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The challenge of planning to minimize interaction effects in multi-seam mining is compounded by the difficulties inherent in extrapolating essential geological and spatial data between sampling points. To predict the effects of ultra-close mining on lower seam entry stability, simulated mine openings were studied using finite element analysis and body loaded photoelastic models. Both symmetrical and unsymmetrical loading was used to represent stress fields generated under multi-seam conditions. Results were correlated with field data to determine stress levels at which failure could be expected to occur. Stability predictions require precise definitions of geologic and spatial data, which could not be accurately defined by interpolation between sampling points. To overcome this problem an expanded roof stability model, SESAME2, was developed to incorporate reliability concepts based on Monte Carlo sampling. The model was demonstrated in terms of variations of innerburden thickness using a case study.

Jan 1, 1994

By Ross Seedaman

The specification of roof support needs to consider rock strength, imposed ground stresses, and more importantly the bedding and joint structure of the immediate roof rocks. A database structure has been developed that allows these considerations to be incorporated into modern mine planning software so that better predictions of mining rates can be made. Rock strength is estimated from core and/or geophysical logs (especially the sonic velocity log) and ground stresses are estimated from depth of cover and knowledge of the regional stress field. The database is unique in the way it addresses bedding structure. Only 10 roof lithologies are allowed and these are allocated a numerical value that reflects an increase in the average spacing of bedding partings. These are referred to as 'Geotechnical Ferm Units' (GFU). The locations of all bedding discontinuities logged in the core are entered into the database and referenced to the GFUs. It has been found that, within each GFU, bedding spacing follows a negative exponential distribution and so it is a simple matter to predict the probability of the occurrence of any roof beam thickness. Output from the database can include plans of roof strength, the onset of overstressing, and the statistics of the distribution of beam thickness in the immediate roof.

Jan 1, 2003

By Francis Kendorski

A longwall coal mine in Appalachia about 1,500 ft deep encountered a fault while developing a new longwall panel. The fault extended from mining depth to the surface near a secondary road and drainage. The fault was located inside the anticipated angle of draw within the mined panel and gob. The fault extended vertically out and up, away from the panel, caved zone, and gob at nearly the angle of draw: the fault very nearly following the angle of draw. It was initially thought that "fault reactivation" could possibly occur. Fault reactivation is the phenomenon of having mining subsidence localized along a fault leading to a "reactivation" of the fault and shearing and displacement along the fault. Such fault reactivation would disrupt and deform the fault plane beyond the normal angle of influence of the subsidence trough, and may provide a conduit for any ground and surface waters to reach the mine. We contacted all operators of longwall mines in Appalachia to determine if any Appalachian longwall mines had ever experienced fault reactivation, and teamed that none had experienced the phenomenon. After studies of possible water intrusion quantities and rates based upon in-fault pump tests, which indicated that water intrusion rates should be manageable, and the prior experience that faults in this particular area were usually barriers to water flow, mining proceeded with caution and monitoring. Mining was successful with no noticeable increase in water inflow rates, and no measurable off-setting of the fault exposure on the surface. It can be concluded that the fault did not reactivate due to its relationship to the mining sequence.

Jan 1, 2003

By John K. Wood

The development of an expanded cement product represents a major advance in the technology of roof control systems. Such a product is gaining recognition as a valuable tool in today's cost- conscious coal mines. The National Coal Board's Bretby Research Lab, in conjunction with Polement Ltd., developed the first lightweight cement for use in the mines of the United Kingdom. The product, Aqualight, is a low-density (about 12.5 PCF) cement with a typical compressive strength of about 19 p.s.i. The final product increases in volume by approximately 15 times its dry powder volume. Aqualight gels in about 2 minutes, becomes self-supporting in 15 minutes, and fully cur& in 24 hours. When subjected to a load, the "cells" within its bubble structure collapse so that the product gains in density and compressive strength while retaining its integrity. Traditional methods to contain and support roof fall cavities through cribbing and blocking are both dangerous and labor-intensive. Aqualight represents a significant advantage over such traditional methods. It is non-toxic, non-cmbustible, and very easy to install. Aqualight can be pumped to the worksite from re- mote locations (as much as 600 feet), thereby reducing danger to men and equipment. Addition- ally, the strength of the cured product can be varied by adjusting the expansion ratio and resulting density. A compressive strength of 150 p.s.i. can be obtained in this manner. Although primarily designed to fill cavities resulting from roof falls. Aqualight has found a wide range of applications in mining industries around the world. In addition to cavity- filling, Aqualight has been used for ventilation stoppings, fire stoppings and emergency fire control, backfilling between arches and the roof and ribs, and backfilling of old workings. Since its recent introduction into the United States. Aqualight has been used by MICON SER- VICES, INC. to fill several roof fall cavities along headgate entries. In all cases, the cavities were contained and the longwall moved through without problems. Roof Pall cavities along main haulage entries and at shaft/slope bottoms have been successfully filled. MICON has also installed Aqualight as backfill material around arches. A current major project is the installation of trial ventilation seals using Aqualight as an alternative to traditional block and mortar construction. Pending MSHA approval, MICON anticipates the use of Aqualight in the construction of both ventilation seals and stoppings. In addition to new construction, Aqualight can be employed to repair stoppings damaged by roof convergence and floor heave. In labor savings alone, this is very attractive for remote stopping repair. Among the many other uses of Aqualight is the backfilling of old auger holes, which will support the highwall and allow access to coal re- serves which are presently sterilized.

Jan 1, 1986

By Deren Zhu

The principle of roof control in longwall mining is to control main roof fractures so as to reduce roof weighting, plus reasonable and effective design of supports to reduce the convergence and premature caving of the immediate roof. This paper introduces a comprehensive test for better roof control based on the geological conditions of coal seam No. 16 in Zaozhuan Colliery, China.

Jan 1, 1990

By Erik Westman

Tomographic imaging, commonly known as a CAT-scan or CT-scan, is used in the medical field to generate a picture of the interior of a body. Current research is applying this method to bodies of rock so that rock failure can be better understood and predicted. This paper discusses the basic principles of tomography and describes recent developments in the use of seismic tomography in longwall coal mines, including results from a bump-prone longwall coal mine and continuing research.

Jan 1, 2003

By Paul A. Lu

This paper proposes an unconventional, simple, and practical method of measuring mining-induced around stresses with hydraulic borehole pressure cells. The method is a direct ground stress measuring technique. It does not require the value of deformation modulus for back-calculation of stresses; instead, it directly measures the ground stress in situ. The applicability and practicality of the technique are shown by two case studies. The technique may be applied to monitoring a stress build-up that may lead to mine roof failure or to rock and coal outbursts.

Jan 1, 1984

By Yunxin Qiu

A new technology has been introduced - the use of the High-Water Solidifying Material for providing pumped roadside supports to maintain a roadway for re-use in longwall retreating. As a gob edge support, its initial use at Hebi No. I Colliery was successful, providing acceptable performances in support and control of convergences and lateral closures of the gob-edge roadways. This acceptability applied to both first use and re-use when the roadway became a gateroad for the adjoining longwall, remaining stable throughout the associated loadings and convergences. The technology promises economic and social benefits.

Jan 1, 1992

By Megan N. Witkowski

The purpose of this study is to investigate the susceptibility characteristics of domestic and agricultural water supplies that may be vulnerable to diminution or total loss of supply when active longwall mining is in the vicinity of the potable aquifer systems of southwestern Pennsylvania. The study focuses on water supplies in Greene and Washington Counties with reported losses or reductions in supply that were attributed to the seven active longwall mines in operation between 2003 and 2008. The undermined water supplies represent a variety of hydrogeological settings and mining conditions prevalent in the southwestern Pennsylvania longwall coalfield. The susceptibility characteristics investigated include hydrogeological setting, proximal location to mining, and climatic conditions at the time of impact. The investigation considers the relationship between geological and mining characteristics. Geological characteristics include overburden composition and geomorphology of the surface; mining characteristics include mining method, depth, and extraction thickness. It was determined from the study that the average overburden thickness at each mine site is indicative of hydrological changes to potable aquifer systems, with the overall impact frequency at each site decreasing as depth to mining increases. However, depth to mining was not the governing factor when hydrological responses were determined on a case-by-case basis. To fully analyze and hopefully predict potential impacts by longwall mine subsidence, it is necessary to consider additional factors including topography, distance to mining, mining method, and climatic conditions at time of undermining. The investigation serves the purpose of enhancing our understanding of hydrogeological responses to longwall mining and will aid in predicting potential impacts to southwestern Pennsylvania?s wells and springs in proximity to future mining.

Jan 1, 2011

By Sanjay Kumar Singh

This paper presents ground control technology associated with a continuous mining operation for mass exploitation of underground coal deposits in the Indian coal mining Industry It shows that competency of roof strata and performances of continuous miners are safer, than other coal mining method as well as productive and economical. Continuous miners keep playing a major role in the underground coal mining industry for their safety and as well as their productivity. Regarding past experiences in Indian coalfields, Chirimiri and Jhanjara mines have achieved exceptional performances, with a potential for over 500,000 tonnes per year. Tandsi mine has difficult roof conditions and does not typically achieve high production and productivity. Even so, the difficult roof conditions have been controlled with modern ?world best practice? roof bolting systems and an output of up to 1,200 tonnes per day has been achieved. It can further be emphasized that if this technology is implemented properly it will bring an unfathomable change to the Indian mining scenario. There are many mines in India that may have potential and economic viability with ground control technology concepts for installing continuous miner systems and beginning mass exploitation of underground coal deposits.

Jan 1, 2011

By Jeffrey K. Whyatt

Estimation of the initial vertical stress carried in a coal seam is an important first step in virtually all methods of evaluating the required size of pillars in coal mines. Such estimates are a trivial exercise in coal fields overlain by gently undulating topography. The LaModel program is easily and routinely applied in such cases to efficiently estimate mining-induced stresses throughout the coal seam. However, application of LaModel to coal mines operating under rugged topography and/or in tectonically disturbed regions is more difficult. LaModel estimates stresses in a twostep process. Topographic and multi-seam mining effects on insitu stresses are estimated in an initial step, and then mininginduced stresses are estimated in an independent second step. A LaModel program function has recently been introduced that decouples these two steps, allowing in-situ stresses to be directly entered from a file rather than calculated. One application of this function is to streamline sensitivity studies by avoiding repeated recalculation of in-situ stress. The function also allows importation of in-situ stress estimates developed by other means. There are no constraints on the imported stress field, which may include significant stress perturbations due to topography, faults, etc. Hence, the range of geologic environments that can be examined by LaModel is significantly increased. This study uses the new decoupling function in an exploration of in-situ stress estimation in mountainous terrain. One option is to use the topographic stress estimation feature included within the LaModel program, and the influence of important parameters in this routine is explored. Another option explored is importation of results from a detailed volume element model. Results of this study suggest that the method used to estimate in-situ stress, and the details of its execution, can have a significant impact for mines in mountainous terrain with strong overburden. More generally, decoupling is an efficient and flexible function that should be considered for most design studies.

Jan 1, 2011

By G. Skybey

The Skybolt is a new bolt concept, point anchored with resin in large diameter holes of specific sizes 38 mm and 45 mm. The new design achieves the optimum annular spacing required for mixing the resin anchor components which is essential for optimum resin bonding of the bolt to the surrounding rock. This paper explains the load transfer mechanisms between bolt/resin/rock, unique to this bolt concept. It compares the pull-out test results to those of paddle and expansion shell type bolts, and highlights the versatility of Skybolt over existing, currently used, rock support systems and the benefits mine operators can achieve when using the Skybolt.

Jan 1, 1992

By Francis Kendorski

One of the most dangerous events in underground coal mining is unexpectedly encountering water inrushes from undetected abandoned mines in the same seam. The surest and most confident method is probe drilling either from the mine or from the surface. However, drilling is expensive and may even miss the suspected mine voids entirely by drilling through pillars. Many operators rely upon one or more of several remote sensing techniques for detecting mine voids. However, mine "voids" often are not air- or water-filled open cavities, but are collapsed, rubble-filled chimneyed columns in the strata. Geophysical techniques, such as seismic reflection and refraction, electrical resistivity, magnetics, ground-penetrating radar, and others, often assume a continuous or fractured rock mass that has varying properties which provide the signatures that allow discrimination of one strata from another, or of strata from voids. However, a rubble-filled cavity has rock block-to-rock block contact throughout its volume and can still respond as a continuous rock mass with the rock blocks allowing signal transmission or mass detection, rather than a void space. Hydraulically, a rubble-filled cavity is essentially as transmissive to water as an open mine void. Thus, the problem of detecting a mine void with confidence is significantly compounded.

Jan 1, 2004

By Tim Burgess

Patton Mining, LLC and J.H. Fletcher Company recently collaborated and mechanized the sometimes hazardous, and always labor intensive, process of installing standing steel supports during the construction of a slope entry of a new mine. The new innovation is a beam setting machine design that can lift and maneuver heavy steel beams into place over and around the belt and vent tubing. In addition, the machine is designed with an integral double extending lifting work platform to allow workers a stable work area from which to install metal sheeting between the beams. The previous method to install the heavy steel supports and the steel sheeting included multiple workers lifting heavy loads frequently on stepladders. This paper will inform the reader of how Patton?s major goal to develop the safest, most continuous slope development process possible was achieved and the beam setting machine that evolved from the project.

Jan 1, 2011

By S. M. Matthews

The magnitude and orientation of the in situ stressfield has been determined as a key factor in controlling the stability of openings for both coal mine development and extraction. Monitoring of roadway and pillar behaviour in conjunction with numerical analysis has identified specific stress control measures that have been successfully applied to improve productivity in underground coal mining operations. The influence of the major horizontal stressfield on the stability of openings has been identified at a wide range of sites including mines in Australia, Britain, the USA, New Zealand and Japan. Stress mapping, stress measurement and stress monitoring techniques have been applied to define the in situ stress regime and, together with the correlation of measurements of rock deformation and rock reinforcement behaviour, has enabled appropriate stress control measures to be developed. Stress control measures for development headings have required the selection of roadway orientation, roadway sequencing, reinforcement density and pillar size. The monitoring of behaviour at a range of trial sites has confirmed significant improvements in development stability. Stress control measures for longwall extraction have required rational selection of longwall orientation and extraction direction. Where a mine layout design incorporating the optimum longwall layout design has not been possible, the use of sacrificial roadways has been successfully applied to protect key roadways from stress concentration effects. Comprehensive in situ monitoring of behaviour has been carried out to confirm the mechanisms involved.

Jan 1, 1992

By C. P. Mangelsdorf

The success of the Birmingham roof truss (Figure 1) in supporting some difficult roof conditions, particularly in the Illinois coal basin, has given impetus to the development of a number of alternate schemes. These schemes attempt to alleviate two major problems with the Birming-ham truss, namely, the time required for installation and the cost of material. Because of the difficulty of drilling angled holes and the number of different pieces of hardware which must be handled manually, most operators have been unable to install Birmingham trusses in the cycle and have had to schedule truss crews during the maintenance shift or whenever they would not impede production. Due to this delay the truss has traditionally been viewed as a supplemental form of roof support. In fact, the truss might qualify as primary support and replace at least two bolts if it could he installed in the cycle (and MSHA would accept it as an alternate in the roof plan.) [ ] Figure 1. The Birmingham truss. Two attempts to deal with the first difficulty have sought to streamline the truss hardware while preserving the essential character of the Birmingham truss. One of these, by Peabody Coal, is reported elsewhere in these proceedings by C. Bollier. Another is a contract issued by the Bureau of Mines to Bendix Corporation for the development of a machine, particularly suited for use in low coal, which will automate many of the operations currently executed manually. This machine is expected to be ready for field testing by fall of 1982. Once in place, a truss installed by either of these schemes will interact with the roof in the same way as a conventional Birmingham truss. An alternate approach has been proposed by several different manufacturers independently. Although the hardware details differ. the essential idea consists of two angle bolts, the heads of which are connected by a horizontal chord tightened to some pre-determined tension. Figure 2 shows the generalized concept and does not depict any one of the four systems proposed. The advantage of this scheme is that the angle bolts can be installed and tightened in the cycle, and as bolts, immediately satisfy the roof control plan. The horizontal chord can be added later to achieve almost any initial desired roof loading, the limits of which are defined below this scheme is referred to here as the angle-bolt truss. Because of a fundamental difference in the way in which load is transferred between chords, this design does not interact with the roof under subsequent loading in the same manner as a Birmingham truss. The purpose of this paper is to examine this fundamental difference and its consequences. [ ]

Jan 1, 1982

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 Brian E. Travis

The recent development of polymer grids for the underground coal mining industry has created new alternatives for supplemental ground control practices. The grids utilize strong, lightweight polymers - usually special grades of polypropylene. High tensile strengths and resulting load support characteristics are achieved by molecular orientation of these polymers in the manufacturing process. One of the most important applications of polymer grids as supplemental ground control is in longwall shield recovery. When shields are moved from one face to another, the determining factor in the success of the recovery is the ground control provided by roof support structures along the old face. Whereas primary support is usually provided by roof bolts and cables which run the full width of the panel, supplemental support is often provided by metallic meshes of welded wire or chain-link fence. lightweight, high-strength polymer grids replace these heavy, cumbersome metallic meshes, giving the operation increased productivity by decreasing installation time and reducing injury downtime.

Jan 1, 1990

By Ihsan B. Tulu, Keith A. Heasley, Aanand Nandula

"The objective of this paper is to present the development of a software tool that will assist in an area calculation of the Analysis of Roof Bolting Systems (ARBS) support intensity while incorporating more detailed geology, stress, and intersection span input. In this area ARBS tool, a detailed CMRR distribution can be determined from the available geologic database at the mine. In addition, the overburden and multiple-seam stresses, as obtained from the boundary-element program LaModel, can be converted to a “pseudo-depth” which is then used as the depth input to the area ARBS calculation. Finally, the section-specific intersection spans can be determined from the mine design for input to the calculation. All this detailed area input information for ARBS is handled by the latest version of the Stability Mapping (StabMap) program, which now outputs an area ARBS suggested support density given the required input parameters. This final ARBS grid can be plotted, analyzed and overlaid on the mine map for optimum use in support design and for presentation to production personnel.INTRODUCTIONSince the inception of roof bolts in the 1940s, there has been a lack of a universally accepted roof bolting design method (Mark, 2002; Mark and Pappas, 2012). To address this situation, the National Institute of Occupational Safety and Hazard (NIOSH) developed roof support design guidelines, which were incorporated into a computer program called the Analysis of Roof Bolting Systems (ARBS). These guidelines were based on the effects of roof quality, stress, and mine geometry (Mark, Molinda and Dolinar, 2001). The roof rock quality in ARBS is represented by the Coal Mine Roof Rating (CMRR), the depth is used as a surrogate for the stress, and the intersection span serves to represent the mine geometry (Mark, Molinda and Dolinar, 2001). These three input parameters are used in the fundamental, empirically derived equation of ARBS to calculate a required support density factor, called ARBS, (Mark, Molinda and Dolinar, 2001):"

Jan 1, 2018

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