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By Shengliyang Yang, Jinghu Yang, Jiachen Wang, Xiaomeng Li

"Safe and efficient mining of extremely inclined thick coal seams less than 20m thick is one of the new challenges in China coal industry. In recent years, the extremely inclined thick coal seams have been encountered in some old mines and western China, and currently the top coal caving longwall mining method has been successfully applied to this kind of coal seams. Accordingly, this paper studies the roof movement and its impact on shield supports of top-coal caving longwall mining in extremely inclined thick coal seams. The structure of main roof before failure was simulated by the fix-ended beam, and provided the solutions for determination of maximum compressive stress of the bottom beam end and maximum tensile stress of the top beam end. The failure mode on the upper end of working face is mainly a combination of compression and shearing, while that for the bottom end is tension and shearing. Roof fracture begins at the upper end of working and propagates downward. The shape of collapsed roof strata can be described as parabolic and divided into three segments from top to bottom, including no filling, uneven filling and densely filling segments. The roof loading conditions of no filling segment is more likely to have dynamic burst impacts.INTRODUCTIONExtremely inclined thick coal seam refers to that the dip angle of coal seam is greater than 45° and the thickness is greater than 3.5m (Wang and Zhang, 2015a; Wang and Zhang, 2015b; Wang, 2005; Xie, Gao, and Shangguan, 2005; Wu, et al., 2014; Deng and Wang, 2014; He, et al., 2015). This type of coal seams can be divided into three categories: 1. The extremely inclined thick coal seam, of which the thickness is less than 5m and the dip angle is less than 60°, is usually mined by fully-mechanized longwall mining method. 2. The extremely inclined thick coal seam, of which the thickness is 5 m-20m, is usually mined by top coal caving longwall method. And 3. When the thickness of extremely inclined thick coal seam is greater than 20m, it is mined by the horizontal section top coal caving longwall method. For example, the average angle ofWudong coal mine in Xinjiang province is 45°, and the thickness is 27m. Wudong coal mine is applying the horizontal section top coal caving longwall mining, producing 3 million tons annually per working face (Figure 1)."

Jan 1, 2016

By Jun Lu

This paper presents the evaluation, enhancement and comparison of two hydraulic fracturing techniques which were employed to mitigate the impact of a massive sandstone channel on two successive longwall faces. The hydraulic fracturing technique and Longwall Visual Analysis (LVA) software were initially employed to mitigate the impact of thick, massive sandstoneroof during mining of longwall Panel 21. Improved longwall face conditions and productivity were observed as Panel 21 mined through the sandstone channel. However, moderate sandstone fractures and falls at the face were still present in areas where hydraulic fracture influence was not present. Such adverse conditions caused two to three weeks of production delays due to large face cavities, jammed face conveyor and subsequent face gluing. Based on the mining experience in Panel 21, and site-specific roof geology in Panel 22, a modified and more effective hydraulic fracturing program was employed. Fewer well-placed holes were drilled, and larger volume of water was pumped into each hole in order to propagate the individual horizontal pancake fractures over a larger area, thereby enhancing caving and relieving face pressure caused by overhang of the massive sandstone. Longwall Visual Analysis (LVA) software was also employed at Panel 22 to predict the cavity risk index and guide the longwall face crew in double-pulling shields behind the shearer drum. This helped to reduce the tip-to-face distance at the critical spots along the longwall face, which helped mitigate the formation of the roof cavities and failure of massive sandstone onto the face conveyor. Underground observations, face advance rate and face rock delay analysis confirmed that longwall face conditions and advance rate in Panel 22were significantly improved compared to those of Panel 21. Consequently, safety and productivity were improved.

Jan 1, 2014

By Stephen C. Tadolini

The U.S. Bureau of Mines (USBM) is conducting research to provide alternatives for traditional secondary support methods. These cost-saving methods are proving to afford safer installation, improve entry stability, eradicate material-handling injuries associated with crib supports, and enhance ventilation. In cooperation with Mountain Coal Company, the USBM replaced timber cribbing with high- strength cable supports to provide stability in a gate road that was used for two longwall panels. The support design consisted of 2.1-m (7-ft) full-column resin-grouted bolts and 4.8-m- (16-ft-) long high-strength resin-grouted cable supports. Three support concepts were evaluated: passive, stiff, and tensioned systems. Cable loading and roof deformations were monitored to evaluate the behavior of the immediate and main roofs during panel extraction. The stress and loading histories for both panels and the abutment and yield pillars were monitored to assist in evaluating the stress transfer and pillar performance in conjunction with the roof behavior. The test results indicated that resin- grouted cable support systems successfully maintained the immediate and main roofs during the extraction of two longwall panels. This paper describes the theory, application, and advantages of resin-grouted cable supports and presents the mine measurements made to assess the cable performance during the retreat process of longwall mining.

Jan 1, 1994

By Stephen P. Signer

A field test was conducted by the U.S. Bureau of Mines at the Cyprus Plateau Starpoint No. 2 Mine. near Price. UT. to study the support rock interaction mechanics. Twelve instrumented. fully grouted roof holts and eight sagmeters were installed in the roadway of a two-entry gate road to measure load changes and roof movements. Readings were taken during section development and as each longwall panel passed the test area. Loads that resulted from development of the en- tries were higher than would be expected if simple suspension of the roof rock was the sole cause of loading. When the first longwall face passed the test section massive beam behavior was exhibited over the entry and adjacent pillar. However, no significant localized bending was detected at any of the strain gauge locations. After the first panel passed the test section. all the roof bolts had at least one zone where the steel had yielded. Loading continued to increase. and when the face from the second panel was adjacent to the test section. 70 pct of the strain gauges at the 6-. 1%. and 30-in locations had passed the yield point of the steel roof bolt. However, even at these high load levels, the supporting pattern was sufficient to provide adequate reinforcement to the mine roof.

Jan 1, 1990

By Monte R. Hieb

Study of moisture-induced swelling strain in Pennsylvanian Period rocks of the Appalachian Plateau in West Virginia shows a 2:1 biaxial horizontal anisotropy which trends NW-SE. Oriented in-situ slabs of coal mine roof rock were collected across West Virginia, dry-sawed to size, air-dried to stability, and then monitored for moisture changes and deformations in the horizontal plane through one wetting cycle and drying cycle. Biaxial swelling strains were exhibited in nearly all rocks tested, with maximum horizontal deformations occurring normally-incident to the strike of regional geologic fold structures. This relationship persists as fold strike varies across the study area. A connection with Alleghanian fold development and/or post-Alleghanian fold relaxation is suggested. Deformations were largest in shales, but occurred in sandstones and siltstones as well. During testing, moisture-induced fractures (MIF) developed parallel to the regional fold structure and ranged in size from hairline cracks to sample-destroying cracks that were orthogonal to the observed biaxial swelling strain direction. Preferential wetting and swelling of clay minerals along NE-trending fractures, related to a fold-parallel fracture fabric of regional extent across West Virginia, is the most likely reason for the observed systematic NW-oriented biaxial swelling strains. The testing methods used in this study are simple and inexpensive and produce robust results that offer insight into a regional, anisotropic mechanical weakness that imparts a dynamic, asymmetrical horizontal stress to moisture-sensitive coal mine roof rocks over time. Because a similar mechanical fabric has been reported in Devonian-age shales, these findings may have implications for shale gas developers in the Appalachian Basin challenged by rapid aperture closure rates along horizontallydrilled induced fracture networks in Devonian rocks like the Marcellus Shale. The paper concludes with an example of how the concept of a preferred swelling strain direction might be applied to improve the effectiveness of roof trusses.

Jan 1, 2013

By Joel Bradley, Kot Unrug, Kyle Perry, Mark Klimek

"A West Kentucky mine operation in No. 11 seam, encountered floor heave, due to the localized increase of the thickness in the fireclay mine floor. Floor heave has overridden seals installed in two mined out panels. The third seal’s location was planned for isolating that area from the Mains. A plan of support has been developed to prevent repetition of the floor heave and related problems outby the seals. The applied ground control measures were successful. An attempt of a 3D numerical modeling was made, that it would match the observed behavior of the mine floor and could be used as a design tool in similar conditions. In the paper described are sequence of events, a mitigation ground control system applied, and the first stage of numerical modeling.IntroductionWest Kentucky coal mine operation in the No. 11 seam has approached an area where the fireclay floor thickness increases to about 5 ft. Delayed floor heave has been observed. In the first sealed area (Panel KK), floor heave has overridden the seals and has begun to progress outby. This could not be allowed at the new seal location PP described in this paper because such override would affect the mains. Previously numbers of standing support systems were used, but their effectiveness was not satisfactory as is illustrated in Figure 1, Figure 2, and Figure 3. Therefore, with sealing of the next area approaching, mine management was looking for a better solution that would eliminate the problem. In that stage, our team looked closely at the geology and strength of roof and floor, as well as the characteristics of ground failure around the seal at the first site. The technical literature has been searched as well Haramy et al. 1986 Hsiung and Peng 1987, Peng 2008, Santos & Bieniawski 1987. This led to the identification of factors responsible for the ground failure. It has been determined that increased fireclay thickness from typically less than 2 ft to about 5 ft, when compared to the previously mined parts of reserve, and the strong limestone strata just above the immediate roof composed of 2 ft of black shale, created conditions of failure. It appeared that, when pillars were punching into the mine floor, the strong roof did not break but was bending, exerting high pressure on outby pillars, causing rib failures and closure. This is a similar mechanism to a strong roof affecting longwall shields. The remedial action planned was additional support."

Jan 1, 2015

By Gregory Molinda

Groundfalls are much more likely to occur in coal mine intersections than in entries. NIOSH is using the experience of U.S. coal mines to determine the factors which influence intersection instability and provide guidelines for the safe excavation and support of intersections. Detailed field investigations have resulted in a database of U.S. coal mines containing 12 mines and 639 roof falls so far. By using the roof fall rate as the outcome variable, correlations between roof geology (CMRR), intersection span, and roof support have been established. Case studies have indicated that replacing 3 way intersections with 4-way intersections may not reduce the total number of roof falls. Additionally, the size of intersection spans tend to decrease with lower (weaker) CMRR. Protocols have been established for the collections of roof bolt parameters. The performance of individual roof bolts can now be tracked with roof fall rate.

Jan 1, 1998

By Thomas M. Barczak

The decade of the 90's brought an unprecedented increase in the development of innovative technologies to provide more effective and easier to install roof support in underground mines. To facilitate the application of these technologies to improve mine safety. National Institute for Occupational Safety and Health (NIOSH) developed the Support Technology Optimization Program (STOP). STOP is a windows based software program that provides mine operators with a simple and practical tool to make engineering decisions regarding the selection and placement strategy of these various standing roof support technologies. This program includes a complete data base of the support characteristics and loading profiles obtained through safety performance testing of these supports at the NIOSH Safety Structures Testing Laboratory. Support design criteria in the form of the required support load density at a specified convergence can he established from four options: ( 1 ) a data base of measured ground reaction data from various mines or ground behavior information inputted by the user. (2) determination of loading requirements based on a detached roof block or rock failure height. or (3) criteria based on the current roof support system, and (4) arbitrary criteria set the by user. Using these design criteria, the program will determine the installation requirements for a particular support technology that will provide the necessary support load density and convergence control. Optimization routines are also available to determine the most efficient support design for a user specified support installation- In addition to these performance measures. STOP can be used to compare material handling requirements and installation costs. Comparisons among the various support technologies are easily made including graphical analysis of relevant support parameters. This paper describes the STOP and its application to optimize standing secondary roof support systems.

Jan 1, 2000

By Kanaan Hanna

Abandoned mines pose a serious threat to public health and safety, as well as the environment. When active workings approach old mine workings, miners could encounter significant hazards. Additionally, the presence of mined-out areas or voids underlying residential/commercial properties, transportation, and infrastructure systems can cause subsidence issues ranging from differential settlements and sinkholes to catastrophic collapse. All these features can result in adverse impacts in terms of cost and public safety. Traditionally, mine void detection and related engineering investigations for mine subsidence risk assessment and mitigation have been greatly dependent on systematic drilling and grouting backfill programs. The unknown location and condition of abandoned underground mines represent significant challenges to geologists and engineers in accurately evaluating subsidence hazards and developing appropriate mitigation measures. A comprehensive, multi-phase mine subsidence investigation was conducted at an abandoned western U.S. mine site. The mine operated in an approximately 8-ft (2.4-m) -thick coal seam using room-and-pillar extraction from 1919 to 1922. The mine lies at depths ranging from 50 to 100 ft (15 to 30 m), and it is overlain by critical pipeline and utility corridors. Any future subsidence/ sinkhole that occurs beneath or adjacent to the corridors could pose a significant threat, specifically to the structural integrity of the pipeline corridor. Therefore, the engineering geophysical investigation was initiated to determine the potential subsidence risk. This paper describes a recent success achieved by using integrated engineering geophysics in subsidence risk evaluation. A summary of significant results with emphasis on subsurface characterization, mine workings and voids delineation, modeling analysis, and high risk zones identification and mitigation strategy is presented.

Jan 1, 2011

By Mostafa Sharifzadeh, Ebrahim Ghasemi, Kourosh Shahriar

"The Tabas Central Mine (TCM) is one of the underground coal mines located in the Tabas coal region, in the mid-eastern part of Iran. This mine is the first mechanized coal mine in Iran that uses the room and pillar method. Pillar design is one of the most important issues in underground coal mines, especially in room and pillar mining. In this paper, a new method for coal pillar design in the main panel of TCM is presented. This method is able to estimate the magnitude of the various loads (both development and abutment loads) that pillars might experience throughout the mining process. Also, the method reduces the pillar failure risk. Based on this method, proper pillar sizes in TCM are obtained (11.6 x 11.6 m (38.l x 38.1 ft)).INTRODUCTIONPillar design and stability are two of the most complicated and extensive mining problems related to rock mechanics and ground control subjects. Although these problems have been investigated for a long time, to date only a limited understanding of the subject has been gained. Prior to this, the dimensions of a pillar were largely determined by experience based on trial and error, intuition, or established rules of thumb; any research available tended to be isolated and sporadic. But nowadays, various pillar design formulas have been developed based upon laboratory testing, fullscale pillar testing, and back-analysis of failed and successful case histqries. In 1980, a number of ambitious field studies conducted by the U.S. Bureau of Mines developed the ""classic"" pillar design methodology. It consisted of three steps (Mark, 1999, 2006):1. Estimating the pillar load using tributary area theory2. Estimating the pillar strength using a pillar strength formula3. Calculating the pillar safety factorAlso, Bieniawski (1981) presented a step-by-step method to determine coal pillar dimensions in room and pillar mines. In this method, similar to the classic method, pillar load is estimated by using tributary area theory.Currently, in mqst of the room and pillar mines, remnant pillars in panels are recovered by retreat mining (pillar recovery). Hence, the above mentioned methods are not appropriate for pillar design, because in these methods pillar load is estimated by the tributary area theory, and the effects of abutment loads, which result from retreat mining and the creation of a mined out gob, are ignored. Abutment loads affect the pillars in the adjacent of pillar line and a load greater than what is estimated by tributary area theory is applied on the pillar. So, pillar design without considering the abutment loads leads to pillar failures during retreat mining. Pillar failures continue to be one of the greatest single hazards faced by underground coal miners. Pillar failures are responsible for unsatisfactory conditions, which include the following (Mark et al., 2003):"

Jan 1, 2010

By Zhanjing Yu

Longwall ground behavior in the Illinois Coal Basin was studied in the past (1, 2, 3). Most of the past studies, however, were concentrated on either surface subsidence or underground structural behavior. In this study, both surface and in-mine ground behaviors are considered, which include: 1) stress and deformation characteristics in the chain pillars; 2) roof and floor deformations; 3) surface subsidence characteristics, including time effect; 4) relationship between the surface subsidence and underground strata behavior; and 5) the ultimate hearing capacity underneath the chain pillars. Field measurements and tests were conducted and the data were analyzed using both analytical and statistical methods. The findings in this study can he used by mine operators in the Illinois Coal Basin for longwall ground control planning and design.

Jan 1, 1994

By Claude A. Goode

Large quantities of high grade coal exist in thick seams in the United States. Many of these thick seams are too deep to be surface mined and do not lend themselves readily to underground extraction. To develop the new mining technology required to effectively mine thick seams, the Department of Energy has entered into a Cooperative Agreement with Mid- Continent Resources, Inc. to demonstrate the multilift longwall mining technique in a 28 foot-thick seam at their L.S. Wood No. 3 mine near Redatone, Colorado. The seam will be extracted in two lifts, with a 5-foot natural partition of coal left between the upper and lower lifts. Proper selection of face supports is critical to the success of this project. Specifications were defined for the roof supports, and it was concluded that the supports selected must provide full coverage, yield at the legs, and have a 60-inch push- out cantilever that can be set at any position under full load. A Hemscheidt two-leg shield was judged as the best qualified candidate and was selected for the multi-lift trial.

Jan 1, 1981

By Denise Y. Dixon

The objectives of this study were to (1) document the hydrologic impacts of longwall mining on ground water, (2) identify the factors which affect the extent of dewatering, and (3) develop empirical trends to predict the extent of dewatering and recovery in advance of mining. The study was confined to three mine sites in north-central West Virginia. At each site, available ground water supplies were identified and monitored for dewatering effects and recovery. Mine A, located in Upshur County, West Virginia, has relatively thin overburden (approximately 715-280 feet). At this site domestic water supplies and specially constructed monitoring wells were monitored, continuing with an earlier study done by Cifelli arid Rauch. Most such supplies were completely dewatered over the longwall panel. Some of these wells have shown significant recovery, especially near a stream. Extensive monitoring of two nested piezometer wells revealed that dewatering generally started in advance of undermining in the lowermost monitored overburden zones first and then progressed upwards. Most dewatered wells completed in bedrock have shown no recovery, except. for valley drilled wells located within 100 feet of a Stream. Affected dug wells completed in valley alluvium rend located within 200 feet. of the nearest stream have shown significant recovery. Some wells have partially collapsed following mine subsidence. Mine B, having relatively thick overburden (approximately 585 to 900 feet), is located in Monongalia County, West Virginia. Ground water supply surveys have been conducted there in an attempt to study past dewatering effects. Owners reported Chat several wells were dewatered by longwall mining arid vertical air shafts that preceded longwall mining. Dewatered wells over longwall panels hove shown some recovery within 3 ½ years of mining. Mine C also has relatively thick overburden (approximately 585-900 feet), and is located mostly in Greene County, Pennsylvania. In addition to a survey of domestic water supplies at this site, five specially constructed monitoring wells were tested. The shallow monitoring wells suffered drops in water level due to mining but totally recovered within one day to three weeks after dewatering occurred. However, they did occasionally exhibit partial collapse during mine subsidence. Subsidence fracturing was beneficial in increasing the lateral hydraulic conductivity by a factor of about S to 22 for rock strata located within 124 feet of the surface, indicating enhanced shallow aquifer potential. One deep well suffered both partial dewatering and structural damage, with the state of water recovery bring uncertain. Also, two shallow domestic supplies out of five located over the mine were reportedly dewatered, but this claim could not, be substantiated.

Jan 1, 1988

By Kot F. Unrug

Since the introduction of longwall systems, the prediction of roof behavior and support requirements have become the major issue referring directly to safety as well as productivity. In more recent times, and especially in the USA where longwalls are exclusively equipped with costly hydraulic self- propelled support systems, a decision whether a longwall is applicable in a given condition, and when so, what kind of equipment should be selected, is of primary importance. There are numerous examples where lack of experience, and subsequently wrong selection of supports or winning machines, resulted in considerable losses. It should be emphasized that careful studies of prevailing geological and mining conditions, especially in a new area, are required to assure a successful operation. An evaluation of the conditions can be carried out in different ways utilizing such methods as: - Theoretical approach. applicable when geological conditions comply with the theoretical assumptions. - Empirical relationship which gives satisfactory results where the coefficients could be adequately determined. - Structural geological studies which must be undertaken in all cases, since the frequency of fractures and their orientation have a prevailing influence on roof behavior. - Scale model study on equivalent material for determination of failure conditions in the roof and mechanism of movement (flow) of broken rock matter. Coefficients for empirical formulas can be determined by these types of studies, as can boundary limits for mathematical modeling. - Mathematical modeling, e.g., finite element analysis. - Measurements and observations taken underground during the development period end utilization of experience for previous longwall panels in the area. Usually it is the most practical method where mining and geological conditions are comparable. An application of me or more of the above approaches remains to be a matter of judgement for particular conditions, however, the utilization of a practical experience, when available, is usually the safest way for planning a successful longwall operation.

Jan 1, 1982

By Zhou Ying

Based on the mining condition and roof lithology of the 2-3 coal seam at Gengcun Mine, the simulated materials modeling method was used to study the movement process and characteristics of overburden strata movement and to analyze the movement laws of overburden strata during top coal caving mining. Based on the modeling results, variation of the peak abutment pressure and its effect on the top coal's crushing and caving in the mining process was discussed.

Jan 1, 2001

By Francis S. Kendorski

Rock reinforcement has been in widespread use and generally has been accepted in underground mining and tunneling since the 1950s. The first rock reinforcement technologies employed were mechanical anchors such as split wedges or expansion shells with 5/8-inch-diameter steel bolts. Failures occurred in weak strata which provided poor anchorage or in ground with corrosive waters. Friction rock fixtures consisting of relatively thin-walled tubes have been in use for about 15 to 20 years. While generally performing adequately, longevity problems have developed from corrosion in water bearing ground Longevity of rock reinforcement is much enhanced with grouted bolts. Portland-cement-grouted rock reinforcement has been in use since the mid-1950s, primarily in funneling and other civil engineering underground construction. Tests of decades-old installations have revealed few problems except in ground with aggressive waters. Polyester-resin-grouted rock reinforcement was introduced in the United states to musing in the late 1960s and to tunneling in the early 1970s. Experience from 30 years of resin-grouted bolt installations and field tests have identified longevity problems associated with degradation of steel reinforcing bars, but in generally unusual situations. Improvements continue in resin chemistries, packaging, corrosion protection, grout quantities, and mixing and distribution in the drilled hole to achieve long-term performance. Specific case histories cited with resin- or Portland-cement-grouted rock reinforcement longevity or performance problems, upon close examination, reveal that the causes of the problems were qualify control procedures being inadequate and not in accordance with good practice. Manufacturers' recommendations and engineering specifications, if followed in the field, and with competent inspection and supervision, would have prevented must, if not all, reported longevity or performance difficulties.

Jan 1, 2000

By Nicholas Chlumecky

One of the most dangerous jobs in mining is that of resupporting the roof after a fall has occurred. The resulting cavity may be more than 30 feet high, with relatively unstable sides and roof. It is often impossible to proceed with rehabilitation without exposing men and equipment to unsupported rock. Temporary supports provide margin- ally effective protection because of the lack of available footing. Furthermore, the usual supports in rehabilitated fall locations are not permanent, require frequent maintenance, and fail to eliminate some remaining serious safety hazards. This is typically the case for high cavities where loose rock drops from considerable heights from between roof bolts. Supports made of cribbing, beams and additional cribbing to the high points of the fall in many cases do not provide good protection due to the deterioration and shrinkage of timber. In mines, high cribbing frequently loses contact with the roof and thus provides no protection against rocks peeling off the sides. This is true in spite of the fact that at time of installation the cribbing was wedged tightly to the roof. Therefore, when considering the difficulties which occur with current practices, the objective is to find alternate methods of resupporting the high roof after a fall.

Jan 1, 1981

By Thomas L. Vandergrift

The type and severity of coal mine entry failures are affected by the strength and stiffness properties of the roof, floor, end coal. Knowledge of the mine-wide trends of these properties Is valuable in developing effective ground control plans. Within the context of a larger effort to Improve entry stability In high horizontal stress fields, the U.S. Department of the Interior, Bureau of Mines, has evaluated three portable, on-site test devices to determine their suitability for identifying mine-wide physical property trends. The devices evaluated were the borehole shear tester, the Schmidt harmer, and the point load tester. Despite the lack of standardized data Interpretation procedures, each device provided useful on-site physical property data. The Schmidt homer was preferred for trend identification because of Its speed and simplicity. Schmidt hammer data were collected over a large area of an underground coal mine to compare calculated roof strength trends with a known geologic feature.

Jan 1, 1990

By Rocky Wu

Rock bursts are one of the greatest challenges to ground control in the mining industry. With increasing mining depth and mining scale, there are more and more industry requirements on yielding rock support. Since 2008, Jennmar has been conducting large scale research and development works to develop a technically reliable and cost-effective yielding rock bolt. This paper introduces a new yielding rock support: the Yield-Lok bolt. The bolt is characterized by the designed yielding ability to produce 150?250 mm (6?10 in) of deflection at 8?10 metric tons (MT) (7.9?9.8 t) loads for every 16.4kJ (12,096 ft lb) energy input. The bolt?s performance characteristics are consistent through multiple and varying amplitude of impacts. In this paper, the design criteria of the bolt and the principle of performance are described; the dynamic testing results are discussed; and the features and application of the bolt are presented.

Jan 1, 2011

By Alan Bugden

Goedehoop Colliery produces 8 million tonnes of coal a year, principally from room and pillar mining, and is situated in the Witbank Coalfield in the Republic of South Africa. The mine has a long and successful record of producing export quality coal from the 2,4 and 5 seams at depths ranging from 20 to 100 metres using modem mining equipment. Following a number of fatalities caused by large and unexplained roof falls in roadways and intersections of supported ground, a review of the roof control system at Goedehoop was carried out. This led in turn to a programme of underground measurements and surveys. This included detailed investigation of the roof falls, horizontal stress mapping, stress measurement and short encapsulation pull testing on roofbolts. These investigations led to a number of important conclusions in relation to the state of stress in the ground, the roof failure mechanisms, standard of rootbolt installation and performance of the roofbolt system. As a result of the work Goedehoop Colliery has made a number of substantive changes to the roof control management system at the mine. These include: 1. A recognition of the importance of horizontal stress as the main factor responsible for roof falls. 2 The forward planning of roof support based on known features which cause the stresses to be elevated. 3. The introduction of a more effective roofbolt system, which can be more easily installed to a high standard. 4. A response system based on risk assessment and monitoring roof movement on a routine basis. The paper describes the knowledge acquired, the conclusions drawn, the changes made and progress to date.

Jan 1, 2001