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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

By G. R. Corbett

The introduction of roof bolts to Phalen Colliery in the Sydney Coalfield, Nova Scotia (annual output of 2Mt) has been successfully implemented in maingate and tailgate entries over the last four years. Monitoring of the roof bolted areas continues to be an integral part of the quality control program as the results are utilized to maintain safety and to aid in long-term design strategies. Although all gateroads in the Phalen Colliery have converted to roof bolts as their primary means of support, the majority of intersections which intersect the main slopes remain supported by large steel structures. Several intersections within the Phalen Colliery were monitored as they were created by the mining process. A comparison is made between intersections supported with only traditional 6.4 to 6.7 m steel structure and intersections supported by 2.44 m fully resin encapsulated roof bolts in conjunction with 7.6 m fully cement grouted cable bolts. Detailed monitoring was conducted using CA NM ET's intrinsically safe sonic probe extensometer datalogger which has the ability to read up to sixteen probes simultaneously at programmed intervals. The density of the data from the datalogger has allowed a better understanding of the deformation of cable bolted intersections than was possible with manual monitoring. Test results have helped mine operators to design safer cable bolted intersections.

Jan 1, 1995

By Alan J. Zeni

Drainage of water from abandoned underground mines has become important in recent years because of safety concerns when mining near abandoned works or reentering abandoned mines for further development. Seepage from inundated mines causes environmental damage and may threaten homes and communities. Where topography permits, horizontal drilling can provide a quick and cost effective method for solving trapped water problems. The mechanics of the horizontal drilling operation as applied to water drainage are discussed in this paper.

Jan 1, 1990

By D. S. Choi

This paper describes an improved source location technique for microseismic events related to coal mining. A system of non- linear distance equations is solved with the use of the Newton-Raphson method. This computational method is- advantageous when the number of geophones is limited. In addition, this paper includes the results of the analysis of data from several instruments which characterize both mine seismicity and environmental noise such as vehicle traffic. Analysis of the mine seismicity has contributed to a better understanding of caving above a longwall gob and of what constitutes stable ground conditions.

Jan 1, 1990

By V. V. Nazimko

Abandoned coal mines cause subsidence and structural damages. Shallow abandoned mines induce the most severe and harmful damages. In addition, they produce time-dependent subsidence which is difficult to predict. Backfilling of underground cavities with waste materials have been used to prevent the time-dependent subsidence or to mitigate its effect. However, this procedure is expensive. A new drill and blast technique has recently been proposed to prevent surface damage from time¬dependent subsidence over abandoned mines. It utilizes the principle that blasting in the caved rock and roof in the vicinity of a cavity will dilate the ground and create a self-supporting effect owing to increase in the volume. Physical modeling has demonstrated that artificial dilation of caved rock using the drill & blast technique creates positive effects due to the following sequence of events: the dilated rock creates a supporting effect for the suspended rock strata and reduces its span which decelerates 3.4 times the process of caving. The roof span is reduced by the next caved layer, which causes the hole boundaries to incline to each other. This effect converts the process of caving from a developing mode to a reduction mode. Finally, the sinkhole zone assumes a triangular shape with a negative angle of draw 64-700 in contrast to a rectangular shape of the chimney zone for natural caving. Vertical dimension of the triangular zone is 3.87 times of the room height. Final surface subsidence decreases at least 2.09 times; displacement 1.31 times, slope 2 27 times; curvature 3.42 times, horizontal strain 1 21 times in comparison to natural caving of the ground over an abandoned mine.

Jan 1, 1999

By W. Smith

The U.S. Bureau of Mines (USBM) is using laboratory and computer-based techniques to investigate the post- failure behavior of yielding pillars and pillar reinforcement techniques to control entry deformation. Poorly dimensioned yield pillars, can cause adverse ground conditions. Laboratory studies to evaluate various reinforcement techniques for controlling yield pillar deformation were conducted. A cracking and crushing model is used to evaluate potential tensile and compressive failure planes within pillars of various widths to assess the degree of yielding and stress redistribution. The use of an elasto-plastic model to evaluate the effect of various reinforcement on yield pillars is also discussed. These procedures effectively account for the residual pillar strength, important in yield pillar design.

Jan 1, 1995

By Ken Mills

A program of stress change and roadway deformation monitoring was undertaken to measure the forward abutment load distribution about a retreating longwall panel at Dartbrook Mine. The results of this monitoring allow roadway conditions observed at various stages of mining to be ranked according to the estimated vertical stress they have experienced. This ranking also provides a means to predict and visualise future roadway conditions at various stages of mining. This paper presents the results of the monitoring and describes the approach developed to predict future roadway conditions. The monitoring results show the vertical stress distribution associated with the front abutment from a longwall goal decreases exponentially away from the goaf edge. The vertical stress distribution peaks at the goaf edge at 5 to 6 MPa stress increase and decreases to 1 MPa within 50 m becoming imperceptible beyond 100 m By scaling this measured distribution to reflect the loading environment, the vertical stress can be estimated for different overburden depths and different stages of mining. Photographs of roadway conditions at particular vertical stress levels provide a way to visualise roadway conditions at various stages of mining in the future

Jan 1, 2000

By Liane J. Terrill

Rockbolt failures at the Waste Isolation Pilot Plant have been recorded since 1990 and are categorized in terms of mode of failure. The failures are evaluated in terms of physical location of installation within the mine, local excavation geometry and stratigraphy, proximity to other excavations or shafts, and excavation age. The database of failures has revealed discrete areas of the mine containing relatively large numbers of failures. The results of metallurgical analyses and standard rockbolt load testing have generally been in agreement with the in situ evaluations.

Jan 1, 1995

By Christopher J. Brown

"Proper ground stability in gate roads has been a critical aspect of success in longwall mining. In particular, the tailgate has proven to be one of the more active mine areas that needs to be managed (Barczak, Dolinar, and Mucho, 1999). As longwall tailgate support technologies continue to be developed and improved, Strata Worldwide has worked to design and manufacture a revised Propsetter to provide additional support capacity and enable applications at greater mine heights. The support is targeted for tailgate applications; however, it can also be used for roof support in various types of mining environments. This paper describes the design changes for enhancing the support capacity of the Propsetter to more closely align its performance with other support technologies currently being employed in longwall tailgates. Balancing changes to each design aspect of the Propsetter was key to successfully improving the roof support load capacity while maintaining controlled deformation. Increasing the load capacity would allow a mine to improve support efficiency with a smaller, less intrusive support compared to support alternatives and to reduce the cost per foot of supported entry. The target support capacity was 80 to 100 tons at two inches of deformation to more closely match the performance of competing tailgate supports, such as the 24-inch-diameter CAN®. To achieve this goal, changes were made to all design aspects of the Propsetter: diameter, wedge cut depth and angle, pod size, and confinement rings. Test results from the NIOSH Mine Roof Simulator verified that these design changes were successful in increasing the capacity of the Propsetter to the 80- to 100-ton range at two inches of deformation. INTRODUCTION Roof support is one of the most fundamental elements of the underground mining process. As materials are removed from the earth, geological conditions will almost always require some form of roof support to keep the extraction area open and stable. Coal mining environments often experience difficult geological conditions that require both primary and secondary forms of roof support to keep the mining environment safe and economical. The secondary support system serves as additional support in the case the primary support system is inadequate. If designed properly, the secondary support system will also assist in maintaining integrity of the immediate roof beam (Barczak, 2000)."

Jan 1, 2017

By Wojciech Masny, Andrzej Walentek

"The most common extraction method in Polish coal mines utilize pillars between adjacent longwall panels. This is mainly due to the significant depth and difficulties in maintaining stability of the gateroads. This paper presents measurements of entry convergence and range of the fracture zone around a gateroad measured with a borehole camera. The entry where the measurements were taken was located in a parallel entry separated from the gateroad by a 5-m- (16-ft-) wide pillar. The gateroad was located in a hard coal seam 900 m (2,952 ft) deep with a dip of 5°. The extraction method was longwall mining with caving and the mining height was about 3 m (10 ft).Furthermore, the ""in situ"" measurements were compared to the convergence forecast for the gateroad and fracture zone by means of numerical modeling conducted using the Phase2 Version X.X finite element program from Rocscience. The determination of the fractured zone around the openings is of great importance to successful mining practice, especially in support planning and design for longwall gateroads. Moreover, proper determination of the fractured rock zone is one of the basic elements in the process of planning the roof bolting for mine workings.INTRODUCTIONIn the Polish. hard coal mining sector, retreat longwall extraction is most commonly used (Prusek and Masny, 2007). This method is connected with the necessity to carry out a number of development operations during the first stage, including among others, driving of gateroads and a setup room.Currently, most Polish mines eliminate gateroads behind the extraction front, using the ""U"" ventilation system (Szlitzak et al., 2008). In such cases, one of the roads for the next longwall panel is driven along the caving goafs, leaving a protective pillar of some chosen width (Figure 1). The question regarding the width of the coal pillar is especially important to the stability of the gateroads that define the panel for the subsequent longwall. When analyzing the previous experience relating to this type of pillar (Junker, 2006; Rajwa, 2008; Stranzet et al., 1973; Betriebsempfehlung, 1982), one can state that there exist two solutions for the determination of its width."

Jan 1, 2010

By A. G. Pasamehmetoglu

This paper describes the conver¬gence and load measurements carried out in inclined seams at five longwall faces, two of which were supported by hydraulic props and the other three by conventional timber supports in Karadon-Gelik mine. The minimum support capacities determined in this study are compared with the results obtained from two empirical approaches suggested by Wilson (1975) and Jacobi (1981). The characteristics of hydraulic props to be used and support patterns in the longwalls are found, conclu¬sions are drawn and suggestions are made. Design nomograms are prepared for field engineers, in order to be able to approach the problem more confidently and realistically.

Jan 1, 1992

By Khaled Morsy

In the past two decades, high horizontal stress has been attributed to many ground control failures. Most believe that entries parallel to the high horizontal stress is most stable and least stable when perpendicular to it. Entry stability decreases when the angle between entry and horizontal stress increases. The concept of 2-D stress shadow has been proposed for selection of proper panel orientation, often with mixed results. In this paper 3-D finite element modeling was used to analyze the stress distribution at the headgate of a longwall panel subject to high horizontal stress at various angles. It was found that the directions of induced principal stresses at the longwall face and headgate are independent of the panel orientation. The induced principal stresses concentrate or relief at headgate based on the panel orientation with respect to the directions of the induced principal stresses. Accordingly, only 3-D modeling can fully account for the effects of high horizontal stress on panel orientation. The paper illustrates in details the changes in orientation and magnitude of all three principal stresses around the longwall face and T-junction area as panel orientation changes.

Jan 1, 2006

By Lawrence M. Gochioco

The interpretation of coal seismic data requires a certain precision and accuracy to make the results more reliable. The signature of the seismic wavelet provides a host of valuable geologic information. Subtle features and anomalies, not easily observed in conventional black and white seismic sections, are enhanced through color attribute displays in terms of frequency, amplitude and phase. Coal seam anomalies like sandstone washouts produce a distinct pattern in frequency and amplitude displays due to the change in the net acoustic impedance contrast. Faults produce frequency and amplitude variations due to interference within the Fresnel zone that straddles the fault. The magnitude of displacement is estimated by studying the effects of faults on reflection amplitudes and frequency from computer-generated models.

Jan 1, 1989

By Karl Zipf

In highwall mining, once a sufficient number of web pillars are developed, they can fail catastrophically in a domino-type failure, posing a safety hazard to highwall miners and sterilizing mineable reserves. Three recent case histories of catastrophic web pillar failure in U.S. and Australian mines are documented and analyzed with two design approaches. The conventional design approach uses only a strength criterion, while the postfailure design approach uses both strength and stability criteria to insure an acceptable failure mode should strength failure occur. Catastrophic highwall web pillar failures can cost money through equipment losses, production losses, coal reserve sterilization and lost opportunity costs. Coal recovery may be higher. but the benefits of higher recovery must balance the potential costs of failure. Application of the conventional or postfailure design approach will decrease coal recovery and revenues, but the risk of potentially costly failure is much less.

Jan 1, 1999

By Gennaro G. Marino

Documented case histories of surface ground movements from mine subsidence were utilized to help determine when the initial collapse of the overburden occurred above longwall panels. By studying this relationship between initial movement at the surface and the amount of face advance, the least-complex conditions exist for empirically assessing the span capacity of the overburden. The objective of this work was to obtain a better understanding of the overburden response to longwall mining. This knowledge will give a better insight on the long-term effects that different overburden types have on the stability and the subsidence potential of room and pillar mines, as well as, the influence of the overburden on subsidence over longwall panels. Theory on the overburden span capacity was developed and correlated to field observations. Data were used on the overburden lithology, depth, width, and face advance of the panel, and the subsidence conditions that were noted on the surface. The subsidence measured on the surface was used to determine when complete failure in the overburden rock had occurred. According to spans predicted by theory and the subsidence measured in the field, the competent lower units failed at a face advance less than when significant subsidence was observed on the surface. In each case studied, there were competent lower beds; however, the full overburden weight was not sustained to the point of subsidence. The best correlation with the surface movement was found with the most shallow, competent bed. Elastic plate solutions with various support conditions were found to best monitor the surface subsidence of these upper roof units.

Jan 1, 1988

By T. N. Singh

An evaluation was made on the cavability of the roof formation of Dishergarh seam including caving sequence, caving span, and load on powered support.

Jan 1, 1994

By Thomas H. Wilson

Common offset and refraction seismic data have been collected over four longwall panels at two different locations within West Virginia. Surveys prior, during and after mining were made in both areas. The velocity of seismic wave propagation in the overburden rocks is observed to decrease in response to panel emplacement. Variations in the magnitude of this reduction, apparent as an additional first arrival time delay in the after mining common offset surveys, do not appear to correlate directly to the amount of subsidence that has occurred. Velocity reduction and signal absorption zones are also produced in the cover beyond the panel face over the adjacent unmined areas. Signal absorption and velocity reduction zones have also been observed over room and pillar entry areas between mined panels. Velocity reduction zones have been- observed beyond the panel face in both shallow and deep mines, but the signal absorption zone has not been observed over the deeper mine. Changes in the compressional wave velocities of the cover rocks are associated with changes in their elastic moduli. Differences between borehole derived and surface seismic derived interval velocities, are related to differences in the properties of the bulk volume sampled by each method.

Jan 1, 1988

By Krzysztof Kotwica

The steady demand for rock materials leads not only to on increase in mining but to the need for decreasing the loss of material in the process of exploitation as well. It brings about an increase in using of explosives in open pits and as a result an increase of after blasting gases volume, vibrations, the scattering (dispersion) of stone ect. All these factors affecting the environment lead to the research work for applying the electrohydrodynamic methods both in open casts and underground mines. In the article the authors describe the concept of this method and construction of equipment which recently have been successfully introduced in mining, the results obtained determine the possibilities of using this method and the future directions. The results of combined method with high-pressure water jets cutting and prototype equipment for separating rock blocks from the rock mass using special head with high-pressure water jets are also described.

Jan 1, 2006

By Thomas M. Barczak

This report examines practical considerations in longwall support selection that have evolved from Bureau of Mines ground control research. The scope of discussion includes trends in support selection, analysis of shield designs, performance testing, and an examination of support and strata interaction theories and their relevance to in situ support loading. Application recommendations are made for two-leg shields. four-leg shields, and chock-shields. Two-leg shields account for 67 pct of the current active longwall installations and are used in a variety of applications. Automated control systems are likely to continue to grow in utilization. The next major change in shield design is likely to be the application of wider supports. The most effective method of performance testing longwall shields is by controlled displacement of the canopy relative to the base. Controlled force application does not control the load transfer through the shield and may not produce maximum loading in all support components. Theories of estimating support capacity based upon a detached roof block that must be maintained in equilibrium by the powered support are being challenged by concepts based upon the equivalent stiffness of the total ground supporting system.

Jan 1, 1990

By Anthony Iannacchione

Coal mine bursts have represented a major hazard for U.S. mining operations for more than 90 years. During this time, many prevention controls have been developed and tested. This paper reviews 11 prevention control techniques. Although coal mine bursts are not common events in most underground coal mines, their occurrence almost always requires a change in mining practice. Over the many years of dealing with these hazards, specialized requirements for layouts and novel extraction sequences have been developed on a site specific basis. The keys to mitigating risks are to properly assess the coal burst hazards and to possess the knowledge and skills to prevent or remediate their occurrence.

Jan 1, 2008