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By James G. Schotsch

Unmapped abandoned mines are hazards for under¬ground mines, surface mines and surface structures. The Radio Imaging Method (RIM) provides a cross borehole technique to remotely detect abandoned mine works. RIM was used at the Buck Creek Mine, an underground coal mine, to determine the extent of unmapped mine works. The information provided by the RIM survey assisted the mine planners in developing their mine.

Jan 1, 1990

By Venkata S. Vutukuri

Compressive strength of cylindrical specimens of a model material and sandstone with various diameter/height (d/h) ratios was determined in unconfined compression tests. It was observed that the compressive strength increases with increase in d/h ratio. Triaxial compression tests were also conducted on the specimens of the same materials with a d/h ratio of about 0.47. It was observed that the axial stress at failure increases with increase in confining pressure. A very interesting correlation was found between the effect of d/h ratio on compressive strength in unconfined compression tests and the effect of confining pressure on axial stress at failure in triaxial tests. The relationships between d/h ratio and confining pressure, s3 in MPa are:- For model material - s3 = -0.95 + 1.7957*(d/h) 0.7883. For sandstone - s- (-0.4554 + 0.9888* (d/h) 1.0355. The correlation coefficients for these equations are 0.9997 and 1. These equations are valid for d/h ratios of up to 10.

Jan 1, 1993

By M. Terry Hoch

This paper presents information on low-coal ATRS systems that are now in use. A study was conducted consisting of an in-mine evaluation of ATRS- equipped roof bolters capable of bolting in seams below 42 inches. Machine manufacturers, MSHA personnel, and bolter operators were asked to assist in reviewing the operation of various low- coal ATRS systems. Features of each system are outlined and operational problems and limitations of each are analyzed. Specific applications, such as ATRS-equipped bolters designed for use with auger-type miners, are also examined.

Jan 1, 1988

By P. R. Sheorey

Four case studies of special geomining conditions from Indian coalfields are discuss- ed. These cases relate to (a) pillar extraction in two seams simultaneously under a difficult roof (Satpura I and II). (b) depillaring in an inclined seam resulting in rib instability (Sudamdih), (c) depillaring resulting in floor lift and side spalling (Jarangdih) and (d) contiguous pillar extraction under hard incavable strata. Solutions to these problems are given based on rock mechanics principles involving stress analysis, classification techniques, past experience and engineering judgement.

Jan 1, 1988

By Robert M. Cox

Abrupt tailgate roadway ground failures, described as floor bumps, sometimes occur in the tailgate entry outby the face during the high-speed extraction of coal from mechanized longwall panels. These floor bumps typically damage the tailgate entry support structures for a distance of from 12.2 to 24.4 m (40 to 80 ft) outby the face. The relative closure of the tailgate entry may be a key indicator of potential tailgate ground control problems. Regression analyses of tailgate entry convergence data conducted by the U.S. Bureau of Mines (USBM) indicate that entry closure may be characterized as an exponential function of the distance outby the longwall face. Assuming that the entry closure is caused by the abutment loads created by the excavation of the longwall panel, the resulting convergence equation can be integrated to locate the centroid of abutment loading. This information can be used to document zones of potential ground failure ahead of the operating face.

Jan 1, 1994

By Thomas M. Barczak

The initial Support Technology Optimization Program (STOP), Version 1.0, was released at the 19th Gmund Control Conference. This original program has since been updated to Version 2.3 which was released in May, 2001. This paper describes the additional features of Version 2.3, focusing primarily on the following three aspects: (I) including uncontrolled convergence into the design requirements for standing roof supports, (21 the addition of design procedures for cable bolts as an alternative secondary roof support, and (3) the addition of new standing roof support technologies. Another new feature which should facilitate the development of design criteria for standing roof support is the capabilily to define ground reaction curves through convergence measurements alone wthout having to make support loading measurements. There are several other new features provided in Version 2.3 which are only briefly addressed in the paper. These include: (I) additional graphics capabilities to facilitate rapid assessment of support comparisons. (2) an East-West designation for support selection to more accurately provide cost and support availability data, (3) additional safety measures including a safety factor to identify support design near the peak support capacity, checks to see if the support dimensions comply with aspect ratio requirements, and measure of roof coverage for the design layout of the support system These new features of STOP provide more capabilities to design and analyze secondary roof support systems for conditions whlch could not be fully analyzed in the original version of the program.

Jan 1, 2001

By Kewal K. Kohli

An investigation was performed to determine the sequence of events which caused the 1987 surface subsidence and related damage to several homes in Walker County, Alabama, USA (see Figure 1). Surface affects compared to mine maps indicated the subsidence to be mine related. However, two coal seams had been worked under this area. The upper seam, the American seam ranged from 250 to 280 feet beneath the surface in the area in question. It was mined-out before 1955 by room-and-pillar method leaving in place narrow-long pillars to support the overburden strata, and abandoned in 1955. The lower seam, the Mary Lee seam, ranged from 650 to 700 feet beneath the surface. The Mary Lee seam had been abandoned in 1966 and subsequently became flooded. The dewatering of the Mary Lee seam workings in 1986 caused the submerged pillars to be exposed to the atmosphere. Due to multiple seam mining and the fact that workings had been inundated then dewatered, a subsurface investigation ensued to determine the sequence and ultimate cause of surface subsidence. Core sample tests with fracture analysis in conjunction with "down-the-hole" TV camera inspections provided necessary information to determine that the subsidence started in the lower seam and progressed through the upper coal seam to the surface. Evidence from the investigation program established that dewatering of the lower seam workings caused the marginally stable support pillars and the roof to collapse. This failure triggered additional subsidence in the upper seam which broadened the area of the influence at the surface.

Jan 1, 1992

By Peter Griesenbrock

In German underground coal mining mostly arch and some rectangular roadways are used in the development work. Due to its positive results from numerical and physical modeling techniques as well as good underground experiences, the numbers of rectangular roadways has increased significantly. Today the bolt support - independent of its cross-sectional shape - represents an undeniable support element. During the introduction of new bolt techniques a detailed investigation of the rock and support mechanical effectiveness of bolt support in roadways at all operation stages is of basic importance. This effectiveness can be predicted and verified using different simulation techniques. For the planning of rockbolted roadways two supplementary simulation techniques are presented in this paper. By combination of all available planning tools the best result for planning assurance can be achieved. Keywords: numerical modeling, physical modeling, arched roadway, rectangular roadway, roofbolting, advancing longwall.

Jan 1, 2002

By Rajendra Singh

In India, pillar mining is contributing more than 90% of underground production which involves extraction of a part of coal from bords with pillars around as natural support in the development stage. #Liquidation of these pillars with splitting and stooking, broken nature of face during mining under complex geomining factors like massive roof, varying treatment of goaf and over or underlying workings result in high stresses and deformation in and around the neighbouring piilars, causing operational problem and hazards to mine safety. This paper suminarises the results of three case studies of depillaring under shallow depth with or without stowing. Assessment of nature and amount of mining induced stresses and deformation was done under these conditions, by insitu instrumentation and observation at three depillaring panels of Girmint. Samla and Lachhipur collieries of ECC at 54, 90 and 110 m depth cover respectively. The value of induced stresses and associated deformations was comparatively low in well caved and stowed waves, whereas for massive roof the roof fall followed overriding of pillars and stooks, with very high value of induced stresses and deformaton in absence of stowing. The stress in the centre and outer edges of the pillars changed with respect to depillaring face advance or splitting of pillars. The caving panel of Girmint colliery under weak coal measure formation, showed maximum induced stress in the pillar at 4 m distance from the face which was 1.2 times (16.6 kg/sq.cm) the preminlng stress of the area. The main roof fall over partially stowed goaf of Lachhipur colliery under massive roof strata caused overriding of pillar after crushing 39 stooks of 7.5 x 7.5 sq.m in rythmic sequence with development of 133lsq.cm maximum induced stress. Well stowed Waf of the same panel reduced this value of abutment stress to 2.3 times (65 kg/sq.cm.) body stress after 40 m further advance of the face from the crushed zone. The depillaring at Samla colliery even under massive roof strata induced low stress, equal to 0.8 times field stress only under the same condition with stowed goaf. The studies revealed the effectiveness of stowing in the goaf over loading of pillars and stooks.

Jan 1, 1990

By Hamid Maleki

A new failure criteria is proposed for assessment of roof stability in underground sedimentary rocks. Unlike other stability assessment techniques, this method is simple and practical, having improved mine safety and productivity in several mines. It is shown that roof movements accelerate to a critical rate prior to actual roof collapse. Critical rates vary between 0.025 inches per day to 0.2 inches per minute depending on rock mass - pillar mechanical properties. Specific critical rates are determined for three rock mass - pillar categories which are common to mining in sedimentary rocks. Time-to-caving varies from one minute to ten days on rock structural controls and type of primary support utilized.

Jan 1, 1990

By Gregory E. Smith

"Tensionable headed roof bolt systems are common in the U.S. mining industry. In the last 15 years or so, they have made a comeback as a hybrid system where a mechanical anchor is used in conjunction with resin. When such a system is used, it is common to use a spherical washer to comply with the requirements of 30 CFR Part 75.204(f)(8). This standard requires an angle-compensating device be used in installations where the bearing plate is offset from the roof bolt axis by an angle greater than five degrees. This paper evaluates system performance of four different traditional angle-compensating device/plate combinations including a new patented extruded plate/extruded washer system that improves overall load capacity and stretch.INTRODUCTIONA large western U.S. underground coal mine was using a fully grouted headed rebar system as their primary support. They had developed their component specifications over many years of working with suppliers to improve and optimize these components to integrate well as a system. As shown in Figure 1, the components included a patented 7 /8"" -diameter Grade 60 headed rebar bolt with a flange capable of full bar load (Walker, 2009) and a patented 8 in x 8 in Grade 3 extruded hole bearing plate manufactured by DieMatic Corporation.The mine decided to pursue a fully grouted tensionable system using a mechanical anchor as the tensioning device. Their primary goal was to eliminate the need for the roof bolt operator to secure (hold) the bolt during resin set time. An additional benefit was the increased initial tension on the bolt. To comply with the requirements of 30 CFR Part 75.204(f)(8), regarding tensioned roof bolts, they were required to include an angle-compensating device because a share of the bolt population would be installed at angles greater than five degrees from the perpendicular to the bearing plate. Also, to improve cycle time and torque/tension consistency, the mine desired to have the washers and anchors assembled at the factory. This required the use of a bearing plate with a center hole large enough to accommodate the 1-3/8-in-diameter mechanical anchor to pass though it during assembly by the roof bolt operator. The mine wanted to continue to use an extruded hole bearing plate in the tensionable system, and EMS was asked to propose a plate and angle-compensating device."

Jan 1, 2016

By Benjamin Mirabile

"Current and emerging practices to ventilate longwall gobs are prompting increased design and analysis of standing support requirements related to longwall mining. Specifically, additional design methodologies are being employed to evaluate standing supports in the #2 entry of a 3-entry longwall system.Numerical modeling will be used to evaluate the performance of standing support in the #2 entry between gobs of longwalls in the Herrin No. 6 seam. The performance of standing support in the #2 entry will be evaluated based on the following: (1) The effectiveness of standing support in maintaining an open airway in the #2 entry; (2) The interaction of standing support in the #2 entry with standing support in the longwall tailgate; and (3) Loading conditions of longwall pillars. Initial numerical modeling activities are focused on evaluating the roof to floor convergence in the #2 Entry and using the ground reaction curve concept for support design.Numerical modeling indicates that, like standing support in tailgates, supports in the #2 entry require some type of yield mechanism to withstand initial uncontrolled convergence. Numerical modeling also suggests that support density can be lower than that used in a tailgate support application. The numerical models used for initial investigation of support performance in the #2 entry are limited in their ability to evaluate support performance. The magnitude of uncontrollable convergence can be estimated with LaModel software. Near-seam conditions have not been investigated in this research since the LaModel software does not have the ability to evaluate inelastic rock behavior.IntroductionDuring the past three decades, many researchers have investigated standing support performance in longwall tailgate entries. Very little attention was paid to the middle entry of a threeentry longwall gateroad. As longwalls retreated, no personnel would travel the #2 entry, and the entry was considered part of the longwall gob. In response to recent mine disasters, regulatory agencies and operators have devoted more attention to these entries. Prior to the Upper Big Branch mine disaster, little or no secondary support was applied in these entries. Unlike secondary support in longwall tailgates, there is little empirical knowledge or quantified research specifically applied to secondary support in the #2 entry. This paper outlines initial steps used to develop a design methodology for secondary support in the #2 entry."

Jan 1, 2015

The properties of coal or rock containing gas are very important both for studying coal and methane outburst mechanism and for controlling underground rock in mining. The theological fracture properties of coal containing gas were studied to obtain its rheological fracture principle both in microscopic scale and in macroscopic scale. The application of this principle is successful in explaining coal and methane outburst mechanism and for putting forward a rheological hypothesis of coal and methane outburst.

Jan 1, 1992

By Yanfa Gao

Abstract In order to control and reduce ground subsidence due to coal mining, and to protect building, railway and other surface construction, a new subsidence control method is proposed. Ground subsidence is reduced by grouting bed separations in overlying strata with fine-coal ash. Engineering application tests have been performed for 5 years in Tangshan Coal Mine. Kailuan Group Corporation. China. The technology has been applied to 4 fully mechanized sublevel caving mining faces. Its effect in reducing subsidence has been significant. The technology including grouting engineering design method and ground subsidence prediction theory is introduced in detail. Keywords: overlying strata separation, multi-layer grouting, subsidence control

Jan 1, 2002

By Alan Campoli

The Eclipse System was developed by Minova USA Inc. formerly Fosroc Inc. to improve the performance of 5/8-inch deformed rebar fully grouted into a one inch borehole. An 1/8-inch offset bolt head combined with specially formulated Eclipse Lokset resin cartridge results in reduced gloving and increased mixing efficiency. The benefits of the Eclipse System have been demonstrated, under the supervision of MSHA, in Kentucky, West Virginia and Illinois coal mines in partnership with Excel Mining Systems, a leading roof bolt manufacturer. Over 100,000 units have been installed to date. Eclipse system bolts exposed during overcast construction at the Panther Mine of Cumberland Resources displayed an extremely well mixed, uniform resin anchorage over the entire bolt length.

Jan 1, 2003

By Tetsuro Esaki

This paper describes the present condition of mining-induced damages in Japan and the characteristics of them. The change of mining operation and environmental condition has caused various significant impacts on the ground environment: subsidence, cave-in, springing out of ground water etc. The characteristics and the influences of these phenomena are discussed by investigation of the actual conditions and by fundamental studies. Some counter measures are also introduced.

Jan 1, 1989

By Robert A. Stansbury

The No. 14 Mine of United States Steel Corp- oration is located at Munson, West Virginia, in &Dowell County. The mine was originally assigned 7,530 acres of Pocahontas 3, 4 and 5 Seams. Production began in 1948 with a listed reserve of 64,500,000 in place tons. It was originally intended to superimpose the 4 Seam workings with the 3 Seam and mine the two simultaneously to minimize the effects of one seam on the other. Roof control problems and economic conditions led to the discontinuance of 4 Seam workings in 1958 and again in 1980, after reopening in 1972. With room and pillar mining continuing in the 3 Seam, the majority of the 4 Seam reserves have been undermined. The mine began operation using track mounted conventional equipment. Off-track conventional equipment was next used, and in 1957 continuous miners were introduced. Since this tie, continuous miners on room and pillar work have been exclusively used with the exception of a brief shortwall trial in the 4 Seam in 1975. By mid 1982, 3 Seam mining will have been completed, leaving an estimated 42 million in place tons of 4 and 5 Seam coal as the focus of mining efforts. Plans for the subsequent reopening of the 4 and 5 Seam workings have been scheduled for June of 1981. With the resumption of mining, management is faced with solving the roof support problems caused by both the inherent physical conditions and undermining.

Jan 1, 1981

By Ben L. Seegmiller

Specially truss systems? including the Intersection Truss®, Continuous Entry Truss®, Cutter Roof Truss® and Roktrus® have been used in many coal mines in the mid- west and western United States during the past four years. These truss systems offer greater strength and support than other standard trusses and many other support devices. Mining operations have found that speciality trusses can give effective long-term support in areas that must remain stable for many years. At some mines, the Intersection Truss® has become the most-widely accepted method of providing secondary support in potential problem areas. Other applications for specialty trusses have included longwall start- up and recovery rooms, arched roofs, access rock tunnels and tailgate entries.

Jan 1, 1990

By John Ellenberger

The nature of competition in the coal market tends to deplete the most favorable coal reserves first, and forces subsequent development of mines in more extreme ground conditions such as those associated with multiple-seam mining. In fact, 70% of the United States coal reserves are in multiple-seam situations. The National Institute for Occupational Safety and Health (NIOSH) is conducting research to develop mine design algorithms that will result in safer multiple seam mines. This paper presents an overview of multiple seam issues in the central Appalachian coalfields. To date, more than 50 case histories have been analyzed from 20 operating mines in Eastern KY, Western VA, and Southern WV. Each case history is classified according to the degree of multiple-seam interaction, ranging from no apparent interaction to severe interaction with direct impacts on mine safety and resource recovery. The case histories are also examined with regard to amount and geologic characteristics of interburden and overburden, and design stability factors. The sequence of mining has also been found to be critical when the lower seam is fully-extracted. This paper compares current case histories to traditional rules of thumb. In addition two situations were modeled using LaModel software. LaModel has been upgraded to import pillar grids and topographic data from AutoCAD files. The cases presented demonstrate vertical stress capabilities of LaModel.

Jan 1, 2003

By Ben Fahrman

The classical approach to engineering design involves the purely deterministic calculation of the factor of safety, the ratio of strength to stress. The factor of safety is an easy calculation to perform in many circumstances, and it is very easy to interpret the results. The simplicity of the method is both a strength and a weakness. The results of the deterministic factor of safety calculation are simple to determine and interpret, but they have no ability to account for the uncertainty present in the inputs or outputs. Uncertainty is prevalent in geotechnical engineering applications. This uncertainty can stem from spatial variability, poor sampling, a dynamically changing environment, etc. Probability analyses allow input parameters to take the form of a distribution rather than a single value, making them uniquely equipped to handle the uncertainty inherent in geotechnical engineering design considerations. A stochastic approach also has the benefit of providing results as a probability of failure, which is more meaningful than a factor of safety. Though stochastic modeling is becoming more common in many geotechnical applications, it is still not widely used for coal pillar design. The objectives of this study are to justify the concept of using a stochastic approach to coal pillar design and to compare the results of a simple stochastic analysis to those of standard industry practice. A simple synthetic study was performed to compare the results of a probabilistic analysis of coal pillar design to the results obtained from running ARMPS, which is published by NIOSH. Normal distributions were assigned to each input parameter that is required to determine the factor of safety of a single coal pillar. The probability of failure resulting from the synthetic study was found to be more conservative than the ARMPS stability factor. A probabilistic approach to coal pillar design is discussed in comparison to the traditional deterministic approach. The greatest strengths of the probabilistic approach were determined to be the effective handling of uncertainty and the increased meaning of the inputs and outputs inherent to a probabilistic approach.

Jan 1, 2013