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By David Newman

Landslides and soil creep often occur with varying degrees of severity on steep slopes within Southern Appalachia. Ground movement may take place over years with subtle changes in topography and vegetation or it can occur rapidly in response to water inflow or disturbance at the toe of the landslide. Although the ground movement typically is restricted within the soil and colluvial layers, failure can extend into the weathered rock zone. Certain areas of Appalachia are described as "slide prone" because of historical precedent. To develop a profile of "slide prone" areas, the strength and physical properties of the soil and colluvium, topography, groundwater and surface water runoff, present and historical land use, and any surface disturbance are examined in detail. These attributes are useful in determining whether an area is potentially unstable before surface development including construction, logging, or mining. Recommendations are provided to avoid initiating ground movement concurrent with mining operations.

Jan 1, 1998

By G. K. Rogers

Portals, which are the surface entrances to underground excavations, are frequently overlooked and often difficult areas In terms of ground control. Failures commonly occur In the typically high angle approach cuts and Initial subsurface portion of the portal. In order to permit rigorous design of all types of portal structures, failures are Identified and subsequently classified. Based on the failure classification and suggested analysis methodology, optimum ground and support loading can be determined.

Jan 1, 1988

By Robert C. Garson

The Mine Roof Simulator at the DOE'S Mining Equipment Test Facility is described. Its use in the research and development on the behavior and response of longwall roof supports to simulated mine environment is investigated. Advanced technology analysis methods such as finite element modeling, strain gage instrumentation, and photoelastic techniques are investigated for application in roof support design two case studies are presented of test data and results.

Jan 1, 1982

By Laxminarayan Holla

There exist many formulae for designing coal pillars. However, when applied to a given set of mining parameters, they lead to different pillar sizes and factors of safety. From the subsidence point of view, the pillars designed as protection pillars not only have to be stable, but also have to limit subsidence over them to a level acceptable to the structure being protected. The subsidence over a pillar of given width to height ratio depends upon the mining depth. A pillar may be stable, but the subsidence over it may be quite large and unacceptable for the structure. In many cases even though pillars may yield, they support the undermined strata and reduce surface subsidence. In addition, the yielding pillars eliminate peaks and troughs in the surface subsidence profile and reduce ground strains. In a given situation, whether a pillar yields or not depends primarily upon its width in relation to mining depth.

Jan 1, 1992

By Olayemi Akinkugbe

As coal production in the United States continues to increase, the availability of unexploited or virgin fields continue to diminish. As a result, mine operators are forced to mine in unfavorable or multiple seam conditions. The safe, productive exploitation of coal in multiple-scam conditions requires specific design technology. At present, there are two general design approaches that the mining engineer can use to analyze the multiple-seam problem in question, either simple empirical relationships or complex numerical models. Often, the empirical approaches are too general for the specific problem and the numerical models require too much time and expertise for the practicing engineer. This paper introduces a new computer program, Lam2D, designed specifically to enhance multiple seam mining operation by quickly and easily calculating, stress, displacement, subsidence, horizontal strain and safety factors associated with multiple seam mining situations. The program implements a simplified, two-dimensional boundary-element method in order to model the complex multiple-seam stress and displacement interactions. Most importantly, the program is greatly simplified by incorporating automatic overburden, interburden, coal and gob property generation thereby reducing typical modeling and solution time to a few minutes.

Jan 1, 2004

By Edward A. Barrett

A significant number of injuries resulting from fa118 of roof and rib may be avoided by modifying the reactive behavior of miners as they encounter potentially hazardous ground conditions. In 1984-85, the Bureau investigated barriers which prevent miners from recognizing and correcting groundfall hazards. One basic problem from which these barriers originate is the inability of miners to recognize dangerous roof and rib conditions. This study is a report of experimental research on the use of stereo scopic (3-D slides for presenting visual cues associated with hazardous roof and rib conditions. Findings reveal that, in comparison to conventional slides, 3-D provides for significantly greater hazard recognition among both experienced and inexperienced miners. Details such as the presence of t cracks and gaps in the surrounding rock are more accurately and realistically perceived. Acceptance by the mine training community has been affirmative and is additionally encouraged by the fact that 3-D slides stimulate trainees' overall interest.

Jan 1, 1986

By E. Bane Kroeger

For many years, researchers around the world have been investigating coal pillar stability. Many have focused on trying to optimize the size of the pillars by examining stable and failed pillars in underground coal mines. For mines that are already in operation or companies that are opening a new mine adjacent to an existing mine where the pillar dimensions and stability can easily be determined, this is the preferred technique. However, when a new mine is planned for an area where there has been relatively little mining, then samples of the coal need to be drilled and tested for strength. Because of the fractured nature of coal, this lab testing is often problematic and may often yield poor results because of the limited size and number of samples that can be obtained from the core. To remedy this problem, research was conducted in the labs at SIUC to determine if improvements could be made when optimizing the size of pillars for underground coal mining in Illinois. Through a greater understanding of the relationship between dimensions and strengths of coal samples tested in the lab, it was hoped the in situ strength of coal pillars could be determined with greater accuracy. This could allow the extraction ratio to be increased and more of the coal resources in Illinois recovered without impacting the safety of the mine workers. Many different agencies around the world have published recommended minimum numbers of samples for strength determination based on the size of the coal samples. For two inch cubes, uniaxial testing of at least seven samples is recommended and this minimum number decreases to four when testing four inch cubes. However, the laboratory testing of coal from two seams thus far has suggested this number should be almost doubled to accurately determine the coal strength. Testing also showed there is a pronounced decrease in the variation in the strength of the samples tested as the dimensions of the sample were increased. From the testing results thus far, it is recommended that a sample size versus strength curve be constructed for every coal seam for Illinois. Creating such a curve will better determine both the minimum number of samples and minimum sample dimensions for that seam or region of a particular scam. A second set of tests were conducted in the laboratory to determine the increase in strength with reduction in height for samples with the same width and length. In Illinois, typical pillar dimensions are 40 to 80 feet (12.2 to 24.4 m) wide and long, with coal thickness varying from about 4 to 9 feet (1.22 to 2.74 m). This provides width/height ratios ranging from 4.5 to 17.5. Coal samples having width/height ratios ranging from 0.5 to 13 have been tested thus far. As with most pillar design formulae, the strength of the Murphysboro coal versus width/height ratio was linear and closely matched shape factors published by other researchers. The laboratory testing thus far has identified three factors that affect the strength of laboratory samples, the number of discontinuities, the angles of critical discontinuities, and the shape of the samples. The factor that probably had the most pronounced effect on the strength of the coal samples was the angle of critical discontinuities. This testing has confirmed that there is still a gap that needs to be bridged between the strength obtained from laboratory testing and the in situ coal strength predicted.

Jan 1, 2004

By Gennaro G. Marino

Site conditions at several shallow room and pillar mines in Illinois are described and compared with the charac¬teristics of the subsidence profiles at the ground surface. The shape and magnitude of the subsidence profiles were found to be closely related to the thickness of the soil and rock over-burden the percent extraction of the coal, and the shape of mine pillars. The room and pillar mines were located at a shallow depth (from 112 to 220 ft), beneath flat to gently rolling terrain. Thickness of the coal seams ranged from 5 to 9 ft and at all sites was underlain by underclays. This information has been developed in order to improve techniques for evaluating the subsidence potential at sites within the Illinois coal basin. he results presented form a small portion of the work carried out by the University of Illinois with Illinois Abandoned Mined Lands Councils and the U. S. Bureau of Mines at the Minneapolis Research Center in Minnesota (Marino and Mahar, 1985). Presented in the paper are the modes of mine failures observed for Illinois room and pillar mines, an overall summary of the site geologic and mining condi¬tions, case histories of each mode of failure, a comparison of sag profiles, and then an empirical relationship between the site conditions and the maximum sag subsidence. The most ideal case histories are presented to illustrate fundamental behavior. A brief of the Paper is given in a summary and conclusions section.

Jan 1, 1984

By Keith Heasley

An eastern longwall mine was required to mine through a set of three entries located midway down the length of a panel. Of course, the mine desired to design a successful support system for the mine-through area at the least cost. To further complicate the design process, the mine-through entries were located directly under the end of a previously mined, overlying longwall panel and the entries were close enough to be subject to stress interactions from the overlying seam. In order to accurately evaluate the multiple-seam stresses and modify the mine-through support system appropriately, the boundary element program LaModel was used to model the stress and displacements in the two mines. Using the results of the model's stress analysis, the support density was systematically varied throughout the mine- through entries for optimum sup@ efficiency and economics. During the actual mining of the cross panel entries, the longwall experienced few, if any, additional delays, and overall, the support and mine through of the cross-panel en- tries at Harris #1 was very successful, saving the mine confineable time and money.

Jan 1, 2003

By William Gray

It has been ten years since the Mine Safety and Health Administration (MSHA) promulgated a safety standard requiring the use of Automated Temporary Roof Support (ATRS) systems in underground coal mines. The use of ATRS systems with roof bolting machines and continuous miners equipped with integral bolters has all but eliminated fatal roof fall accidents associated with manually setting temporary roof support. The last ten years have seen an evolution of the ATRS systems themselves and of MSHA's policy regarding ATRS systems. These changes are a response to operational and safety issues regarding ATRS systems often brought about by the ever-changing coal mining environment. As a result, MSHA's Technical Support personnel receive numerous inquiries from all segments of the coal mining industry on various ATRS topics. These requests for technical assistance range from an interpretation of a facet of the ATRS standard to an in-depth evaluation of a prototype ATRS system. This paper will address the aforementioned evolution of ATRS systems and will also summarize the factors MSHA Technical Support uses to evaluate these systems in the field. In addition, some of the more common misconceptions regarding the design, use, and regulatory requirements regarding ATRS systems will be covered.

Jan 1, 1998

By N. P. Kripakov

The U.S. Bureau of Mines (USBM) is conducting research to develop a practical computer-based tool that will allow coal mine planners to anticipate rock mass behavior surrounding mine entries prior to actual mining. More specifically, this tool estimates to what degree and extent the immediate roof and floor strata and the coal pillar ribs surrounding an opening will weaken or fail for a given set of mining parameters. The technical approach couples together two numerical techniques: the boundary-element method and the finite-element method to allow for an approximate three-dimensional simulation of actual mining situations. Outputs from plan-view, linear-elastic, boundary-element models executed at different mining stages are used as input to a detailed, section-view, finite-element model to estimate the degree and extent of failure expected to occur around the periphery of an entry system. Using a pseudo-elastic approach. elastic rock mass properties are continually updated as different zones are predicted to fail. The procedure is relatively easy to use and is being set up to work interactively with the user who will not be expected to be a computer expert. Inputs include easily understood parameters obtainable from the field and rock mechanics laboratories. Examples of computer-generated output from generic sample models representing typical mining situations are presented and results discussed.

Jan 1, 1994

By E. M. Williams

The U.S. Bureau of Mines is investigating the use of in-seam seismic methods to monitor stress-induced changes in coal near the working face of longwall mines. Seismic surveys performed through a longwall panel and pillars near the face can provide valuable information on geologic anomalies, high stress regions, tailgate support performance and other conditions that could endanger miners or interrupt production. This paper describes the details of the equipment and data analysis techniques used, and the significant results obtained and their implications for ground control. Using seismic tomography, it is possible to conduct measurements on the pillar and reconstruct an image representing the internal velocity distribution. Successive measurements over several days identify changes in velocity attributable to changes in stress. Several field measurements were conducted at a western U.S. longwall mine to observe stress induced changes within the panel and pillars during mining. A permissible data acquisition system was designed to meet mine safety requirements for operation in gassy air. Certification from the Mine Safety and Health Administration (MSHA) was obtained, and this approved system was used to monitor stress changes in several pillars as the longwall face passed during first panel mining. Tomographic surveys were completed across the longwall panel to map the apparent abutment stresses ahead of mining. Velocity distributions show an increase in vertical stress across the panel from the headgate to the tailgate. Additionally. a yield zone along the face near the tailgate and the forward abutment approximately 100 feet outby the face in the tailgate side of the panel were detected. These results agree well with data obtained from other instrumentation emplaced in the panel near the tailgate. Using velocities for both compressional and shear waves, the Poisson's ratio was calculated for the panel.

Jan 1, 1994

By Wei Yin, Yu Wu, Xiexing Miao

"For engineering problems of “three under” coal (coal trapped under buildings, waters-bodies and railways) exploitation, environment protection and gangue separation from raw coal underground exist in Tangshan Coal Colliery. By analyzing concrete technical problems, a technical approach of closed cycle “coal mining-gangue washing-backfilling-coal mining”, i.e. integration of coal mining, gangue separation and solid backfilling, is put forward with key technologies including gangue transportation with great depth, gangue separation from raw coal underground and integration of coal mining and backfilling. Based on the specific geological conditions of Tangshan Coal Colliery, 591m vertical feeding transportation system with great depth is designed; meanwhile, for efficient gangue transportation, ancillary wear-resisting pipe size and buffer equipment are optimized. Underground gangue separation system is created to be joined with the existing production system and backfilling system; besides, as per separation characteristics of coal and gangue, buddle jig is adopted for gangue roughing of raw coal underground. By cooperation of backfilling hydraulic support and other key equipment, the designed stope backfilling system completely realizes integration of coal mining and backfilling. Engineering practice shows that, through the research and implementation of the above key technologies, integration of coal exploitation, gangue separation and solid backfilling is successfully implemented in Tangshan Coal Colliery; moreover, it completely solves the three major engineering problems and realizes waste disposal, underground washing and separation, and ground surface subsidence control.INTRODUCTIONSo far, “three under” coal (coal trapped under buildings, watersbodies and railways) and key state-owned coal resources trapped under villages in China have reached 13.7 billion t and 5.22 billion t, respectively. With the development of coal enterprises, China currently has more than 1,600 gangue dumps (Miao et al., 2010a) with accumulated stack amount of 4.5 billion t, occupying a land area of 150,000 km2; moreover, surface subsidence caused by mining activities has damaged the environments of industry, agriculture, transportation and living, while new environmental pollution sources formed by coal related industries also result in damage to ecological environment (Huang et al., 2011a). On the one hand, due to large scale coal mining, some coal collieries suffering from resource exhaustion are faced with survival problems; on the other hand, coal mining has caused and been faced with increasingly prominent environmental problems, such as “three under” coal exploitation, waste disposal and ground surface subsidence control (Miao et al., 2010b; Zhang et al., 2009)."

Jan 1, 2015

By Lorraine Kent

Comparison of in-situ stress overcore measurement results with those determined from laboratory evaluation of Acoustic Emission (AE) testing on oriented sub-core samples has been carried out for a variety of mining environments. These include UK and German Coal mines at moderate depth, shallow-level South African Coal mines and deep-level South African gold mines. Results show that the `Kaiser Effect' or 'Stress Memory-Damage is readily determinable throughout the brittle deformation process, although particular care is required in interpretation of results during the 'bedding-in' phase of testing and the region associated with unstable crack growth prior to failure. The results suggest that AE provides a useful complimentary method for comparison with existing methods of stress determination. The success of the method can, however, be dependent on both rock type and the likely magnitude of in-situ stress in comparison to the strength of the rock. Keywords: in-situ stress, acoustic emission, Kaiser Effect

Jan 1, 2002

By Herryal Anwar

The application of roof bolting technology to control the stability of roadways in coal mining within weak strata or under high ground pressure has improved progressively. One of several factors that affect the design of rock bolting is the immediate roof characteristics of the roadway. On the competent rocks, the mining conditions may indicate a high level of stability and a low density of bolting patterns may be adequate to control the ground stability. However, at a weak strata, the roadway will be affected by both horizontal and vertical stresses that may generate a high level of deformation in the immediate roof. This sensitivity of the roadway will require a mine plan design which consider the pillar sizes and sequences of extraction as well as a conservative reinforcement to maintain the integrity of the deforming weak roof strata. Rock bolting technology has been used to maintain the stability of roadways in Indonesia and Japan for a few years. In this paper the overview of the application of rock bolting reinforcement in Ombilin Coal Mine, Indonesia and Miike Coal Mine, Japan is given.

Jan 1, 1999

By H. Gene Wilson

Mobile Roof Supports (MRS) look similar to a longwall shield on crawler tracks. The MRS units offer a safe, productive method of extracting the 40% to 60% product left normally unrecovered in room and pillar mining. The units feature radio control, self-contained power units, crawler track drive, and a 600 ton yield. Cribbing and setting posts in retreat mining has been a necessary burden to production. The MRS reduces this burden. Long blocks of coal can be developed to further reduce move and tram time, thus increasing production. The MRS units have successful safety records. The workers are removed from the immediate fall area, and we feel back injuries have been reduced by the workers not setting posts. While MRS units have been damaged in falls, the other capital equipment has been unharmed. The MRS product line has undergone normal product improvement and evolution. Product evolution is seen in our development of machines for particular mine requirements. Through the continuing development of the MRS, Fletcher presents the coal industry with a safe, productive method of retreat mining with potential to develop new mining methods.

Jan 1, 1990

By Edward McHugh

While less than 1% of reported accidents are associated with slope stability problems. slope failures were responsible for about 15% of all U.S. surface mine fatalities between 1995 and 2001. Small rockfalls, which may involve hand-sized rocks weighing only a few kilograms, can cause fatal injuries to workers away from the protection of large machinery. Massive highwall failures containing a million cubic meters of material or more can be fatal even for heavy equipment operators. As part of an ongoing study at the Spokane Research Laboratory of the National Institute for Occupational Safety and Health, several remote-sensing technol¬ogies are being evaluated as tools to monitor slopes for hazards and to assess slope stability. Field tests of a hyperspectral imager were conducted to assess its value for improving geologic maps of poten¬tially unstable alteration zones on mine slopes. An interferometric radar device capable of detecting very small displacements on slopes awaits final assembly and field testing. Computerized moni¬toring methods using images from digital and video cameras are being assessed for application to mine slope surveillance. These and other techniques will eventually provide new tools to augment current methods for monitoring ground control hazards in mines.

Jan 1, 2002

By Stephen C. Tadolini

A joint research program was designed and conducted at Lodestar Energy?s Baker Mine to investigate the performance of a high-capacity tensioned cable supported gateroad. The secondary system consisted of a 4.5 m (14.5 ft) 7 strand cables that were 23 mm (.9 in) and 18 mm (.? in) in diameter with a designed capacity of 515 kN (58 tons) and 355 kN (40 tons), respectively. The cables ware installed with an effective resin column length of 1.25 m (4 ft) and then pre-tensioned using a hydraulic jacking system. Roof separations, caving characteristics, and support performance was monitored and evaluated during the critical extraction of the adjacent panel, complex geological conditions of the west Kentucky No. 13 seam were mapped and the support performance recorded. This paper will describe the theory of tensioned cable systems and present an assessment of the support performance during the longwall retreat mining process.

Jan 1, 2000

By James Arthur

In deep coal mining the support of the underground roadway is fundamental and without knowledge of the mechanics of ground control a mine is unlikely to be operating safely and efficiently. It is therefore important for the support system to be designed sat¬isfactorily for the size of the excavation required and to do so an understanding of the behaviour of the surrounding strata is re¬quired. Over the last 15 years there has been a major change in the industry and the support systems adopted. The industry has been privatised, legislation has been updated, a comprehensive research programme has been carried out and guidance docu¬ments produced. The paper will show how privatisation has not allowed support standards to deteriorate, highlight research, the legislation and guidance documents updated and how this has led to a reduction in accidents and falls of ground..

Jan 1, 2002

By Karl Brandt

Longwall panel 580 has recently been retreated in the Zollverein 1/2 seam at a depth of approximately 1000m at Auguste Victoria mine with rectangular rockbolted roadways used for both the maingate and tailgate. Although Auguste Victoria mine has been increasingly using rockbolted support since the mid 1990's. this has previously been restricted to tailgates for single use. This panel represents the first use of a rectangular rockbolted roadway as a maingate at Auguste Victoria mine. As such, it represents a significant change in support strategy. As part of the strategy numerical modelling was used to examine expected behaviour of rockbolted roadways at the site, stress changes during face retreat, the feasibility of adopting rockbolted support for the maingate and the reinforcement pattern required. Monitoring instrumentation was installed in both gates to confirm that the support systems were performing satisfactorily as the gates were driven and as the face was retreated. Although the panel is isolated from others in the Zollverein 1/2 seam, markedly different roadway conditions have been experienced in the two gate roads. Favourable conditions were obtained in the maingate, but particularly difficult conditions were encountered in the tailgate. Previous work for the mine had examined interaction with old workings in other seams and shown a vertical stress of 28MPa for the maingate and up to 45MPa for the tailgate. The values from the earlier work were used in the modelling work described, which showed contrasting results given the different stresses. The difference between the gates can be attributed to the interaction. The paper describes the numerical modelling work, the reinforcement systems adopted, the monitoring results, the interaction effects and the comparison between expectations from the numerical modelling results and the conditions actually experienced.

Jan 1, 2002