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By Jingyi Cheng

Many longwall panels in China are laid out along the dip direction such that the direction of longwall retreat mining is along the strike direction of coal seams. Downward mining longwall panels in steeply inclined seams refers to those that are laid out in a non-uniformly developed fold structure where the seam is not only steeply dipping, but also highly undulated along the strike direction, causing longwall mining extremely difficult because it has to deal with large dip angles that vary both in the mining and faceline directions. Obviously, the characteristics of mine pressure and overlying strata movement in downward mining longwall panels in steeply dipping seams have unique patterns that are very much different from those cases of mining the flat or gently inclined coal seams. The effects of those unique patterns presented a big challenge to production and safety. Almost all previous and current researches on ground control have been concentrated on issues related to the flat and gently inclined coal seams. Conversely, research on steeply inclined coal seams, especially those with large angle variation both along the seam dip and strike directions is almost none. Therefore, it is very important to initiate a study to better understand the characteristics of mine pressure and overburden strata movement for this special type of geological condition. The objective of this paper is to monitor and analyze the characteristics of mine pressure and overlying strata movement in downward mining longwall panels in steeply inclined seams, the angle of which varies greatly along both the seam dip and strike directions. The measured data has conclusively demonstrated that the characteristics of mine pressure and overlying strata movement in downward mining longwall panels in steeply inclined seams are different from those for the flat and gently inclined coal seams. The large downward angles of coal seam undulation along the strike (mining) direction can obviously affect the roof movement and reduce strata pressure. Study in this research showed that appropriately increasing the rate of mining (or face advance) is positive to roof control.

Jan 1, 2013

By Keith Heasley, Christopher Newman, Zach Agioutantis

"Previously, in 2013, a laboratory version of the computer code ARMPS-LAM, introduced at the 32""d International Conference of Ground Control in Mining, successfully integrated the laminated overburden model of LaModel into an ARMPS-style pillar stability analysis. The ARMPS-LAM analysis has now been fully integrated into the ARMPS program allowing users to more accurately classify the stability of a given mine design utilizing a laminated overburden model for the determination of pillar loading within theAMZ. ,This paper introduces the new Windows-based ARMPS-LAM program. The program's ease of use, output result generation, and limitations are highlighted through the parametric analysis of three hypothetical case studies where traditional ARMPS output is compared to output generated by LaModel. As mining operations continue to produce at greater depths and in more complex geometric and geological conditions, flexible and efficient analyses of mine stability for underground room and pillar mining has become more and more essential. The ARMPS-LAM program provides the mining industry with an empirically backed, numerical design tool for the evaluation of underground room and pillar mine plans.INTRODUCTIONIn the Southern Appalachian coal fields of the United States, retreat room-and-pillar methods have allowed mining operations to maintain high rates of production in the face of adverse geologic conditions and shrinking coal reserves. Over the years, research has been dedicated to understanding and mitigating mining-related dangers due to second mining practices, such as: pillar squeezes, floor heave, roof falls, pillar bumps, etc. However, as mining operations continue at deeper depths and with more complex geometric and geologic conditions, there is an inherent industry need for more accurate, flexible, and faster evaluations of stability for underground room-and-pillar mining."

Jan 1, 2016

By Chris Mark

Pillar recovery continues to be a significant ground control hazard. During the past decade, 10 miners were killed during pillar extraction operations in southern West Virginia. Studies conducted during the past decade have identified a number of "risk factors" that can be used to evaluate pillar extraction plans: Cut sequence Final stump Timber or Mobile Roof Supports Roof bolting Intersection span Depth of cover Roof quality Age of workings For each of these factors, rock mechanics science suggests which alternative would be expected to be more risky. For example, numerical models were used to evaluate different cut sequences, and indicated that less roof convergence occurred with the outside lift method than with the Christmas tree in the particular environment simulated. For many of the risk factors, accident statistics confirm the science. One finding was that currently almost 70% of the retreat coal in southern WV is being mined with MRS. In contrast, timber supports were used in 70% of the past decade's pillaring fatalities. This paper discusses each of the risk factors in turn, presents the relevant accident statistics, and shows how the risk factors can be combined to estimate the overall hazard. It also addresses the use of pillar design to minimize the risk of global stability hazards including squeezes. massive collapses, and bumps.

Jan 1, 2002

3-D finite element modeling was performed to study the effect of bedding plane sliding and separation and tensioned bolt in layered root It was found that the major influence zones of a tensioned bolt are restricted to the neighborhood of the anchor points; that bedding plane sliding and separation releases the vertical stress in the roof above entry but greatly increases the horizontal stress within the first layer of the roof, and that there is a triangular zone between the two adjacent bolts at and near the roofline level that is beyond the influence zone of the bolts which is liable to fail if conditions exist. Based on the results, three possible modes of roof failure are proposed for the design of tensioned bolting.

Jan 1, 2001

By Anthony Spearing

There are approximately 68 million rockbolts installed annually in underground coal mines in the USA (Tadolini and Mazzoni, 2006). The most utilized is the passive fully grouted resin rebar bolt, which constitutes almost 90% of the primary support in US underground coal mines. Resin-grouted rockbolts are a very effective and safe support, but their performance still needs to be further optimized and improved. This paper investigates their performance and suggests operating conditions to optimize the performance of resin-grouted rockbolts. In addition, this paper discusses a small-scale test that can also be used to evaluate the performance of rockbolts that is quicker, easier, and less costly than short encapsulation tests.

Jan 1, 2014

By Michael Alber

Pullout tests on resin grouted rock bolts have been executed in coal mines and surface test sites. The goal of this study was to provide some qualitative information about the rock mass quality from mandatory tests with a bit little more effort. Movements of rock bolt head and steel plate at different load levels were analyzed and were found to yield information about the rock mass deformability. The tests were interpreted similar to plate bearing tests and a rock mass compressibility index C was assigned. This index reflects the complex interactions between the rock mass, resin grout and bolt under load. Although further research is necessary it may be concluded that those tests may aid in recognizing geological conditions.

Jan 1, 2003

By Michael Alber

Coal resource extraction reaches higher depth of overburden and rockbursts as well as associated seismic events appear to become an additional problem to he addressed by ground control engineers. For example, German coal mines approach a depth of overburden of some 1400 m (4200 ft). Certain strata at those depths and associated high stresses may react upon resource extraction and subsequent deformation by violent release of strain energy, termed rodcbursts. Rock mechanics tests on numerous rock types have been conducted and three types of brittle rock behavior were classified. This paper describes different types of rock behavior in uniaxial compression and discusses a possible classification of rock with respect to their likelihood of violent response upon loading.

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

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 L. Munsamy

The bulk of primary mining at the Anglo Coal's Bank Colliery was carried out by drill and blast method, in a bord and pillar layout exploiting the No. 2 Seam. Secondary extraction, top/bottom coaling, also took place using both the drill and blast (D&B) method and continuous miners (CM). Extensive mining in this seam resulted in the risk of sterilising the No. 4 Seam reserves. Therefore, multiseam design guidelines established by Salamon and Oravecz (8) were re-evaluated in light of the low safety factors and the low pillar width to mining height ratios of pillars in the No. 2 Seam. Two and three dimensional (2D & 3D) numerical modelling was carried out to quantify and verify the parameters that influence the multiseam mining. The modelling was conducted primarily in two dimensions (plane strain), with 3D models to confirm the validity of the 2D results. A panel risk assessment flow chart was developed to assess the panels with respect to pillar failure and multiseam mining. This flow chart was extended into the evaluation of risk of surface subsidence using the current rock engineering knowledge. The aim of this risk assessment tool is to assess all underground workings at Anglo Coal collieries simply and rapidly. The identification of high-risk areas would warrant further investigation and possible backfilling to reduce the risk of pillar failures ensuring that reserves in the No. 4 and 5 Seams above are intact.

Jan 1, 2004

By Tom Denton

The bolt design criteria, since it was first published by Dr. John Stankus (Stankus, 1997), has been recognized as an important tool in ground control design. This concept is based on the Optimum Beam Building Effect (OBE), which is defined as the roof beam that has no separation above or within the bolted range and having the shortest bolt possible. This paper will present an application of this concept at the American Coal Company. Galatia mine. This mine previously used a 6' and 7' length bolt. However, since seam thickness has gotten smaller in the Southern area of the nine, a two-piece bolt is required. A two-piece bolt increases ground control costs and delays production. Therefore, a one-piece, shorter bolt, if feasible, can reduce costs and expedite development. In this analysis, Computer modeling is first conducted to determine bolt length and installed load. Second, a special bolt is developed, that can achieve the proper installed load as determined by the computer modeling. Third, underground bolt pull and load cell tests were conducted to evaluate bolt performance. Finally, an underground "bench" test was conducted. The test results have shown that entry convergence in the short bolt (5) test area is less than the 6' bolt area. Overall roof condition in the test area was as good as the 6' bolt area. Based on this analysis, the mine has converted to a shorter bolt in the low seam area and it is working well.

Jan 1, 2000

By Axel Preusse

Stowing or waste fill is common in the German mining industry since the beginning of mining activities, With increasing mechanization, flat and gently inclined seams (0 -- 18) were mined. These mines were located within the densely populated areas close to important infrastructures such as industrial complexes, roads, highways, railroads, rivers and canals. These buildings and infra¬structures were rarely protected against subsidence influences and other ground movements and dump capacities close to the mines were exhausted. For subsidence reasons and because of the low dump capacities pneumatic stowing methods were continuously developed and used in German longwalls until 1997. Due to techni¬cal standards and because of some restrictions pneumatic stowing in Germany is only used at a minimum seam thickness of 2.00 m and average costs of this method are $20 - 30 per ton. A significant reduction of the disturbance potential and by that a decrease in expenses for subsidence regulations due to reduced subsidence and ground movements could not be achieved. In this paper the experiences with pneumatic stowing in the Ger¬man mining industry are described. Possible subsidence reduction and economic aspects of pneumatic stowing are taken into account.

Jan 1, 2002

By J. M. Girard

Ground control problems at surface mining operations can occur for a variety of reasons. Stress, gravity loading, rock strength, geology, pore pressure, weather effects, underground workings, and many other factors contribute to slope instabilities that range from small rock falls to massive slides of material. While some of these failures can he predicted or controlled by preventive measures, each year many completely unexpected failures occur. Current methods for monitoring generally involve measuring displacements at a few, selected points in and around the suspected area of instability. While most of the displacements along these points will be in a downslope direction, freeze-thaw cycles of water-filled joints, horizontal stresses or pressure, buoyancy in saturated soils, human measurement errors, or other situations can produce deformation in almost any direction, even without any instability in the slope. Determination of which, if any of the observed movements represents a potential hazard is essential.

Jan 1, 1998

This paper presents a two-dimensional numerical procedure which incorporates concepts related to the mechanics of strata deformation' as well as' empirical indices associated with subsidence engineering. Regional deformation data were employed in order to establish overburden deformation zones, while material properties were kept constant. Scaling of final displacements was based on empirically predicted values for subsidence and strain for the Appalachian coalfield. The model was validated with a number of regional case studies and predicted subsidence and strain curves were compared to those obtained using the semi-empirical influence function formulation developed by VPI&SU.

Jan 1, 1988

Since the initial development and trials of FLEXIBOLT flexible roof bolts, further comparative testing and product development has been completed as part of the changeover to this roof support system at two Australian longwall operations, Ellalong and Angus Place Collieries. Details of the practical implementation of FLEXIBOLTS at both collieries are outlined together with their impact on roadway development rate productivity. At Ellalong where fully encapsulated 2.1 m long bolts are used, the reduction in bolt density is discussed with respect to both support system design and work force acceptance. The impact of shear deformation on bolt loading is described. Bolts longer than the working height have been required at Angus Place to achieve a suitable bolt anchorage horizon. Details of the long hole drilling and the benefits of a two stage grouting procedure are outlined. Improvements in roof conditions which have resulted from the inclusion of FLEXIBOLTS into the overall roof support strategy at Angus Place are described. Their importance to the viability of the Angus Place operation is also highlighted.

Jan 1, 1994

By Alan D. Smith

[A standardized checklist in a questionnaire format, was established to investigate selected factors associated with coal nips roof falls, as derived from an intensive review of the literature. A plot study was undertaken to aspect and explore possible statistical relationships that may exist with these parameters. the Purposes of toe study were to: 1. Study in a systematic and empirical fashion selected parameters that may be capable of differentiating characteristics of roof falls; 2. Obtain some predictive indices cased on selected physical and management related variables so that predictions of future problems associated with mine roof falls can be completed, prior to its actual occurrence. Accomplishment of these goals should result in valuable guides to the mining engineer in scheduling exploration work and 4 determining economic feasibility of certain ground control and .lining pro and practices. The parameters associated with mine roof failure that where included in the questionnaire are: working section, county, spar., orientation degrees), pillar dimensions width, length), seam thickness, roof fall dimensions (length, width, surface area, volume), shape of fall (arch, dome, laminar), thickness of thinnest immediate layer, lithology of the first four i.e.-diate roof layers, thickness of h e first four immediate roof layers, type of initial support systems before failure, type of resupport system after failure, length and spacing of bolts in use before failure, length and spacing of bolts planned after allure, presence of .cater, time failure after It coal excavation, distance t3rest ace, physical operation during, time of coo failure, location of the roof fall entry failure occurred ence of sloughing of ribs before failure, and presence of floor heave condition before failure. The typical roof fall had an average roof spar of 20.3 feet, -06 feet depth o coal seam, occurred 136 feet from nearest face, coal seam thickness of inches, p--ar :width off 45 feet surface area D' roof fall 1151 ft2, mainly lamin- shaped, previously rat fore fall between good to very good, little floor heave presence, usually cracks before the fall about 40 percent of reported cases, shales in most of the immediate layers, and usually located in an entry or intersection. in addition, multiple linear regression techniques were employed in the testing process of 18 major research hypotheses in a search for relationships among the various parameters studied of which were found to be significant, once corrected for multiple comparisons.]

Jan 1, 1984

By Brad Seymour

In cooperation with Cyprus Twentymile Coal Co., researchers from the National Institute for Occupational Safety and Health (NIOSI-I), Spokane Research Laboratory, conducted a study at the Foidel Creek Mine, an underground coal mine near Oak Creek, CO, to evaluate the stability of underground working conditions as a longwall advanced through a series of backfilled cross-panel entries. Instruments installed in the cross-panel entry pillars, backfill, longwall panel, and adjacent headgate entry were continuously monitored by a computerized data acquisition system as the longwall approached and advanced through the backfilled section of the panel. Data collected from these instruments were analyzed to determine the magnitude and direction of the secondary principal stress changes ahead of the longwall face, deformation and closure of the headgate entry, and stability of the cross-panel entry pillars and backfill. A three-dimensional, boundary element model was calibrated to accurately predict mining-induced stress changes and the distance they occurred ahead of the longwall face. As the longwall advanced through the backfilled entries, most of the mining-induced load was supported by the cross-panel entry pillars. The backfill provided stability for the root and Moor of the in-panel entries and also confined the entry pillars significantly improving their load-carrying capacity. Comprehensive information derived from backfill material property tests, instrument data, underground observations, and numeric modeling results document the safety and stability of the 8-Right minethrough and should provide beneficial case study information fur other longwall backfilling applications in the future.

Jan 1, 1998

By William D. Gallant

This paper describes a joint cooperative project between the CANMET Cape Breton Coal Research Laboratory and the Cape Breton Development Corporation to conduct a trial of split set cable slings for remedial support in longwall gateroads. Slings were installed in two test sections of the 2 West panel, Phalen Mine which exhibited deformation and the potential for excessive deterioration when subjected to the front abutment of the wallface. Roadway support behaviour was monitored at the trial sites, including lengths of roadway with the standard support of steel sets without remedial support. Observations were made on convergence, loading of the steel supports, loading of the slings, and wallface performance. Comparisons are made of the results obtained from the areas with remedial support to that without, which demonstrates that the slings provided effective remedial support limiting further deterioration of the roof. Improved face end conditions have contributed to increases in safety and productivity of the longwall panel.

Jan 1, 1990

By David L. Kuck

This paper describes a system for providing structural, support in underground mines, employing water ice for pillars. packwalls and brattices. It consists of a refrigeration brine chiller, brine circulation system, and disposable plastic containers. The system provides for the timely freezing of uniform ice pillars, and for ice maintainance and/or melting on demand. Unique, useful ice properties include: expansion upon freezing, resilience to dynamic loads, and plasticity. Ice will not dilute or contaminate coal or ore. Economic advantages include: 1) lower labor and material costs (water can be piped to the ice pillar site through mine-water, spray-water, or drill-water lines); 2) replacement or supplementation of timber. concrete or other roof support equipment; and 3) potential use of ice brattices as ventillation control; and 4) conversion of ice bratices to ice pillars upon retreat. See Figure . A safety advantage for personnel and equipment is that ice pillars can be placed in hazardous sites, by remote control, if neccessary, without human entry. All filling, freezing and melting operations can be controlled from a safe distance.

Jan 1, 1987

By Maynard O. Serbousek

The mechanics of load transfer of fully-grouted roof bolts in coal mines has been investigated in laboratory and analytical studies. The purpose of this research is to increase the understanding and better interpret data from pull tests which are routinely performed in the field. Laboratory work includes variation of bolt length, hole diameter and grout type in pull tests. Four-foot bolts were tested in holes of 1- and 1-3/8-inch diameters. Both polyester resins and inorganic grouts were used as the anchorage medium. The bolts were strain gauged at six locations to observe the rate of load transfer from the bolt to the rock mass when a force was applied at the bolt end using standard Jack pull testing procedures and equipment. Analytical studies using closed form solutions and finite-element techniques were compared to experimental results. The models are for the elastic regime only but do include slip elements. A detailed analysis of the load transfer mechanisms from the bolts through the grout to the rock mass is presented.

Jan 1, 1984