Search Documents

By Jay Keng

During the construction of shaft on the fractured and weak rock strata, the stability of construction plays an important role. This study includes earth stress estimation, support method, and stability analysis. Stresses on the site of three shafts include structural residual stresses, earth pressures, and hydrostatic pressures were determined. The basic method of estimating the support strength is dependent upon the' size of the plastic ring after rock excavation. During the construction of the shaft, geotechnical measurements, physical properties of the rock, and the change after excavation have to be evaluated again. Geology and construction methods need further consideration.

Jan 1, 1988

By Wilfried Ufer

[1. Einführung in die Problematik 1.1 Die Bedeutung des Schildausbaus Seit fast 30 Jahren ist die Konkurrenzsituation auf dem Primärenergiemarkt der Bundesrepublik Deutschland durch einen von Erdöl and Erdgas geführten and insbesondere gegen die Steinkohle gerichteten Verdrängungswettbewerb gekennzeichnet, der den Steinkohlenbergbau zu tiefgreifenden RationalisierungsmaBnahmen zwang. In diesem Zusammenhang kam es Anfang der 70er Jahre zur Einrührung des Schildausbaus, der eine erhebliche Produktivitätssteigerung in den Strebbetrieben zur Folge hatte and damit die Uberlebenschance des Steinkohlenbergbaus in der Bundesrepublik Deutschland enorm verbesserte. Der Grund hierfdr lag darin, daB der Schildausbau im Vergleich zu dem vor ihm eingesetzten Rahmen- and Einzelstempelausbau eine wesentlich hdöhere Ausbauleistung erbrachte, weil er sich weit weniger empfindlich gegen Hangendausbruche and aus dem Alten Mann hereinbdschende Bruchberge erwies. So erklärt sich auch die stürmische Entwicklung and die schnelle Verbreitung des Schildausbaus. Bereits 1975 stammte rd. 50 % der Fdrderung aus Schildstreben, 1990 waren es fiber 75 % and heute sind es fiber 90 %. 1.2 Die Staubentstehung beim Schildausbau Die Erfolge des Schildausbaus sind unbestritten. Jedoch nahmen :nit seiner Einführung die Probleme der Staubentstehung and Staubbekämpfung im Vergleich zum Ein zelstempel- and Rahmenausbau erheblich zu. MaBgebend dafür sind hauptsächlich folgende Gründe: - Abbau von dozen nit gebrächen, weichen Hangendschichten, die erst durch Schildausbau abbaubar wurden, - Zerkleinerung des auf den breiten Kappen aufliegenden Bergematerials infolge der höheren Ausbaustiltzkrafte des Schildausbaus, Zermahlen der sick in die Spaltabdichtungen hineinarbeitenden Bergestückchen, - Erhöhung der Wettergeschwindigkeit infolge der durch die Baufarm des Schildausbaus bedingter. Verkleinerung des Strebquerschnitts verbunden mit der Aufwirbelung and Aussichtung von Staub, - Aufwirbelung von bereits abgelagertem Staub im Bruchraum beim Hereinbrechen der Dachschichten. Die genannten Gründe treten zumeist nicht in jedem Abbaubetrieb gleichzeitig auf. Sie rind vielmehr u.a. abhängig vom Ausbautyp, von den Gebirgsverhältnissen and von der Abbaugeschwindigkeit. Trotzdem ergeben sich beim Vorrücken des Ausbaus in der Regel hohe Staubkonzentrationen, die deswegen besonders kritisch sind, weil es sich um quarzhaltigen Feinstaub handelt, der besonders gesundheitsschädlich ist. Die Hauptzutrittsstelien]

Jan 1, 1984

By Binchuan Zhang

Based on the theory of fracture mechanics and blasting, computer simulations were performed to predict the original rock mass structure and those rock mass structures damaged at different levels uing the properties of joints and fratures obtained in the field.

Jan 1, 2001

By S. Mehrdad Heidari

The concentrator plant is located near a very high (105m), large (- 500m) and steep (a, > 45' ) wall. Geologically, the wall was composed of very complicated formations and broad range of soils and rocks type in which a variety of local typical failures models have been occurred on different soil and rocks formations. The construction of concentrator plant structure and other activities have been overshadowed by these local failures. Safety and risk of huge failures were serious concern. For distinguishing the wall conditions a broad campaign of slope stability investigation with detailed geotechnical drilling on berms of wall have been done and the structure of slope was fully identified and further Lab tests and slope simulation models done. Slope stability of the wall was analyzed and the effects of instability factors were described in short term (for construction phase) and long term (for production phase).The results indicated, if a well-appointed drainage system is implemented, the overall stability of the wall in short term will not cause any particular problem but about long term stability, the wall must be supported by rock bolting, consolidation grouting, shotcrete reinforced with fibers. The results have been confirmed by passing one year after this investigation.

Jan 1, 2005

By Takashi Sasaoka

EGAT Mae Moh Lignite Mine in Thailand produces about 16 million tons of lignite annually from open-cut mining. The coal is used to generate 2,400 MW of electricity. In the near future, however, the coal must be extracted from underground at 400? 500 m (1,312?1,640 ft) deep from the surface. The problem is the thickness of the coal seams. There are two coal seams that are about 25 m (82 ft) thick with 20?25 m (66?82 ft) of interburden between them. Up to now, many mining systems for thick coal seams have been used and improved in the world. However, where the thickness of coal seams is beyond the limitation of the current mining technology and system, an applicable mining system has to be introduced, considering influencing factors such as caving and subsidence. In order to investigate thick seam mining systems and propose a new mining system in ultra-thick coal seams in Thailand, a joint research group was established by Japanese and Thai researchers and mining engineers in early2009. This paper describes underground mining systems for thick coal seams and proposes an innovative underground mining system for thick coal seam, ?eco-friendly underground mining system?, considering geological, geotechnical, and environmental conditions in this mine. This paper discusses its applicability to this mine by means of numerical analysis from the geotechnical point of view.

Jan 1, 2011

By Douglas Scott

Highly stressed rock in stopes continues to be a primary safety risk for miners in underground mines because it can result in failures of ground that lead to both injuries and death. Spokane Research Laboratory personnel investigated electromagnetic (EM) emissions in a deep underground mine in an effort to determine if these emissions could be used as indicators of impending catastrophic ground failure. Results suggest that (1) there is no increase in the number of EM emissions prior to recorded seismic activity, (2) some EM signals are generated during blasting, (3) interference from mine electrical sources mask seismic-generated EM signals, (4) EM emissions do not give enough warning (compared to seismic monitoring) to permit miners to leave a stope, (5) the distance an EM signal can travel in the rock is between 17.7 and 39.6 m (58 and 130 ft), and (6) current data acquisition systems do not differentiate between EM signals generated from seismic activity and random mine electrical noise. These results preclude monitoring EM emissions as precursors of impending catastrophic ground failure.

Jan 1, 2004

By John Feddock

This study deals with underground mines and ground control and the prediction of seats strength characteristics based upon ultrasonic logging. Exploration drill holes, both rotary and core holes are used for proving coal reserves and determining mining parameters. Drill hole cores can be subjected to geologic study and geotechnical evaluation. In addition, the use of geophysical logging techniques is well established in determining certain strata characteristics and ground parameters. Since the characterization of the rock mass in mines remains insufficient in most cases, the idea of possibly characterizing the strength parameters without expensive core retrieval and laboratory testing is very attractive. The elastic properties of the rock can be deduced from measurement of the sonic velocity if the density is known. Through the use of in-hole geophysical density logging combined with an ultrasonic logging tool, the estimation of strata properties is possible. An investigation was conducted at two Indiana underground coal mines using geologic logging, geophysical logging, ultrasonic logging and laboratory strength testing to establish the strength properties of the roof rock. A specialized ultrasonic logging tool with one transmitter and two receivers enables nearly continuous readings along the length of the hole. The results of correlating portions of the data are presented. It is anticipated that the ultrasonic logging will be a supplemental tool for extending laterally the strata characteristics obtained from the existing program to surrounding areas. This may be obtained from the relatively inexpensive logging data obtained by ultrasonic logging.

Jan 1, 2003

By M. Karmis

mining factors and representative ground movement parameters. Based on this analysis, the previously developed prediction methods were modified and tested for their applicability in the Appalachian coalfield. Finally, in order to facilitate the implementation of the prediction methods, as well as the data processing of the monitoring program, a number of computer software were developed and will be discussed in the paper. Surface deformations above underground mines and their prediction and control have been the topics of an extensive research effort by Virginia Polytechnic Institute and State University over the past few years. During the initial stages of this research, a number of case studies were collected from the literature, the mining industry and various government and state agencies and, based on the analysis of this information, appropriate prediction methods were proposed (Goodman, 1980; Webb, 1982; Hasenfus, 1984; Karmis et al., 1984). Although the prediction methods were based on sound concepts, it became evident that their accuracy and implementation were a reflection of the size and quality of the collected case studies. In this respect, the data bank was rather insufficient and posed certain questions regarding the development of subsidence information due to inappropriate length and spacing of monuments used in subsidence surveys, density and accuracy of such surveys, lack of monitoring horizontal movements, etc. In an effort to alleviate these problems, a comprehensive monitoring program was initiated in the coal mines of southwest Virginia, which included: - Two longwall and five room and pillar mines. - In total, seven longwall and sixteen room and pillar panels. - Monitoring lines in excess of 35,000 feet. - Vertical as well as horizontal measurements. A high accuracy digital computer tacheometer was used in all surveys and the type and spacing of all monuments were in accordance with well accepted guidelines. The data from this monitoring program completed the initially collected data bank and, thus, enabled a much needed statistical analysis between

Jan 1, 1987

By S. S. Peng

In recent years many roof falls have been conveniently attributed to the adverse existence of a high horizontal stress. The normal practice of not conducting a follow-up study in a roof fall investigation usually leads to a wrong conclusion. This paper describes two cases of massive oriented roof falls in two separate room and pillar mines. The investigation in each case involved the analysis of past history and current conditions from which remedial measures were recommended and implemented. A follow-up period of up to three years was performed to evaluate the effectiveness of the recommended remedial measures. In both cases, high horizontal stress was proven positively not the cause, contrary to the original conviction of mine management Rather, a weak immediate roof was the basic cause Under a weak immediate roof, a proper roof bolting plan and adequate entry width and intersection span must be strictly observed.

Jan 1, 1999

By Thomas Barczak

A new generation of hydraulic mine support prestressing devices has been developed. These thin-walled steel shells are machine-welded and can be inflated with water or any liquid to provide prestressing for a wide variety of roof support products ranging from Can supports to props and cable bolts. With an expansion capability of several inches, depending on the geometry and size of the unit, they can also establish roof contact eliminating the need for wooden wedges or crib blocks that are commonly employed with several standing roof support products. Capable of withstanding pressures from 1,000 to 6,000 psi, these cells are able to transfer roof loading into the support structure without rupturing. A recent development has been the addition of an inexpensive yield valve that provides control of the maximum pressure and load development on the support. This paper examines the performance capabilities of these inflatable prestressing units and the impact they have on the performance of various support systems, including an evaluation of the overall stiffness of the support system and the load control during yielding of the prestressing unit. Recommendations are made regarding the design requirements of the prestressing unit to optimize the support performance. A summary of mine applications using this technology is provided with general comments regarding their impact on ground control.

Jan 1, 2004

By Yingda Zhai

The range of interburden thickness between coal seams in Datong Mining District of China is large. From mining operation point of view, the closer is between the two seams, the greater is the impact from the upper seam when the lower seam is mined. This impact is most notable when the two seams are ultra-close. In this paper the definition of ultra-close seams and its practical method of determination are presented. Based on the difference in strata thickness in the interburden and the concept of "yield depth ratio" which is defined as the yield zone depth in the interburden to the total thickness of interburden, the roofs of the ultra-close multiple seams in the Datong District of China were divided into 3 types: (1) false roof or rock partings in coal seam. This type of roof does not require special handling except mining them simultaneously as one single seam. The roof thickness is slightly less than 0.5 m; (2) completely broken roof. In this type of roof, the yield depth ratio is larger than (or equal to) 1. When the roof thickness is larger than 0.5 m but less than 2.0 m, the yield depth ratio must be smaller than 1; and (3) fractured roof. In this type of roof, the yield depth ratio is less than 1 while the roof thickness is larger than 2.0 m. In retreat longwall mining, if the gateroads of the lower seam are located under the gob of upper seam, roof bolting can be used in the 3rd type of roof. But if the 2nd type roof exists, powered supports must be used.

Jan 1, 2005

By Kewal K. Kohli, Stefanie Self

"Three cases of surface subsidence investigated over abandoned coal mines after flooding in one case and dcwatering in two cases are presented in this paper. Mining was conducted by the room and- pillar method at all the mines leaving stable pillars. This paper will discuss the background chain of events and the likely causes of the pillar failure resulting in surface subsidence.CASE NO.1BackgroundThe Pittsburgh scam was mined in 1960 by the room-and- pillar method, leaving pillars (Figure I) through Mine A. located in Monongalia County. West Virginia.The mining height in U1is area was 1.83 m (6 ft) with an average mining depth of 140 m (460 ft). The mining recovery was 62% and the safety factor of the pillars was calculated at 1.15 using the Bieniawski ( 1984) fom1ula. For stable pillar design. a 1.5 safety factor is recommended. A 1.15 safety factor is considered marginal. Pumping continued after the mine was shut down in 1960 to prevent water seeping into an adjoining mine owned by the same company. The pumping ceased on December 12. 2003, and the mine was allowed to flood. The water level rose about 17 m (55 ft) by August 3 1, 2004, based on observations in a nearby borehole. On September 3, 2004 surface subsidence occurred above this area causing damage 10 a residence (Figure 2).Summary of InvestigationThe floor of the Pittsburgh coal scam played a strong role in the pillar failure. In this area, the immediate floor of the Pittsburgh seam consists of about two feet of fireclay. Extensive damage to the surface house was an indication that a major collapse below the surface had occurred. The pillars supporting the overlying strata were evaluated to find the cause of their failure. The pillars in the Pittsburgh seam (sec Figure I) had a marginal safety factor of 1.15 before flooding and were stable for 26 years. Once the mine was flooded the water level in the Pittsburgh seam rose by 17 m (55 ft). Shortly thereafter the fireclay in the floor weakened, resulting in several pillars punching into the floor unevenly making the immediate roof unstable. The overburden strata supported by these pillars also subsided do"" n into the mine, causing damage to several house on the surface."

Jan 1, 2010

By Murali M. Gadde

Perimeter mining is a special form of very productive partial extraction method practiced at some mines in the United States. In the Illinois Basin mines where all major coal seams have weak underclay in the immediate floor, experience shows that any long-term ground control issues will arise due to floor failures rather than instability of the coal pillar itself. While there is a significant amount of work done on floor stability associated with regular pillars, no work has been done so far on the stability of perimeter pillars. This paper reports the results of a comprehensive study that was conducted for the first time on floor stability during perimeter mining in the Illinois Basin mines. A special plate template, which mimicked a common perimeter pillar configuration was created to conduct in-situ bearing capacity tests at five mines in three states of the Basin. Additionally, because of the complex shape of pillars created in perimeter mining that defies any closed-form solution, floor bearing capacity was studied using three-dimensional nonlinear numerical modeling. Based on these in-situ and numerical studies, some guidelines are provided for perimeter pillar stability analysis.

Jan 1, 2009

By Paul Singh

Blasting is an integral part of mining activity and is an inherently destructive process. The quality of the rock mass in which an excavation is being driven has a strong influence on the level of dynamic forces to which the rock can be subjected and sustain damage. Though each specific rock mass occurrence is unique, yet there are common rock mass features which influence the outcome of controlled blasting in a similar way. A field study was conducted which involved assessment of blast damage at several operating mines and blasting of small scale models. The effects of block size and strength, joint parameters, ground water, weathering of rocks and rock mass rating on the results of controlled blasting have been investigated and discussed in this study. The influence of number and thickness of weak layers on overbreak control has been discussed in the light of practical data. Critical particle velocity ranges for damage to rock masses with different qualities have been outlined. An approach for the judicious design of perimeter hole pattern and charge concentration has been proposed.

Jan 1, 2007

By Karsten Zimmermann

The paper presents a study on the influence of face retreat rate in longwall coal mining on surface subsidence. It shows possibilities to influence dynamic ground movement by using a specific and controlled winning regime. For this, a dynamic stochastic prediction model used by DMT in Germany will be proved and adjusted on the specific character of geology in the Northern Appalachian coal field. Occurring ground movements such as inclination, curvature and deformation can be analyzed under static and dynamic points of view. It is theoretically shown that the face retreat rate has only a small influence on the static deformation values, but directly affects rate and acceleration of subsidence and deformation processes. The study shows that because of low mining depth and high mined thickness, static deformation values have the largest impact to surface objects. This implies that high face retreat rates don?t affect the impact on surface objects.

Jan 1, 2007

By D. J. Maconochie

This paper describes the investigations and results of monitoring of deformations of houses located within the area of influence of a pillar collapse over the Westfalen No. 3 coal mine near Ipswich, Queensland. The subsidence resulted in minor subsidence of at least 18 modern houses and serious damage to 4 others. The history of the events and the measures taken to deal with the physical problems arising are described. The investigations and results are described and related to the mining methods and geology. The stability of coal pillars up to 9.6 m high was considered and computer modelling undertaken to relate surface subsidence to estimates of the extent of pillar failure. Assessments were made of the likely extent of subsidence during the incident. Measurements of distortion and tilt were obtained as the ground slowly subsided and criteria established to determine when the structures were deemed to be unsafe. Detailed surveys of houses affected or anticipated to become affected were also undertaken. Four houses were condemned and subsequently demolished as a result of excessive tilt. The methods of assessment are described and the implications of the results related to the various house designs.

Jan 1, 1992

By Chris T. Franke

The Waste Isolation Pilot Plant is a deep underground facility mined in bedded salt interspersed with persistent clay inter- beds. The clay seams delineate beams of salt above and below the excavations which strongly influence excavation performance. This paper reviews available rock mechanics information relevant to improving drift stability by removing the roof beam. Conceptual deformation mechanisms, relevant field data, and numerical analyses were used to investigate the effects of mining the roof of the excavations along a clay seam. Finally, a case study that applies the results of this investigation is presented.

Jan 1, 1997

By Reha Ozel

The stability in longwall faces depends on the interaction beman the roof strata, face supports and floor strata. The load distribution on the other hand, depends upon relative stiffness of the three supporting elements namely, the coal face, support and gob. Therefore, in defining support requirements, it is particularly important to analyze the strata loading, the face convergence and the controlling mechanism provided by supports. The controlling mechanism however, depends on the type and characteristics of supports used in long- wall faces. The design guidelines presented in this paper have bean developed based on a number of strata control oriented projects carried out in Turkey, load and convergence measurements carried out in 10 longwall faces, in Zonguldak Coal Region, and procedures given in literature. Evaluation of load and convergence measurements, and analyses of face supports were carried out by means of a computer program, called L0NGWAI.L-MEW, developed by the authors. The output of the design analyses include the following: (1) estimation of support capacity for roof supports namely; individual hydraulic props, chock-type power supports and various types of shield supports, and (2) analysis of loading conditions and response of shield support components in terms of stability and structural integrity.

Jan 1, 1990

By Ross Seedsman

There are many models for how roof bolts behave, one of which is prevention of shear along bedding. The basis of this model is that a roof beam will not delaminate if bedding parallel shear can be prevented. A key point in such a model is that bedding discontinuities are present naturally in the roof and that mining induced stresses do not generate new surfaces. The presence of these discontinuities means that the rock mass must be modelled as a transversely isotropic material if continuum codes are used. A limit-equilibrium type design method for specifying roof bolts is being developed using voussoir beam and excess shear force concepts. The method incorporates much of what operators know intrinsically about roof reinforcement, and allows mining engineers to focus on the key uncertainty - the frequency and location of bedding surfaces in the immediate roof. Areas where more research is required are highlighted.

Jan 1, 2000

By David Bartsch

The Ohio Valley Coal Company (Ohio Valley) has operated the Powhatan No. 6 Mine in Belmont County, Ohio since 1972. Ohio University owns a 455-acre research farm over a portion of the Ohio Valley reserve containing 51 acres of old-growth forest known as Dysart Woods. In 1988, when Ohio Valley applied for a new mining area for its first longwall located several miles away from Dysart Woods, Ohio University claimed that mining at that distance would lower the regional water table and kill the old trees. In response, Ohio Valley began to study potential impacts from longwall mining on hydrology, soil moisture, and tree growth. Early studies examined the impacts of longwall mining on hydrology, soil moisture, and tree growth directly over mined areas compared to woodlots that were not undermined. A subsequent study examined tree-ring growth for a five-year period before and after longwall mining for several woodlots, some directly over panels and others at distances of up to 2000 ft away. No significant differences in growth rate associated with longwall mining were observed. New research was begun that compared longwall-mining impacts on groundwater hydrology, available soil moisture, and tree growth in two stands of mature trees located near Dysart Woods in order to confirm the earlier results. Using a test technique known as "Before-and-After-Controlled-Impact-Pairs," data was collected from one woodlot (test) that was undermined and from another (control) that was not undermined. Data collection began several years prior to longwall mining and has continued for several years after mining. The data for the test site shows that although the shallow and deep groundwater levels were affected by longwall mining, the soil moisture, vigor rating, or the growth rate of trees did not decline significantly compared to the control site where there were hydrologic impacts. The study shows that there are no known significant impacts to trees from longwall mining. The results of these studies were used by Ohio Valley to obtain State approval to longwall to within 300 ft of Dysart Woods

Jan 1, 2005