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By Adam Mackenzie, Dan Payne, Yass-Marie Rutty

"Historically, the Crinum mine has experienced significant falls of ground when longwall production slowed to prepare for recovery in weak roof areas. These conditions continue through the recovery process and result in both safety concerns and delays. When mine plans and exploration revealed that most of the mine's future longwall recoveries were located in weak roof areas, a decision was made to try pre-driven recovery roads as a solution to the problem. After completing eight pre-driven recovery roads with varying degrees of success and numerous lessons, the Crinum North mine now utilizes a modified Pre-driven Recovery Roadway (PDRR) to improve the longwall take-off process in weak roof areas. During mine development, a standard roadway is driven where the final recovery location of each longwall is planned. After the installation of secondary support, the PDRR is backfilled with a cement-flyash mix to provide support to the roof, and confinement to the ribs and floor of the roadway. The method has been refined over the last four years to provide greater strata stability and improved operational and safety performance compared with conventional take-offs at Crinum, and has resulted in a site record of longwall relocation in 11.5 days (pull mesh to picks in coal). This paper describes the evolution of the PDRRs from Crinum East to Crinum North, including lessons from initial attempts and changes to the secondary support regime, the operational approach during the final stages of retreat, the backfill strategy and plans for the future.INTRODUCTIONThe Crinum mine is the underground component of BHP Billiton Mitsubishi Alliance's (BMA) Gregory Crinum mine, located northeast of Emerald, Queensland (Figure 1).The Crinum mine has a history of roof control problems coming into and during longwall recoveries. Weak roof, combined with the slow mining, which is a consequence of preparing for equipment recovery, pulling mesh (which also creates tip-to-face issues), and the lengthy bolt-up process, often results in loss of immediate roof and subsequent roof falls. In fact, approximately 50% of the first 13 longwall recoveries (which were at depths of 180 to 200m) experienced roof fall delays, the longest of which took four months to mine the last pillar and recover the longwall. This recurring problem prompted the mine to investigate options to reduce or eliminate the problem."

Jan 1, 2016

By Mark F. Sindelar, Yi Luo, Hua Jiang, Michael T. Shook

"Convergence of roof and floor in underground mine openings is a common occurrence. This convergence not only adversely affects the ability of workers, equipment and supplies to travel through the mine, it also reduces the effectiveness of the mine ventilation system, which is essential for the dilution of methane gas and airborne respirable dust. While installing secondary standing supports to control floor and roof convergence, such supports, by nature, partially obstruct a portion of the airway. These added obstructions inhibit the ability of the ventilation system to operate as efficiently as it could by increasing the resistance in and reducing the cross-sectional area of the airway.This study introduces and demonstrates the benefits of The Eye CAN™ standing roof support, which controls floor and roof convergence and is less obstructive to air flow than conventional wooden cribs. Laboratory findings show that the normal resistance of a supported lined airway is reduced by using this new product from Burrell Mining Products, Inc., while providing the same roof support characteristics of an established product-The CAN®. Load vs. displacement curves generated from laboratory tests demonstrated that this new product behaves with the same roof support characteristics as others in The CAN product family. Ventilation data gathered from a simulated mine entry was then used for computational fluid dynamics (CFD) modeling. The CFD analysis showed an improvement with The Eye CAN versus other accepted forms of standing roof support.This proof-of-concept study suggests that, when using this new product made by Burrell Mining Products, Inc., not only will the convergence from the roof and floor be controlled, but airway resistance will also be reduced.INTRODUCTIONOne of the basic elements of underground mining is the necessity to support the mine roof. It is well-known that easier reserves have been mined so that today's underground mines present challenging conditions. Factors influencing roof support decisions include mine depth, mining method, overburden composition, and agency regulations. Mining engineers, therefore, have to balance three objectives: safety, engineering, and cost. While safety is obviously paramount, and engineering often complements safety, the cost effectiveness of any product, method, or device warrants additional consideration in today's harsh business climate. Avenues for adaptation and improvement are found at the intersection of the three objectives."

Jan 1, 2016

By Enguang Zhu, Kangning Zhang, Yang Li

"Due to the use of outdated mining technology or room and pillar mining process in small coal mines, the coal recovery ratio is only 10% - 25%. In many regions of China: the damage area caused by the small coal mines amounted to nearly one hundred square kilometers. Therefore, special mining techniques must be taken to reclaim the wasted resource in disturbed coal areas. This paper focuses on the different mining methods by analyzing the longwall panel layout and abandoned gateroad (AG) distribution in in the abandoned area of Cui Jiazhai Coal Mine in northwestern China. On the basis of three-dimensional geological model, FLAC- 3D numerical simulation was employed. The abutment pressure distribution was simulated when the panel face passed through the disturbed areas. The proper angle of the inclined face was analyzed when the panel face passed through the abandoned gateroads. The results show that the head end of the face should be 13-20m ahead of the tail end. The pillars on both sides of abandoned gateroads had not been damaged at the same time, and no large-area stress concentration occurred above the main roof. Therefore, the coal reserves of disturbed areas can be successfully recovered by using underground longwall mining. INTRODUCTIONDuring the 70-90's, there were a lot of small coal mines in China. Due to their disordered mining, most of the small coal mines left a great many abandoned gateroads (defined as AG in this paper) and a large area of damage coal seam. In these type of coalfields, there exist many mining risk issues, including nonuniform stress in the overburden, flooding and hazardous gases accumulated in the gob. So how to lay out a longwall panel and successfully mining under this type of abandoned small mines is a big issue nowadays in China.As mentioned above, longwall panel is being performed in the damaged coal seams in order to increase recovery of coal reserves (Wang, 2009). However, the abandoned geteroads intersect to each other all around the area. So a series of production issues arose while the panel face is passing through these AG. Gang and Gong (2015) analyzed the roof stability and abutment pressure distribution during the face was passing those AG that were parallel and inclined to the faceline. Xie, et al. (2015) proposed the ground control mechanism by passing the AG in top-coal caving longwall mining. He recommended to stop the face advance until the roof is over, using high strength bolts and cable bolts, and grouting consolidation. This paper studies the different mining methods by analyzing the longwall panel layout and AG distribution in damage coal seams. Theoretical analysis and field observation were conducted to determine the overburden movement when the face was advancing under the AG. The pillar between face and parallel AG changes from elastic to plastic and eventually to the residual supporting status. All these three status was combined with the roof structure to establish the theoretical model to calculate the shield support capacity. Numerical modeling was employed to simulate the pillar stability and determine the abutment pressure distribution as the face inclined to the AG during longwall mining."

Jan 1, 2016

By John R. Poland, Benjamin Mirabile

"There are significant ground support hazards to both personnel and equipment when longwall equipment must mine through cross-panel entries. Backfilling support strategies are often cost prohibitive. Additionally, it is often very difficult to install backfill material in full contact with the mine roof in backfilled entries. This paper will demonstrate the use of fiber-reinforced concrete crib material as a method for standing support in longwall cut-through entries. Despite conceptions of poor performance in potentially high convergence environments, fiber-reinforced concrete crib material can be used in longwall support environments subject to high abutment loads and convergence. Central to the proper design of these supports is the use of yield material between crib layers and at the mine roof/crib interface. The placement location of cribs within the cut-through entry has a significant effect on the main roof behavior and associated ground conditions in the longwall abutment zones. It is particularly important to engineer the proper load displacement characteristics of the installed crib to support expected ground conditions. The cost of fiber-reinforced crib supports is less than 50% of backfilling methods.INTRODUCTIONThe design and execution of a longwall cut-through is perhaps one of the most difficult and risky endeavors in the field of ground control. The magnitude of abutment loads and potential for ground failure present a significant safety hazard to underground personnel. In addition, there is significant financial risk, with replacement costs of face equipment exceeding $200 million. Faced with these consequences, it is both advisable and common for an engineer to design ground support with a significant margin of safety. This paper outlines a robust support system that possesses a significant margin of safety along with significantly lower costs than most other support systems employed in similar conditions.SITE PARAMETERSThe mine site described in this study operates in the Herrin No. 6 seam in southern Illinois. The seam height is typically 76- 84 inches. Mining height in gateroads and mains is typically over 96 in, and typical mining height on the longwall face is 82 in. The overburden depth is 950-970 feet in the area of the longwall cutthrough."

Jan 1, 2016

By Houquan Zhang, Ming Li, Guimin Zhang, Bei Zhang

"The support quality of bolts in deep roadways is one of the important factors for efficient and safe coal production. A new kind of non-destructive testing technique and equipment was used to monitor the axial bolt load in real time in deep roadways. Based on the test results, the working status of bolt support in deep roadways was evaluated. The research results show that the variation characteristics of axial bolt load is consistent with the distribution characteristics of rock pressure no matter whether it is in the initial support stage or mining disturbance stage. The axial load of bolts located 20m outby the development face has an overall rising trend within 3-5 days after installation. Within a certain distance in the front abutment pressure zone in front of the face, the axial bolt load increases with the advance of coal extraction. When coal and rock in the abutment pressure zone yield, the axial bolt load is dropped correspondingly. This kind of non-destructive testing technique provides an advanced means of detection and evaluation on bolt support quality.INTRODUCTIONMany coal seams more than 800m deep are being mined in eastern China. Roadways of large cross-section are being developed in coal seams more than 600m deep in western China (Kang et al. 2014). Moreover, these roadways are commonly supported by roof bolts and have encountered many support problems, including soft rock strata, intense mining disturbance, and abnormal tectonic stress. The stability of its surrounding rocks is difficult to maintain, the roof bolt even fails before mining (Shen 2014; Jiang et al. 2015). Therefore, it is very important to develop an effective method to detect the bolt quality in real time and evaluate the bolt's safety status.During installation of roof bolt, the installation quality is heavily affected by installation equipment and tools, field conditions, and operators' skills (Li et al. 2005; Shan 2009). The anchorage length will be shorter than the designed one if the resin cartridges are pushed to the bottom of excessively long drill hole and stay there without being shredded and mixed. The support function of the bolt would be weakened by the shorter anchorage length."

Jan 1, 2016

By William J. Conrad, Ryan J. Molka, Erik C. Westman

"In order to study pillar and overburden response to retreat mining, a ground control program was conducted at a Central Appalachian mine. The program consisted of several monitoring methods including a seismic monitoring system, borehole pressure cells in the pillars, and time-lapse photogrammetry of the pillar ribs. Two parallel geophone arrays were installed, one on each side of the panel with the sensors mounted 3m (IO ft) into the roof. A total of fourteen geophones recorded more than 5,000 events during the panel retreat. A MIDAS datalogger was used to record pressure from borehole pressure cells (BPCs) located in two adjacent pillars that were not mined during retreat. A series of photographs were taken of the pillars that had the BPCs as the face approached so that deformation of the entire rib could be monitored using photogrammetry.Results showed that pillar stability and cave development were as expected. The BPCs showed an increase in loading when the face was 115 m (380 ft) inby and a clear onset of the forward abutment at 30 m (100 ft). The photogrammetry results displayed pillar deformation corresponding to the increased loading. The microseismic monitoring results showed the overburden caving inby the face, again as expected. The significance of these results lies in two points, I) we can quantify the safe manner in which this mine is conducting retreating operations, and 2) we can use volumetric technologies (photogrammetry and microseismic) to monitor entire volumes of the mine in addition to the traditional point-location geotechnical measurements (BPCs).INTRODUCTION AND BACKGROUNDExcavation of underground openings is a difficult job in a challenging environment. The rigor of the process is compounded by the lack of a method that allows quantification of changes within the rock mass as excavation progresses. Statistics kept by the Department of Labor, Mine Safety and Health Administration show that 16% of fatalities and lost time incidents in the underground mining industry are due to unexpected rock mass failure (MSHA, 2015). A recent example is the Crandall Canyon, Utah, coal mine accident caused by the vertical collapse of a longwall coal mine on August 6, 2007 (Dreger, Ford, Walter, 2008)."

Jan 1, 2016

By Michael Gauna, Christopher Mark

"Underground coal mining in the U.S. is conducted in numerous regions where previous workings exist above and/or below an actively mined seam. Miners know that overlying or underlying fully extracted coal areas, also known as gob regions, can result in abutment stresses that affect the active mining. If there was no full extraction, and the past mining consists entirely of intact pillars, the stresses on the active seam are usually minimal. However, experience has shown that in some situations there has been sufficient yielding in overlying or underlying pillar systems to cause stress transfer to the adjoining larger pillars or barriers, which in turn, transfer significant stresses onto the workings of the active seam. In other words, the overlying or underlying pillar system behaves as a ""pseudo gob."" The presence of a pseudo gob is often unexpected, and the consequences can be severe. This paper presents several case histories, summarized briefly below, that illustrate pseudo gob phenomenon:• Pillar rib degradation at a West Virginia mine at 1100-foot (335 m) depth that contributed to a rib roll fatality.• Pillar rib deterioration at a Western Kentucky mine at 570-foot (175 m) depth that required pillar size adjustment and installation of supplemental bolting.• Roof deterioration at an eastern Kentucky mine at 1300- foot ( 400 m) depth that stopped mine advance and required redirecting the section development.• Coal burst on development at an eastern Kentucky mine at 1700-foot (520 m) depth that had no nearby pillar recovery.• Coal burst on development at a West Virginia mine at the relatively shallow depth of 1100 feet (335 m) that also had no nearby pillar recovery.The paper provides guidance so that when an operation encounters a potential pseudo gob stress interaction the hazard can be mitigated based on an understanding of the mechanism encountered.INTRODUCTIONThe U.S. underground coal mining industry has conducted mining in multiple seam environments, where the active mining has underlying or overlying old workings at varying interburden distances, throughout its history. Often no serious consequences arise from the multiple seam mining. However, sometime mines have been confronted with hazards from underlying or overlying workings that include localized roof and rib failure, pillar system failures through propagating roof falls and floor heave, and also pillar bursts."

Jan 1, 2016

By Meng Xiao, Peng Huang, Lizin Lan, Feng Ju, Shuai Guo

"Through changing the axial load on backfilling material compaction test to reflect different overlying strata pressure on backfilling material, the stress-strain relations in the compaction process of backfilling material under the geological condition can be obtained. Based on the characteristic of overlying strata movement in backfill mining, a model of roof thin plate is established. By introducing the stress-strain relation in compaction process into the model and using RIZT method to analyze the bending deformation of roof, the bending deflection and stress distribution can be obtained. The results show that the maximum roof subsidence and maximum tensile stress occurring at the center are 255mm and 5 MPa, respectively. Tensile fracture of roof under the geological condition of Dongping mine did not occur. The dynamic measurement results of roof in Dongping mine verify the theoretical result from the aforementioned model, thereby suggesting the roof mechanical model is reliable. The roof thin plate model based on the compaction characteristic of backfilling material in this study is of importance to research on backfill mining theories and application of backfilling material characteristics.INTRODUCTIONSolid backfilling mining (SBM) is a green mining technology in which the solid waste materials is placed into the gob to support the overlying strata and to control roof's subsidence and movement (Miao, 2012; Miao et al., 2010, 2015). SBM has been successfully used in several mines to solve many problems, including coal extraction under buildings, water bodies and railways, surface subsidence, and environmental problems. Good results have been obtained in many mines (Zhang et al., 2009). The key in the application of SBM technology is controlling strata movement. However, the critical factor influencing the controlling effect of strata movement is compaction characteristics of backfilling materials. Thus, a roof model of SBM is built based on the filling materials' compaction characteristics. A subsidence equation and the critical failure condition of roof was given and field verification was performed at Panel 15061 of Donping Mine."

Jan 1, 2016

By Douglas Tesarik, Mark K. Larson, Habte Abraham, Heather E. Lawson

Dynamic failures, or "bumps", remain an imperative safety concern in underground coal mining, despite significant advancements in engineering controls. While many factors have been empirically linked to the occurrence of dynamic failure events, identifying a consistent, repeatable set of criteria within a field setting has proven elusive; conditions generally associated with dynamic failure might produce an event at one site, but not another. Conversely and more troubling, dynamic failure could occur where relatively few of these factors exist. The presence of spatially discrete, stiff roof units, such as paleo channels, are one such feature that has been linked to the occurrence of dynamic failure events. However, an empirical stratigraphic review investigating the relative frequency of discrete units in bumping versus non-bumping deposits indicates that no significant difference exists based on this criterion alone, and that instead an apparent relationship exists between reportable bump history and the overall character of the host rock with respect to stiffness. Due to the complexity of the bump problem, however, these results are not conclusive, as they do not take into account any variable other than the presence or absence of stiff members in the roof lithology; To weight the relative impact of changes in a single variable, such as the thickness or location of sandstone members, it must be examined in isolation-i.e. in a setting where all other variables are held constant. Numerical modelling provides this setting, and the effects of variability in a stiff discrete member in a hypothetical longwall mining scenario are investigated within the context of three stratigraphic "types'', as determined by the ratio of stiff to compliant stratigraphic members; Compliant, Intermediate and Stiff A modelling experiment examines changes in rupture potential in stiff roof units for each stratigraphic type as discrete unit thickness and location are manipulated through a range of values. Results suggest that the stiff-to-compliant ratio of the host rock has an impact on the relative stress-inducing effects of discrete stiff members. In other words, it is necessary to consider both the thickness and the distance to the seam, within the context of the host rock, to accurately anticipate areas of elevated rupture induced hazard; acknowledging the presence of a discrete unit within the overburden in general terms is an insufficient indicator of risk. Through modelling of anticipated changes in the placement and dimensions of discrete units within their stratigraphic setting, elevated rupture-induced bump hazard can be anticipated on a case by case basis. Were similar modelling studies conducted at mine sites in tandem with tracking of problematic discrete stiff units, areas of elevated rupture risk could be anticipated in advance of mining. Developing this predictive capability beyond identifying rupture potential in discrete roof members is essential to the eventual elimination of dynamic failure related worker injuries and fatalities. As stress is a necessary component in the occurrence of dynamic failure events, this finding helps to refine our understanding of the role of individual stiff, strong roof members in bumping phenomena, and suggests that a more holistic view of overburden lithology, combined with site-specific numerical modelling, may be necessary to achieve greater miner safety.

Jan 1, 2016

By I. Sedat Buyuksagis, Jamal Rostami, Ali Naeimipour

"Improving the safety of underground openings and optimizing ground support systems requires reliable ground characterization. This includes understanding the joints, discontinuities, and rock strength. Joint information can be obtained from borehole cameras, but measuring in-situ rock strength is very difficult. Use of borehole probes can be an ideal and efficient way to meet this requirement. This paper discusses the development of the Rock Strength Borehole Probe (RSBP) and presents the preliminary laboratory/field test. This device can be an accurate, flexible, quick, non-disruptive, and cost-effective alternative to estimate the rock strength inside boreholes in underground mines and tunnels. In addition, the scratch testing procedure in the laboratory by means of a newly developed miniature linear cutting machine is explained. Based on the results of these tests, two equations are developed to estimate the uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of the sedimentary/metamorphic rocks. These equations, are based on testing 27 different sedimentary, igneous, and metamorphic rocks by full-scale scratch tests, including the cutting tests by a miniature disc. The results show a good correlation between the normal force and the compressive strength of sedimentary rock if the depth of the scratch is known. No significant correlation was observed for igneous rocks, due to the impacts of grain size.INTRODUCTIONEstimated rock mass properties are essential input for geomechanical studies and stability analysis for any structure constructed in or with rock. The availability of geological information is the crucial component of rock mass classification. One of the important parameters in evaluating rock mass properties is the intact rock strength. This parameter is usually measured by testing the core samples, obtained from exploration boreholes. These samples are subsequently tested in geomechanics laboratories. The test results offer limited information about the rock at the few boring locations despite all the efforts and costs. In addition, these results may not necessarily be representative of the behavior of the rock in the field as the test cannot provide the insitu condition of the ground."

Jan 1, 2016

By Dongfeng Yun, Zhu Liu, Wendong Cheng, Zhendong Fan, Dongfang Wang, Yuanhao Zhang

"For the purpose of studying the strata behavior due to multislicing top coal caving longwall mining along-the-strike direction in steeply dipping extra thick coal seams, the shield support pressures of the upper and lower slices of Panel 37220 in Dongxia coal mine were monitored using the KJ513 dynamic monitoring system. The set up rooms adopted the ""horizontal line-arc segmentinclined line"" form and used different types of shield supports. The results showed that the strata pressure of upper slice Panel 37220- 1 changed slightly along the strike direction, while along the dip direction it exhibited strong to weak pressure from bottom to top. The first weighting interval oflower slice Panel 37220-2 was about 60.Sm, and the average periodic weighting interval were about 22.6m. The strata behavior of Panel 37330-2 exhibited a spatiotemporal characteristic in that periodic weighting occurred first in the middle-upper part, followed by the middle and upper parts, arc segment, and finally the lower part. During the periodic weighting, the weighting interval and intensity also exhibited strong space characteristics. The average dynamic load coefficient was 1.48 and the maximum lateral pressure of the side shield was 900Kn1000kN.INTRODUCTIONThe steeply dipping coal seams account for about 20% of proven reserves and 10% of output in China (Wu, et al, 2014). About 50% of coal mines in the western China have steeply dipping seams, and are mainly distributed in Sichuan, Gansu, and Chongqing. When the steeply dipping seam employs longwall mining along the strike direction is employed, the waste rocks fill the gob nonhomogeneously along the dip direction, the deformation and caving of surrounding rocks exhibit obvious asymmetry and spatio-temporal characteristics with particular and complex strata behavior. In recent years, many research on strata behavior due to multi-slicing top coal caving longwall mining along-the-strike direction in steeply dipping extra thick coal seams have been performed with significant results (Shi, 1999; Wu, Xie, and Ren, 2010; Wu, Xie, Wang, and Ren, 2010). However, there has been a complete lack of research on monitoring the strata behavior due to multi-slicing top coal caving longwall mining in steeply dipping extra thick coal seam. Therefore, the strata behavior of multi-slicing panels 37220-1 and 37220-2 was systematically investigated in this research."

Jan 1, 2016

By Chaojun Fan, Du Wenzhang, Sheng Li, Hong-Hong Shi

"Coal and gas outburst is an extremely complex dynamic disaster in coal mine production process which will damage casualties, equipment facilities and disorder the ventilation system by suddenly ejecting a great amount of coal and gas into roadway or working face. This paper analyzed the interaction among the three essential elements of coal and gas outburst dynamic system. A stress-seepage-damage coupling model was established which can be used to simulate the evolution of the dynamical system, and then the size scale of coal and gas outburst dynamical system was investigated. Results show that the dynamical system is consisted of three essential elements, coal-gas medium (material basis), geology dynamic environment (internal motivation) and mining disturbance (external motivation). On the case of C13 coal seam in Panyi mine, the dynamical system exists in the range of 8-12 m in front of advancing face. The size scale will be larger where there are large geologic structures. This research plays an important guiding role for developing measures of coal and gas outburst prediction and prevention. INTRODUCTIONCoal and gas outbursts are a complicated mine gas dynamic phenomenon that pose a serious threat to coal mine safety production. Since the first recorded coal and gas outburst occurring in Isaac coal mine of the Lule coal field in 1843, more than 40,000 outbursts have occurred in the world. China ranks first in outburst frequency and intensity. In recent 20 years, China on average increases 37 pairs of coal mines and more than 280 times outburst accidents every year (Yan, 2013). The coal and gas outburst occurred on Oct 20, 2004 in Daping Coal Mine, Zhengzhou Coal Group, caused serious gas explosions and ejected 1,894 tons of coal into the face, causing 148 fatalities. In recent years, despite implementation of numerous control measures, coal and gas outburst still occur frequently ash mining depth and mining intensity increase. The outburst mechanisms can be summarized in the following four aspects: the gas leading role hypothesis, the geostress leading role hypothesis, the chemical effect hypothesis, and combination hypothesis. The last hypothesis has won the acceptance of most scholars who consider that an outburst is the result of combined effect of stress, gas and coal (Yu, 1992).Numerous experimental measurements and numerical simulations were conducted to investigate the permeability and damage development process in coal seam. Sobczyk, et al (2011) carried out a laboratory research of the influence of sorption processes on gas stresses leading to coal and gas outbursts. Wang, et al (2013, 2015) conducted laboratory experiments to investigate the rapid decompression and desorption induced energetic failure in coal using a shock tube apparatus. Xu, et al (2006) developed a coupled gas flow and solid deformation numerical model and applied to simulate the coal and gas outbursts in underground coal mines using RFPA2D-Gasflow. An, et al (2013) and Xue (2014) analyzed major parameters and the effect of gas desorption on outburst initiation and established a model of gas migration and mechanical processes during excavation."

Jan 1, 2016

By Wenbing Guo, Yi Tan, Erhu Bai

"It is important to study the mining technology under structures for raising the coal resources recovery ratio. Based on the geological and mining conditions, the top coal caving harmonic mining technique in thick coal seam beneath the earth dam was put forward and studied. The 5 factors such as the panel mining direction, panel size, panel location, panel mining sequence and panel advance velocity were taken into account in this technique. The dam movement and deformation were predicted after the thick coal seam mining and the effects of mining on the dam were studied. By setting up the surveying stations on the dam, the movement and deformation of the dam were observed during mining. By taking some protective measures on the dam, the top coal caving mining technique in thick coal seam beneath the earth dam was carried out successfully. The study demonstrates that harmonic mining in thick coal seam is feasible under the dam. The safety of the earth dam after mining was ensured and the coal resources recovery ratio was improved.The surface movement and deformation caused by coal mining not only influence the ecology environment in the mining area, but damage the surface structures such as buildings, railroads, highways, water bodies and damsr1-31_ The movement of strata and surface caused by mining had disturbed various aspects of industrial and agriculture productions in the mining arear41. The earth dam is a very important water retaining structures, so it must makes sure the safety of dam if mining under it. Therefore, to study the effect of mining on dam and control measures to ensure safety of mining under the dam are important factors for improving the mining recovery ratio, reliving the mining continuity, preventing or reducing damage to the dam.By means of the harmonic mining technologyrs1, theoretical analysis and field observation, the mining method under an earth dam and the mining influences were studied and analyzed in this paper. The mining of a thick coal seam under the dam was carried out safely and successfully."

Jan 1, 2016

By Daniel W. H. Su

"This paper presents results from a recent study conducted to evaluate the effects of longwall-induced stresses and deformations on the mechanical integrity of shale gas wells drilled over a longwall abutment pillar. The primary objective is to demonstrate that a properly constructed gas well in a standard longwall mining abutment pillar can maintain mechanical integrity during and after mining operations. Successful designs would allow for the safe recovery of both coal and gas reserves. Major elements of this comprehensive study include: (1) modeling of rock movements to predict impacts on gas wells, (2) measurements of actual rock movements at the surface and in the subsurface, (3) measurements of actual impacts on test wells designed similarly to real shale gas wells, ( 4) comparison of modeling results to actual rock movements to validate the model, and (5) employing the validated models to evaluate various casing and cementing designs to minimize casing deformations and absorb longwall-induced strains along the intermediate and production casings.A study site was selected over a southwestern Pennsylvania coal mine, which extracts 1,500-ft-wide longwall faces under about 600 feet of cover. Four test wells and four monitoring wells were drilled and installed over an abutment pillar with 125-ft by 275-ft centers. The four test wells were drilled to a depth of 642 ft, or 42 ft below the Pittsburgh seam, and were designed like a real shale gas well, except that only three casings (namely the surface, water protection and coal protection casings) were installed in each well. Casing steel grades, wellbore diameters and annular spaces were purposely varied in each of the four test wells to evaluate the effect of different well designs. The four monitoring wells - one vertical extensometer and three in-place inclinometers (IPI) - were drilled to different depths to measure the vertical settlement and horizontal displacements as a result of longwall mining on both sides of the abutment pillar. In addition to the test wells and monitoring wells, surface subsidence measurements and underground coal pillar pressure measurements were conducted as the 1,500-ft-wide longwall panels on the south and north sides of the abutment pillar mined by."

Jan 1, 2016

By William Kendall

"A tremendous amount of research, analysis, and engineering time is used to design a proper roof support system including the type, length, and location of the roof bolts. Unfortunately, since the roof bolts are being installed under unsupported roof, the exact location for the bolt holes cannot easily be determined and then marked onto the roof. The actual location where the roof bolts are installed is typically left to visual estimates by the operator. This frequently results in either (1) the operator overestimating the space between roof bolts and installing more bolts than required, thereby increasing cost and reducing efficiency; or (2) the operator underestimating the space between roof bolts and installing fewer bolts than required, thereby reducing safety, leading to potential roof failure or possible violations.A patented laser light grid system has been developed by J .H. Fletcher and Monitech, a South African Company, to aid in proper machine positioning in the heading and proper bolt spacing. The system can also show when an entry is over width, requiring additional roof support. The system is relatively simple and inexpensive. The concept is applicable across the full range of roof bolters from low to high seams and from single boom to multiple boom bolters. The system can be configured to meet most bolting patterns.The system consists of several very small 1 milliwatt, class 2, line type lasers that project a line onto the roof. The actual laser is 27mm in diameter x 47mm long (1"" x 1.8""). In South Africa it is approved as intrinsically safe and is mounted inside a 50mm diameter x 64mm long (2""x 2.5"") protective housing. In the USA, we are seeking an X/P approval and the laser will be mounted in a headlight enclosure 110mm diameter x 125mm long (4.3"" x 5""). Fifteen of the systems have been installed in South African coal mines with good results.The system has aided the mines in meeting the bolt spacing tolerance used in the Republic of South Africa, which is typically 15% of the nominal bolt spacing or 7 in for 4-ft bolt spacing. Fletcher has submitted the system to MSHA for approval in the US."

Jan 1, 2016

By Bowler Jonathan, Lorraine Kent, Tereza Crisu, Stuart Walker, Nicholas Lightfoot

"It has been the practice in Europe to extract the most economic seams first: taking the seams sequentially, top down, to avoid operating within the fractured strata formed by the subsidence trough above previously mined coal seams. In the 1990s, the UK coal industry found itself at a number of sites having to operate over one or more previously mined seams. This led to specific geotechnical challenges with respect to maintaining economic, safe and stable rectangular roadways with rock-bolted support.Within this paper, the current challenges and mitigation strategies of overmining in the UK are described following the completion of a -three-year European Commission-funded project in 2015. The challenges and mitigation strategies are related to:• A case study with overmining of older workings of variable geometry;• Numerical modeling for overmining layout and support design; and• A case study site planning mine layout when considering future overmining.INTRODUCTIONAt the first case study site, case histories were examined for a mine operating at a depth of approximately 700 meters where five longwall panels were extracted above workings 35-40 m below. The overmining of various extraction geometries below led to challenging conditions in areas of high vertical stress concentration. It was found that results from one longwall panel could be suitably used to predict behaviour in a subsequent panel. The experience was used to update previously existing guidelines on the positioning of roadways in relation to subsidence troughs. Existing guidelines recommended that only as a last resort should longwalls be planned to retreat over narrow pillars, or from solid ground into a subsidence trough. Existing guidelines regarding the layout of overmining panels are conservative, and new work indicates that such multi-seam geometries are possible with appropriate support management strategies."

Jan 1, 2016

By Guorui Feng, Min Zhang, Yi Luo, Jian Yang, Yujiang Zhang, Junwen Bai

"Safe mining of coal seam sandwiched between abandoned upper and lower room-and-pillared mines (ULPM) ·is increasingly becoming the focus of attention in recent years, which is closely related to the damage intensity of the upper and lower interburdens. The #7 seam with ULPM in Baijiazhuang coal mine was selected for this research. According to the mining and geological conditions, the vertical stress and plastic zone distributions were determined first by numerical simulation. Then, a theoretical model based on the elasti-plasticity theory was developed. The stress distribution and failure zone created in the interburden by mining the upper and lower seams were determined. Finally the feasibility of mining #7 seam between the abandoned upper and a lower seam was evaluated. The results show that: (1) the distributions of abutment pressure and plastic zone coincide, both of which can be used to evaluate the failure zone in ULPM. The failure zone penetrates the whole upper interburden, while only parts of the lower interburden fail. (2) the theoretical failure zone coincides with the maximum distribution zone of abutment pressure and plastic zone obtained by numerical simulation: the failure zone height in the lower interburden is less than its thickness, while that in the upper interburden is larger than its thickness. (3) the #7 seam is located in the failure zone created by the upper seam room-and-pillar mining, which leads to well-development fractures and blocky fragments in the roof, thereby it is unstabled. (4) when mining the #7 seam in the interburden, the key is to control the roof strata and proper support measures should be taken timely to ensure safe mining.INTRODUCTIONMany coal mines in China mine the thick, superior and easily mineable resources preferentially, while the thin, inferior and difficult-to-mine resources were abandoned (Chappells and Trentrnann, 2015; Zhenfu, 2012; Xu, et al., 2015; Guorui, 2009). As the results of deficient geological data and shortage of investment capital, the residual coal resources distributes in many mining areas in China.In recent years, many residual coal seams sandwiched between the abandoned upper and lower room-and-pillar mines (ULPM) were explored in Shanxi Province, especially in the mining area of Datang, Xishan and Luan (Figure.1). The reserves of residual coal seams in ULPM are considerable, increasingly becomes the focus of attention among scholars and engineers."

Jan 1, 2016

By David R. Burkhard

"Comparative roof beam performance, as measured by delamination within the bolted horizon, was used to evaluate two types of roof bolt drill hole geometries in a development setting. Short encapsulation pull tests had demonstrated a higher grip factor in drill holes featuring helical grooves in the side walls in comparison to drill holes featuring continuous smooth to slightly rough walls. The study incorporated the two geometries during development mining in which fully grouted mechanically anchored bolts were installed as primary roof support.bolts were installed as primary roof support.The study site, in an entry adjacent to a longwall panel, was instrumented with extensometers and data collected during longwall retreat. Statistical analysis was conducted to validate null and alternative hypotheses used to compare drill hole geometries. Analysis yielded no statistically significant difference between drill hole geometries. Inspection of the data does reveal less delamination within the smooth walled site in comparison to the site containing grooved hole geometry.INTRODUCTIONFrom their introduction as a means of ground control over sixty years ago, roof bolts today are the primary mechanism of roof support utilized throughout mining. Whether through suspension, keying, or beam building, roof bolts are employed to reinforce the inherent strength of the strata comprising the immediate roof with the goal of creating a competent bolted horizon of sufficient load bearing capacity to be self-supporting for a given mine's design life, stress regime, and geomechanical properties.For grouted bolts in sedimentary strata, axial loading due to vertical rock movement and bending due to horizontal rock movement are the principal means of loading (Signer, 2000). Regardless of the type of bolt and extent of grouting employed, the success of any roof bolting design is determined, to a large extent, by the effectiveness of load transfer between the rock, grout, and bolt.At San Juan Mine, an underground longwall mine located in the northwestern corner of New Mexico, a number of different roof bolt types, grades, and lengths have been used over the years in an effort to optimize primary roof support. One common denominator shared throughout has been the use of full length grout. Load transfer for full length grout is achieved primarily through mechanical bonding between the grout and rock. It is this interaction that is the focus of the study described in this paper. The study assessed and compared two types of bolt hole geometries employed during gate road development at San Juan. Underground instrumentation and evaluation of the bolted roof provided the means of assessment and comparison."

Jan 1, 2016

By William G. Pariseau, Michael K. McCarter

"The challenge of estimating mine-wide subsidence and linkages to seismicity over tabular deposits is addressed by a special finite element technique (dual node - dual mesh). Subsidence and mine-induced seismicity begins near the face when caving occurs and propagates to the surface as extraction reaches a critical extent. Thus, the challenge is to obtain details at the face at the meter scale and also at the surface over the whole mine at the kilometer scale. Interactions between old and new sections of a mine are automatically taken into account with this technique. The finite element method is well established technology based on fundamentals of physical laws, kinematics and material laws. With this technique, no empirical ""scaling"" or fitting computer output by input data ""adjustment"" to mine measurements is necessary. Capability is demonstrated for doing practical whole-mine subsidence analysis from first principles. Mine-induced seismicity is shown to correlate well with face advance and element failure.INTRODUCTIONSeismicity associated with coal mining has been under study for several years by a team at the University of Utah. Team members include mining faculty, research geophysicists and students from the Departments of Mining Engineering and Geology & Geophysics. Mines in central Utah that have been studied include the Trail Mountain Mine (Pariseau, 2015; Pariseau and McCarter, 2015), the Beehive Mine, also known as the Des-BeeDove (Pariseau, 2014), and the Crandall Canyon Mine (Pariseau, 2015). These mines were developed from outcrops in the Wasatch Plateau coal field west of Price, Utah, where the topography is characterized by . steeply incised canyon drainages and high plateaus with relief of a thousand meters or so.Seismicity associated with coal mining in central Utah has been of interest for many years and includes studies in the Book Cliffs to the east of Price, Utah, where mining is still active (Smith et al, 1974; Agapito, Goodrich and Moon, 1997; Arabasz et al, 2001; Arabasz et al, 2002; Fletcher and McGarr, 2005; McGarr and Fletcher 2005; Maleki, 2005) and to the northwest (Ellenberger et al, 2001). Results of many micro-seismic studies are summarized perhaps best by lannacchione, et al (2005) in stating, ""Deviations from normal strata response can provide useful stability information.""This study concerns a fourth underground coal mine in the southern portion of the Wasatch Plateau coalfield, hereafter referred to as the MINE. Focus is on mining from 2004-2008 with the objective of examining mining in relation to seismicity."

Jan 1, 2016

By Srisharan Shreedharan, Gang Huang, Hongqing Song, Sijing Cai, Pinnaduwa H. S. W. Kulatilake

"Subsidence prediction due to ore extraction and backfilling during open stoping operations for an underground iron mine in China is reported in this paper. Geologic complexities including faults and interfaces between different lithologies, and the stoping and backfilling sequence adopted from the mine plans are incorporated in building a 3-D discontinuum numerical model. The stoping was simulated in two vertically stacked horizontal layers (Fig. 6), with a total of 16 stopes. Large displacements of up to 50 cm were predicted by the model along the roof of the stopes, and a maximum surface subsidence of 22.5 cm was predicted by the model . Backfilling was found to control subsequent deformation and subsidence. The extraction of the upper orebody led to relatively higher deformations in extracting the lower orebody. Finally, the predicted subsidences at all locations along a subsidence profile on the surface are shown. INTRODUCTIONThe Luohe iron (pyrite) mine, located in Hefei city, Anhui, is an underground mine in China, being mined through the open stoping and backfilling method. The orebody lies at a depth of about 400 m and has an average thickness of 250 m (Magang Steel Company, 2012a). Discovered in the 1960s, the location has a reserve estimate of 300 million tonnes, which have been mined since 2007. The orebody has been divided by the mining company into an east and a west section to facilitate planning for ore extraction.Figure 1 shows the surface above the underground mine, which is seen to contain many human settlements including villages, pastures and other infrastructure. These locations are sensitive in that they need to be protected from potential adversities due to the underground mining, such as surface subsidence. While it may be near impossible to completely eliminate the subsidence due to ore extraction, operations such as backfilling have been adopted by the mine in an effort to substantially reduce it. Hence, this paper focuses on describing the stability of stopes in the mine and estimates future subsidence in a part of the mining region through numerical modeling."

Jan 1, 2016