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By Kevin J. Ma, John Stankus, Dakota Faulkner

"Expandable rock bolts are widely used in hard rock mines as an efficient ground control product. However, capacity and service life can be significantly reduced if the metallic body is subjected to corrosion. In some hard rock mines in the U.S., highly corrosive ground conditions exist, and it has been reported that inflatable rock bolts have corroded within a few months after installation. To provide mining industry a cost-effective inflatable bolt and combat the corrosion issues, Jennmar Corporation, Inc., and its subsidiary Keystone Mining Services, LLC (KMS), analyzed corroded bolt samples, identified root causes, evaluated properties of various coating materials, and developed a new inflatable rock bolt, Python M3TM, that is protected with an innovative PyFlexU2TM coating. The new generation Python M3 features improved steel chemistry for reliable performance, modified profile for better inflation, and surface preparation and coating application. The PyFlexU2 is impervious to liquid and air, durable, and UV resistant. With a flexible adhesive, and highly corrosion-resistant undercoating, and a very hard sacrificial surface coating, the PyFlexU2 coating system provides the Python M3 superior protection against chemical corrosion and physical scratch damage. The under-coating has exceptional flexibility and adhesion to prevent coating micro-cracks or fractures after bolt inflation and possesses excellent corrosion resistance to acids (pH <3), alkalis (pH >11), fuels, and salt solvents. The corrosion and scratch resistant PyFlexU2 coating offers very effective bolt protection for extra longevity in highly corrosive environments. The Python M3 coated with PyFlexU2 has been tested in the most challenging conditions, including laboratory corrosion tests in extreme acidic and basic solvents, rock slurry, and borehole scratch insertion tests. With demonstrated corrosion and scratch resistance, the product has been greatly welcomed by hard rock mines in the West and is currently installed in large scale. This paper identifies the root causes of the bolt corrosion, discusses the analysis process, and details laboratory and underground tests carried out on the Python M3 coated with PyFlexU2. The Python M3TM and PyFlexU2TM are subjects covered by pending U.S. Patent Applications assigned to FCI Holdings Delaware, LLC."

Jan 1, 2017

By D. G. Lynch, M. R. Martin, R. J. Coutts

"Broadmeadow Mine is an underground longwall mine located in Central Queensland, Australia. The mine introduced a top coal caving (TCC) longwall face in 2013 but since then has experienced severe convergence events at the start of each panel after 60–70m of retreat, resulting in equipment damage and the longwall almost becoming iron bound. A significant geotechnical monitoring effort during LW10 and LW11 to characterise the caving mechanics and operational changes during LW11 were successful in mitigating the risk posed by these initial convergence events. This paper describes the geotechnical monitoring programme undertaken during LW11, the operational methods used to mitigate these initial convergence events, and the contribution to these events of the TCC technique.A thick sandstone unit close to the extraction roof was likely the cause of the convergence events at the start of each longwall panel. However, stress change monitoring cells, surface extensometers, an inclinometer, and the blockage of holes designed for pre-conditioning using hydraulic fracturing indicated that the convergence events were not caused by the sudden collapse of sandstone bridging across the goaf. Rather, they were caused by the propping action of strong units within the overburden strata. Equipment design modifications were made to allow the longwall to remain operational during the convergence events and an operational strategy was implemented to mitigate convergence in LW11. The initial convergence event was successfully negotiated, and Broadmeadow went on to be the highest producing longwall for CY16 in Australia.INTRODUCTIONBroadmeadow Mine is an underground longwall mine located in Central Queensland, Australia, owned and operated by BHP Mitsubishi Alliance (BMA). The mine is a punch longwall mine using open cut pit access provided by Goonyella/Riverside Mine. Broadmeadow commenced longwall operations in 2005 using a conventional high reach longwall, but later changed to the top coal caving (TCC) method of extraction. Broadmeadow extracts the easterly dipping 5.5–7.5m-thick Goonyella Middle Seam in ranging in depth from 90m to 330m. The coal is washed and blended at the adjacent Goonyella/Riverside open cut mine to produce a premium coking coal product for export."

Jan 1, 2018

By Ry Stone

"There have been many design practices utilised within the coal mining industry to arrive at the minimum densities of primary ground support required during roadway development. This paper demonstrates the practical use of empirical databases, and focuses on the main drivers for ground support as demonstrated in conceptual models.Golder Associates’ empirical databases used for ground support include a Primary Roof Support Database and a Primary Rib Support Database. Both are based on successful ground support designs installed in mines in Australia, the US, the UK, South Africa, New Zealand, and Europe. The term “successful” refers to those designs that were used on a repeated basis for the purpose of roadway development.The Primary Roof Support Database indicates that the major factors influencing successful roof support designs are roof competency, expressed as the Coal Mine Roof Rating (CMRR), and in situ stress. As roof displacement is essentially a function of horizontal stress and roof competency, in order to provide some form of measure as to the likely magnitude of roof deformation during roadway development, the depth of cover is divided by the CMRR to arrive at a “Stress Strength Ratio” (SSR). The database indicates that the higher the SSR, the greater the likelihood that the roof will require higher densities of support.In regard to the Primary Rib Support Database, it is evident from the current database that the primary factors affecting the capacity of rib support required for a successful design are roadway height and depth of cover. In order to provide some form of measure as to the likely magnitude of rib deformation during roadway development, the depth of cover is multiplied by the height of the roadway to determine a “Rib Deformation Rating” (RDR). Similar to the roof, the database indicates that the higher the RDR, the greater the likelihood that the rib will require higher densities of support.These databases have been used to help determine the minimum primary ground support designs required at many mine sites in Australasia, Europe, and the US. This paper will demonstrate the effectiveness and practicality of these databases at two selected mines in Australia and the US.In order to improve the Primary Rib Support Database, this paper will also propose a new rib deformation rating based on the addition of site specific coal strength data for the Australian mines. The proposed rating attempts to capture the main variables that define the behaviour of a buckling column."

Jan 1, 2015

By I. L. Follington

A breaker line support (BLS) monitoring system, BLSmon, has been designed and constructed by the CSIRO and installed and commissioned at Laleham No.1 Colliery, Queensland. This system was designed to record hydraulic leg pressure and canopy position measurements and relay these, in real time, to the surface. The system has shown itself to be capable of operating on the BLSs without any adverse affect on production, Analysis of the results of the monitoring exercise has shown that rate of change of leg pressures on the BLSs could be used as an aid in the prediction of adverse mining conditions. Under favourable mining conditions the supports were observed to initially unload from the set pressure, this unloading reduced with time and by the end of a typical lift cycle had either ceased or reversed slightly. This behaviour was considered to be due to one of four possible causes, these being; the compaction of floor debris, and/or compaction of the floor, and/or crushing of the roof and /or support creep. The actual cause can only be determined through detailed monitoring of both roof and support convergence. However observational data would suggest that compaction of debris and softened floor material beneath the supports was the most likely cause. The few positive loading rates recorded under these conditions were of short duration and occurred towards the end of individual lifts. Where mining conditions were unfavourable the negative rates of change of pressure, unloading of the support, were reduced throughout a lift, in both duration and magnitude, when compared with favourable mining conditions. Over the same period the positive rates of change were observed to be greater. The rate of change of loading and convergence can be utilised to identify the onset of instability in the lift area. However, before this facility can be utilised by the mine for the reliable prediction of instability more monitored data and sophisticated processing techniques are required. A mechanism has been postulated for the deformation behaviour of the roof and pillars in a mechanised pillar extraction operation from the continuously monitored data, observational data and results of previous studies. The 7 m wide fenders were observed to yield under abutment stresses before lifting commenced. The stability of these fenders throughout the lifting sequence was considered to be dependant upon the magnitude of their post peak load carrying capability. This is influenced by the post peak stiffness and the extent of roof lowering in the vicinity of the fender. Difficulties with fender extraction occurred where remnant coal left standing in the goaf caused uncaved goat to bridge to the mined fender. Difficulties were also experienced where sub-vertical jointing occurred in the roof of the split reducing it&apos;s ability to bridge effectively. Despite the relatively short monitoring period, the potential role and application of continuous monitoring in advancing understanding of the rock mass response to mechanised pillar extraction operations has been demonstrated. This understanding now requires enhancement and shows great potential for aiding the optimisation of mechanised pillar extraction operations.

Jan 1, 1992

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 R. Quentin Eades, Kyle Perry

"Surface mines continue to implement highwalls for several reasons, such as increasing recovery, improving margins, and justifying higher stripping ratios. Highwall stability is a complex issue that is dependent upon a variety of mining and geologic factors, and a safe design is necessary for a successful surface operation. To improve highwall stability, it is important to understand the connection between local geology and blasting.Explosives are employed throughout the mining industry for primary rock breakage. There are a number of controlled blasting techniques that can be implemented to improve highwall stability. These include line drilling, smooth wall blasting, trim blasting, buffer blasting, air decking, and presplitting. Each of these techniques have associated advantages and disadvantages. Understanding local geology is necessary for selecting the appropriate controlled blasting technique. Furthermore, understanding the limitations and conditions for successful implementation of each technique is necessary. A discussion of the impact of geologic conditions on highwall stability is provided. Additionally, discussion is provided for the successful incorporation of the controlled blasting techniques listed above, and the associated mining and geologic factors that influence the selection and design of controlled blasting plans. Finally, a new methodology is proposed.INTRODUCTIONExplosives are used throughout the mining industry as the standard for primary rock breakage, a critical part of the mining cycle. In 2015, the U.S.. consumed 2.2 million tons of explosives (Apodaca, 2015). The coal mining industry accounted for the majority of explosive consumption, accounting for approximately 63% of total explosives. The quarrying and nonmetal mining industries accounted for 12% of explosive consumption, and the metal mining industry accounted for 9% (Apodaca, 2015). This constitutes 84% of the explosives used in the U.S. However, the energy released during the detonation process is often in excess of that required to adequately fragment the surrounding rock (Jhanwar and Jethwa, 2000). This excessive energy, along with over confinement and poor blast geometry, will cause damage to the undisturbed rock mass beyond the intended boundary of the blast. This event is known as overbreak or back-break (ISEE, 2011)."

Jan 1, 2018

By Kousick Biswas

The main objective of occupational health and safety research is to minimize or eliminate the events that may cause fatal or non¬fatal injuries to human workers. A commonly used technique is to devise an "incident prevention plan", which is more often the product of thorough investigations of past reported incident events. Incident documentation and methodical reporting and systematic and thorough data collection, often help identify the root cause of the incident - in other words, the etiology of the incident. These retrospective analyses of the incidents can efficiently identify the future steps to take to achieve the objective of minimizing occurrence of "events of interest". This paper introduces a novel technique - "Taxonomic Analysis", which identifies the root causes of an event (an incident in this case) and can provide future direction for corrective measures to reduce the probability of occurrence of the event. A taxonomic analysis involves systematic and organization of data based on observation, description, and classification. This paper utilizes the rock fall related incident narratives, available with the Mine Safety and Health Administration (MSHA) database (1984¬1999), for a taxonomic analysis. The study found that 67.6% of groundfall incidents occurred in supported areas with the remainder (32.4%) in unsupported areas. Some form of rock mass failure appears to cause about 50% of groundfall incidents, although in 39.7% of the overall groundfall incidents or two-thirds of those involving rock mass failure, the exact nature of the rock mass failure could not be determined from the narratives. Human activities factors such as scaling or barring down, drilling or bolting, and setting timbers or cribbing accounted for another 34.5% of the groundfall incidents. Finally, support system failures made up the remaining 15.5%. Results from this taxonomic analysis may suggest focus areas toward which preventive measures and future research activities could concentrate.

Jan 1, 2003

By Zach G. Agioutantis

The prediction of ground movements due to underground mining using the influence function method is a mature technology, widely used by researchers and planning engineers around the world. Surface strain, either tensile or compressive, is an important indicator of potential impacts on structures such as buildings, bodies of water, pipelines, railway and power lines, and tailings dams. Calculation of static or dynamic surface strains, for varying surface terrains and slopes, should be accurately predicted and be independent of the methodology applied for the calculation. This paper discusses and compares the development of horizontal and ground strains on the surface due to underground mining for different surface topologies (sloping terrain, monitoring lines, etc.) and presents the steps needed to ensure accurate calculations. Examples are given to demonstrate how ground strains can be calculated for one- and two-dimensional gridded surfaces.

Jan 1, 2013

By Brian White

Two examples of en echelon mining-induced fractures seen in hard¬rock mines provided a basis for inferring that fracture zones and bedding plane separations immediately surrounding mine openings are promoted by oblique shear into the openings. It is hypothesized that initial fractures or separations form at the comers of openings as a result of high stress and physical constraint on the rock&apos;s ability to deform elastically toward the opening. These conditions result in a locally preferred direction of shearing. The shearing, in turn, generates tensile stress that initiates a progression of systematically offset fractures approximately parallel to the direction of greatest compressive stress. The fractures or bedding separations create tabular rock layers that amplify shearing displacement through bending and dilation. Such shearing effectively reduces and redistributes the compressive stress, but significant dilation is an inevitable consequence. The combination of dilation and shearing and the progressive development of fracture zones have important implications with respect to ground support. The concept of mining-induced fractures forming as a result of shear is illustrated by two examples from coal mines. First, frac¬tures seen at longwall faces probably result from shear associated with subsidence. The fracture zone that develops approximates or possibly defines the draw angle of subsidence. As the face advances, fractures extend downward along the lower edge of the fracture zone, while upper extensions of the fractures are pressed closed. Fracture zones in entry roofs provide a second practical example. Here, mining-induced fractures typically follow bedding planes. The shear zone model suggests that the first bedding separations develop near the edges of the roof and successive separations progress upward and toward the center. However, if the direction of greatest stress is inclined with respect to the roof, a fracture or bedding separation zone may propagate from one side only and also extend higher. Because coal ahead of the face provides some support against lateral shear deformation, bedding separation is inhibited near the face. Rock bolts installed close to the face ultimately become more strained and bent than bolts installed a few meters from the face, and bolts installed through the more remote part of a separation zone may ultimately experience the greatest tensile and bending strains. This model is supported by field data documenting progressive bolt failures that rapidly propagated downward across the roof during face advance.

Jan 1, 2002

By Brian E. Travis

Recent Developments in the utilization of polymer grid structures for Longwall Shield Recovery operations are discussed. Specifically: various Longwall screen designs and the numerous methods employed during installation. Also discussed is the role of polymer grid structures in head and tailgate mf and rib control and their role in controlling soft bottom often associated in shield recovery operations.

Jan 1, 1993

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 Daniel Su

Following several roof falls in the E3 longwall development of a Consol Pennsylvania Coal Company underground coal mine, an underground roof geology reconnaissance program consisting of twenty-nine 20-foot deep roof holes had identified the presence of thick sandstone layers with abundant shale and micaceous streaks. The base of the sandstone was 4 to 8 feet above the roof line within the fall areas. The presence of micaceous streaks created extremely pronounced planes of weakness in the sandstone. A structural irregularity, which extends into the E4 and E5 developments, exists between crosscuts I 1 and 30,where all roof falls occurred. Immediately to the east of this structural irregularity lies a huge syncline. The presence of thick sandstone units within the typically all shale environment and within such a structural irregularity helps to maximize stress concentration and creates closely spaced joints in the sandstone, which explains why many cracks are present in the macroscopically massive sandstone upon development. The approaching E2 longwall gob to the south and on the down-dip side, on the other hand, provided horizontal stress relief in the sandstone, which helps to explain the many roof falls in the E3 development that occurred during or immediately after the formation of the E2 gob. Finite element modeling confirmed the presence of such horizontal stress relief. Since the E3 longwall was a right-handed face, stress concentration was expected at the longwall headgate T -junctions, and further delamination of the sandstone was expected upon arrival of the E3 longwall face. Based on the results of the roof geology reconnaissance program and a roof stability analysis that took into account up to eleven parameters, supplemental headgate and track roof support consisting of 16-foot and 20-foot long cable bolts was successfully implemented within the zone of thick sandstone with micaceous streaks and structural irregularity and at other potential roof instability areas along the E3 development. The cable bolts were designed to be anchored at least 4 feet above the sandstone unit into the mostly competent sandy shale layers. No headgate roof control problem was reported within the sandstone and structural irregularity zone during E3 and the subsequent E4 longwall extractions.

Jan 1, 2002

By Yoshiaki Fujii

Displacement Discontinuity Method (DDM), which was originally developed by Crouch,S.L., is a powerful tool to calculate mechanical disturbances due to tabular excavations. Three topics on DDM applications to strata control problems in Japanese deep coal mines are described. First, is numerical simulation of microseismicity induced by longwall mining in Horonai Coal Mine. Microseismicity in the mine had been monitored by a mine-wide seismic array. Location of microseismic events and intensity of seismicity were well simulated. In the simulation procedure based on DDM, first, zones where a failure condition is satisfied by the advance of mining are detected. Then, the seismic moments, which indicate the intensity of seismicity, at the failure zones are evaluated. Second, is prediction of the shaft damage due to mining in Sumitomo Akabira Colliery. In this mine, the limit angle of the shaft pillar was changed from 600 to 800 to increase the amount of minable coal volume without increasing mining depth. Displacement of the shaft axis has been measured to assess the damage due to mining around the shaft pillar. In the calculation based on DDM, a fault intersecting the shaft and the ground surface are considered. Observed and predicted displacement of the shaft axis agreed well. Third, is the roadway deformation in Taiheiyo Coal Mine. Attainable maximum stress for a roadway was calculated considering three faults intersecting the roadway. It was realized that the roadway&apos;s convergence is related to the calculated stress by simple equations.

Jan 1, 1992

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&apos; 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 Joseph A. Cybulski

In response to the mining of reserves with increasingly adverse round conditions and the roof support recommendations of current rock mechanics theories, roof support systems have continued to improve. A few of these newer bolting systems. while giving improved performance, require a new method to check bolt installation. Previous1 , a torque wrench had been the sole means to check the installed torque of a roof bolt. However, due to the characteristics of soma of the newer bolting systems which can prevent a reliable manual torque check and a recent change in the federal roof control regulations, an alternative method to a manual torque check is gaining acceptance. This alternative method improves monitoring the hydraulic pressure of the roof bolting machine torque circuit and provides a safe, reliable and quick wav to check bolt installation in those instance when an accurate manual torque check cannot be made.

Jan 1, 1990

By Jimin Su, Enguang Zhu, Kangning Zhang, Yang Li

"The effect of interburden on overlying strata movement during the mining of a lower group coal seam is still a challenge in China. Based on the multiple coal seams in western China, numerical simulation and field tests are applied to study the interburden and overburden movement during the undermining process. This study focuses on the impact of the thickness and structure of the interburden, the proportion of hard rock, and the ratio of the overburden thickness to interburden thickness (OB/IB). In this paper, four typical underground coal mines are simulated for lower seam longwall mining with different interburden parameters. The results indicate that the ratio of the overburden thickness to the interburden thickness is not the dominant actor for multiple seam longwall mining, especially in the mines in western China,which feature shallow depth. The thick and hard interburden could strongly affect the lower coal seam mining process. INTRODUCTION The project background is based on four typical underground coal mines in western China.The information on the overburden and interburden is shown in Table 1. Different overburden to interburden thickness (OB/IB) (Ellenberger, 2009) values of the four coal mines are also studied: 6.2 in Bulianta coal mine, 7.2 in Kaida coal mine, 8.2 in Shigetai coal mine, and 9.4 in Halagou coal mine. The proportions of hard rock in the interburden of the four coal mines are also different: 0% in Kaida coal mine, 70% in Shigetai coal mine, 80% in Bulianta coal mine, and 100% in Halagou coal mine. To be specific: the thickness of interburden are listed as follows: 7m in Halagou coal mine, 6m in Kaida coal mine, 10m in Shigetai coal mine, 28m in Bulianta coal mine. The depth of the upper coal seam are: 66m in Halagou coal mine, 54m in Kaida coal mine, 79m in Shigetai coal mine, 182m in Bulianta coal mine. NUMERICAL SIMULATION UDEC 4.0 is applied in this paper to analyse the overlying strata movement and the interburden failure.(Liu, 2007) This is based on mining in the lower coal seam under the mined-out upper coal seam (Majdi, 2012, Morsy, 2006)."

Jan 1, 2017

By Winton Gale

"The aim of this paper is to summarise the results and conclusions of Australian Coal Association Research Project (ACARP) Report Cl3013 which relate to water inflows into a mine which occur through the overburden above and adjacent to longwall panels. The study assessed available data of inflows into underground coal mines and utilised computer simulation of water flow through fracture networks. The study concluded that flow into mines is typically via an interconnected network of pre-existing and mining induced fractures. The height above the coal seam that mining induced fractures extend is typically related to the width of the panel. However the potential for those fractures to form a connected network which can facilitate flow, is related to the amount of subsidence and the depth of mining. The study compares model simulations with measured data and provides guidelines to estimate the average hydraulic conductivity of the overburden above extracted longwall panels in Australia.INTRODUCTIONWater inflow into coal mines has been a design issue for many years. Guidelines as to the potential for water inflow have been developed in many countries based on local experience and the form of mining being undertaken. In most instances, the guidelines relate to inflows which would endanger underground personnel and operations.In more recent times, water inflow criteria for mines has been widened to include lesser inflows which may not impact on mine safety or operations, but have the potential to reduce water flow within streams and surface aquifers. For the purpose of this paper the larger inflows which are readily measured in a mine or may impact on mining safety are defined as mine inflow and the lesser inflow relating to aquifer water loss as environmental inflow.The water losses referred to are those which enter the mine from the surface or from near surface aquifers.The empirical relationships developed as mine design guidelines or regulations typically relate to high flow (mine inflow) situations and in this paper, these have been reviewed as to their application to environmental inflow. In many cases environmental inflows were unlikely to have been noted or recorded in many mining operations in the past."

Jan 1, 2010

Results of direct shear tests on rock discontinuities and triaxial compression tests on intact rocks are presented and - discussed. The main parameters considered area stress functions, angle of internal friction and cohesion variations. Primary objective of this work is to determine relationships that adequately describe the rock behaviour for design of mining excavations, while still maintaining a certain degree of simplicity.

Jan 1, 1987

By Liu Xiao, Lin Xiaoying, Ma Geng, Tao Yunqi

"The soft coal in China has several issues, low permeability, high gas content and prone to gas outburst, making it difficult to drill and improve its permeability. Using the rock mass loading test, the relationship of stress-strain-permeability-time of sandstone was investigated. The fracture network that communicates with coal seams to provide the pathways for gas migration can be established by drilling, hydraulic fracturing or loose blasting in the roof and floor about 5m from coal seams top and bottom. The gas migration can be summed up as ""desorption-diffusion-two levels of seepage"" for gas drainage of the quasi-protection-layer in hard coal seams, and ""desorption-two levels of diffusion-seepage"" in soft coal seams. In the quasi-protection-layer, different gas drainage techniques were used during different stages of mining. Gas drainage of the quasi-protection-layers was demonstrated at Hebi Zhongtai Mining Co., Ltd. The results showed that the technique promotes the gas seepage flow, and improves the efficiency of drainage. The influence zone of the quasi-protection-layer was 1601 m2 and the average amount of gas drainage was 328m3/d, with the maximum being 661m3/d. INTRODUCTIONGas is one of the main factors that cause disasters and influence safety production in underground coal mines (SACMS, 2009). The coal-bearing formations in China have been subjected to multiphase tectonic stress field during the period of geological evolution. Coal body was often crushed into fragmented coals and mylonitic coals under the tectonic stresses (Su and Lin, 2009). The gas permeability of coal is generally poor. So in underground, drilling and hydro-fracturing technology have been used to improve the permeability of coal, such as intensive drilling, hydraulic punching, hydraulic cutting, hydraulic extrusion and deep hole blasting. But the gas drainage rate was low, only 23% (Liu, Li, and Li, 2006; Li and Wei, 2006; Henan Polytechnic University, 2008; Ma, et al., 2014; Lin and Wu, 2009; Zhou, et al., 2011) that was much lower than the rates achieved in the main coal-producing countries such as America and Australia whose average rate of gas drainage was 50%. The protection layer mining technology has been used widely as an effective technique to improve the permeability of coal in the mining of multiple coal seams (Cheng and Yu, 2003; Diaz and Gonzalez, 2007; Karacan, et al., 2007; Palchik, 2003; Latham, et al., 2013; Yuan, et al., 2013; Shi and Liu, 2007; Wang, et al., 2008, Guo, et al., 2015; Lu, et al., 2015; Slazak, Obracaj, and Swolkien, 2014 ). In the single low permeability coal seam, there is no protection layer. This kind of coal seam has low permeability, high gas content, soft coal body, and is prone to serious gas outbursts. During drilling, the holes very often spray, collapse, stuck and wedged the drilling tool. The hole length drilled is difficult to reach the required minimum, the service life of holes for gas drainage is short, the construction cost is high, and the holes are difficult to maintain. The gas drainage efficiency of single low permeability coal seam, especially soft coal seams, cannot be improved even though hydro-fracture technology has been implemented, because its permeability is not improved."

Jan 1, 2016

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