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By Yuanfei Chen, Jianfeng Zha

"China is the largest producer and consumer of coal in the world. The mining-induced surface subsidence has bad influences on the surface and structures above the surface. In order to minimize disasters, removal, reinforcement, or maintenance structures are often adopted. In the application of maintenance methods, it is necessary to carry out dynamic surface subsidence prediction to choose maintenance methods, optimize maintenance time, and evaluate the amounts of work. Time series methods and influence function methods are common for dynamic surface subsidence prediction, but the former is difficult to consider with underground mining conditions, and the latter has low prediction precision. Therefore, this paper develops a dynamic subsidence prediction model aided by field-measured data and realizes the model programming. The model could achieve high-precision prediction of dynamic surface deformation through optimizing the parameters in time by using field-measured data of surface subsidence. The research results of engineering cases show that, with the method of dynamic prediction, the standard error can be controlled in the range of 5%, greatly improving the accuracy of dynamic prediction of mining subsidence, which provides strong technical support for the maintenance and management of structures. INTRODUCTION With the rapid economic development and continued industrialization process, the demand for energy is growing in China. Today, China is one of the largest coal, oil, and gas consumers in the world. Coal consumption accounts for 47.7% of the total consumption in the world (Tian, 2016). In order to meet the demand for coal resources in the process of modernization, more and more coal mines carry out coal mining under villages, buildings, highways, and bodies of water. The mining-induced overlying strata and surface subsidence have bad effects on surface and on various structures (such as buildings, railways, highways, high-tension transmission lines) and could even cause various disasters (Williams et al., 1998; Bell et al., 2000; Doyle et al., 2002). Generally, methods, such as removal, reinforcement, or maintenance are taken to eliminate the adverse impacts (Kraatz, 1984; Bell and Genske, 2001; Wang, 1989). When reinforcement or maintenance is selected to remove bad effects, the proper maintenance methods must be chosen. In addition, maintenance time, as well as an evaluation of time it will take to do the work are necessary to predict the surface subsidence with high precision."

Jan 1, 2017

By William D. Gallant

This paper presents the results of a joint cooperative research project between the CANMET Cape Breton Coal Research Laboratory and the Cape Breton Development Corporation to observe the subsidence profile over the stopline of 2 West panel, Phalen Mine. A novel technique was designed and Implemented to determine vertical displacements of the overlying strata from within a near horizontal borehole drilled over the 2 West panel. Restrictions on data collection techniques due to the submarine nature of the coalfield are discussed. Development and implementation of the borehole technique using a piezometer and inclinometer Is described. Performance of the instruments and profiles obtained by them are presented and compared. Recommendations for design improvements are made to Improve the efficiency of the technique.

Jan 1, 1990

By Christopher Mark

The demographics and safety record of the pillar retreat segment of the U.S. coal industry was analyzed using statistics collected by the Mine Safety and Health Administration. Pillar recovery is practiced primarily by mines in Appalachia and the Midwest. Using 1993 data, the accident rates and productivity of a large sample of pillar re- mines were found to be similar to other room-and-pillar mines in the same geographic areas. Pillar recovery apparently accounts for about 10% of all U.S. underground production, but has been associated with about 25% of the mf and rib fatalities during 1989-96. However, of the 28 fatalities that were analyzed, only 4 occurred for which no citations were issued for violations of mining law. Nearly one- half of the fatal incidents occurred during the mining of the last lift or pushout. All four no-citation incidents occurred during the removal of the last lift during a "Christmas tree" extraction sequence.

Jan 1, 1997

By C. W. Bollier

In recent years, Peabody Coal Company has enjoyed a great amount of success using roof trussing as a secondary support system. Since 1975, over 180,000 trusses have been installed in 12 different Peabody mines with varying geological conditions. Projections from Peabody, and throughout the mining industry, indicate a continuous growth in the trussing principle for roof control. Peabody's primary supplier has sold over 1,000,000 trusses to 50 different mines throughout the country. (1) Roof trusses provide an improved means of controlling difficult roof conditions which, in turn, improves worker safety and mine production. Since the original development of the truss, (2) the only major modification to the trussing procedure has been the addition of the resin point anchor system in the mid-70's. The resin point anchor was the catalyst needed to provide a reliable anchor and create acceptance of the roof truss by both management and labor. Peabody began using trusses in their mines in 1975. For the first few years, most of the truss effort was geared toward determining proper anchorage, spacing, and gathering historical data. In recent years, Peabody's activities have centered on the development of improving trussing procedures. Through monitoring and trussing activities, a number of areas of improvement have been found.

Jan 1, 1982

By Richard R. Wilding

The United States Coal Mining Indus- try had the opportunity to greatly improve their roof control techniques during the nineteen seventies by the use of fully grouted resin roof bolts. This new tool was first approved for underground coal mines by M.S.H.A. ten years ago and during the next decade has been perfected to meet many problems previously thought to be unsolveable. The initial approved cartridge was very similar to the ones used in Europe in the nineteen sixties and since then has undergone a great deal of modification for our mines. These refinements in cartridge construction have been obtained by the close cooperation of resin manufacturers with mining personnel in perfecting pro- ducts customized to particular needs. This type of continuing program naturally necessitates a responsibility upon the resin anchor manufacturer to maintain a competant technical department. These roof control technicians by constant exposure to many of the most demanding underground problems, have developed through the years into leaders in successful applications. Today, Celtite has over twenty technically trained underground technicians with an accumulation of over one hundred years experience in resin anchors. Our documented technical reports are in excess of five thousand, involving over six hundred mines representing every major coal mining area in most mineable seams. This department has been the implement used to work with our research and development people in perfecting a continual line of improved resin anchors. This program has been a significant factor in leading the resin anchor industry into a position where approximately one third of the 1980 under- ground coal production used the fully grouted system. However, as gratifying as this accomplishment is, our experience has lead us to believe that there is an additional demand for a roof control system capable of combining the mechanical bolts ability to apply tension with resins proven superiority in anchoring. A significant number mines visited during the last decade had problems that we believed could be better answered by applying tension rather than the fully grouted approach. In most in- stances, their current mechanical installations were doing an adequate job until anchor slippage occured. Fully grouted systems solved this bleed-off problem. However, an acceptable number of falls still occured. In these some- what unique areas which we believe may amount to as much as fifteen percent of the total bolt installations, the need for improved anchors was a necessity. In developing this program we listed the ultimate requirements necessary for both the bolt and the anchor. These are for the bolt: A. Have one end manufactured so it can be grouted to the mine roof with polyester resin, obtaining a variable length from 12" to 36". B. Have a mechanism which allows the operator to tension the roof from zero to 10,000 psi. This mechanism should indicate if the roof is in compression and the bolt in tension. C. Have a mechanism which allows the operator to thoroughly mix the resin. D. The head of the bolt should not extend below the roof line any more than a normal mechanical bolt. E. Not require any extra tools for installation. F. Be bendable for use in low seam coal. G. Be durable and inexpensive. The ultimate point anchor resin should have the following characteristics: A. Have a mix and gel cycle which would compete with a mechanical bolt for speed of installation. B. Have a pull out strength in excess of a normal 5/8" mechanical bolt.

Jan 1, 1981

By Keith D. Koper, Kris L. Pankow, Derrick J. A. Chambers, Michael K. McCarter

"In a mining environment, high quality seismic event catalogs are often useful in interpreting local stress states and identifying areas with elevated ground control risk. Installation, operation, and maintenance of local/in-mine seismic networks, however, may be prohibitively expensive, and mine operators may not anticipate the need for seismic data until unusual mining conditions arise. If regional, generally public, seismic instrumentation could be used to reproduce the results generated by local/in-mine instrumentation to an acceptable degree of fidelity, it would be a valuable and inexpensive tool for mine planners and ground control engineers.In this study we apply subspace detection—a non-traditional seismic event detection technique—to data from a sparse, regional network. The process is employed to identify mining induced seismicity (MIS) from an underground coal district. The results are compared to a seismic event catalog produced by a local seismic array operating within the permit boundaries. Additionally, we analyze the performance of two different stations of the same sparse, regional network in identifying blasts at a surface coal mine for which we have a detailed blasting log. In both cases data from stations between 10 and 60 km away from mining activity are used. We also explore the trade-offs between the number of detections and the number of false positives, which is influenced heavily by detection thresholds and the number of stations used in the process.For the surface mine we are able to identify more than 90% of the production blasts documented in the blasting log. We also find that the detected blasts from each of the four active pits produce waveforms similar to one another. The results are not dependent on source-receiver distance, and by requiring detections to occur on both stations the number of sure false positives is reduced to zero. In the underground mining district we identify between 30% and 75% of the events detected by the local array, depending on the acceptable number of false positives and the source-receiver distance. We also find many events that were missed by the local array, showing that regional subspace detection can usefully augment traditional local catalogs. Moreover, subspace detection can provide an estimate on event location and classification using data from as little as one seismic station."

Jan 1, 2015

By Ezzeddin Bakhtavar

There are several geotechnical challenges and risks inherent in the interaction between the open-pit and block cave mining environments. This is especially true when they have to work simultaneously for a short time, as well as when only the caving operation is continued. Some of these challenges and risks include the induced zones of stress due to the large and deep open-pit, instability of the slope, instability of the crown pillar and water inflows, subsidence, and sometimes instability of the main accesses to the block cave portion of the mine. These challenges usually occur due to cave propagation. In this paper, these geotechnical challenges and associated risks have been studied and discussed. It was concluded that the majority of the mentioned geotechnical risks could be decreased, and often eliminated, by considering the appropriate dimensions of a stable crown pillar, especially in simultaneously working open-pit and block caving operations.

Jan 1, 2011

By S. J. Jung

The goal of this research is to demonstrate how optimization methodology can be coupled with the finite element method for greater stability of underground mine openings. As a result of increasing mining depth and intersection of geologic discontinuities, mining environments are becoming more complex. Current design procedures are rapidly becoming inadequate. In this research, the finite element method has been coupled with optimization criteria to design more stable and safe underground openings

Jan 1, 1993

By A. G. Pasamehmetoglu

The swelling process is an important problem causing damages to the structures in or on swelling rocks, both during construction and operating life. To understand swelling problem, a number of testing methods have been developed by many researchers. In these studies, the swelling parameters, in most cases, are derived from pedometer tests. The swelling parameters determined from oedometer type tests represent one-dimensional behaviour (one-dimensional swelling law) therefore, it is quite difficult to extrapolate the pedometer type test results to the three-dimensional in-situ conditions. To overcome these problems, a three-dimensional approach is suggested for clay bearing rocks. Results of triaxial swelling tests conducted on marl from Dodurga Lignite Coal Mine are presented. Triaxial swelling characteristics of the marl are presented and design approach for tunnels is described.

Jan 1, 1992

By Gregory M. Molinda

Difficult mining conditions in deep western U.S. Iongwalls have necessitated the use of novel tailgate support systems. Extreme ground movement in these yielding gate systems has caused operators to utilize secondary support systems which match yield and strength characteristics with expected ground reaction. Other benefits include ventilation and safety gains, as well as lower costs. Recently, the use of novel support has been tried at longwall mines in other U.S. coal basins. One of the main considerations is the capability of the support to maintain an adequate airway for gob ventilation in gassy eastern coal mines. In one large Pennsylvania mine working the Pittsburgh seam, a number of support configurations were monitored over a 2,300 ft tailgate test area. The test included 4-pt wood cribs, Link-N-Lock cribs, Propsetter yieldable posts, cable trusses, and vertical cable bolts. Ground reaction, and thus support performance, was documented by roof sag and convergence instruments, ventilation measurements, and photographs. Various combinations of standing support and cable truss and vertical cable bolts provided adequate support for ventilation and safe escape. A cribless configuration consisting of only cable trusses and vertical cable bolts was inadequate to provide inby gob ventilation to the next open crosscut. Instrument ground movement data and visual documentation are presented.

Jan 1, 1997

By Kevin M. Connor, O&apos

An example application is presented in which Time Domain Reflectometry (TDR) was utilized to monitor roof strata movements during pillar extraction in a potash mine. The study was initiated when Western Ag-Minerals decided to implement secondary mining of pillars in order to extend the life of their Nash Draw Mine. A prototype operation was conducted in one mine panel to assess mining equipment and procedures, and to determine if ground control problems would develop. An instrumentation array was installed by personnel from New Mexico Tech and Western Ag to monitor strata movements, changes in pillar stress and surface subsidence, and these data are being analyzed by the Bureau of Mines. This paper is limited to a discussion of roof-floor convergence and roof strata movement to illustrate the application of TDR to ground control. Plots are presented which demonstrate the capability of distinguishing location, magnitude and mode of rock movement using TDR to interrogate coaxial cables grouted into holes drilled in the roof.

Jan 1, 1990

By Behdeen Oraee-Mirzamani

Since the advent of New Austrian Tunneling Method (NATM), shotcrete as a primary means of support in tunnels has been widely applied. It?s most important features are durability, speed of application and cost effectiveness. This paper introduces some tables that provide guidelines for the thickness of shotcrete required in some common situations of mine roadways. In order to devise such tables, two different arch sections, together with three different overburden types, were considered. Geotechnical parameters such as apparent cohesion and angle of internal friction of surrounding rocks were chosen, based on the five-category classification of Bieniawski. Two K0 factors (the ratio of horizontal stress to vertical stress) and an average rock density were utilized. Using numerical methods, 60 models were then devised in this way. By applying interaction diagrams of axial force and the bending moment for different thicknesses of shotcrete, appropriate shotcrete thickness for these models were calculated. The results of this research, as well as the methodology applied, can be used in mining roadway support design and all types of civil engineering tunnels.

Jan 1, 2011

By M. Karmis

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

Jan 1, 1987

By Jim Galvin

4 and 6 point timber chock constructions are used extensively on both a systematic and spot basis by Australian longwall operators to support tailgate roadways. In 1996, the School of Mining Engineering at UNSW published design and performance criteria for timber chocks constructed from Australian hardwoods. The research was funded by the Australian Coal Association Research Program (ACARP). In 1997, ACARP awarded funding for a stage 2 testing program. This testing focussed on examining the effect of using thinner timber elements in chock constructions to improve OH&S and comparing the full-scale performance of traditional 4 point chocks to Link-n-Lock constructions. It was established that chocks constructed from thinner elements have failure loads much less than thicker elements. However up to the failure loads of the thinner elements there was no significant difference in the response to convergence of chocks constructed from 25, 50 or 100mm thick elements. Chocks constructed from 150mm thick elements have a similar ultimate strength to the 100mm thick elements. However, they have a significantly lower resistance to load, thereby permitting more convergence to occur. There is more potential for chocks comprised of thin elements to be constructed 'out of plumb' and so suffer eccentric loading. The full scale testing program established that at any given level of convergence up to 10% strain, the timber in a Link-n-Lock chock generates twice the support resistance of the same quantity of the same timber in an equivalent size 4 pointer chock. On the basis of support resistance per cubic metre of timber, there is only a marginal difference in the performance of 1.0m Link-n-Lock chocks and 1.2m Link-n-Lock chocks constructed from select Blue Gum. The cost per tonne of support provided by a Link-n-Lock chock is effectively half of that provided by a 4 pointer chock of equivalent dimension and timber. Up to a strain level of 4%. Link-n-Lock chocks constructed from 1.2m long elements are slightly more cost effective than the same chocks constructed from 1.0m long elements. Thereafter, there is no significant difference in cost per tonne of support resistance. Beyond a strain level of about 4%, Link-n¬Lock chocks constructed from landscape grade Blue Gum are just as cost effective as Link-n-Lock chocks constructed from structural grade 4 Blue Gum.

Jan 1, 2000

By John P. Dunford

U.S. Bureau of Mines researchers are investigating the ability of mine-wide monitoring systems already in place at many coal operations to provide a direct link between geotechnical instruments and the mine-wide monitoring console on the surface. This paper describes a number of field tests using instruments such as-string potentiometers to measure roof-to-floor closure and bed separation and pressure transducers to monitor pillar loading. The advantages of using existing systems include on-site data collection and analysis, real-time understanding of geological conditions, and long-term data recovery from areas that have become inaccessible to mine personnel. However, because data are generated constantly, large files develop very quickly. In many cases, the data are redundant, such as during times of reduced mining activity or in areas not yet in the vicinity of active mining. To reduce the volume of data, a software program was written that eliminates unnecessary readings and generates a more concise file that can be output to a mine-wide monitoring system, personal computer, or as hard copy.

Jan 1, 1993

By Ulrich Langosch

In the 1990s the German mining industry introduced a new generation of shield supports. The new design of support has a maximum load capacity of 10,000 kN, making these units as strong as the shields used in Australia and in the USA. DMT took more than 3,100 underground observations in order to verify the roof fall frequency by statistical analysis. The results of this work have led to practical recommendations for roof control and the required shield support system on longwall faces. The underground observations have been correlated to Rock Mass Classification, to stress calculations and to the angle between the direction of the fissures and the direction of longwall mining_ The analysis work yielded the following two sets of results: 1. There is a critical distance between the canopy tip and the coal face (Tip to Face TF,n,). The TF,n, is predictable and relates to: the thickness of the first roof layer and its uniaxial compressive strength. The face support should have a TF that is less than the TFcrtt in every underground longwall situation. Exceeding the TF crit call immediately result in a roof fall. 2. Using the obtained regression equation DMT is able to calculate the probability of the roof fall frequency (FF), which describes the roof fall sensitivity. When TFcr;, is exceeded the predicted roof fall FF relates to: the measured support resistance (MSR) of the shield support the calculated vertical stress (p?) the fissure-direction index (DI = angle between main fissure direction and direction of mining) and the distance by which TFcrit is exceeded (ATF). Armed with these results DMT is now able to predict the critical distance between the tip of the canopy and the coal face (TFcrit), as well as the roof fall frequency, for all shield designs. By applying the new calculation method it is now possible to compare alternative longwall layouts and different shield support types under pre-set geological conditions. Mining engineers on site are therefore in a position to make the necessary roof control preparations required to run the longwall operation to maximum efficiency. The results provide a useful basis for making practical recommendations and for selecting the most effective design of shield support. The paper uses practical examples to demonstrate the R&D results and present the various methods now available for calculation and prediction in longwall roof control.

Jan 1, 2003

By Jiacheng Wang

The current state of thick seam coal mining methods is illustrated in three typical cases of thick seam longwall mining, each pointing out the outstanding achievements in top-coal caving mining and large cutting height mining in China. At the same time, based on current thick seam mining practices in China, some problems urgently need to be solved. These include improving the recovery ratio of coal reserves, determination of overburden strata pressure, shield support selection, supporting methods for large cross-section in-seam roadways, top coal bulk flow theory, and gas flow and control technology. In addition, the rational production capacity should be studied from both economic and technological perspectives in order to optimize coal recovery and efficiency.

Jan 1, 2011

By K. Goshtasbi Goharizi

This paper discusses experimental results of physical scale models employed to study the stability of a pillar between rectangular roadways. A programme of laboratory investigations utilising a bi-axial test rig has been undertaken to examine the influence of various stressfields on the stability of pillars between mine roadways. The effect of pillar height/width ratio on the overall stability is studied. Observations of failure characteristics in and around pillars are discussed especially in relation to the various stressfields applied to the models.

Jan 1, 1992

By Bob Thomas

The roof drill operator productivity can be enhanced by the introduction of control technology The operators control station can be improved by considering human factors such as handle forces and control location. The smaller electrical controls can be located much easier than the traditional hands on valves. The operators control can he improved by using processors with programmable subroutines that assist the operator in the decision making process. For example to increase feed rate - to slow rotation - to avoid clogged steels - etc. The overall affect is to improve drilling and bolting consistency. The control system uses a dedicated processor packaged as an intrinsically safe control station. The roof drill operator is assisted in the drilling; arid bolting by a closed loop feedback system. The processor monitors the drilling parameters such as feed force, feed rate, rotation torque, RPM, drill position, and vacuum condition Based on the drilling parameters the processor executes pre-determined condition statements intended to enhance drilling The drill operator has an active display to alert him to the real time machine status. For example if the feed were to slow or delay due to a high vacuum level the display would show "high vacuum". The dedicated processor is available on the arm feed style machines, The prototype machines used programmable logic controllers to develop the feedback relations. The ability to record drilling parameters was extremely helpful in this development project. The extended use of the recording feature will aid operators in mapping the mine roofs Interpreting the recorded drilling parameters can reveal a void in the top or hard competent drilling The prototype machines also showed the importance of vacuum monitoring This feature is extremely valuable in softer materials, The benefits of the control system range from efficient use of the consumable bolting materials to uniform operator performance.

Jan 1, 1999

By Hideki Shimada

A low cost methodology that allows the determination of in- situ stress using oriented core specimens has been investigated. The technique can be used to determine the stresses during the early stages of a project, even in undeveloped areas of a mine. The research aim was to compare the experimental results estimated by the AE and DRA methods to those estimated by conventional ANZI (Australia and New Zealand Inflatable) cell measurements. The studies have been focused on fill stress tensor determination from a single oriented cored rock. In all cases the rock core specimens recollected the in-situ stress reasonably well compared with the standard overcoring method.

Jan 1, 2001