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By John L. Edwards

The underground coal mines in the Lake Macquarie area of the Newcastle Coalfield, New South Wales, Australia are constrained by surface subsidence restrictions as low as 150 mm. The mining environment is shallow, generally between 100 m and 200 m, often multi-seam and commonly overlain by residential development or tidal waters. Most mines use partial or panel and pillar extraction techniques to meet the subsidence restrictions and allow maximum resource recovery. This paper gives an overview of the results of a recent two year government funded research project aimed at developing a mechanistic, geomechanically based mine design criteria for subsidence control. Three extraction layouts were monitored in detail to assess the relationship between mining geometry, pillar behaviour and surface subsidence. Pillars at each site were instrumented with stress cells, convergence monitors and extensometers. Field data was used to initially calibrate, and subsequently, verify stress and displacement predictions made by the three-dimensional displacement discontinuity code, SUBSOL. Back-analysis of the modelling results indicate SUBSOL's capability as a tool to satisfactorily predict surface subsidence magnitudes and pillar loads for alternative pillar and panel layouts.

Jan 1, 1993

By David J. Reddish

Longwall systems are inflexible in layout, intolerant of disruption and represent a substantial investment. It is therefore essential drat all understanding of the likely strata behaviour and support requirements is obtained prior to panel development. For many tears rock mechanics engineers have applied numerical modelling based kill finite element techniques to the design of the support and layout of underground excavations. Whilst such design methodology has worked well in civil engineering and hard rock situations, it has been less reliable when applied to excavation design in the soft rocks of the coal measures. This lack of reliability has been identified largely as being the result of the utilisation of unsatisfactory input data, This paper describes the results of an ongoing research programme at the University of Nottingham in which a novel rock mass rating system known as the UK Coal Mine Classification system was developed to enable the prediction of the strata properties that are required as input parameters for use in numerical modelling of the deformation of soft rocks around excavations such as roadways and longwall faces in coal mines. The paper describes the development of the system. the way in which classifications are applied to derive input data for numerical models and gives two case studies ill which deformations and stress re-distributions around coal mine excavations have been simulated by numerical modelling using the FLAC finite difference code.

Jan 1, 2000

By John L. Ellenberger

The National Institute for Occupational Safety and Health (NIOSH) has continued the research role of the former U.S. Bureau of Mines to develop techniques that will reduce the hazards in the mining work place associated with coal bumps. Current research focuses on both analyzing historical seismic data from bump-prone operations and utilizing a mine-wide seismic network to investigate the exact strata failure mechanics associated with bump-prone geology. The anticipated outcome of this research will be reduced bump incidences through advanced engineering concepts and designs which implement the new understanding of strata behavior. The analysis of the historic seismic data consists of correlating observed mining seismicity with the geologic and geometric parameters at the sites. The primary seismic parameters are the timing, location and magnitude of a recorded seismic event. These parameters are correlated with such mining parameters as: the overburden, the size of the immediate gob, the size of the district gob area, etc. This detailed analysis of historical seismic data has provided an informative quantifiable relationship between many of the specific mining parameters and the induced seismicity. The second aspect of the coal bump research is the instrumentation of an appropriate field site to determine the main roof, floor, and gob behavior associated with hump behavior. The chosen field site is a deep-cover longwall mine with competent geology in a historically bump-prone area. The primary field instrumentation is a three-dimensional, full-waveform, seismic array with both surface and underground sensors surrounding an active multi-panel district. The purpose of this seismic array is to determine the timing, the exact location, and the mechanism (tensile fracture, bedding plane slip. etc.) of the failure of the strata surrounding the active and multi¬panel gobs. The preliminary results presented in this paper help to define the strata failure areas around the longwall panel.

Jan 1, 2000

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 Matthew J. DeMarco

Research personnel at the U.S. Bureau of Mines have conducted longwall gate stability studies at four western U.S. mines attempting to employ yield pillars for improved ground conditions. Located in the Book Cliffs and Wasatch Plateau coalfields of north-central Utah, these operations are generally characterized by multiple-seam mining, cover depths averaging 450 - 600 m (1,500 - 2,000 fl), occasionally extending beyond 760 m (2,500 ft), abrupt cover depth variation due to the overlying canyon/mesa topography, and massive, rigid sandstone roof units. Such conditions encourage severe gate and panel coal bumping, as well as various types of roof instabilities and occasional floor-heave problems. To alleviate these adverse conditions, several mines have employed yield pillars to-reduce hazard-inducing excessive gateroad stress concentrations. This paper describes the evolution of gateroad designs at four of these operations, the specific mining conditions involved, and the general stability performance attained by using yielding gate systems. Mine experiences are "compared" in terms of basic setting conditions, and the general concepts of yielding system applicability and success potential are summarized.

Jan 1, 1993

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 Tetsuro Esaki

This paper describes the present condition of mining-induced damages in Japan and the characteristics of them. The change of mining operation and environmental condition has caused various significant impacts on the ground environment: subsidence, cave-in, springing out of ground water etc. The characteristics and the influences of these phenomena are discussed by investigation of the actual conditions and by fundamental studies. Some counter measures are also introduced.

Jan 1, 1989

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 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 Jinsheng Chen

To maintain the stability of longwall tailgate entries, they have to be supported by not only the primary roof support but also the secondary roof support due to the impact of the longwall mining¬induced abutment loads. Depending on the mining condition of a typical coal seam and its distance from the previous panel's gob, the longwall tailgate entry is often reinforced by the secondary roof support in the form of standing supports and/or cable bolts or trusses during longwall retreat, Even though lots of research work has been done to study the behavior of different standing supports in the laboratory. their function and requirements for a typical mining condition are still not fully understood due to lack of field data and correct assumptions about the behavior of the already-bolted entry roof under mining-induced abutment loads. Therefore, the application of the secondary roof support for tailgate entry roof control is still limited to trial and error, which often results in either higher cost for tailgate roof control if the design is too conservative or more production delays due to roof falls in the outby tailgate entry if the design is inadequate. To have a better tailgate roof control with reasonable roof control cost, RAG American Coal, NIOSH, and HeiTech have been conducting a joint research project to monitor actual roof loading, roof deformation, and entry convergence in the tailgate entry of 10 North panel at RAG Emerald mine. The actual roof loading data are used to calibrate and improve the roof control model for longwall tailgate entries, which has been developed by RAG American Coal, and to further reduce the roof control cost for longwall tailgate entries. The authors in this study attempt to discuss the Roof Control Model developed by RAG American Coal. in which some guidelines or important parameters for designing the secondary roof support for longwall tailgate entries are proposed.

Jan 1, 2003

By J. R. M. Hill

The U.S. Bureau of Mines is involved in research to improve geological sensing (or geo-sensing) techniques. This paper presents results from field trials of two research projects concerned with new technologies for geosensing. The goal of the first project was to develop a "smart" roof bolter drill so that it could probe into roof rock to evaluate rock conditions. The goal of the second project was to modify an existing mine-wide monitoring system in a continuous mining operation so that the system could interface with geotechnical instruments to provide near real-time geosensing. Integration of this mine-wide monitoring system with the smart roof drill to collect, reduce, and analyze geotechnical data and the potential applications of the resulting technology in mining, are described.

Jan 1, 1992

By S. K. Sharma

The present study attempts to critically review the pillar-design as required by Coal Mines Regulations of India vis-a-vis latest rockmechanics formulae, Equivalent material modelling was the approach adopted for testing the safety and stability of the pillar sizes predicted by various formulae. Two parameters, considered here for calculating pillar sizes was the stresses acting over the pillars and the strength of the pillars. Stresses acting on the pillars were calculated by the tributary area method. Based on the studies of Coates and Hustrulid, the stress obtained was reduced by 40 percent. For calculating the strength of the pillars, three formulae, namely Holland and Gaddy, Salamon and Munro and Central Mining Research Station, India, were used. The pillar widths were then determined by equating the product of recommended factor of safety and pillar stress with the pillar strength.

Jan 1, 1992

A high strength steel strand bolt has been developed by Barrett, Fuller & Partners as a replacement for conventional rigid bars for primary roof support in coal mines. It is based on a 23mm diameter multiwire steel strand with a tensile strength of 55 to 60 tonnes, The paper summarizes the development of FLEXIBOLT flexible roof bolts, their reinforcement performance and their potential to provide operators, currently reliant on medium to high density roof bolting systems, with a viable, low density roof bolting system offering high roof reinforcement capacity along with the option of installing bolts longer than headroom, in a single pass at the face.

Jan 1, 1993

By Robert A. Stansbury

The No. 14 Mine of United States Steel Corp- oration is located at Munson, West Virginia, in &Dowell County. The mine was originally assigned 7,530 acres of Pocahontas 3, 4 and 5 Seams. Production began in 1948 with a listed reserve of 64,500,000 in place tons. It was originally intended to superimpose the 4 Seam workings with the 3 Seam and mine the two simultaneously to minimize the effects of one seam on the other. Roof control problems and economic conditions led to the discontinuance of 4 Seam workings in 1958 and again in 1980, after reopening in 1972. With room and pillar mining continuing in the 3 Seam, the majority of the 4 Seam reserves have been undermined. The mine began operation using track mounted conventional equipment. Off-track conventional equipment was next used, and in 1957 continuous miners were introduced. Since this tie, continuous miners on room and pillar work have been exclusively used with the exception of a brief shortwall trial in the 4 Seam in 1975. By mid 1982, 3 Seam mining will have been completed, leaving an estimated 42 million in place tons of 4 and 5 Seam coal as the focus of mining efforts. Plans for the subsequent reopening of the 4 and 5 Seam workings have been scheduled for June of 1981. With the resumption of mining, management is faced with solving the roof support problems caused by both the inherent physical conditions and undermining.

Jan 1, 1981

By William Monaghan

Over the period 2000 to 2003, roof falls have accounted for 4 to 14% of the fatalities in underground mining operations. The National Institute for Occupational Safety and Health (NIOSH) is conducting research to reduce the frequency, exposure, and risk of these events through an ongoing program of field and laboratory studies. One area of research involves the evaluation of polyurethane grouting technology that is commonly used to stabilize fractured mine roof strata. Concurrently, NIOSH is conducting work to evaluate the application of ground penetrating radar for advanced delineation of problematic mining areas. In this study, NIOSH partnered with Sub-Technical, Inc. who injected a polyurethane grout (also known as glue) into a roof area of NIOSH's Safety Research Coal Mine. The mine roof area was scanned using ground penetrating radar technology before and after grout injection in an attempt to determine the extent of grout infiltration. A comparison of the pre-and post-grouting radar records showed a significant change at a mine roof depth of about four to five feet. The interpreted radar records were then compared with drill core information, borescope evaluation of roof-bolt holes in the study area, and underground observations. At this site, the interpretations of the radar records correlated with data obtained from the core holes, borescope evaluations and underground observations. This study showed that ground penetrating radar technology can be a useful tool for detecting changes in mine roof due to the injection of the grout.

Jan 1, 2004

By E. H. R. Schumann

The local stratigraphy and composition of the coal measures, including competent dolerite sill and massive sandstone lavers is shown to have a restricting influence on the development and magnitude of surface subsidence above total extraction panels in South Africa. The critical panel width necessary to induce nonviolent failure of a dolerite sill is quantified. Small subsidence due to the deflection of a 70 metre thick dolerite above subcritical panels is shown by example. Maximum surface subsidence tilt an; ground strain is compared to the NCB model. An exponential subsidence profile curve, SPC, describes a trough half-profile. A parabolic relationship between horizontal displacement and tilt, which has been discovered to exist can be substituted in the first derivative of the SPC in order to generate transverse displacement and strain profiles.

Jan 1, 1988

By Andre Vervoort

The roof in coal room and pillar panels is normally stratified and can be thought of as beams or plates supported by the pillar sides in the roadways and by pillar corners in the intersections Underground measurements showed the effect of the face advance on the additional total movement of the roof skin and on the relative movement between various layers in the roof. The latter consists of the opening of bedding planes and of the lateral sliding of layers over one another. Both phenomena increase locally the axial load along full column anchors. Four models have been used to come to a better understanding of the roof behavior: a beam either clamped above the pillar side or laying on the pillar sides and a three-dimensional boundary clement model with and without bedding planes. The shape ref the curvature of the roof deflection is host approached by a clamped beam: the other models overestimate the movement at the sides. The largest roof deflection for a given Young's modulus is estimated by the model incorporating bedding planes. This model estimates that the bed separation occurs close to the face (within the first meter) and within 0.2 m of the sidewalk. In some simulations, openings are even recorded just ahead of the face. Further underground measurements should focus on these findings, as the effectiveness of the support is directly related to the amount of bed separation and sliding, which have occurred prior to the support installation and which still cart occur abler installation.

Jan 1, 2000

By Thomas M. Barczak

The engineering of a support system is driven largely by economics. The goal is to provide effective support at minimal cost. For this reason, wood has been extensively used as a support material for centuries. The cost of timber for mining applications has risen by more than 50% in the past 5 years and is likely to continue to increase as the supply diminishes and further environmental restrictions are placed on timber harvesting. The increased cost and lack of high strength wood in the Western United States has provided incentives to improve the utilization of wood and to develop alternative support materials. This U.S. Bureau of Mines' (USBM) report discusses the basic engineering requirements for the application of various materials for supplemental roof support construction and provides an overview of support systems that use materials other than wood. A comparison of support performance and cost for various material constructions is made to assist the mine operator in support selection. The scope of materials discussed in the report include: (1) conventional mine timber loaded perpendicular to the grain, (2) parallel to the grain timber loading, (3) steel fiber reinforced and air entrained concrete, (4) steel, (5) granular fill materials, and (6) combinations of these as composite support structures. The range of support systems analyzed include wood and concrete cribs, concrete columns and props, steel beams, friction props, and several novel support concepts.

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 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