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By John E. Feddock

Retreat mining plays an important role in the coal production within Kentucky and the Appalachian Coal Basin. In Kentucky, the majority of retreat mining is performed in the Eastern coal field. However, since September 2004, Kentucky has suffered four mining fatalities during retreat mining operations, and the coal industry has focused attention on the safety concerns associated with retreat mining practices. The Kentucky Department of Natural Resources (KYDNR) engaged Marshall Miller & Associates, Inc. (MM&A) to conduct a study to ensure that retreat mining is utilizing the best technology currently available and that the current available employee training programs afford maximum safety to miners. MM&A studied 34 coal mines that were conducting active retreat mining operations and represent about one third of all the mines with approved retreat mining plans in Kentucky. This paper summarizes the major research work conducted (Feddock and Ma, 2006) and recommends the practical methods for improving safety during retreat mining operations.

Jan 1, 2006

By Leo L. Van Sambeek

Specification of properly sized pillars to support the overburden is one of the most challenging aspects of salt mine design. Interest in salt pillar design is heightened by the recent flooding of the Retsof salt mine, water inflows to the K2 potash mine, and closing of the Belle Isle salt mine because of ground control problems. A series of numerical modeling analyses show that a simple pillar design equation for salt pillars adequately reproduces results of extensive modeling efforts. The paper describes (1) the basis for the pillar design equation, (2) equation verification by comparison with numerical modeling results, and (3) equation validation by comparison with measurements and observations of salt pillar behavior.

Jan 1, 1997

By Bruce K. Hebblewhite

BHP Billiton Illawarra Coal operates Dendrobium Mine in an area 10-20km west-northwest of Wollongong in the Southern Coalfield of New South Wales, Australia. The mine recently completed longwall mining in Area 3A adjacent to an overhanging rock feature known as Sandy Creek Waterfall, which had been identified as a significant, and potentially sensitive natural surface feature of the environment. This waterfall lies within the Sydney drinking water catchment area, in a surface terrain of variable topography where non-conventional subsidence behaviour such as valley closure, and far-field horizontal movements are known to occur, over and above conventional subsidence responses to mining. As a part of the conditions of approval to mine, Illawarra Coal undertook to protect the waterfall and the section of Sandy Creek immediately upstream of the waterfall from the effects of longwall mining using an innovative management process and an array of very high resolution monitoring systems. This paper outlines the type of non-conventional subsidence effects that can occur; the range of different monitoring regimes adopted in response to such effects in order to develop an understanding of the valley closure phenomenon in proximity to the waterfall and provide suitable early warning data. The paper also describes the management processes that were adopted, incorporating the use of these monitoring regimes in order to successfully protect the waterfall from the valley closure effects of mining four adjacent longwall panels in close proximity to the waterfall while continuing to maximise recovery of the coal resource in the area. The management structure adopted involved a technical committee, a steering committee, and an external independent reviewer. The technical committee was responsible for design of the monitoring systems, interpretation of the results, and making timely recommendations to the company steering committee who were then able to make informed decisions on when to cease mining each adjacent panel. The steering committee comprised Illawarra Coal management and technical personnel. Although the steering committee took advice from the technical committee, all decisions relating to mining were made by the steering committee. An external reviewer was engaged by the steering committee at the end of each longwall panel to review the results, interpretation and management decisions. This management structure was effective in successfully protecting the very sensitive structure of Sandy Creek Waterfall from potential impacts of nearby mining in the midst of active ongoing natural erosion processes.

Jan 1, 2014

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 Frank Schmidt

Due to changing geology, rib bolting is an ever-changing problem in ground control. With the economic status of the coal market, the need for safely increasing productivity in rib bolting is at an all-time high. The current solutions used in the market often require a long installation time (e.g. if collapsed holes have to be redrilled) or result in poor quality installations that can lead to insufficient ground control. A new bolting product based on the simple screw principle has been developed to bolt ribs faster and with a more repeatable, higher level of installation quality. The paper covers the product invention and development, the fastening principle and its advantages over current systems and first experiences in the market. The first underground trials have shown that the screw anchors can be installed safely and efficiently, often faster than traditional methods. The screw anchor does not suffer from conventional bolting issues such as collapsed holes due to bad ribs. The screw anchors are designed to obtain steel failure and load testing underground shows consistent fastening in all types of conditions.

Jan 1, 2013

By David Newman

The latest version of the Surface Deformation Prediction Software (SDPS) package is presented through its application to a number of case studies. The package now exploits all the benefits of the Microsoft Windows platform and has a direct interface to CAD software, thus facilitating input and output. Also, the package features advanced calibration routines to handle predictions over specific regions. The case studies presented highlight the features and capabilities of the new package.

Jan 1, 2001

By Joshua Hescock, Zach Agioutantis

"The Surface Deformation Prediction System (SDPS) has been developed as an engineering tool for the prediction of subsidence deformation indices through the implementation of an influence function. SDPS provides a reliable and fast method for the prediction of mining-induced displacements, strains, tilt, and so forth at any elevation between the seam and the horizontal or varying surface topography. One of the key aspects in obtaining reliable ground deformation prediction results is the determination of the edge effect offset. The value assigned to the edge effect corresponds to a virtual offsetting of boundary lines delineating the extracted panel to allow for roof cantilevering over the mined out area. The objective of this paper is to describe the methods implemented in updating the edge effect offset code within SDPS. Using known geometric equations, the newly developed code provides a more robust calculation of the offset boundary line of the extracted panel for simplistic, as well as more complex, mining geometries. Assuming that an extracted panel is represented by a closed polyline, the new edge offset algorithm calculates a polyline offset into the extracted panel by the user-defined edge effect offset distance. Surface deformations are then calculated using this adjusted panel geometry. The MATLAB® program was used for development and testing of the new edge effect offset feature. In completing rigorous testing regimes, the new offset features will be integrated into SDPS, further increasing the speed and reliability of the programs resulting in a retrospective increase in capability and flexibility. INTRODUCTION Underground operations have been known to cause mining-induced subsidence inside and outside of the mine permit area (Karmis, Agioutantis, and Andrews, 2008). Additionally, subsidence can impact surface water bodies, such as rivers, streams, lakes, and wetlands (Karmis and Agioutantis, 2015; Newman et al., 2016), as well as infrastructure, such as roads, railroads, pipelines, and buildings. With an increase in regulatory focus on mining-induced impacts to local structures, the calculation of mining-induced subsidence indices has become necessary in determining potential damage and mitigation efforts. The accurate prediction and evaluation of mining-induced ground deformations is required to obtain underground mining permits due to potential impacts to nearby structures, as well as hydrogeological sources. The prediction of ground deformation indices is often a complex task due to the number of input parameters required, such as mining geometries, overburden lithology, surface topography, the rate of mining (Karmis, Agioutantis, and Andrews, 2008)."

Jan 1, 2017

By Kot F. v. Unrug

In spite of the extensive research and accumulated experience from mining operations, an appropriate pillar design remains an open issue. Due to the shrinking reserve base, present mining operations move to more challenging conditions. There are usually thinner seams and geologic conditions are often unfavorable. For instance, mine roof and floor are weak or deteriorate rapidly when exposed to moisture fluctuations in mine atmosphere. It is common that pillars of current operations are more- squat than several decades ago when the bulk of pillar research have been carried out in thicker seams. The methods of pillars calculations were developed regionally (in particular countries) to suit design needs for the most important seams, from which the majority of coal production was coming (e.g. Pittsburg or Pond Creek seams in the eastern of US). Most of the pillar formulae use similar approach by assigning weights (using constants) to the influence of coal (seam) strength and pillar widthheight ratio on its final strength. That mechanistic approach has sound theoretical base and good data supporting its validity. However, what seems to be missing is a qualification system of the mine conditions, which are outside of the data base or do not comply with the theoretical model applied in pillar strength formulae. This paper attempts to address that issue in two major categories, first when only a drill core data are available, and second during the mine development observations can be made directly on a coal seam. The composition of a coal seam is also addressed, (which often changes rapidly across the reserve), and discussed its influence on pillar's structural performance. In summary a set of practical design rules is presented.

Jan 1, 2005

By Hideki Shimada

In underground coal mines, grouting method is employed in order to reinforce the floor and to control the movement of groundwater into the roadway. However, the seepage and the reinforcement behavior of the grouting material into the floor are not clearly understood. Therefore, grouting is today normally based on empirical relationships and on the experience of the grouting personnel. To assist grouting projects, it must be acknowledged that many of the flow and the hardening processes occurring during grouting so far defy mathematically analysis. From this point of view. this paper discusses the behavior of grouting material, when it is injected into the roadway floor, by means of 3-D Eulerian-Lagragian seepage analysis. Moreover, the effectiveness of reinforcement grouting on the mechanical properties of slaking-prone mine tunnel floor are studied by means of several laboratory tests. Keywords: Mine tunnel floor, Grout, Seepage, Reinforcement

Jan 1, 2002

By R. Fritschen

In order to investigate locations, source parameters, and source mechanisms of mining induced seismic events, a local network of seismic stations was installed at a coal mine in the eastern part of the Ruhr District (Germany). The recorded events were located with the help of an anisotropic velocity model, which accounts for the fine layering of the carboniferous strata. Most of the events took place about 50 m above the working Luise 76-10. Their locations correlated with the advancing working face, and the number of events increased when pillar edges were undercut. The source mechanism, i.e., the orientation of the fracture plane and the direction of displacement on this plane, could be determined for several seismic events. The majority of them was characterized by a fracture plane parallel to the working face and an almost vertical dislocation on this plane towards the goaf a mechanism resembling the breaking down of the hanging wall. The fracture plane had a dimension of about 100 m. Probably the fracturing of a sandstone layer, located approximately 40 m above seam Luise, was responsible for the observed seismicity

Jan 1, 1999

By Axel Preusse

Underground coal mining can cause seismic events. There is currently no way to predict such phenomena reliably, in particular stronger events. That is why, according to the current state of the art, empirical methods are employed in this field. Some assessment criteria, which relate to the geological and mining situation and either stimulate or rather help to avoid seismic events, are presented in this paper. These criteria are examined for a practical mining situation in Germany, with a view to estimate possible seismic events.

Jan 1, 2009

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 E. C. Westman

Anomalous geologic or stress-induced conditions can create a hazardous working environment for underground miners. Seismic attenuation tomography provides a valuable tool for understanding static and dynamic conditions induced by mining. As a longwall shearer cuts coal, it generates seismic energy. As this energy travels through the rock mass it is attenuated in a manner proportional to the degree of fracturing of the rock mass. By calculating this attenuation at specific locations underground, the degree of fracturing of the rock mass, and hence the relative stress state or material properties can be inferred. The goal of this work has been to create a tool which can be easily used by the mining industry to obtain information about the distribution of stress concentrations or material properties across a broad area in advance of mining.

Jan 1, 1996

By Erik Westman

Coal bumps remain one of the industry?s most devastating but least understood phenomena. If changes to the internal conditions of the rock mass could be observed there is hope that bumps could be forecasted. Seismic tomography has been used over the past 25 years in an attempt to image these changing conditions in the vicinity of the longwall face. This paper describes the history and practical considerations of using seismic tomography in bump-prone coal mines. The implementation of seismic tomography at six different longwall mines will be described along with lessons learned. Early studies used mining independent sources of seismic energy, including explosives and sledgehammers. Subsequently more operator friendly sources, such as the mining equipment itself and mining-induced seismicity, were used. Seismic energy sensors have been placed in gateroads and on the surface above the mine. Each of these configurations has associated advantages and disadvantages. Although the results obtained have been encouraging, the application of seismic tomography to monitoring a bump-prone longwall face is still immature. The ultimate goal of clearly imaging changing stress conditions in the longwall panel in a manner that does not inhibit mining operation is still distant, yet drawing nearer. When this goal is achieved, the industry will have a capable tool for identifying locations where bumps are imminent.

Jan 1, 2008

By Alan A. Campoli

"Pumpable crib support for longwall gates and ventilation bleeder entries is becoming more prevalent in United States coal mines (Figure 1). The pumpable crib selection and spacing design has been greatly refined by the full-scale testing conducted at the National Institute for Occupational Safety and Health (NIOSH) Mine Roof Simulator. The peak load on 24-, 27-, 30-, and 36- inch diameter J-Cribs is, on average, 300, 400, 450, and 650 kips, respectively. Standard J-Cribs have useful deformation of approximately 8 inches. The maximum useful deformation can be extended to 18–20 inches with an exterior reinforcement layer or an interior double wall, for all four J-Crib diameters. J-Crib diameter is primarily limited by a maximum 4.5:1 height-to-diameter aspect ratio. Spacing is controlled by immediate roof stability, anticipated pillar deformation, and roof bolting practice. Approximately 500,000 J-Cribs have been successfully placed in 18 different United States longwall coal mines. The selection and spacing of the J-Crib utilized to date is summarized for each mine.IntroductionLongwall productivity and safety depend on ground stability in gate and ventilation bleeder entries. Numerous support technologies have been developed and employed in United States longwall mines since the 1990s to replace traditional wooden cribbing. Many, if not all, of these technologies have been evaluated at the NIOSH Pittsburgh Research Laboratory since the mid-1990s (Mucho, et al., 1999). The NIOSH Mine Roof Simulator has a 3,000-kip vertical load and 24-inch displacement capacity, which has facilitated in-depth analysis of complex multimaterial support technologies like the pumpable crib. The extreme cost and human exposure risk associated with modern longwall mining prevent the trial and error development that would have been required absent the Mine Roof Simulator research. As a direct result of this research, pumpable cribs are becoming a major component of the standing support industry, providing the peak capacity and extended deformation characteristics necessary for successful gate and bleeder support. Recent research by Zhang, et al. (2012) and others have defined the required performance characteristics."

Jan 1, 2015

By Kazem Orace, Navid Hosseini, Mehran Gholinejad

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

Jan 1, 2010

By Jian Yong Chen

The results of a laboratory investigation of pullout tests conducted on grouted, plain cable bolts are reported. The main purpose of the study is to determine experimentally the shear bond stiffiess of cement grouted and resin grouted cable bolt systems, which is an important input parameter for numerical modeling of cable bolt support. Three nominal embedment lengths of 152mm (6 inch), 203mm (8 inch) and 254mm (10 inch) were used and two types of grout namely cement and Anchortite resin were used. Two water- to-cement ratios of 0.3 and 0.4 were employed for the cement grout. The concepts of effective shear stress and effective shear stiffiess are explained and adopted to calculate the shear bond strength and the elastic shear bond stiffiess per unit length. A comparison of results with previous research is presented to reveal the effect of water-to-cement ratio and embedment length on the shear bond characteristics of grouted cable bolts.

Jan 1, 2005

By Hani S. Mitri

The behaviour of grouted cable bolts used for rock reinforcement as a means of ground control in hard rock mining is investigated. The study utilizes an analytical model which is based on the variational principle to calculate the shear bond stress distribution along the embedded length of cable bolt. In this paper, a comprehensive parametric study which covers both geometric and mechanical design parameters involved is presented. Special emphasis is placed on studying the characteristics of the grout model represented by Winkler springs. This involved varying the maximum shear strength of the grout, its residual strength and the slip occurring between the cable and the borehole wall.

Jan 1, 1990

By Brian White

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

Jan 1, 2002

Large-scale shear apparatus is designed to investigate the shear hehaviour of simulated soft rock joints under constant normal stifmess condition. Regular saw-teeth profiles having inclinations between 9.5" and 26.5" have been tested. The strength envelope based on these test results indicates that predictions made by Panon (1966) are accurate for the lower asperity angles. However, for higher asperity angles, Patton's model overestimates the shear strength especially in the low to medium normal stress range. In contrast, while Barton's model (1973) is realistic for Constant Normal Load (CNL) condition, it seems to be inappropriate for modelling the shear behaviour of soft joints under Constant Normal Stiffness (CNS) condition. An empirical strength envelope for the prediction of peak shear strength of joints is proposed in this study to account for the change in normal stress and surface degradation during CNS shearing.

Jan 1, 1997