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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

Virtually all mineable Appalachian coal seams exist in a multi-seam environment. This makes it inevitable that most seams will eventually experience interaction induced ground control and mining problems. Indeed, it has been estimated that every working face will experience interaction effects from previous or current workings at least once during its lifetime (1), and that these problems are considerably exaggerated when seams are in close proximity -- a distance of less than 110 feet. The continued increase in multi-seam problems has resulted in considerable research activities over many years (2,3,4,1). Theoretical analysis, numerical and physical model studies, statistical and empirical analysis of numerous interaction related field data have been applied to multi-seam mining situations and have identified many useful trends and design criteria (4,5,6,7). To fully utilize research results and transfer multi-seam mining technology to field engineers, a design model -- USEAM was constructed (8). This model, designed for close seam under-mining situations, was computerized to facilitate utilization. In the current research, a new computer program "MSEAM" was developed to produce a model for both under- and overmining close seam situations. It is hoped that both of these software packages will aid field engineers in using important interactive design criteria to gain a better understanding of interaction mechanisms. Through advance planning with these programs, detrimental interaction may be avoided and minimized, and occasionally a design can be selected which will allow interaction effects to be utilized to the benefit of mining operations.

Jan 1, 1987

By Jeffrey Johnson

To measure the loading behavior of friction bolts, researchers at the Spokane Research Laboratory of the National Institute for Occupational Safety and Health (NIOSH) installed strain gauges on the interior of friction bolts and developed a battery-powered miniature data acquisition system (MIDAS) that fits inside the hollow portion of the friction bolt. The advantages of this system are that it is protected from face blasts and eliminates the need for external wiring. Laboratory pull-out tests showed that friction bolts installed in a concrete block with resin were loaded to about 1.8 tons/ft of bolt length; bolts installed without resin were loaded to 1.3 tons/ft. Three strain-gauged friction bolts were installed at Hecla Mining Company's Gold Hunter Mine, Mullan, ID, in the wall or rib of a mechanized cut-and-fill stope. The object of these tests was to establish an installation procedure for the bolt-and¬MIDAS combination and to evaluate performance. The stope was advanced in three 15-ft increments and strains induced in the rock bolts by stress changes in the rock were recorded every 30 minutes. The MIDAS proved to be rugged enough to withstand the shock and vibration from nearby (5 ft) face blasting. Data from MIDAS showed that the friction bolt installed with resin was the most sensitive to each face advance. It showed a steady increase in loading to a maximum value of 1000 microstrain. The friction bolt installed without resin showed stick-slip behavior with loads to a maximum of 400 microstrain before the stope was completed.

Jan 1, 2003

By Ismet Canbulat, John Naylor, Jason Emery, Peter Craig, Andy Sykes

"Longwall mining is by far the most common method of underground coal extraction in Australia. The industry trends and expectations are placing increasing emphasis on the reliability and productivity of these operations. The longwalls are becoming wider and longer while retreat rates are continuously increasing due to significant improvements achieved in longwall equipment reliability and automation. This increased longwall productivity is placing significant emphasis on the reliability of longwall panel development.Although there have been significant improvements in the reliability of continuous miners and hydraulic drill rigs, the traditional resin encapsulated bolt installation is still the principal method used in all major coal-producing countries around the world. Anglo American realised an opportunity existed to introduce an alternative roof bolt installation technique called “spin to stall” in Australia. Spin to stall was first introduced in Anglo American Coal in South Africa where it has been successfully used for over a decade, though implementation of South African spin to stall resin in Australia has proven to be near impossible due to a significant difference in geotechnical conditions, mining method, and, subsequently, roof bolting equipment. Therefore, a new spin to stall development project was initiated between Anglo American Coal and Jennmar Australia (SPIN2STALL®). This paper summarises the journey of this project, the results, and the successful implementation of spin to stall achieved at Grasstree Mine.INTRODUCTIONThe Anglo American Coal business unit operates Grasstree and Moranbah North underground longwall mines in the Bowen Basin of Central Queensland, with a third longwall mine, Grosvenor, currently being developed, and two more (Aquila and Moranbah South) in the project pipeline. The vision for Anglo American is to achieve “Zero Harm” through the effective management of safety at all operations, while for the coal business unit, at the same time to achieve industry-leading operational performance. Currently, both Grasstree and Moranbah North longwalls are operating at industry best practice rates. This is placing increased pressure on the development process to allow such high productivity levels to be sustainable."

Jan 1, 2015

By Stephen R. Iverson, Jeffrey C. Johnson, Donovan J. Benton, Michael J. Raffaldi, Lewis A. Martin

"The NIOSH ground control safety research program at Spokane, Washington, is exploring applications of photogrammetry to rock mass and support monitoring. This paper describes two ways photogrammetric techniques are being used. First, photogrammetric data of laboratory testing is being used to correlate energy input and support deformation. This information can be used to infer remaining support toughness after ground deformation events. This technique is also demonstrated in a field application. Second, field photogrammetric data is compared to crackmeter data from a deep underground mine. Accuracies were found to average 8 mm, but have produced results within 0.2 mm of true displacement, as measured by crackmeters. Application of these techniques consists of monitoring overall fault activity by monitoring multiple points around the crackmeter. A case study is provided in which a crackmeter is clearly shown to have provided insufficient information regarding overall fault ground deformation. Photogrammetry is proving to be a useful ground monitoring tool due to its unobtrusiveness and ease of use.INTRODUCTIONNIOSH Mine Safety ResearchPhotogrammetry systems have been implemented by the National Institute for Occupational Safety and Health (NIOSH) as part of its ground control research to improve mine safety. Conventional monitoring of ground movement has typically focused on movement of a few discrete points that are marked or anchored to instruments. Loss of a designated point or anchor, or the ability to identify a stable point in an unstable area, have often frustrated monitoring efforts. NIOSH researchers are using photogrammetry to conduct full-field measurements of rock surfaces underground. Periodic measurements of the entire surface of a ramp allow patterns of displacement to be observed. Full-field measurements provide much more insight into ground behavior than point measurements.BackgroundPrevious work by Benton, et al. (2014) discussed laboratory calibration and verification testing of two photogrammetry systems being used by NIOSH researchers. Both systems utilize stereoscopic image pairing techniques for photogrammetric reconstruction. This paper discusses how a laboratory system was used to conduct volumetric analyses of testing of shotcrete panels with varying types of reinforcement. The laboratory system was found to be accurate to within 2 mm. Additionally, a field photogrammetry system was found to produce linear measurements within 1 mm of known lengths in laboratory conditions. This system is currently being used at a deep underground mine to observe ground support conditions and deformations that have occurred. This paper discusses comparison of preliminary volumetric measurements of rib deformation to laboratory tests, as well as comparison of the field system against a crackmeter installed across a fault surface where it intersects the ramp."

Jan 1, 2015

By Winton Gale

"Rock and coal fractures and micro seismic vibration are common occurrences during development mining. It is very uncommon for coal and rock to be propelled into the roadway during normal mining operations. However, such occurrences do occur and appear to require significantly more energy than is available from strain energy release during coal cutting. The sources of energy, which can contribute to the propulsion of coal from the face or ribs, are typically strain energy from the surrounding ground, seismic energy from a rapid rupture of the ground in the vicinity, or rapid expansion of gas from within the burst source area.The aim of this paper is to briefly review the bursts that could be related to strain energy or seismic energy. However, the greatest emphasis is placed on the effect that gas within the coal could play in moderate to gassy mines.It has been found that the bursts related to the expansion of gas can occur in coal and stone. The volume of gas involved in coal bursts is typically lower than in gas outbursts; however, the process is generally similar.INTRODUCTIONA coal burst is defined as a rapid expulsion of coal (and potentially gas) from the boundary of the roadway. The volume of a burst can be variable, but volumes above 10-50m3 are noted and cause significant disruption to operations.Rock and coal fracturing is common about roadways, particularly under the influence of elevated stresses, either tectonic or related to mining abutment stress. Shear fracture is very common; however, it is very uncommon that the coal is propelled from the face or ribs as a result of fracture of the material. The nature of rock fracture about roadways under elevated stress is presented in Figure 1.A burst requires energy to propel the coal or rock from the rib or face of the roadway. The depth of material impacted may vary from 0.5m to greater than 3m inside the roadway boundary. The strength of the ground in this zone is variable depending on the nature of the coal seam (or surrounding material). Typically, this material has significant residual strength as confinement increases into the ribside.The energy required to propel this material is typically in addition to that which is associated with normal fracturing about the roadway."

Jan 1, 2018

By Jonathan Duncan, Tim Burgess, William Kendall, Jens Lange

"Steel wire mesh is the accepted standard for roof and rib skin control at most coal mines in the United States. Wire mesh is delivered to the mine in bundles that are heavy and awkward to handle. The large size, stiffness, and weight of the wire mesh can present a safety hazard in transporting underground and storing on the roof bolter. Installing wire mesh on the roof and ribs with the roof bolter can be a challenge as well.Synthetic mesh is lighter than wire mesh and can be folded and rolled into a safe, manageable size. A single synthetic mesh roll large enough to cover the roof and ribs in a deep cut can be safely handled by two men. The roof bolter is designed to carry and dispense the roll as it advances and installs primary roof support, resulting in a single pass roof and rib ground control solution. This paper focuses on the design and implementation of the roof bolter synthetic mesh handling system developed by J. H. Fletcher & Co., Huesker, Inc., and Oxbow Mining.INTRODUCTIONRoof and rib skin control in some coal mines has been an issue since mining first began. Roof and rib skin problems vary from mine to mine. The type of roof rock material exposed after mining; the mine atmosphere; and stresses from depth of cover, over mining, and/or undermining are some of the variables that can contribute to roof skin problems from mine to mine.Potential roof and rib skin problems can be time dependent as well. Some mines have roof skin rock, sometimes called draw rock, that falls when drilling the hole for the roof bolt as the initial roof support is installed. Some roof skins are more stable but can fail over time. The failure of roof skin can even be between properly installed roof bolts with roof plates (Figure 1).Mines have most commonly used a wire mesh that comes in individual panels anywhere from 5 ft x 5 ft (1.5 m x 1.5 m) all the way up to 5 ft x 16 ft (1.5 m x 4.9 m) in size. They are typically constructed of 8- or 9-gauge wire welded on a 4 in (102 mm) square pattern. A 5 ft x 16 ft (1.5 m x 4.9 m) panel weighs approximately 35 lbs (16 kg). These steel wire mesh panels can make it a difficult and sometimes dangerous task to deliver them from the surface to the roof bolter and then store on the machine. Manipulating the mesh panels from the storage area on the machine to the final installation position on the roof or rib can also be a daunting task (Figure 2)."

Jan 1, 2010

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

By Jaco J. van Vuuren

Modikwa Platinum Mine, in the Eastern Bushveld of South Africa's Limpopo Province, is a new operation employing a hybrid mining method where mechanised methods are used for the main developments and the narrow, 60cm reef is conventionally stoped using a down-dip conventional mining method. Throughout the mine, the hanging wall immediately above the reef comprises 3 jointed and laminated layers of varying thickness, commonly known as the triplets, below a non-cohesive leuconorite parting plane. At North shaft, using pre-stressed standing support and mechanically anchored rockbolts, it was found difficult and hazardous to hold all three triplets in the hanging wall, however bringing them down caused a significant increase in dilution and therefore cost of mining. A novel solution was conceived whereby two of the triplets are kept up using short, stiff resin anchored rockbolts installed systematically within 0.5 m of the face. This resulted in both safety and productivity benefits. The rockbolts create a stable and safe hanging wall and allow the mine to extract UG2 reef more economically. New drilling equipment, developed locally from available drilling technology, can be operated from a safe position, and in situ tests and measurements are made to confirm effective support. The technology and underlying concepts were successfully tested in a trial stope prior to rolling out the new support system across all the stopes at North Shaft. This has involved an extensive training programme to ensure that the rockbolt system is installed correctly and that the conditions are appropriate for this technology. The paper describes the motivation behind the project, the underlying technology and its application to Modikwa, and the benefits now being realised.

Jan 1, 2004

By Tobias U. Papst

The German Ruhrgebiet is slowly transitioning into a post-mining state. It has been subjected to industrial-grade hard coal mining operations for more than 150 years. Due to a political decision, German hard coal mining will come to an end in 2018. By then the surface will have subsided up to 20 meters. After all mining activities in the area have ended, there will be no need to maintain the current mine water level. Accordingly, the company operating the last remaining coal mines has decided to let the water level rise to an as yet undetermined level. Alongside other issues that may be caused by rising groundwater levels, the protection of the area?s drinking water supply is of utmost importance. This notion is also represented by European and German law. The primary intent of the applicable laws is to protect the health of the citizenship. This means protecting ground water that may be used by humans from being contaminated by the mine water. This paper outlines the consequences of European and German legislature on mining aftercare using the example of one of Europe?s largest agglomerations.

Jan 1, 2014

By Christopher Mark

"Many problems in rock mechanics are limited by our imperfect knowledge of the material properties and failure mechanics of rock masses. Mining problems are somewhat unique, however, in that plenty of real world experience is generally available and can be turned into valuable experimental data. Every pillar that is developed, or stope that is mined, represents a full-scale test of a rock mechanics design. By harvesting these data, and then using the appropriate statistical techniques to interpret them, mining engineers have developed powerful design techniques that are widely used around the world. Successful empirical methods are readily accepted because they are simple, transparent, practical, and firmly tethered to reality.The author has been intimately associated with empirical design for his entire career. But where his past papers have described the application of individual techniques to specific problems, the focus of this paper is the process used to develop a successful empirical method. A six-stage process is described:1. Identification of the problem, and of the end users of the final product2. Development of a conceptual rock mechanics model, and identification of the key parameters in that model3. Identification of measures for each of the key parameters, and the development of new measures (such as rating scales) where necessary4. Data sources and data collection5. Statistical analysis6. Packaging of the final productEach of these stages has its own potential rewards and pitfalls, which will be illustrated by incidents from the author’s own experience. The ultimate goal of this paper is to provide a new and deeper appreciation for empirical techniques, as well as some guidelines and opportunities for future developers."

Jan 1, 2015

By Liane J. Terrill

A 9O) ft (275 meter) section of a highly fractured beam of halite was mined from the roof of a supported thirteen year old drift at the Waste Isolation Pilot Plant (WIPP). The operation was conducted with a continuous miner and allowed the unique opportunity to collect spatial information on roof beam geology and to observe ground support conditions during the mining advance. Photographs and fracture maps of the mining face document the progress of the operation and the deteriorated condition of the strata. This case study details the drift's excavation and support sequences. the geomechanical response, and the conditions found in the exposed roof beam.

Jan 1, 1997

By Syd Peng

"As the International Conference on Ground Control in Mining (ICGCM) enters its 35th year in 2015, it is time to look back and identify the areas that need to be emphasized and to look forward to see what areas need to be researched in the future. In the past three decades, ground control has made a tremendous advancement, and many case studies published in the 36 volumes of proceedings have demonstrated its important role in the daily mining operations. However, there is still plenty of room for improvements. This paper discusses the research needs in 12 subject areas, including mine geology, rock property, zones of disturbance in overburden, computer modeling, underground stress measurements, research method, roof bolting, coal pillars, failures, subsidence, shield supports, and coal bumps.INTRODUCTIONThe International Conference on Ground Control in Mining (ICGCM) was founded in 1981. Since then, 1,546 papers have been published in the 36 conference proceedings, including the three surface subsidence workshops held in the 1981, 1986, and 1992. All types of topical areas regarding mining, from geotechnical core loggings in the exploration phase through backfilling after mining to finally spoil piles stability on the surface, have been addressed. A review of these papers, and other related literature as well, indicate that ground control has developed to become an inseparable part of mine design and a problem-solving tool for safe production.After 34 years, it is time to look back and identify the areas that need to be emphasized and to look forward to see what areas need to be researched in the future. There is no doubt that the conference series has achieved the goal for which it was originally designed: to provide an annual forum for the exchange of information among the researchers, government regulators, equipment manufacturers, consultants, service providers, and—above all—mine operators. There have been many papers addressing the application of ground control techniques for successful mine design and safe production, and, without these papers, many projects would have failed. In fact, the conference emphasis on application types of papers may have steered too far toward the application side. A review of the conference papers shows that papers have been leaning mostly toward the applied side, leaving most, if not all, fundamental issues behind in nearly every topical area. This paper addresses research needs in 12 topical areas: mine geology, rock property, zones of disturbance in overburden, computer modeling, underground stress measurements, research method, roof bolting, coal pillars, failures, subsidence, shield supports, and coal bumps."

Jan 1, 2015

By Winton J. Gale

The subsidence over a longwall panel at Tahmoor Mine in the Southern Coalfield of NSW, Australia, was found to be approximately twice the size it had been in previous measurements. An investigation into the potential causes was conducted using computer modeling together with hydrological characterization and detailed geotechnical characterization of the strata. The abnormal subsidence was found to be consistent with localized weathering of joint and bedding planes above a depressed water table adjacent to an incised gorge. The study showed that other factors such as variation in stress field, joint zones, variation in rock strength and topographic factors did have sufficient impact to induce the abnormal subsidence. The results have significant implications to subsidence prediction in areas that may be prone to the phenomenon found at Tahmoor. Key indicators of the potential for this form of abnormal subsidence are presented.

Jan 1, 2011

By Jialin Xu

Bed separations position, size, development characteristics and their influence factors have been analyzed in-depth by experimental and theoretical methods. The results show that the key strata determine the creation, development and space-time distribution of the overburden bed separations and fractures. Based on the dynamic growth principle during the two-stage development of bed separations, the theory of section-grouting for the overburden bed separation space and the O-ring theory for the pressure-relieved methane drainage are proposed. The technique has been applied in some coal mines in China to reduce surface subsidence and for methane drainage. Keywords: rock strata movements; key stratum; bed separation; bed separation grouting; pressure-relieved methane drainage

Jan 1, 2003

By Christopher Mark

After the United States and Australia, South Africa has the largest. modern underground coal mining industry in the world. Historically, South Africa has been the cradle of many innovations in ground control, particularly in the area of pillar design. Today, South African mines are grappling with many of the same issues faced by their U.S. counterparts, including safety during pillar retreat operations, selecting the proper roof support, and maintaining long-term pillar stability. The author recently visited seven underground mines in the Mpumalanga, Free State, and KwaZulu-Natal provinces. Mining methods included longwall, room-and-pillar with continuous miners, and drill-and-blast. The mines represented a cross-section of geology and ground support practices. At each mine evaluations were made of the Coal Mine Roof Rating (CMRR), roof support practices, pillar design methods, and general ground control experience. The coal seams observed were generally thick (2-5 m), the depths of cover moderate (less than 200 m), and the roof rocks relatively strong (CMRR greater than 45). Unfortunately, the South African roof fall fatality rate is approximately three times greater than in U.S., perhaps in part because roof bolts seem to be more widely spaced in most South African mines. Roof bolting equipment was generally outdated, and the quality of bolt installation was a major concern. Pillar design, on the other hand, is quite advanced, and pillar failures are rare. Several novel partial pillaring techniques are employed, including "checkerboard" mining in which every other pillar is removed, 3-cut systems, and high-extraction mining where engineered final stumps are left by design. The paper also offers observations on ground control management techniques (including recently introduced Codes of Practice), the role of the mine inspectorate, and the status of the research community.

Jan 1, 1999

By Robert J. Coutts, Dan A. Payne

"The Broadmeadow mine is a punch longwall mine owned and operated by BHP Billiton Mitsubishi Alliance (BMA) in the Bowen Basin of Queensland, Australia. In 1999, an exploratory adit was driven as part of the feasibility study for the establishment of the mine. Subsequent development of the mine in 2004 started some distance away from the initial test adit. Ten years later, the trial adit would be used as the headgate of the 5'h longwall panel. However, multiple roof falls had occurred in a heavily jointed area over a distance of 1, 000 ft (300 m) during the past 10 years. Due to the immediate coal roof, low stress environment and time, some of these falls had progressed to 38 ft (11.5 m) above the mining floor. As a result of the extensive work involved and safety implications of trying to recover the roof falls conventionally, a strategy was developed to fill these roof falls with a cement based product from the surface, down boreholes, and redrive the roadways through the consolidated roof fall material. This paper describes the process of rehabilitating these roadways, the results when the roadway was redriven and the headgate performance as the longwall mined through the area.INTRODUCTIONBMA operates 7 open cut and 2 underground mines in the Bowen Basin of Queensland, Australia producing over 50 mt per year of high quality coking coal. As a result, BMA has established over 150 miles (250 km) of open cut highwall.Broadmeadow Mine is a punch longwall mine located 22 miles (35 km) north of Moranbah in Queensland, Australia on the western limb of the Bowen Basin Coal Measures (Figure 1). Broadmeadow Mine commenced development in 2004 and began longwall operations in 2005. Broadmeadow is currently completing the fifth longwall panel and produces over 4 Mt per year of high quality coking coal. Mining is undertaken in the Goonyella Middle Seam, which is 21 to 25 ft (6.5 to 7.5 m) thick in the current mining area.The mine layout required the use of an old exploratory gateroad as the headgate of its 5th longwall. This gateroad had experienced numerous large roof falls and required extensive rehabilitation."

Jan 1, 2010

By J. D. Dizon

Conventional strata control methods (i.e. roof bolts. cable trusses) are not always effective for ground control of very weak coal strata. An alternative method, termed presupport. is being investigated by the U.S. Bureau of Mines. In this paper structural modeling of presupport conceuts and field teatinn of a DresuDuort application is presented. Pinite-elem&; modeis indicate that forepoles significantly lower beam stresses in the roof strata overlying a coal seam. but they cannot he expected to prevent or reduce I roof strata failure at the coal face due to the presence of a high stress concentration at that location. However, their presence near the coal face is needed to sustain the fall of roof if it does occur. Because of an ever present severe stress concentration at the coal face, it would appear that stresses could exceed material strengths, causing local structural damage, especially if the rock is very weak. Therefore previous coal face positions along an entry may have a higher than normal probability of roof fall. In the field investigation. a loorcost air injection test has thus far shown promise as a tool for evaluating that effects of forepoling on the roof strata. Observations of coal mine en- tries in which forepoles have been installed indicate forepoling is effective in controlling very weak roof strata.

Jan 1, 1990

By Daniel S. Mazzei

This paper will be a general discussion of surface flooding considerations as they affect mining facilities site selection, based primarily on experience with several such problems with which MSHA's Bruceton Technical Support staff has been involved. The detailed analytical procedures used in arriving at engineering solutions of these problems will not he presented here; the emphasis is on drawing attention to this additional aspect of mine design which hitherto has been largely overlooked due to insufficient awareness, information and criteria. The paper's purpose is to stimulate thought and offer guidance concerning the selection of sites for mining facilities in light of the potential for flooding problems caused by surface waters. Flooding by surface waters, would generally not be a serious consideration in areas of relatively low topographical relief, i.e. flat lands, although there are exceptions to this rule, for example, in Western areas where flash flooding is a major concern. Therefore, this discussion will mainly apply to areas where the severity of surface flooding would be amplified by the topography-large, well defined watersheds of considerable relief, i.e. mountainous areas. In these regions, steep valley walls cause any rainfall to flow quickly into the relatively narrow valley bottoms. These valley bottoms provide little flow area during storm conditions, so deep and rapidly flowing streams result.

Jan 1, 1982

By Feiya Xu, Syd S. Peng

"As a highly efficient and new surveying and mapping technique, 3D laser scanning technology has been gradually applied to surface subsidence monitoring in mining areas. 3D laser scanning technology was used to monitor the mining subsidence in a coal mining area in this paper. Based on the 3D laser scanning data obtained in March, May, and December 2016 in the studying mining area, the surface subsidence basin and points deformation were acquired. The 3D laser scanning data were compared with that of the conventional surface movement surveying method. The results show that the 3D laser scanning technology could obtain the data of the subsidence basin more efficiently and reflect the true shape of surface subsidence caused by mining. The maximum surface subsidence obtained by 3D laser scanning technology was 3.60m, while the conventional surface movement surveying was 3.56m; the relative observation error between 3D laser scanner and the conventional surface movement surveying was less than 10%. Therefore, it is feasible to apply 3D laser scanning technology to monitor surface subsidence in coal mines.INTRODUCTIONWith the over-exploitation of coal resources, the problem of surface subsidence has become the focus of attention (Peng, 2011; Guo Wenbing, 2012). Setting up observation stations for surface movement was the traditional method to study the characteristic of surface subsidence and its parameters. At present, hundreds of observation stations have been set up in longwall mining, and a large number of measured data have been obtained (Ministry, 2017). However, due to the length of time surveying requires, great workload in the field, the high cost of observation, and difficult protection for monitoring points, conventional observation stations for surface movement have not met the research on surface subsidence. Therefore, as a new surveying and mapping technique, 3D laser scanning technology has been gradually used for surface subsidence monitoring in mining areas (Ma Liguang, 2005). Li Qiu, Qin Yongzhi, and Li Hong (2006) first proposed 3D laser scanning technology in the application of monitoring surface subsidence in 2006. It was showed that the 3D laser scanning technology had obvious advantages in efficiency and accuracy of data acquisition than other methods of deformation monitoring technology of surface subsidence (such as total station, precision level technique, GPS, etc.). Subsequently, Zhang Shu, Wu Kan, and Wang Xiang (2008) and Chen Ranli and Wu Kan (2012) analyzed the feasibility and precision of 3D laser scanning in subsidence monitoring, concluding that the 3D laser scanning can be used to obtain the subsidence basin and the monitoring precision can reach millimeter. Hu Dahe, Wu Kan, and Chen Ranli (2013) introduced the data processing method of 3D laser scanning for surface subsidence in detail. On the basis of a case study, the subsidence basin in subsidence area was obtained, which reflected the shape of mining subsidence basin intuitively and comprehensively. Wang Qisheng, Wu Kan, and Zheng Ruyu (2010) carried out the research on prediction parameters of mining subsidence by using 3D laser scanning data and got the parameters of major influence angle and the offset distance of inflection point. Meng Wanli, Cai Lailiang, and Yang Wangshan. (2017) made a profile analysis for the 3D view of the surface subsidence using 3D laser scanning data and put forward a “Geomagic” method of surface subsidence prediction."

Jan 1, 2018