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By Yi Luo

The responses of a section of railroad to ground subsidence process was monitored as it was undermined by a longwall panel. The subsidence data collected and the observations made through this monitoring program could help us understand betteer the ground subsidence process and its impact on linear structures such as railroads. The data analysis techniques used and the assessment methods presented could be useful to researchers practitioners in the field of mining subsidence.

Jan 1, 1994

By Eric G. Zahl

Researchers at the Spokane Research Laboratory of the National institute for Occupational Safety and health are evaluating stress and displacement measurements in a longwall coal mine. The objective is to determine the best indicators of coal bump hazards during operations so that mine foremen and technical stall can make more informed intervention decisions to protect miners from coal bumps. Instruments were clustered in two panels, a yield pillar, and the immediate roof and floor of a two-entry longwall coal mine. Data were gathered continuously from a variety of instruments as mining proceeded toward and past the instrument cluster. Researchers and the mine's technical staff evaluated these data with respect to coal bumps and bump mechanisms. Selected graphs were then presented to mine foremen on a periodic basis to test their usefulness in identifying hazards. Of particular interest was the use of horizontal stress data from the immediate roof. To measure changes in horizontal stress, a new technique was devel¬oped for installing a grouted biaxial stressmeter in the roof. An evaluation of the development of this stress monitoring system in producing data beneficial to mine foremen is presented.

Jan 1, 2000

By D. W. H. Su

This paper describes geomechanical criteria employed by Consol Energy for selecting mine-specific longwall face supports in the past decade. The criteria include immediate and main roof rock characteristics, floor rock characteristics, critical tip-to-face distance and shield operating range. Detailed roof rock properties from high-density core holes as well as in-mine scope holes are used to evaluate the set load density and shield stiffness required to control the immediate roof and the yield load density required to absorb the load density developed from main roof weighting. Detailed floor rock properties from core holes and in-mine floor bearing capacity tests are used to specify the maximum peak toe pressure as calculated by the Jackson method. The critical tip-to-face distance is evaluated based on the immediate roof rock strength, layering and thickness. The shield operating range is evaluated based on main bench thickness, the presence of thick draw slate, the potential of minor roof falls at the face and transportation restriction. Three case examples representing three different geologic conditions are presented to illustrate the successful application of these geomechanical criteria for selecting longwall face supports within Consol Energy in the past decade.

Jan 1, 2004

By Alan Peacock

Shield supports have been in use in the USA underground mines since 1975, and their development in the intervening time has been progressive and inovative. Specialized techniques are used to optimize their performance in a particular application and to design the component parts.

Jan 1, 1981

By Xianming Zhou

Mining economics is such that too conservative in safety will result in a considerable penalty in mining cost. However, initial planning and design of a mining project often must be done without complete information. The assurance of economical and safe mining is thus difficult. This study is focused on the improvement of the mine design associated with Zhaoyuan Gold Mine in P.R. China as more information becomes available. Attention is given to the selection of backfill structures. Based on a proposed practical finite element model, a design, which is believed to be not only reliable but also cost-effective, is recommended for further mining operations in this mine.

Jan 1, 1989

By William J. Gray

The Roof Control Division of MSHA's Pittsburgh Safety and Health Technology Center has been conducting a program to evaluate methods employed by the U.S. coal mining industry during recovery of longwall faces. The objective of this effort is to provide information on safe and efficient roof control methods currently being used to recover longwall faces. In addition to a literature review and extensive contacts with MSHA and industry personnel, 14 mines were visited to observe firsthand various aspects of longwall recovery. It is hoped that the dissemination of this information will aid in the prevention of accidents and a reduction in costly downtime during recovery.

Jan 1, 1993

By Thomas M. Barczak

The initial Support Technology Optimization Program (STOP), Version 1.0, was released at the 19th Gmund Control Conference. This original program has since been updated to Version 2.3 which was released in May, 2001. This paper describes the additional features of Version 2.3, focusing primarily on the following three aspects: (I) including uncontrolled convergence into the design requirements for standing roof supports, (21 the addition of design procedures for cable bolts as an alternative secondary roof support, and (3) the addition of new standing roof support technologies. Another new feature which should facilitate the development of design criteria for standing roof support is the capabilily to define ground reaction curves through convergence measurements alone wthout having to make support loading measurements. There are several other new features provided in Version 2.3 which are only briefly addressed in the paper. These include: (I) additional graphics capabilities to facilitate rapid assessment of support comparisons. (2) an East-West designation for support selection to more accurately provide cost and support availability data, (3) additional safety measures including a safety factor to identify support design near the peak support capacity, checks to see if the support dimensions comply with aspect ratio requirements, and measure of roof coverage for the design layout of the support system These new features of STOP provide more capabilities to design and analyze secondary roof support systems for conditions whlch could not be fully analyzed in the original version of the program.

Jan 1, 2001

By A. Wahab Khair

This paper presents an analysis of surface ground movements recorded from two longwall mines in Northern West Virginia which operate in the Pittsburgh Seam. The instrumentation areas consisted of four panels, two at each mine, covering various sections with unique topographic features. Instrumentation consisted of survey monuments on 25 to 120 ft. spacing. Vertical and horizontal ground movements were measured at specified intervals to determine subsidence rate, developing and final subsidence profiles, angle of draw, horizontal displacements and associated strain profiles. A relationship between panel depth and width and the subsidence factor was also developed.

Jan 1, 1988

A two-dimensional time-dependent analysis of a overburden-coal pillar-weak floor strata interaction problem is presented as a beam model consisting of a composite roof beam resting on multiple elastic foundations (pillars) underlain by a composite rock mass representing immediate floor strata. Several different material models may be considered for the immediate floor strata. The analysis can include all openings and pillars in a panel and permits bed separations in the roof composite beam. The model has enabled identification of the relative significance of different geometric and mechanical behavior parameters which govern the system. The paper presents the theoretical background for the model as well as its application to a mine in Illinois where surface and underground geotechnical observations have been conducted over the last two years.

Jan 1, 1988

By Jim Sandford

The South Bulga Colliery longwall operation, owned and operated by Cyprus Coal Australia. Oakbridge Pty. Ltd., and located near Singleton, NSW, is currently operating under an average 80-ft-thick (24-nt) sandstone unit residing immediately above the coal seam, resulting in sudden and severe face weightings. To date, nine severe weightings have occurred at the property (within Panels 3, 4. and 5), three of which resulted in face closures accompanied by significant equipment damage and several weeks of downtime. The remaining six events nearly resulted in face closures, incurring single-pass vertical convergence of up to 8 in (200 mm) along the pan line. In an effort to mitigate and/or eliminate the occurrence of these severe weighting events, mine management has established an in-house program to immediately address the geotechnical and operational mechanisms underlying rapid weightings, as well as specific measures to mitigate these events on future panels. In support of this in-house effort. NSA Engineering Pty. Ltd., is assisting the engineering staff at South Bulga in developing a more aggressive face monitoring program. The aim of this program is to provide weighting occurrence predictions sufficiently ahead of time to ensure that operational controls are optimized prior to attempting to mine through potential weighting areas. This paper reviews the occurrence of weightings to date at the South Bulga Colliery as well as the latest developments in shield monitoring technologies to forecast these events in near-real time.

Jan 1, 1999

By Christopher Mark

Mines with exceptionally low-strength roof (UCS <3,500 psi and CMRR <40) are much more likely to struggle with roof falls than other mines. Weak-roof is a particular problem for many room and pillar mines in the Midwestern and Northern Appalachian coal basins. Traditional roof support techniques are often not up to the challenge at these operations. This paper focuses on two mines, one operating in the Upper Freeport seam and the other in the Herrin No. 6 seam. Together, the two mines had more than 300 roof falls during a recent 5 year period. Each has experimented with a variety of roof bolt types and lengths, and with different supplemental supports. Detailed statistical analysis was conducted to determine which support combinations have proven to be most effective. Geology, horizontal stress, and time are also important at both mines. Successful control techniques have included; ? Identifying particularly troublesome lithologic roof units; ? Installing longer and stronger roof bolts; ? Installing supplemental support in intersections, and; ? Limiting the duration that a panel remains open. The lessons learned from these mines, and others like them, could help improve ground control safety for the entire U.S. mining industry.

Jan 1, 2004

A computerised influence function approach to subsidence and horizontal displacement prediction is described, with particular emphasis being placed on the applicability of the method to irregular- shaped mine workings. Based on previous work [1], this approach has been put for- ward for inclined seam situations. Examples of graphical output presenting surface subsidence contours, horizontal displacement vectors and principal strain vectors are given and their significance discussed in relation to current problems.

Jan 1, 1988

By Axel Preusse

In the Ruhr district, pipelines of public and private infrastructure are made of cast iron, steel, plastics or asbestos cement. Legal framework, technical regulations and normative standards define which pipeline materials may be used for the transmission of which kind of product Thus ground water endangering substances as well as inflammable or explosive products are only permitted to be transported in steel-made pipelines. Ground movements, due to underground mining, are transmitted via the soil to the pipeline and cause extra strain within the steel pipeline (Figure I). In extreme cases durable deformations may occur, characterized by an oval profile or a fold in the pipeline. To avoid or minimize damages, balancing elements are installed into the concerning pipeline, reducing the ground movements which might otherwise cause damages. [ ] The distance between the balancing elements is not arranged by random, but by a calculation method developed in a doctoral thesis [Spielberg, 1999] which represents the actual available standards in science and technology. The calculation method considers all relevant influencing variables with impacts on the movement behaviour of steel pipelines in mining areas, such as technical data of pipeline design (e.g. steel grade, wall thickness, weld seam quality), soil conditions (e.g. friction), laying depths of the pipelines, the operational impacts (working pressure, corrosion) and the mining impacts. As of today, mining has caused no damages to steel pipelines protected by this calculation method.

Jan 1, 2004

By Wm. Mark Hart

Under a specific geological condition, roof supporting method, and pillar-entry system, an entry convergence concept may be the most effective means that can be used to effectively indicate the longwall entry stability (i.e. pillar bumps, roof falls, or floor beaver This concept may also be used to verify the effectiveness of the current pillar-entry system and roof supporting method. Furthermore, convergence measured under different mining phases may lead to a better understanding of the longwall mining-induced abutment loads and may be used to estimate stress change in pillars and thus pillar stability. In this paper, a remote entry activity monitoring system was designed; a comprehensive entry convergence monitoring strategy was proposed; thee abutment loading phases in longwall mining were defined; the relationship between roof deflection and stress change in a pillar was derived, and finally the extent and magnitude of the mining-induced abutment loads as well as their impact on entry convergence were discussed using the field data obtained so far.

Jan 1, 1995

By Nikolaos Polysos

For the planning and driving of gateroads supported by roof bolts a practical concept has been developed in order to determine the geological and rock mechanical parameters derived from exploration drillholes. Based on this, an assessment scheme for the design of roof bolting has been established. The new methods of investigation comprise of geotechnical logging of drill cores for the determination of structural-geological rock characteristics and complementary geophysical well-logging which enables the evaluation of petro-physical and rock mechanical properties. The tools and their measurements will be briefly presented. The relationship between the geophysical log readings and the geotechnical parameters will be illustrated. The aim of the data acquisition is to improve roof bolting design which is based on the assessment scheme. This will be adjusted to the prevailing rock mechanical conditions and stands up to the required stability of the gate roads. In order to ensure consistent data acquisition, a method of core logging has been standardized for the respective demands. To achieve this it was necessary to introduce specific parameters and new methods. For the recording of linear and planar structural elements at the drill core, a special system for the documentation of the angles in relation to each other has been set up. The rock mechanical parameters and their acquisition will be explained. In order to carry out an objective analysis as fast as possible, software has been developed for the acquisition, management and presentation of the data. These programs and their functions will also be presented. The software is characterized by being user-friendly and the flexibility of its interfaces, Different options for the combined presentation of input and evaluated data give a more objective basis for the planning of roof bolt design. Examples will illustrate the operational implementation of the results during the planning and driving phases.

Jan 1, 2001

By Daniel W. H. Su

This paper presents the results of an extensive geomechanical testing and monitoring program conducted at a longwall panel. The field program included the monitoring of roof caving sequence and mechanism, surface subsidence, change of pillar stress, roof displacement and entry convergence, and strength characterization of the overburden rocks. The response of eight headgate pillars and the adjacent entries was monitored as the longwall face approached and passed the instrumented locations. Overburden response to longwall mining was monitored using time domain reflectometry (TDR) technology; and, the height of the highly fractured zone above the gob was determined by postmining drilling. Good correlation was found between the height of the highly-fractured zone and the TDR, subsidence, and pillar stress data. The results provide a detailed picture of the response of overburden strata and chain pillars to longwall mining. A preliminary model representing the overburden strata behavior at the test site in response to the longwall mining is proposed.

Jan 1, 1987

By T. L. Dobecki

As a means of demonstrating the effectiveness of reflection seismology in determining continuity of coal seams, three U. S. field projects are reviewed. The three projects involve coals of varied thickness (2-14m) and age (Pennsylvanian to Eocene) from three coal areas of the U. S. (Pennsylvania, Wyoming, and Washington). Each project also employed its own particular seismic technique, recording system, and seismic energy source although all are considered state-of-the-art, high resolution, digital seismic surveys. Project 1 (thin, Pennsylvania coal) sought detection of sand channels using dynamite and standard in-line (2-D) seismic technique. Project 2 (thick, Wyoming underground coal gasification) involved a gas-explosion (Dinoseis) source with areal (3-D) acquisition methods. Project 3 (thick, Washington underground coal gasification) employed a shotgun-type source and standard in- line methods. Data processing was handled by different contractors for each project. Each project was successful in accomplishing its own particular objective; however, data quality and interpretation seem to be more a function of thickness of the target seam, complexity of the overburden, and processing contractor than a seismic source, acquisition scheme (2-D versus 3-D), or recording instrumentation.

Jan 1, 1981

By E. Bauer

During 1987 and 1988, the Eighty Four Complex Mine of BethEnergy Mines, Inc. used the open entry longwall recovery method to recover one partial and three complete longwall faces. Various cement- concrete supports were utilized to support the open recovery entry until the approaching longwall face cut into this entry. This recovery method and the supports used were studied by the mine personnel and the Bureau of Mines. This paper discusses the findings, results and conclusions of that study.

Jan 1, 1988

By K. Y. Haramy

Strong roof helps minimize roof fall problems in coal mine entries. However, the Inability of strong roof to cave readily may contribute to major ground control problems In Iongwall and retreat mining operations. The concern expressed by mine operators prompted this Bureau of Mines study to analyze the effects of strong roof members on ground stability around Iongwall openings. The problem was approached from three directions: development of a theory to analyze the strain energy conditions In the coal and surrounding strata, modeling the effects of different thicknesses and strengths of Coal and roof strata, and field Instrumentation of powered supports In two Iongwall mines. Results from the theoretical and modeling analysis confirm the accepted belief that a strong roof does, In fact, play a major role in high stress concentration problems In and around the Iongwall panel. Analysis of the effect of different roof overhang dimensions and properties on relative strain energy buildup In the coal and roof Is presented. Shield pressure data Indicate possible methods for detecting noncaving roof behind the shields. Strategies to monitor roof overhang and control dangerous conditions caused by the noncaving roof are also presented.

Jan 1, 1988

By Gift Makusha

Pre-feasibility work at Goedehoop Colliery indicated that stooping of the undersized pillars could be undertaken safely and economically. In light of the findings a decision was taken in may 2003 to undertake the project in the 600 area where three panels (628, 630 and 632) were identified for pilot test sites. The findings of the pre-feasibility studies were presented in a paper to the 22nd International Conference on Ground Control in Mining held at Morgantown in 2003 (1). This paper is a progress report for the project 12 months down the line. Work commenced to prepare the sites for mining including, acquisition of equipment, equipping the panels, selecting and training people to undertake the project. Three monitoring sites were set up distributed evenly along panel 628. Each site comprised of a surface extensometer station in the overburden strata adjacent to a pillar underground containing hard inclusion vibrating wire extensometer cells. This combination would be used to record pillar loading ahead of stooping as well as the depth of caving and strata deformation in the goal zone behind the stooping face. In July 2003, support work began to secure the roof and rib sides. The support was required to be at least three-pillar center distances ahead of the mining front to ensure that the effective stooping zone is secured at all times. The NEVID method of pillar extraction developed at Sasol and described in detail by Ismet and Moolman (2) in a Coaltech 20-20 report was adopted for the pilot project. As part of training the selected stooping team was send for a week to Sasol&apos;s Bosmanskrans Colliery to familiarize with the NEVID method of stooping. Further training sessions were carried out on site especially on the use of Mobile Roof supports. The first cut was taken on 20 August 2003 by implementing a form of chequerbord mining taking every second row of pillars. Three rows were mined this way which period was considered training to get workers familiar with the new equipment and mining method. On the fourth row the full design span equivalent to mining 4 pillars in a row was implemented taking out all the pillars in successive rows. Production figures gradually increased from 300 to more than 1,000 tons run of mine coal per shift. Panel 628 was mined out at the end of December 2003 and the second of three panels (630) is being mined. Substantial data from the monitoring set up has been recorded since the start of the project. Monitoring will continue to the end of the pilot project and the data will be analysed and fed back into the design tools to improve the design in future undertakings. The pilot project has been a success so far and other old workings are being evaluated for stooping.

Jan 1, 2004