, including ultra- close mining situations were evaluated considering conventional pillars. Pillar case study data for under mining were analyzed to determine if empirical trends in stable pillar sizing could be derived. Recommendations for multi-seam pillar design are made, based on anticipated loading conditions within a pressure bulb. Applications of the research results are demonstrated using case studies

Jan 1, 1995

By K. H. Brandt

A standard planning system for the development of roadways was adopted for German coal mines based on the results of geotechnical and rockmechanical investigations. Its goal is to provide for sufficient support systems under conditions of multiple seam mining at great depth. The report points out the required determination of geotechnical parameters and the basis for achieving a high level of planning reliability and resulting high performance in roadway development and longwall mining. The instrumentation and the planning procedure for selecting the support design most appropriate for the geotechnical conditions are described and demonstrated by examples.

Jan 1, 2004

By Brijes Mishra

This paper presents a correlation of acoustic emission (A.E.) with physical and mechanical properties of different types of rock and coal specimens which were tested under aegis of a consultancy project from a Columbian Mining Company. In this study, three types of rocks which are sandstone (Arneisca), siltstone (Arciolita) and claystone (Limolita) and two different types of coal were tested. The tests were carried out under constant loading rates according to ASTM Standards for determining Young?s Modulus and Poisson?s Ratio. In both cases a MTS electro-hydraulic loading system was used. Mode of failure in each material was characterized by the acoustic emission and the results were substantiated by the deformation characteristics of the materials during failure.

Jan 1, 2006

By Swapan Bhattacharya

United States federal and state regulatory authorities require underground mine operators to adopt adequate measures to minimize material damage to the surface caused by nine subsidence. This paper presents an approach to define and determine the extent of material damage due to subsidence from underground coal mining. The basic steps involved in the development of adequate criteria have been enumerated together with the approaches and methodologies used.

Jan 1, 1984

By Barry Voight

The law [ ] where [ ] is a measurable quantity such as strain and A and cu are empirical constants, describes the behavior of materials in terminal stages of failure under conditions of approximately constant stress and temperature. Applicable to intact rock and rock masses, the relation may be extended to conditions of variable stress and cyclic stress, and may be used to predict time to failure. Applications in rock mechanics include slope and excavation stability and various topics in ground control.

Jan 1, 1989

By M. J. Beus

This paper will describe the research approach being initiated by the Spokane Research Center to assess hazards and design criteria to prevent ground and muck falls in and around ore passes in hard-rock mines. The major goal of this research is to compile detailed information about ore pass processes and hazards, identification and testing of prevention strategies, and development of computer-based measurement and design methods. Recent ore pass failures have underlined the lack of OE pass design capabilities and standards available to both mine engineers and MSHA personnel. Design criteria and ore pass hang-up prevention and remediation strategies will include the effects of internal ore pass loads, blasting to relieve hang-ups, and rock mass stress redistribution and structural interaction from nearby mining. New visualization and three- dimensional analysis methods will be presented as an extension of existing ore pass design and analysis techniques. A sophisticated particle-flow analysis program will be used to simulate the response of various ore pass designs to a wide range of loading conditions driven by rock mass deformation, muck flow, ore pass blockage, and blasting in both nearby stopes and the ore pass. Analysis techniques will be calibrated and design criteria validated at the Spokane ore pass test facility. These tools will serve to reduce research costs by limiting the number of experimental field tests required.

Jan 1, 1996

By R. Karl Zipf

Highwall mining is an important coal mining method. Upwards of 60 highwall miners are presently in operation, and they may account for approximately 4% of total U.S. coal production. A review of the Mine Safety and Health Administration (MSHA) accident data over the 20 year period from 1983 to 2002 identified 9 fatalities attributable to auger and highwall mining of which inadequate ground control accounted for 1/3. In the past 5 years, 1 fatality occurred in highwall mining. Estimates of the manpower requirements in highwall mining suggest that its fatality rate is essentially the same as for surface coal mining, thus highwall mining appears to be a very safe modern mining method. Highwall stability is the major ground control related safety concern, and operators are required to develop and follow an appropriate highwall mining ground control plan. The plans usually specify the following geotechnical parameters: hole width, maximum hole depth, maximum overburden depth, seam thickness, web pillar width, barrier pillar width and number of holes between barriers. Calculated web pillar stability factor exceeded 1.3 for most designs evaluated. This study examined records from 5,289 highwail miner holes with a total completed footage of about 2,560,000 feet to understand the reasons for early pull out. Average lost footage is typically about 20% of planned footage. Only 35% of the holes reached planned depth, and 20% were short due to rockfalls. Water and adverse geology accounted for 15% of the losses. Mechanical/electrical problems, guidance, and slope stability problems accounted for the remaining 30%. Web pillar stability factor for these holes also exceeded 1.3 in 95% of cases. Trapped highwall miners present a safety hazard to workers during their recovery. Best practices to avoid trapped highwall miners include: avoid mining in stream valleys, avoid mining near outside corners, careful alignment of each hole and the use of an onboard guidance system, Several issues in highwall mining ground control require further investigation including highwall mining through old auger workings, highwall mining near old underground mines, multiple-seam and multiple lift highwall mining and finally the size and frequency of barrier pillars.

Jan 1, 2004

By Wojciech Masny, Andrzej Walentek

"The most common extraction method in Polish coal mines utilize pillars between adjacent longwall panels. This is mainly due to the significant depth and difficulties in maintaining stability of the gateroads. This paper presents measurements of entry convergence and range of the fracture zone around a gateroad measured with a borehole camera. The entry where the measurements were taken was located in a parallel entry separated from the gateroad by a 5-m- (16-ft-) wide pillar. The gateroad was located in a hard coal seam 900 m (2,952 ft) deep with a dip of 5°. The extraction method was longwall mining with caving and the mining height was about 3 m (10 ft).Furthermore, the ""in situ"" measurements were compared to the convergence forecast for the gateroad and fracture zone by means of numerical modeling conducted using the Phase2 Version X.X finite element program from Rocscience. The determination of the fractured zone around the openings is of great importance to successful mining practice, especially in support planning and design for longwall gateroads. Moreover, proper determination of the fractured rock zone is one of the basic elements in the process of planning the roof bolting for mine workings.INTRODUCTIONIn the Polish. hard coal mining sector, retreat longwall extraction is most commonly used (Prusek and Masny, 2007). This method is connected with the necessity to carry out a number of development operations during the first stage, including among others, driving of gateroads and a setup room.Currently, most Polish mines eliminate gateroads behind the extraction front, using the ""U"" ventilation system (Szlitzak et al., 2008). In such cases, one of the roads for the next longwall panel is driven along the caving goafs, leaving a protective pillar of some chosen width (Figure 1). The question regarding the width of the coal pillar is especially important to the stability of the gateroads that define the panel for the subsequent longwall. When analyzing the previous experience relating to this type of pillar (Junker, 2006; Rajwa, 2008; Stranzet et al., 1973; Betriebsempfehlung, 1982), one can state that there exist two solutions for the determination of its width."

Jan 1, 2010

By Takashi Sasaoka, Hiroshi Takamoto, Kikuo Matsui, Hideki Shimada

"Indonesia is the second largest coal exporter to Japan. Almost all the coal is produced from open cut mines. However, a great deal of coal is left in the highwalls of the mined-out pits. The use of highwall mining systems has increasingly come into play in the U.S. and Australia, when overburden depth exceeds economical recovery in an open cut mine. However, the stability of the highwalls is always a major safety concern in such mining. This paper describes the characteristics of the highwall mining system and discusses the appropriate highwall mining system for use in Indonesia.INTRODUCTIONIndonesia produces over 200 Mt of clean coal and is the second largest coal exporter to Japan, accounting for about 32 Mt of coal annually. Over 99% of the coal produced in Indonesia comes from surface mines. More open cut mines will be developed and more coal will be mined in order to fill the great demand both in Indonesia and the rest of the world.In open cut mines in Indonesia, there are many sites where mining operations have developed long highwalls that have been abandoned due to the current economics. Mining operations have been transferred to lower stripping ratio blocks of coal or overlying seams. In some cases, coal lies buried beneath spoil heaps or is covered with mud and water. It is estimated that there is a great deal of coal beneath abandoned and working highwalls. Considering these situations, it seems to be worth introducing highwall mining systems into Indonesian open cut mines.Final highwalls of open cut mines can form the starting point for other mining methods, such as highwall or underground mining. In its basic application, highwall mining is a technique utilized after an open cut portion of a reserve has been mined, sometimes prior to the introduction of underground mining (Seib, 1993). In this system, the coal seam is mined by remotely operated equipment, such as an auger machine or a modified continuous miner incorporated into a highwall mining system. The major problems with highwall mining systems are less coal recovery due to leaving coal as the pillars and the instability of openings and highwalls due to the pillar and roof failures."

Jan 1, 2010

By David Bigby, Tim Ross, David Conover

"Extensive arrays of telltale roof monitoring instruments were recently installed in a Mexican copper mine and a large underground mined storage facility in the eastern U.S. The data were used to evaluate roof stability during development and retreat mining and after installation of supplemental supports. Both manual-reading and automated systems were employed and consisted of up to 64 instruments. This paper will discuss the practical issues involved with installation and monitoring, including reliability and maintenance. Examples will be given for telltale response in relation to known events affecting roof stability, including nearby pillar extraction roof caving, installation of supplemental cable bolts, and separation of the immediate roof layer. The strategy for processing the large quantity of data, presenting the data for review, monitoring the system remotely, and identifying and reporting critical events will be described.INTRODUCTIONTelltales have been used for many years with many varied applications. They are relatively inexpensive, easy to install and interpret, robust, and adaptable. The term ""telltale"" generally denotes a strata extensometer that incorporates a visual indication (and warning) of strata movement. The most common dual-height telltale (Figure 1) was developed by British Coal in the early 1990s as roof bolting was replacing steel arch support (Bigby, 2001). Dual-height telltales provide immediately visible measurements, distinguish between movements above and below the bolted height, and are an established means for providing preemptive warnings of roof falls.Many improvements and modifications on the basic design have been developed to adapt to different mining conditions. For example, triple-height telltales are commonly used where roof bolts of different lengths are installed. The standard manuallyread telltales are limited by the difficulty of obtaining frequent, consistent, and accurate readings, especially in high openings. The instruments may also be located in unstable or inaccessible areas. Consequently, an intrinsically safe electronic telltale system was developed that combines high accuracy and both local and remote reading options. The system supports a network of up to 100 dualheight telltales on each of four separate branches. The instruments are connected with a two-conductor cable and can be read both underground, using a portable readout, and on a surface computer (Figure 2). The automated system still provides the visual warning indication underground."

Jan 1, 2010

By Kevin J. Ma, John Stankus

"In order to access remote reserve areas, some U.S. coal mines have to maintain aged underground entries for a great distance. However, high humidity, warm temperature, and time dependent deterioration can cause progressive roof deterioration and unexpected roof falls can, pose a great challenge to ground control engineers. With an active belt structure in place and limited space, re-bolting becomes very costly, less effective, and, sometimes, impractical and unfeasible. To gain long-term entry stability and serviceability, operators typically rehabilitate the aged belt entries by installing standing steel set supports. In the last several years, Keystone Mining Services, LLC, (KMS) has assisted many coal mines with their belt entry rehabilitation projects, evaluated the ground condition of various aged belt entries, and designed different standing steel set support systems. This paper presents a case study of a large-scale roof fall that occurred at an aged belt entry in a mine located in an eastern coalfield, analyzes root causes of excessive deformation of square sets that were installed in an adjacent entry, evaluates the adequacy of an existing rehabilitation square set, and develops remedial recommendations for future rehabilitation practice. Based on the case study, the paper outlines design guidelines for rehabilitation steel sets that include field evaluation, engineering considerations, design assumptions, steel structural analysis, and field installation quality control. INTRODUCTION With gradual depletion of shallow coal reserves, some underground coal mines have to maintain long-term entries (belt, track, return airway, etc.) for a great distance in order to access remote coal reserve areas. However, due to high humidity, warm temperature, and aging in the belt entry, roof strata weathering and pillar degradation become more and more severe. Progressive roof deterioration poses a great challenge to ground control engineers. Pillar rib sloughs at certain locations, entry width increases in some areas, immediate roof sags, immediate roof rock falls out between bolts, existing bolts lose functionality due to corrosion, cutters develop deeper in corners, and strata separation develops deeper up into the main roof. As a result, unexpected roof falls occur in a random manner resulting in loss of production, damage of belt structure, and even injuries to underground personnel."

Jan 1, 2017

By Marvin B. Thompson

"The depositional model for major Illinois Basin coalbeds is well documented and defined on a regional scale. The model was a driving force during past exploration for lower sulfur and thicker coal deposits. The most attractive coal reserves were known to lie along the flanks of contemporaneous sandstone filled stream channels and were overlain by thick silty gray shale roof. At various distances away from the channels, the depositional model transitioned to black shale I limestone roof, sulfur content of the coal bed increased, and the coal bed often thinned. Understanding the character of roof rock types associated with this depositional model is essential to predicting ground control factors on both a regional scale, and on resolving roof control problems at the mine-site. Additionally, horizontal stress and overburden depth are significant factors that impact roof rock quality and ground control in Illinois Basin mines.Determining the character of several rock types, and defining the primary horizontal stress direction were crucial to a recent successful project at New Future Mine, located in southern Illinois. An inclined slope was constructed from the Illinois No. 5 Coalbed up to the Illinois No. 6 Coalbed through strata that ranged from extremely weak ""stackrock"" and a weak underclay unit, to a massive sandstone unit. Engineering geology, operations management, and Jennmar technical services personnel teamedup to select and install roof support for each strata transition. The project was completed with no injuries and no roof falls.INTRODUCTIONAbundant published information concerning coal deposition, geographic distribution, quantity, quality, and mining conditions exists for Illinois Basin coal reserves. The State of Illinois, through its State Geological Survey (ISGS), has provided decades of research, record keeping, and service to the coal industry. Other excellent sources of Illinois Basin coal information include the Indiana Geologiq1l Survey and the Kentucky Geological Survey. Past research by the U.S. Bureau of Mines (USBM) supplemented the work by the geological surveys, especially in the area of horizontal stress and mining hazards. The National Institute for Occupational Safety and Health (NIOSH) continues to produce publications focused on roof control issues common to many coal basins, including the Illinois Basin. Many of the illustrations in this paper originated in ISGS and USBM publications."

Jan 1, 2010

By Peter Hayes

Moonee Colliery operates a longwall extraction system in the Great Northern seam of the Newcastle Coal Measures, approximately 100km north of Sydney, NSW. In the initial mine area of longwall blocks1-4a, the Great Northern seam is overlain by a massive conglomerate approximately 35m in thickness. Unanticipated sudden, blocky caving of this material has produced windblasts with associated velocities of 100m/sec and over-pressures of 35kPa. Although these events have not resulted in fatality, the potential safety risk to face personnel was such that the mine was threatened with closure. The development of a Windblast Management Plan to minimise the exposure to windblasts, a Micro-seismic Management flan to predict caving events, and the use of hydraulic fracturing to generate caving on demand, have all contributed to the salvation of the mine. Prior to the introduction of hydraulic fracturing, falls were highly variable and ranged in goaf area from 2000m2 to 30,000m2 with an average of around 7.000m2. Hydraulic fracturing has introduced consistent and far less variable falls, planned as averaging around 5000m2 and all accompanied by microseismic warning, Moonee Colliery is believed to he the only operation in the world using real-time microseismic warning and using hydrofracturing as a day-to-day operational process. These processes have enabled it to return to financial viability in an environment of strict procedural control, whilst ongoing efforts are made to optimise and enhance these systems. Moonee's story is a case study of the successful application of research and development work to the economics of a mine.

Jan 1, 2000

One of the problems associated with the maintenance of roadways in underground coal mines is that of dealing with roadway closure. Sidewall weakening technique is based on the transference of the high stress zone further away from the vicinity of roadway. This transferral is carried out by weakening parts of sidewalls of roadway by cut- ting slot, drilling a series of parallel holes or blasting during development stage. In the paper, the effect of sidewall weakening on the stability of roadway is studied by finite element analysis and field experiment. The finite element analysis shows that sidewall weakening can control the development of yield zone around a roadway, improving the stability of roadway. It is also shown that if in- situ horizontal stress is lower or higher than the in-situ vertical stress, it is difficult to obtain roadway stability by sidewall weakening. The field experiment shows that roadway closure can be controlled by sidewall weakening with blasting.

Jan 1, 1990

By Kot F. Unrug

In the premining stage of engineering design, the only available data are obtained from core drilling. It is often not sufficient for a realistic design of strata control. During the development, an access to the geological formation is created, enabling in situ testing. Obtained data can be utilized accordingly to improve preliminary design. The available methods for testing are described with emphasis on their application for a longwall system. The optimum design ensuring continuous operation of the high output longwalls is critical because their downtime is very expensive. Optimization of ground control measures also has the potential for substantial savings by elimination of unnecessary support.

Jan 1, 1994

By Christopher Mark

The Bureau of Mines has recently completed a comprehensive study of coal strength. More than 4000 individual test results from over 60 seams were extracted from the literature and combined in the most complete data base of the uniaxial compressive strength of coal ever assembled. In addition, more than 100 case studies of in-mine pillar performance were available in the Analysis of Retreat Mining Pillar Stability (ARMPS) data base. Statistical analysis of this wealth of data has yielded valuable results. The data shows clearly that the "size effect" is related to coal structure. The widely-used Gaddy formula, which predicts a significant strength reduction as the specimen size is increased, was found to apply only to "blocky" coals. For friable coals, the size effect was much less pronounced or even non-existent. Case histories of failed pillars are the best available data on in situ coal strength. This study found no correlation between the ARMPS stability factor of failed pillars and coal specimen strength. Pillar design was much more reliable when a uniform coal strength was used in all case histories.

Jan 1, 1996