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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 Thomas M. Barczak

A theoretical evaluation of the impact of horizontal load on shield support capacity is made from a static rigid body analysis of the shield structure. Parameters affecting horizontal support resistance are investigated for a typical too-leg shield design. Horizontal forces acting on a roof support element are found to be both roof-generated and shield-generated. The impact of shield-generated horizontal forces on roof strata is also discussed from a theoretical viewpoint in relation to desired ground control. A technique is described whereby horizontal loading of shield supports can be measured underground. Horizontal load measurements from two different longwall faces were found to be significant, ranging from 20-35 pct of measured vertical load.

Jan 1, 1984

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 B. T. Wells

This work concerns the stress fields encountered around mining tunnels. A critical review is undertaken of the various analytical assessments of the support requirements for mining tunnels. Comments are made regarding degree and type of support together with method and timing of installation. The results have been used to indicate the type of support required in different mining and geological conditions.

Jan 1, 1981

By Edward S. Custer

Recent investigations of mine roof falls have demonstrated that roof failures are generally associated with geologic conditions. The roof falls can be predicted by using the techniques of depositional modeling for the coal bed and roof rocks, and by lineament analysis. The ability to predict potential roof failure areas will allow the engineer and mine planner to develop a mine plan to avoid the roof failure areas and thus reduce overall mining costs. The ability to avoid roof failure areas also will permit maximum recovery of the coal resources.

Jan 1, 1981

By Al Campoli

The majority of the 100 million roof bolts installed each year in the United States are 5/8 inch deformed rebar fully grouted into a one inch borehole. Commonly referred to as B-Series or No. 5 bar, this system is proven effective and cost efficient in coal mines with average to above average roof conditions. One of the critical variables affecting resin bolt performance is the size of the resin annulus, calculated as the difference between the hole and bolt diameters. The optimum annulus has been proven to be '/4 inch, which provides for effective mixing of the two polyester resin components and incorporation of the plastic film packaging within the cured resin. Glove fingering occurs when the plastic film is forced against the borehole wall potentially interfering with the mechanical interlock of the resin and the rock mass. Glove fingering is not a problem with the optimum '/n inch annulus but has been know to occur with the B-Series 3/8 inch annulus. Laboratory testing correlated the degree of Glove fingering with resin formulation and the bolt head to shaft axes alignment. Glove fingering occurred over 45 % of the grouted length of standard B¬Series bolts. The newly formulated Eclipse B-Series resin when combined with a 1/8 inch offset between the bolt head and shaft axes reduced the glove fingering 70%. The Eclipse system allows the 3/8 inch B-Series annulus to achieve the positive mixing characteristics associated with the / inch optimal annulus systems.

Jan 1, 2002

By Peter Cain

In 1993 an opportunity presented to monitor the effects of undermining an abandoned roadway by a longwall panel in the Sydney. N.S. coal field. Interaction subsidence data was collected by survey leveling to benchmarks in the undermined gateroad as well as by a standpipe system equipped with 15 vibrating wire piezometers measuring changes in elevation in the gateroad relative to an outby header tank. The piezometers were monitored at 30 minute intervals using a datalogger. while the leveling surveys were conducted weekly over the life of the project. The monitoring program resulted in the collection of a very large both of data. relating vertical subsidence to the relative position of the underlying face. The most basic analyses derived a travelling subsidence curve from the leveling data only. which hinted at a relationship between rate of extraction in the panel below and the amount of strain developed in the undermined strata. The complexity of the relationships between the amount of subsidence obtained, the location of' the individual monitoring stations, the rate of face advance below and the potential for "periodic" subsidence due to geological conditions has made analysis difficult. and the amount of data has compounded this problem. Recently. an analytical approach using a commercial neural network analysis package has been applied. which appears to have resulted in the ability to draw sonic meaningful conclusions from the data set. In this paper a short history regarding the collection of the data set is followed by a brief' description of neural networks. This is followed by a description of the several analyses performed. some of the results obtained, and conclusions drawn.

Jan 1, 1998

This paper describes the experiences with the application of the Coal Mining Roof Rating (CMRR) System to South African strata conditions. Roof classification studies using the CMRR system were undertaken as part of a SIMRAC investigation into falls of ground in South Mean collieries. Colliery roof rating exercises were undertaking in a range of geotechnical conditions from shallow level coal seams under flat topography to workings with cover depths of greater than 300m A comparison is made between the CMRR and other Rock Mass Rating systems used to classify different roof geotechnical conditions. The need for geological discontinuity orientation, blasting and rockmass stress adjustments to the CMRR is discussed. The effects of acid mine water on strata weatherability and the need to incorporate immersion tests using acid mine water are also detailed. In addition limited correlation is given between CMRR values and other geotechnical factors such as joint trace length, joint shear strength, joint orientation, weatherability and roof damage due to horizontal stress. Taking cognizance of these observations, a concept of stress induced roof damage triggering is discussed.

Jan 1, 2001

By I. Geldmacher

In-Seam Seismic (ISS) methods have been used extensively worldwide for the past 10 years to assist mine planning, espe¬cially longwall mining in coal seams. The technique is only starting to gain wide acceptance in North America where it is being applied in a much wider variety of applications than was initially considered. Surveys elsewhere have concentrated on the detection of faults (structures) in coal mines prior to longwall mining. The majority of surveys in North America has been the location of abandoned workings which were not adequately surveyed prior to closure. Modeling data based upon the lithological logs, geophysical logs and interpreted sections show whether the method will be successful prior to carrying out the survey. The surveys have been performed to locate abandoned wor¬kings from the surface and underground using both seismic reflection and transmission techniques. Data from coal seams in both Illinois and West Virginia will be presented. A second method where ISS surveys are being applied to detect old workings will be presented. The ISS tomography produces an image of the P-wave and Channel Wave velocities which is representative of the material through which the signal traveled thus identifying the location of the old workings. Data from Texas will serve as an example.

Jan 1, 1990

By Syd S. Peng

Full-face shield leg pressures in a longwall panel for a three-month period were collected and analyzed. The pressure data were presented in the following forms: full- panel full-face shield pressure, individual shield pressure, full-face shield pressure, full-panel time-weighted-average pressure, and relationships among setting pressure, final pressure and pressure increment. Although shield pressure varies from shield to shield and from cycle to cycle, the setting pressure and face advance rate do control the 6nal pressure and time-weighted average pressure.

Jan 1, 1997

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 Zhanjing Yu

In this paper, an equation is developed to characterize the relationship between the UBC and plate size using a boundary integral approach. The equation was validated by the results from mo& than seventy (70) plate loading tests of different sizes conducted in various underground coal mines throughout the Illinois Coal Basin. The equation indicates that the UBC decreases as the plate size increases. The fundamental solution for this boundary integral problems is the Boussinesq equation. The load exerted by the plate on the floor surface is assumed to be uniformly distributed. Both normal and tangential loads are considered. It is also assumed that the floor fails in shear in a plate loading test. The equation may provide the mine operators with a useful tool to obtain from a plate load test of any plate size the UBC value required by the regulations.

Jan 1, 1993

By Gabriel Esterhuizen

When designing pillars in coal and hard rock mines it is necessary to determine the strength of the rock mass forming the pillars. Empirical strength equations, based on rock mass classification techniques, assume that the rock mass is isotropic, this simplification may result in under estimation of pillar strength. Numerical model studies showed that the effect of jointing on pillar strength diminishes as the width to height ratio of a pillar increases. Therefore, the weakening effect of joints should not be equally applied to all pillars regardless of their width to height ratio. The paper presents equations that were developed from laboratory tests on jointed rock samples and numerical models to account for the effects of joint orientation, friction, frequency, and pillar width to height ratio on pillar strength. The equations were calibrated using field data of actual pillar performance in South African coal mines. The method was applied in two case studies in which the strength of jointed coal pillars was assessed and layouts were designed accordingly.

Jan 1, 2000

By Roy H. Grau

The trend in underground room-and-pillar cod mining is to employ remote-control continuous mining machines to take extended cuts of 40 A or more. Roof fall safety hazards to the mine worker associated with 4ed cutting are not completely de6ned but are known to include removal of the miner operator from the protective canopy, non-compliance with approved cutting depth and CM operator positioning. This report summarizes ground control research performed by the National Institute for Occupational Safety and Health (?-JIOSH) researchers at the Pittsburgh Research Laboratory concerning extended cuts. A combination of statistical analysis and underground investigations have been conducted. Statistical analysis of extended cut use, along with roof fall accidents and fatalities data delineate the extent of the problem in U.S. coal mines. Additionally, an underground study is described where the long-term roof stability of extended cut areas are compared to standard cuts.

Jan 1, 1997

By Khaled Morsy

This study presents a typical stress-strain model for coal material using the available in-situ and laboratory tests data conducted on coal. This model can be used as a basic coal model in finite element applications The effects of pillar width-to-height ratio and the confining pressure have been considered in this model. The extended Drucker-Prager model with mobilized friction angle was found to be very successful in simulating the proposed model.

Jan 1, 2001

By David C. Johnson

Coal mining in Illinois has resulted in many structures being exposed to subsidence damage. Damage mitigation techniques (DMT) applied in the foundation design/construction have proven successful in minimizing damage in several test cases. To determine the practicality of these techniques, the Costs of their application are investigated. The AMT costs are compared to foundation and total house costs for various classes and sizes of houses. An economical and effective subsidence resistant foundation construction is proposed.

Jan 1, 1993

By Ali Benbia

The paper shows results from the physical modelling of longwall excavations concentrating on the fracture pattern development above longwall panels. The modelling technique is briefly described and the detailed analysis of the fracture pattern is discussed. The physical modelling is particularly useful in visualising the caving process above longwall panels. This advantage has been exploited using the image analysis technique. Black and white pictures have been taken while the models are tested in successive stages and then enhanced and stored as binary images by scanning using an image analyser coupled with a video camera. These images are then processed using a custom C program which allows the discretization and characterisation of the fractures. This provides a valuable data base for further numerical and statistical analysis which subsequently may allow the assessment of the water inflow hazard to the workings. In this paper a sequence of different extraction thickness have been analysed using the technique mentioned above to show the effect of the extraction thickness on the fracture distribution and intensity.

Jan 1, 1993

By Quanzhong Gu

Stability of a pre-exnacted recovery room plays a vital role when longwall face approaches and during a longwall face move. In an attempt to extend the application of pumpable cribs into recovery room support and to limit roof bolt installation when a longwall face approaches the recovery room, yieldable and cuttable pumpable cribs (YCPC) were employed in the recovery room at the northern West Virginia mine. The YCPC consists of two layers of materials with different strengths. This allows considerable deformation from the floor and/or roof by sacrificing the soft layer while maintaining relatively high load capacity under mining¬induced front abutment loads. The thickness and stiffness of the soft layer, installation and quality control are the key factors when using the Yieldable and Cuttable Pumpable Crib to stabilize longwall recovery room- Underground observation and monitoring results show that the Yieldable and Cuttable Pumpable Crib is a viable solution to insure stability of the recovery room and can save at least two days for a longwall face move at the mine.

Jan 1, 2004

By Cao Shenggen

Experiences in the developed countries have shown that continuous increase of panel width (or face length) is one of the major technical trends for high production high efficiency mines. Increasing the panel width will increase not only the panel output, simplify the gateroad layout, facilitate high concentration of production, but also increase resources recovery and facilitate protection of surface structures. This paper uses the No.4326 super- wide panel, Wangzhuang Coal Mine as an example. This mine employs the fully-mechanized top-coal caving longwall mining method. Through surface subsidence monitoring, the dynamic characteristics of surface movement were obtained. The dynamic surface movement during mining and the final surface movement after mining were predicted using the Mining Subsidence Prediction System. The results indicate that after mining, the surface above the super-wide panel reached a state of full subsidence, So it can ensure the No.309 National Highway above is located in the flat bottom of the subsidence basin, and there is little impact on the national highways when panels on both sides of 4326 Panel are mined.

Jan 1, 2003

By Hanjie Chen

Mining experiences have shown that in a pitching seam, roof behavior is significantly different from a flat seam. Uphill mining usually experiences more roof problems than downhill mining. Based on a case study at RAG American Coal Company, Willow Creek Mine, this paper presents the roof control problems experienced in a high pitching seam. Then, finite element modeling is conducted to analyze the roof stress distribution for an entry developed in different directions relative to the seam strike. The results shows that seam inclination has a significant effect on roof stability in terms of tensile stress. Uphill mining experiences higher tensile stress than downhill mining. The modeling technique utilized in this analysis presents a first of kind methodology.

Jan 1, 2000