Search Documents

By D. W. H. Su

This paper presents the results of ill situ horizontal stress measurements using a Minifrac system in several northern Appalachian coal mines. The effect of stress magnitude and orientation on longwall gate entry stability was analyzed using a series of three-dimensional finite element analyses. The best headgate stability is achieved if the maximum horizontal stress is aligned with the direction of longwall retreat or if the panel is oriented such that the maximum stress relaxes over the headgate due to the presence of the newly formed gob. The degree of horizontal stress damage to longwall gate entries depends largely on the stress magnitude and roof geology. Accurate assessments of support or design techniques which may mitigate longwall headgate or tailgate instability in areas of thinly laminated roof and high horizontal stresses must account for the in situ horizontal stress state and site specific roof geology. The ability to measure stresses and map geology is thus essential to prevent ground control failures at the longwall headgate.

Jan 1, 1995

By Francis S. Kendorski

High-extraction mining of coal and other stratified minerals has a predictable effect on the surface and subsurface. Impacts on ground waters in overlying strata and on surface waters, that are associated with overlying sequential zones of collapse, fracturing, aquiclude, constrained strata, and surface disturbances can be anticipated. Since first quantified around 1979 in Bureau of Mines sponsored contract research work and others (and often adopted by state regulators), with zone extents based upon multiples of mined seam height of 24 to over 60 for the fractured zone, much new data have become available. In examining the sources of data and the methods and intents of the researchers of over 65 case histories, it became apparent that the strata behaviors were being confused with overlapping vertical extents reported for the fractured zones and aquiclude zones depending on whether the researcher was interested in water intrusion into the mine or in water loss from surface or ground waters. These more recent data, and critical examination of existing data, have led to the realization that the former "Aquiclude Zone" defined for its ability to prevent or minimize the intrusion of ground or surface waters into mines has another important character in increasing storage of surface and shallow ground waters in response to mining with no permanent loss of waters. This zone is here named the "Dilated Zone." The existence of the dilated zone explains the ratios of up to 60 times the mined thickness. Surface and ground waters can drain into this zone, but seldom into the mine, and can eventually be recovered through closing of dilations by mine subsidence progression away from the area, or filling of the additional void space created, or both. A revised model has been developed which accommodates the available data, by modifying the zones as follows: ? collapse and disaggregation extending 6 to 10 times the mined thickness above the panel ? continuous fracturing extending approximately 24 times the mined thickness above the panel, allowing temporary drainage of intersected surface and ground waters ? development of a zone of dilated, increased storativity, and leaky strata with little enhanced vertical permeability from 24 to 60 times the mined thickness above the panel above the continuous fracturing zone, and below the constrained or surface effects zones, whose thickness or existence is dictated by the zones above and below ? maintenance of a constrained but leaky zone above the dilated zone and below the surface effects zone, whose thickness or existence is dictated by the zones above and below ? limited surface fracturing in areas of extension extending up to 50 ft or so beneath the ground surface

Jan 1, 1993

By Gautam Benerjee, Veera Reddy Boothukuri, Bhattacharjee Ram Madhav, Panigrahi Durga Charan

"India’s tryst with mechanized longwall coal mining started with the introduction of the first self-advancing powered support longwall (PSLW) face at Moonidih Colliery of Jharia Coalfield in 1978 and at Godavarikhani (GDK)7 Incline of Singareni Collieries Company Limited (SCCL) in 1983. During the last 37 years, about 30 longwall units in Coal India, Ltd., (CIL) and 10 longwall units in SCCL have been introduced with powered roof supports of varying capacity, ranging from 280 to 800 tonnes, in many mines in India under varying geological and geotechnical conditions. The majority of the longwall faces in India have been worked under relatively shallow cover (up to 200m), and significant strata control problems have been encountered due to poor caveability of the roof, inadequate capacity of the supports, a lack of knowledge on longwall caving mechanisms, less than adequate strata monitoring systems, and the non-availability of quality spare parts, etc. This has resulted in structural damage to supports and increased downtime of the equipment, thereby making longwall mining in India a case of technology failure. Energy demand for a developing country like India with a population of 1.2 billion is huge, and the thrust on increasing coal production continues. However, the share of coal production from underground mines in India continues to decline (current share is around 6%) because of absence of successful mass production technology in underground coal mining. Under this backdrop, a high-capacity longwall with state-of-the-art technology was introduced in 2014 at Adriyala Longwall Project (ALP) of SCCL for the first time in Indian Coal Mining Industry. The first longwall panel (LWP) has been completed successfully. This paper highlights the major geotechnical challenges encountered during development of the longwall gate roads due to the presence of two overlying clay bands, significant in-situ horizontal stresses and the experience of using rigid (welded) steel wire mesh with resin-anchored roof bolts. Efforts have been made to analyze longwall weighting and caving behavior, such as main and periodic weightings, the effect of front and side abutment pressures, and the behavior of gate roadway support systems under immediate friable weak roof with overlying massive sandstone."

Jan 1, 2017

By K. Hanna

This manuscript describes an extensive ground control study at the Inland Steel No. 2 Mine near McLeansboro, IL, conducted by the U.S. Department of the Interior's Bureau of Mines (USEM) in cooperation with Inland Steel Coal Co. The mine experiences severe ground control problem primarily due to high horizontal stress, particularly at entry intersections. Mine experience has shown that reorienting mine entries, modifying the bolting pattern, and altering the mining sequence are effective in reducing the severity of roof falls and out-of-seam dilution. However, the frequency of roof falls has not been significantly reduced. This research project was designed to provide a thorough explanation of the intersection failure mechanism through combined analyses of company in-mine experience and Bureau field measurements. Stresses and deformations were monitored in a four-way intersection during all stages of development and were related to site observations and theoretical analyses. The results of the combined analyses indicate that high horizontal stress is the predominant factor contributing to intersection roof falls in the Inland Steel No. 2 Mine. The horizontal stress induces shear zones to form along the outby 1 ribs, causing the immediate roof layer to detach 1 and behave as a cantilever beam oriented diagonally across the intersection and parallel to i the maximum horizontal principal stress. As the shear zone progresses upward, roof layers successively detach and fail, forming a dome-type roof fall.

Jan 1, 1986

By David F. Gearhart, Khaled M. Mohamed

"Trusses are primarily used as passive roof supports in coal mines. They are constructed of three main parts: two grouted bolts installed at opposing forty-five degree angles into the roof so that they are anchored over the ribs and a cross member that ties the angled bolts together. There is also hardware used to assemble these components. The capacities of the angled bolts are typically 30 to 40 tons and the tensile capacity of the cross member is also 30 to 40 tons. Importantly, the direction of the immediate roof loading on the cross member is unlike the direction of the loading on the angled bolts. The load on the cross member is transverse to the longitudinal axis instead of along it, and therefore the cross member is loaded in the weakest direction.Previous tests conducted on truss systems applied loads such that the increasing tension in the two diagonal bolts increased the tension in the horizontal cross member, resulting in a stiff response. By contrast, if the load is applied directly to the cross member, which then transmits those forces to the diagonal bolts, it results in a much softer response.Based on this difference, laboratory tests to apply transverse loads and measure the vertical load capacity of three different types of cross members were conducted using the Mine Roof Simulator (MRS) located at the National Institute for Occupational Safety and Health (NIOSH) in Pittsburgh. The length of the samples was about 16 feet. Single-point load tests, with the load applied in the center of the specimen were conducted to verify the performance of the test arrangement and the finite element models. Double-point load tests, with a span of eight feet, were also conducted. This arrangement replicates the performance of the cross members with a distributed load. Both of these test arrangements were conducted on one-inch-diameter threaded steel bars and 0.7-inch-diameter cable and 0.6-inch-diameter cable cross members.For the single-point load configuration, the yield of the one-inch bar was nominally 22 kips of vertical load, achieved at 17 inches of deflection. For both sizes of the cable cross members, yield was not achieved even after 18 inches of deflection. Peak vertical loads were about 20 kips for the 0.7-inch cables and 15 kips for the 0.6- inch cables. For the double-point load configurations, the one-inch bar cross members yielded at 33 kips of vertical load and 10 inches of deflection. The 0.7-inch-diameter cable cross members broke strands at 30 kips of vertical load and 10 inches of closure, and the 0.6-inch-diameter cable cross members broke strands at 25 kips of vertical load and 10 inches of closure. Finite element models of each of the six different configurations were developed and show the variation of the vertical capacity of the cross members and the difference of the behavior of the bar versus the cables."

Jan 1, 2015

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 Dakota D. Faulkner

Cable bolts anchored with traditional two component polyester resin cartridges have successfully supported difficult roof conditions in underground mines. Resin cartridges provide a costeffective cable bolt anchoring system with consistent anchorage performance characteristics when properly installed. The most commonly used cable bolts in the U.S. mining industry are 270 ksi (1,862 MPa), 0.7 and 0.6 inch (18 and 15 mm), seven-strand smooth cable with resin mixing bulbs (also known as bird cages), and 40- and 30-ton nominal capacity, respectively. However, there are other types of cable bolt anchoring systems aside from bird cages. Recently, many questions have been raised regarding the anchorage characteristics of various types of cable bolts. Keystone Mining Services, LLC (KMS), the affiliated engineering company of Jennmar Corporation, conducted a variety of controlled tests developed to closely model actual underground installations. These tests compared the performance of three commonly used cable bolt varieties, including plain, bird caged and indented seven-strand cable. Details of the laboratory testing and comparative analysis of the results are provided.

Jan 1, 2013

By Bill A. Kyslinger

"In underground mining, machine design is predominantly dictated by mine conditions and individual customer desires. In partnership with Foresight Energy, J. H. Fletcher & Company was tasked to design and manufacture a new roof bolting machine with six independent drilling apparatus on board capable of drilling and bolting the roof and ribs with material handling. This is the first Fletcher® six-head machine to be designed and built for the mines in the United States. The machine is intended to work in the Illinois Coal Basin.The objective was to produce a machine capable of drilling and installing six bolts simultaneously with a limited number of operators. The goal of the mine is to decrease the time to bolt a cut to improve the safety level of the current roof bolting method, improve efficiency and to improve the bottom line cost of entry development. The customer wanted four mast feed drills at the front of the machine dedicated to installing roof bolts and then another two mast feed drills behind them dedicated to rib bolts. This dictated the requirement of latched controls, which would allow the operator to start drilling one hole and then latch the controls to be able to move on to the next. To accomplish this, we developed a unique hydraulic latch circuit to maintain operator safety and compliance. Guarding was added to prevent an operator from coming into accidental contact with a latched drill.The result of the design is a machine with a single platform and six independent masts with drillheads: four masts strictly for drilling and installing roof bolts on the front of the platform and two masts on the back of the platform for rib bolts. The feed and rotation controls at each operator's station include a latch control for drilling. The latch control will allow the operator to lock in the feed and rotation once the hole has been collared, allowing the operator to move on to the next hole. The rear of the machine is equipped with material handling. There are two material pods with winch controls as well as a mesh rack that includes mesh lift, mesh tilt, and mesh sump.The six-head roof bolter allows fewer operators to drill and install roof and rib bolts, which in tum lowers the miners' roof exposure per cut. This design reduces the operator's exposure from the inherent pinch points and rotary hazards once he has engaged the latch drilling. Therefore, the machine will help to decrease the time to bolt a cut, improving productivity while enhancing the ability to operate the machine safely."

Jan 1, 2016

By Kazem Orace, Navid Hosseini, Mehran Gholinejad

"Selection of the optimum support system for underground openings such as tunnels is a complex process. In this paper a new approach, based on a combination of the Analytical Hierarchy Process (AHP) the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and the Preference Ranking Organization METHod for Enrichment Evaluations (PROMETHEE), is introduced. For this purpose, the selection process is assumed to be a multi criteria decision-making problem. First different support systems using FLAC3D numerical code, based on technical safety and stability parameters of the tunnel are specified. Then taking economic and performance parameters as the decision criteria by using the combination of Al-IP, TOPSIS, and PROMETHEE the optimum support system is selected. As a real mine case study this approach is used in the main access entry to the C, coal scam of Tabas collieries. Results clearly demonstrate that the proposed support system selection method is more advantageous than other alternatives.INTROD CTIONGenerally, the support system for a tunnel is selected primarily with the aid of design engineers experience. In other words personal judgment instead of intellectual and scientific criteria is mostly the main basis (Oracc. 2005). However since various support systems can be applied in any particular situation, accurate selection of the optimum support method depends on the integration of many technical, economical and performance parameters, and also on the analysis of the intensity of influence by each of the criteria.In this paper an applicable approach for se lection of tunnel support systems based on Multi Attribute Decision Making (MADM) techniques including: Al IP (Orace et al.. 2009a; Saaty, 1980), TOPSIS (Hwang and Yoon, 1981: Yoon and Hwang, 1995), and PROMETHEE (Brans and Vincke. 1985; Brans and Mareschal. 1992) is introduced. As a field study, this approach was applied to tunnel C1 as one of the main entries in the Tabas coal mine which is the major collieries in the central pan of Iran (Hosseini, 2008).Due to the coal seam conditions coal is mined by mechanized longwall mining (Hosseini 2008). This method requires the 58 excavation of several entries some of which will be used for many years and even for the entire life of the mine (Peng, 2006). Therefore the selection of the support system in these entries is·very important in mining design."

Jan 1, 2010

By Nan Zhou, Jixiong Zhang, Qiang Zhang

"Mining activities under hard roof could easily induce rock burst. Based on the geological conditions of widespread hard roof in China, this paper discusses the type, mechanism of occurrence and prevention of rock burst caused by hard roof from energy evolution point of view. It analyzed the interaction between the solid backfilled body and roof under different backfilling ratios. And by establishing and applying the mechanical model, the deformation of hard roof and energy evolution of the panel under different backfilling ratios were determined, revealing the control effect of solid backfilling on disaster-causing energy. As a result, an innovative method using the solid backfilling method was proposed as a solution to the hard-roof-induced rock burst hazards. Moreover, mine trial was conducted in Panel 6304-1 of Jisan Mine. The result shows that the stress concentration factor of the front abutment stress was only 1.44; the coal dusts in drill holes didn’t exceed the limits and microseism of large energy didn’t occur during mining mining, indicating that solid backfilling mining could be applied as an effective method for preventing rock burst caused by hard roof.INTRODUCTIONSHard roof refers to the thick strata above the coal seam or thin immediate roof. It is strong with poor joint development. After mining, instead of immediate caving, it will overhang for a large area in the gob, resulting in high stress in front of the face and difficulty in gas dispersion. As a result, the face spalls, the roof exposes and the gas accumulates in the gob. With the continuing advance of the face and increase in area of overhang, the stress in the hard roof will eventually exceed its ultimate strength and cause a large area of caving, followed by quick release of energy concentrated in the roof and coal seam, which may cause rock bursts and other dynamic disasters in the mine as well as serious equipment damage and casualties. Therefore, the hard roof becomes one of the main factors causing rock bursts at the face.Hard roofs in China varies in conditions. It ranges from dozens of meters to hundreds of meters in thickness. However, coal reserve under hard roofs accounts for about 1/3 of the total reserve; moreover, nearly 40% of the fully-mechanized coal mining panels are those with hard roofs and more than 50% of the mining areas are associated with problems of hard roofs. Aiming at this problem, researchers at home and abroad have proposed many solutions, e.g. coal pillar support, strength weakening and forced caving, to prevent rock bursts caused by hard roof. These solutions have been employed in some cases with good results. However, due to the variability in geological conditions of mining and hard roofs, the application of the above solutions is limited."

Jan 1, 2015

By Jun Lu, Greg Hasenfus

"In this paper, the mining experience and challenges for the first right-handed longwall panel in the Pittsburgh seam are introduced. The longwall headgate T-junction experienced very high face convergence (up to 2 feet), accompanied by roof sag, floor heave, and rib loading. The headgate convergence was so large that, in a few places, it threatened longwall retreat and ultimately required the bottom to be re-graded.Different underground instruments, such as a roof scope, de-gas drill, tell-tale, laser meter, and Borehole Pressure Cell (BPC), were employed to explore the roof geology and to monitor the entry convergence and the stress changes in the pillar. In addition, the impact of other geologic factors, such as large overburden depth, laminated sandstone roof geology, soft floor, and large headgate equipment, were also analyzed. Subsequently, geotechnical solutions were provided to avoid or mitigate the impact of these challenging geologic factors.INTRODUCTIONIt is well known that high horizontal stress will affect the stability of roof, floor, and ribs within underground mines. In general, the headgate entries will experience stress concentration for the right-handed longwall face. On the contrary, the stress concentration will be in the tailgate entries for the left-handed longwall face (Hasenfus and Su, 2006). Without the stress shadow, the stress concentration in the headgate for the first longwall panel may be more significant (Figure 1).A mine in the CONSOL Pennsylvania Operation was extracting the first right-handed longwall panel in the Pittsburgh seam, which created high horizontal stress concentrations at the longwall headgate. Because of concern over soft wet floor within the syncline, floor coal had been left in place on development. Early on, upon retreat, the longwall headgate T-junction experienced very high face convergence, accompanied by roof sag, floor heave, and rib loading. The floor heave was exacerbated by the presence of floor coal, which buckled upward near the center of the beltline. Roof movement was occasionally aggravated by laminated roof conditions, but was kept in check by aggressive supplemental support including cable bolts, yielding props, cribbing, and roof mesh. Rib bolting and rib mesh helped to further maintain the entryway stability by keeping sloughage at a minimum. Nevertheless, despite the heavy support, headgate convergence was so large that, in a few places, it threatened longwall retreat and ultimately required the bottom to be re-graded."

Jan 1, 2018

By Pengfei Wang, Guorui Feng

With increase of cover depth, dynamic incidents, such as large gateroad convergences and coal bursts, are frequently encountered when mining deep longwall panels. It would be more adverse due to large inclination of the coal bed. Because of the shearer and armored face conveyor (AFC) sliding downhill, toppling of shields, disconnection of AFC to the stage loader are related to it. Tangshan coal mine is a typical deep, inclined coal mine situated in the east of China. The split-level longwall panel layout is being adopted for mitigating problems above, where tailgate entries of longwall panels are driven below gob edge and along the floor, while headgate entries are driven along the roof. Wire mesh and steel sets have been used empirically for support for tailgates for about a decade, which reduces the tunneling speed. In view of this fact, the paper serves to investigate the proper adjustment of the tailgate locations and to analyze the resulting stress and yield conditions according to support strategy. First, field measurements and observations were carried out. Stress data distributed within surrounding rock mass were obtained, especially within the roof since the roof consists of only a coal sheet with a thickness of 2–4 m. Roof pressure of the tailgate represents the pressure at the gob edge since it is below the gob edge. The convergence data were also collected. Numerical modelling using FLAC3D™ was conducted and validated by side abutment stress data. The double-yield constitutive model was used to simulate the gob. The finalized tailgate layout and design were determined through comparison of three scenarios. The research in this paper can help engineers choose the proper tailgate layout and support strategies for coal mines that are going to adopt a split-level longwall panel layout for mining deep, inclined longwall panels.

Jan 1, 2018

By Thomas M. Barczak

Wood cribs have been the dominant form of supplemental support in coal mining for many years. Recently, there has been a renewed interest in prop supports as a replacement for wood cribbing due to the increasing cost of mine timber and engineering advancements in prop design to improve their stability and yield capability. Prop supports generally consume less material, can be installed in less time with less labor, and provide less restriction to mine ventilation than wood crib supports. Several prop supports are now available or under development'. These include: (1) Strata Products Propsetter? Support System; (2) Heintzmann ACS and Super Prop; (3) MBK-Hydraulik MEGA prop; (4) Advanced Mining Technology Inc. (AMTI) BTS Mortar prop; (5) Dywidag Coal Post; (6) Western Support Systems YIPPI support; and (7) "The Can" support by Burrell Mining Products. A comparison of the performance and cost of these support systems to wood cribs is made to provide mine operators with information needed to assess their application potential. Examples of current underground installations are discussed. Included in this assessment are full scale tests of these supports conducted in the U.S. Bureau of Mines' Mine Roof Simulator.

Jan 1, 1995

By Kot Unrug

For the purposes of underground mine design, twelve cores of the Springfield (V) Coal (Pennsylvanian) roof and floor were retrieved. Each core was photographed, described fresh in the barrel, and the rock quality designation (RQD) was measured. Cores were wrapped in plastic and delivered to the rock mechanics lab. At the lab RQD was remeasured and new photographs were taken before running geotechnical tests including weatherability. Significant differences in barrel RQD's vs. lab RQD's have been noticed in spite of careful handling. The drill site RQD is generally used to calculate geotechnical results, but in some types of coal measure rocks, further fragmentation of core takes place with slight changes of moisture content, which occur even in well wrapped core. This creates a dilemma which RQD should be used for support design. Rocks around excavations are exposed to the significant changes in moisture content due to the seasonal weather changes and related fluctuation of humidity of air ventilating a mine. Therefore, it appears to be more realistic using laboratory RQD which corresponds closer to the actual rock condition around the excavation. Weatherability test, developed for characterization of time dependent behavior of rock exposed to fluctuations in moisture content, is thought to be related to the above-mentioned changes of RQD. In weak shales, mudstones and claystones which weather rapidly, it is essential to characterize their future behavior in the pre-mining stage. This can allow for a realistic design of primary, and particularly secondary support in coal mines, especially in coal fields where such geologic conditions exist.

Jan 1, 2003

By Eric Westman

Ground control problems caused by multiple-seam interaction frequently sterilize coal reserves. Interaction mechanisms differ for overmining and undermining and are controlled by mining, spatial. and geologic conditions at each site. A multiple-seam interaction analysis software program, UGLY (Uppersearn Gateroad Longwall Stability), has been used to evaluate sterilization of coal reserves due to overmining at three locations. Four case histories were reviewed to determine the effectiveness of improved ground control in mitigating interaction effects.

Jan 1, 1997

By Alan Bugden

Goedehoop colliery in South Africa has experienced a number of substantial roof falls in roadways and intersections. Many of these have been associated with geological slips and/or horizontal compressive stresses. This paper describes a numerical modelling study conducted after one such fall with the objective of clarifying the roof failure mechanism associated with these falls. The fall was located at an intersection and occurred as the last cut was being made to complete the intersection. One bounding surface of the fall was formed by the geological slip; the others were formed by fresh failure surfaces. The fall took place despite the slip being identified as a hazard and additional bolts being placed by the workforce. In conjunction with the modelling work tests were conducted on samples from the roof in which the fall occurred, these gave a U.C.S. of 80 -100MPa. Several in-situ stress tests had already been conducted at the mine; a further test was conducted close to the fall site. The tests show that the largest stresses are horizontal. However, the maximum stresses of 6-12MPa are small compared to the compressive strength of the root. Computer modelling highlighted a mechanism arising from the conjunction of a geological slip and horizontal compressive stresses that could result in tensile failure of the roof leading to the fall. Sensitivity studies were conducted to identify risk factors associated with this mechanism and the modelling results used to assist in formulating a support strategy to combat falls of this nature.

Jan 1, 2003

By K. Y. Haramy

Rock burst and coal mine bump research using static and dynamic rock mechanics instrumentation has been conducted for several decades. Research efforts typically have been conducted using static instrumentation such as pressure cells, convergence measurements, multipoint borehole extensometers, and shield loading pressure measurements; dynamic rock mechanics instrumentation, for example, microseismic monitoring, has been used to help provide precursors to those violent failures. Unfortunately, these different styles of study have never been used in tandem. We report in this study the unique opportunity to have both static and dynamic instrumentation available for monitoring a longwall panel in a deep western coal mine and show that the two methods used in tandem provide information to understand the causes of a major bump. Several static rock mechanics instrumentation sites were carefully chosen along the longwall panel in the coal seam, packwalls, roof, and floor to provide the stress history during mining, including the stress redistribution that occurred before and after the major failures. Monitoring of the shield pressure on selected shields of the longwall face revealed that the cyclical loading anticipated during normal caving processes was not occurring. In addition, by locating each microseismic event (rock noise), the areas that were not adjusting to the changing stress field were clearly delineated by a lack of microseismic activity. The area of the longwall panel that did not adjust to the changing conditions ultimately failed. The combination of static and dynamic rock mechanics instrumentation data analysis provided the necessary information to determine the interaction of the structural members and the cause of the major failures at this mine.

Jan 1, 1988

By David Hill

"End of panel longwall face recovery is almost certainly the most involved recurring geotechnical problem faced by operators, with major loss potential should problems occur. The paper presents Australian experiences and updates the outcomes of an industry sponsored research project on the geotechnical issues associated with conventional longwall recoveries.A number of critical features of the geotechnical environment, support design and mining geometry have a pronounced impact on ground control during face recovery. A model of roof behaviour at the take-off point has been developed and validated. Key geotechnical issues include low roof competency, an adverse weighting environment, geological structure, horizontal stress concentrations at the gate ends and the capacity and. integrity of the shields. All of these are identifiable either at the support design stage or, at worst, prior to the start of powered support removal, which is the critical stage of the recovery process.Key aspects of the geometry and process are the ability to maintain powered support resistance during bolt-up and recovery, the direction of shield removal, the impact of chutes and the speed of the shield removal process.The author presents case studies that illustrate these issues and the associated ground behavior.INTRODUCTIONEnd of panel face recovery is almost certainly the most involved recurring geotechnical problem faced by operators, with major loss potential should problems occur. However, unlike most geotechnical aspects of coal mining, very little research has historically been undertaken on the issue of conventional longwall recoveries. This is in marked contrast to the design of pre-driven recovery rooms, an issue which has attracted considerable research interest (Thomas, 2008). In 2006, Strata Engineering completed an Australian industry (ACARP) sponsored research project aimed at defining and minimising the geotechnical threats during longwall face recovery (Strata Engineering, 2006). The research project had the overall objective of developing guidelines for the specification of ground control strategies, so as to minimise the likely geotechnical threats relating to the safety, operational costs and production delays associated with the recovery of a longwall face."

Jan 1, 2010

By Behdeen Oraee

Constructing tunnels underground is generally described as a high-risk activity because conditions in the surrounding area tend to be unpredictable. This would and can create unique dangers in every situation. It is important to gain a deep understanding of the risks associated with tunneling in order to reduce the likelihood of their occurrence and severity of their consequences should they occur. For this to be achieved, different risks should first be evaluated and ranked according to their relative importance and criticality. The Amir Kabir tunnel is considered one of the most dangerous tunnels in Tehran, Iran, in terms of the risks involved in its excavation and their potential consequences. In particular, part T4 of the tunnel passes through a zone of different strata and also a compound of various soils. This paper studies part T4 of the Amir Kabir tunnel from a risk analysis and risk management point of view. In doing so, factors increasing total cost, causing delay in the project completion time, decreasing the operation rate and downgrading project quality were identified and ranked according to their importance using the aggregate primary index risk method. For this purpose, a comprehensive questionnaire was designed and completed by tunneling experts. By responding to the questionnaires, the experts determined the relative likelihood of occurrence of the studied factors and their potential consequences. As a result, the experts suggested several alternatives to reduce the risks involved in this particular study. Moreover, the experts completed new questionnaires whilst taking into account different alternatives. In the next step, the risks before and after applying the alternatives were compared. As a result of performing the said analyses, it was concluded first that the aggregate primary index risk is an effective tool in identifying the risks involved in such projects. Second, it was concluded that, by taking into account different alternatives when analyzing and ranking the risks, severity of the said risks can potentially be reduced. Also, by considering such matters when analyzing tunneling risks, the projects? efficiency can greatly increase as a result of reducing risks that threaten financial and human resources. The approach introduced in this paper, together with the methodology described, can be adopted by the mining design engineer in all similar situations. They will be of particular advantage in such methods as room and pillar mining, where the number of similar tunnels required is high.

Jan 1, 2014

By Zbigniew Lubosik, Andrzej Walentek, Stanislaw Prusek, Sylwester Rajwa, Aleksander Wrana

"Underground coal gasification (UCG) provides a solution to supply electricity from high ash coal or deep deposited seams. The coal is consumed in situ, and, accordingly, the ash is left underground. UCG could play a major role in the future of coal, which is expected to fuel 44% of the world’s energy in 2030, in a more environmentally friendly and commercially viable manner. Nevertheless, it is known that the UCG can impact the environment. One of the most important factors in safe UCG process should be the evaluation of rock mass quality and the monitoring of its behaviour. The changes of rock mass parameters and quality have an influence on numerous aspects, such as subsidence and the stability of underground workings in georeactor vicinity, however, they also increase the possibility of pollutant migration through fractures and pores. These issues are especially important in cases of gasification conducted in an operating mine or on areas of high ecological vulnerability. This paper details observations made in two underground trials of UCG performed in Poland recently. The first of which is the Experimental Mine Barbara (under the project entitled HUGE-2 Hydrogen oriented underground coal gasification for Europe – Environmental and Safety aspects, (Wiatowski et al., 2015). The other trial has been conducted at an operating mine, Wieczorek, which is in the framework of a research project on the development of coal gasification technology for highly efficient fuel and electricity production (Czaplicka-Kolarz et al., 2013). During these trials, investigations were carried out aimed at assessing geomechanical parameters of rock mass and support behaviour in surroundings of UCG geaoreactors. Investigation comprises assessment of geomechanical parameters of coal, floor and roof strata, roof displacements, and concrete support strength parameters variation, as well as standing steel support load. Hydraulic penetrometer, endoscopic camera, Schmidt hammer, pull-out method, telltale, and ground penetration radar (GPR) were used in the investigation. Research conducted at both EM Barbara and Wieczorek Collieries revealed that the UCG process did not adversely affected the competency of rock mass (expressed by number of fissures and strength parameters of rocks), the stability of roadways and the support performance in the areas located in the vicinity of the georeactors."

Jan 1, 2017