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By Alan D. Smith

[A standardized checklist in a questionnaire format, was established to investigate selected factors associated with coal nips roof falls, as derived from an intensive review of the literature. A plot study was undertaken to aspect and explore possible statistical relationships that may exist with these parameters. the Purposes of toe study were to: 1. Study in a systematic and empirical fashion selected parameters that may be capable of differentiating characteristics of roof falls; 2. Obtain some predictive indices cased on selected physical and management related variables so that predictions of future problems associated with mine roof falls can be completed, prior to its actual occurrence. Accomplishment of these goals should result in valuable guides to the mining engineer in scheduling exploration work and 4 determining economic feasibility of certain ground control and .lining pro and practices. The parameters associated with mine roof failure that where included in the questionnaire are: working section, county, spar., orientation degrees), pillar dimensions width, length), seam thickness, roof fall dimensions (length, width, surface area, volume), shape of fall (arch, dome, laminar), thickness of thinnest immediate layer, lithology of the first four i.e.-diate roof layers, thickness of h e first four immediate roof layers, type of initial support systems before failure, type of resupport system after failure, length and spacing of bolts in use before failure, length and spacing of bolts planned after allure, presence of .cater, time failure after It coal excavation, distance t3rest ace, physical operation during, time of coo failure, location of the roof fall entry failure occurred ence of sloughing of ribs before failure, and presence of floor heave condition before failure. The typical roof fall had an average roof spar of 20.3 feet, -06 feet depth o coal seam, occurred 136 feet from nearest face, coal seam thickness of inches, p--ar :width off 45 feet surface area D' roof fall 1151 ft2, mainly lamin- shaped, previously rat fore fall between good to very good, little floor heave presence, usually cracks before the fall about 40 percent of reported cases, shales in most of the immediate layers, and usually located in an entry or intersection. in addition, multiple linear regression techniques were employed in the testing process of 18 major research hypotheses in a search for relationships among the various parameters studied of which were found to be significant, once corrected for multiple comparisons.]

Jan 1, 1984

By Guorui Feng, Min Zhang, Yi Luo, Jian Yang, Yujiang Zhang, Junwen Bai

"Safe mining of coal seam sandwiched between abandoned upper and lower room-and-pillared mines (ULPM) ·is increasingly becoming the focus of attention in recent years, which is closely related to the damage intensity of the upper and lower interburdens. The #7 seam with ULPM in Baijiazhuang coal mine was selected for this research. According to the mining and geological conditions, the vertical stress and plastic zone distributions were determined first by numerical simulation. Then, a theoretical model based on the elasti-plasticity theory was developed. The stress distribution and failure zone created in the interburden by mining the upper and lower seams were determined. Finally the feasibility of mining #7 seam between the abandoned upper and a lower seam was evaluated. The results show that: (1) the distributions of abutment pressure and plastic zone coincide, both of which can be used to evaluate the failure zone in ULPM. The failure zone penetrates the whole upper interburden, while only parts of the lower interburden fail. (2) the theoretical failure zone coincides with the maximum distribution zone of abutment pressure and plastic zone obtained by numerical simulation: the failure zone height in the lower interburden is less than its thickness, while that in the upper interburden is larger than its thickness. (3) the #7 seam is located in the failure zone created by the upper seam room-and-pillar mining, which leads to well-development fractures and blocky fragments in the roof, thereby it is unstabled. (4) when mining the #7 seam in the interburden, the key is to control the roof strata and proper support measures should be taken timely to ensure safe mining.INTRODUCTIONMany coal mines in China mine the thick, superior and easily mineable resources preferentially, while the thin, inferior and difficult-to-mine resources were abandoned (Chappells and Trentrnann, 2015; Zhenfu, 2012; Xu, et al., 2015; Guorui, 2009). As the results of deficient geological data and shortage of investment capital, the residual coal resources distributes in many mining areas in China.In recent years, many residual coal seams sandwiched between the abandoned upper and lower room-and-pillar mines (ULPM) were explored in Shanxi Province, especially in the mining area of Datang, Xishan and Luan (Figure.1). The reserves of residual coal seams in ULPM are considerable, increasingly becomes the focus of attention among scholars and engineers."

Jan 1, 2016

By E. Bane Kroeger

In underground coal mining, there is often a need for supplemental support for mine openings. In the past, one of the most common types of supplemental support was wooden posts that were installed against the roof using opposing wooden wedges. Underground, wood has the tendency to shrink from moisture loss and dislodge if not under load. Another drawback to using wood is the variability in strength between posts. Defects in the wood such as knots can cause weaknesses that often lead to premature failure of supplemental support. Many mines that install large amounts of supplemental support in certain areas of the mine such as bleeder entries in longwall mining have switched to using steel props rather than wood posts or cribbing. The reactions of steel props under loading are well- defined and there is little variability in strength between props. Steel props and can be fabricated so they can be used in a variety of roof heights without modification. Wooden posts often have to be cut to a usable length underground before installation. This adds to the installation time of the wooden posts. Steel props are more compact and can be lighter than their wooden counterparts, depending on the length and carrying capacity. Often times it is desirable to prestress the supplemental support to improve roof stability. This is often problematic and time consuming with some types if supplemental support. With these factors in mind, research was undertaken at Southern Illinois University Carbondale (SIUC) to design a new steel roof prop. Several new clamping designs were developed and prototypes were fabricated and tested in the labs at SIUC in the spring of 2003. The designs were modified and refined and the first full-size prototype roof prop was tested in January 2004. With the success of the full-size prototypes, a cooperative research program was established between SIUC and Excel Mining Systems, Inc. to further develop the new prop. Development went smoothly and the prop has performed as expected. In February 2005, SIUC and Excel entered into an exclusive licensing agreement. The prop design under license, the K-Prop, will be installed using a lightweight portable hydraulic jacking system under design that can be used to prestress the props, applying load to the roof and floor during installation. By varying the installation load, the prestress load can be varied from about 1,000 to 10,000 pounds (4.448 to 44.48 kN) and at the same time, the carrying capacity of the K-Prop can be varied from 10,000 to 100,000 pounds (44.48 to 444.8 kN). The K- Prop is composed of only 3 pieces and laboratory testing has suggested that it can be installed by a pair of workers in less than two minutes. The speed of installation of the K-Prop should significantly reduce the total installed cost for supplemental support and should provide a safer working environment by prestressing the prop, which will add support load to the roof and floor during installation.

Jan 1, 2005

By M. Y. Fisekci

This paper concentrates on subsidence measurements, applied over the thick and steep seam mining in the Rocky Mountains Region of Western Canada. The studies to date indicate that two new subsidence monitoring techniques appear to be the most suitable methods for these conditions. The computerized telemetry and aerial photogrammetry systems are being tested for the reliability of the systems during the winter months within the net- work of laser surveying over the workings of the new hydraulic mine.

Jan 1, 1981

By Alan Peacock

Shield supports have been in use in the USA underground mines since 1975, and their development in the intervening time has been progressive and inovative. Specialized techniques are used to optimize their performance in a particular application and to design the component parts.

Jan 1, 1981

By David Bigby

The paper describes research undertaken on an ECSC/K HSE project which investigated several potential physical principles which might be harnessed to provide a non-intrusive means of determining the extent of failure in the near roof of mine roadways and tested the most promising in the laboratory and in the field. It was concluded that the principles which warranted further development were thermal response and laser vibration measurement. In the latter case there is a need to develop an efficient means of imparting energy to the seam to induce sufficient vibration. A new, SIMRAC funded Project will progress work in the field of thermal response.

Jan 1, 2004

By Daniel W. H. Su

This paper presents the results of an extensive geomechanical testing and monitoring program conducted at a longwall panel. The field program included the monitoring of roof caving sequence and mechanism, surface subsidence, change of pillar stress, roof displacement and entry convergence, and strength characterization of the overburden rocks. The response of eight headgate pillars and the adjacent entries was monitored as the longwall face approached and passed the instrumented locations. Overburden response to longwall mining was monitored using time domain reflectometry (TDR) technology; and, the height of the highly fractured zone above the gob was determined by postmining drilling. Good correlation was found between the height of the highly-fractured zone and the TDR, subsidence, and pillar stress data. The results provide a detailed picture of the response of overburden strata and chain pillars to longwall mining. A preliminary model representing the overburden strata behavior at the test site in response to the longwall mining is proposed.

Jan 1, 1987

By D. W. H. Su

This paper describes geomechanical criteria employed by Consol Energy for selecting mine-specific longwall face supports in the past decade. The criteria include immediate and main roof rock characteristics, floor rock characteristics, critical tip-to-face distance and shield operating range. Detailed roof rock properties from high-density core holes as well as in-mine scope holes are used to evaluate the set load density and shield stiffness required to control the immediate roof and the yield load density required to absorb the load density developed from main roof weighting. Detailed floor rock properties from core holes and in-mine floor bearing capacity tests are used to specify the maximum peak toe pressure as calculated by the Jackson method. The critical tip-to-face distance is evaluated based on the immediate roof rock strength, layering and thickness. The shield operating range is evaluated based on main bench thickness, the presence of thick draw slate, the potential of minor roof falls at the face and transportation restriction. Three case examples representing three different geologic conditions are presented to illustrate the successful application of these geomechanical criteria for selecting longwall face supports within Consol Energy in the past decade.

Jan 1, 2004

By Thomas L. Vandergrift

With the inevitable expansion of homes, businesses, and infrastructure in coal mining regions, the potential for future subsidence above abandoned mines is of increasing concern. Of particular concern are areas underlain by room-and-pillar coal mines. Unlike areas above longwall mines, where total extraction causes subsidence in a predictable and timely manner, subsidence above room-and-pillar mines is difficult to predict and may be active for many decades. As part of a geotechnical assessment of a water pipeline replacement project, NSA Engineering recently performed an evaluation of tong-terns subsidence potential along the proposed alignment due to time¬dependent failure of underlying room-and-pillar workings. The alignment of the replacement pipeline closely follows an existing concrete pipeline, which lies 150 11 to 300 fl above workings that both pre- and post-date the pipeline. Annual surveys along the existing alignment indicate that some subsidence has occurred, primarily from partial pillaring performed in the early 1980's, but that this subsidence is not active. Using the boundary-clement code LAMODEL as the primary analysis tool, NSA followed a three-step approach to estimate future subsidence impacts on the replacement pipeline. First, historical information for the mine was compiled, allowing for calibration of models to actual field conditions. Then, numerical models of workings directly under and adjacent to the proposed alignment were nun, with model input parameters varied until resulting loading patterns matched historical data, and subsidence in the model approximated that measured along survey lines. Finally, time-dependent deterioration of coal pillars was simulated by decreasing the coal strength in the calibrated model until a realistic "worst-case" condition (stability of barriers, but Yielding of production pillars and pillar remnants) was attained. Subsidence from the previous calibrated model was then subtracted from that of the worst case model to estimate future subsidence and related ground movement parameters that slay occur along the proposed alignment. The replacement pipeline design, incorporating couplings capable of withstanding the ground movements predicted, is now being finalized.

Jan 1, 2000

By Gexin Sun

This paper presents the physical modelling results of subsurface fracture development associated with longwall mining operations and an application of image processing techniques to interpretion of the results. Physical modelling results have been obtained by employing a large sand and plaster model loaded purely by gravity as a means of fracturing the subsurface strata above the longwall excavation. The results have shown fracture development and crack propagation as a longwall face advances and demonstrated that the strength of stratified rocks, the presence and position of a weak band-, and the extraction thickness, have significant effects upon the overall fracture patterns above the excavation. Binary images of fracture patterns were scanned from the black and white photographs of the tested models using an image analyser coupled to a video camera. These images were manipulated by a custom written C program which allows the images to be processed in both vertical and horizontal direction. The images were filtered to quantitatively differentiate between vertical and horizontal fracture intensities. The vertical fracture intensity is particularly important as vertical fractures are considered to provide the main avenues for surface and subsurface water inflow into the excavation. The use of the image analysis techniques has shown a promising improvement in image enhancement and in model results interpretation in a quantitative manner. The numerical nature of the image analysis results will allow further statistical comparison with other modelling techniques to be undertaken and significantly increase the scope for use of the modelling technique results.

Jan 1, 1992

By P. K. Kaiser

The purpose of deformation monitoring for the evaluation of the stability of underground openings is reviewed briefly and some results from laboratory tests of small tunnels are presented. The ground behaviour is described by comparison with the response of structural systems and illustrated by the data from the testing of small tunnels. It is concluded that the main objective of a deformation monitoring system for stability evaluation is to determine the actual process of deformation and instability in the area surrounding the opening. Only when this process has been established is it possible to use deformation measurements to design support systems or to improve construction or mining procedures. Present monitoring practice is not sufficiently orientated toward the aim of process description.

Jan 1, 1981

By Greg Hendon

Longwall developments in the UK have historically consisted of single entry gate roads. Adjacent developments were separated from existing panels by large barrier pillars (designed of sufficient width to get away from the longwall abutments of the previous panel) or by small barriers driven in the shadow, or de-stressed zone, of the previous panel. Some 2nd panel tailgates were also driven skin to skin leaving no coal barrier between the newly driven entry and the heavily supported existing gateroad. With the developement and wide acceptance of fully bolted entries and the pressure to reduce production costs, alternatives to single entry drivage, particularly yield pillar developments, were examined. Through the Rock Mechanics Branch of British Coal, a cooperative study was begun with Jim Walter Resources, Inc., USA, (JWR) to look at the yield pillar alternative in detail. This study was to determine the feasibility of utilizing yield pillars in the UK and to determine, through monitoring, the possibility of reducing stable pillar widths at JWR. The study has included extensive monitoring of the yield-stable-yield pillar system at JWR No. 7 Mine and an underground trial of a two entry yield pillar test area at Welbeck Colliery in the UK. This paper describes results from the JWR study and the subsequent results of the first advancing yield pillar development in the UK at Welbeck Colliery.

Jan 1, 1995

By Thomas L. Vandergrift

Multiple-scam mining is becoming more common in the United States, especially in the East, where primary reserves arc being depleted, forcing mining companies to develop secondary seams, Although mine engineers and planners are aware of the basic effects of seam interaction and generally follow guidelines for columnizing entries and avoiding load abutments, mine design earn greatly benefit bum more quantitative estimates of scam interaction effects. This paper presents case studies from two eastern mines subject to seam interaction effects where pre-mining stresses were quantified: the Mingo Logan Coal Company's Mountaineer Alma A Mine, and Peabody Group's Lightfoot No. 2 Mine. In each of these mines. mining is being carried out within 60 to 90 ft of overlying longwall and pillar panels under maximum cover of about 1,100 ft As part of overall mine planning and design efforts al these mines. NSA Engineering performed numerical modeling analyses using the non-linear boundary-element code MULSIM/NL Input parameters were calibrated by modeling areas where ground conditions resulting from seam interaction were well documented. By incorporating actual cover loading based on topography and seam dip, and the integrity of remnant, gate road, arid harrier pillars in the overlying mines, the pre-mining vertical stress in the underlying scants was estimated based on the pre-mining stress, plans for mains, gate road, bleeder, and pillar panels were developed. Although mining experience in these areas has beers somewhat limited to date, she designs developed as a result of these analyses have so far proven successful.

Jan 1, 2000

By Z. T. Bieniawski

A major study was performed on determination of long term strength of coal strata directed to the design of coal pillars to ensure their stability beyond the life-time of a mine. Based on field investigations, numerical modeling and reliable data from 12 case histories, three aspects of time effect in the strength of coal strata were studied; (1) strength reduction based on the concept of volumetric strain estimate from in-situ tests, (2) strength reduction in terms of three failure criteria applicable to coal strata: original Hoek-Brown criterion, modified Hoek-Brown criterion, and Generalized criterion, and (3) long-term strength estimation as a function of coal strata quality RMR based on case studies. From these investigations, an integrated approach to long-term pillar stability is proposed, based on numerical modeling and empirical pillar strength formulation. The values of factors of safety for coal pillars are analyzed in terms of probability of failure and practical meaning for mine design purposes.

Jan 1, 1994

By Chris Haycocks

The relevant literature concerning ground control, mine planning and reserve conservation in multi- seam mining is reviewed. Factors affecting interaction, interaction mechanisms, and design guidelines are presented in detail. The impact of multi-seam mining on future mining, measures for ameliorating negative interaction effects, and future research needs are also discussed.

Jan 1, 1990

By Brian Clifford

Thoresby Colliery is in the process of recovering an old roadway that was flooded following the closure of an adjacent mine. The aim is to re-use the roadway as a gate road for a longwall retreat panel and it is therefore important to establish the condition of the existing rockbolt support during the recovery operation. Two NDT methods, ultrasonics and RMT's newly developed RF (Radio Frequency) system were used in combination to interrogate the rockbolts to determine their condition. This paper describes the condition of the rockbolt supports, the NDT methods used and the problems that had to be overcome to successfully apply the two methods.

Jan 1, 2002

By W. G. Pariseau

A new approach to the direct inclusion of the effects of joints and geologic structure in rock mechanics analyses is applied to an elastic analysis of stability of a Lucky Friday undercut and 4111 longwall stope (WL) using the finite element method (FW). The approach is base+ on the concept of equivalent properties of a heterogeneous test volume, but does not depend on the assumption that a test volume is a representative volume element. Comparison with conventional FW results show greater variability in fields of stress, strain, displacement, safety factor and energy densities. Stability requires a knowledge of rock mass strengths as well as elastic moduli.

Jan 1, 1989

By David C. Oyler

Few studies have specifically measured and documented the large-scale loading behavior and durability of ventilation stoppings to mining induced movements, particularly from longwalls. Ventilation stoppings are more commonly the concern of ventilation engineers, and ventilation, topping response to ground movement has only been documented in an incidental manner. This paper presents the investigations of underground measurements that have been conducted to determine the loading response of stoppings constructed from lightweight aggregate concrete masonry units (CMU). These investigations have produced some interesting results that may prove beneficial, not only for developing and assessing alternative stopping construction techniques, but also for designing and selecting standard construction methods for use in varying mining conditions. For instance, the interface friction that results from wedging a CMU stopping during construction plays a substantial role in its ability to resist both lateral and vertical loads. Although they are not intended for ground support, the study showed that block stoppings can resist vertical loads of at least 2,700 to 3,000 kN. Asymmetric loading of a stopping may result in localized failure of blocks within a stopping, which, depending on the severity, can be a precursor of impending stopping failure. In addition to measurement results and implications, the paper will also present details of field measurement methods used to assess stopping response. Stopping stiffness and material strength characteristics will also be presented,

Jan 1, 2001

By Clifford J. Roblee

In this paper, various seismic indicators are evaluated for ability to discern fractures induced into a rock mass by blasting. This is accomplished by presenting results from in situ crosshole seismic studies performed prior to and after a sequence of controlled blasts within limestone and dolomite rock near Austin, TX. Indicators investigated are compression (P-) and shear (S-) wave travel times, first peak and maximum amplitudes, first arrival rise rate, and the linear spectrum of the received signal. Compression wave travel time yielded the most consistent results, while the various amplitude indicators yielded the poorest results for the equipment configuration utilized. In addition, this study documents magnitudes of change in seismic measurements which occurred following blasting. Both P- and S-wave travel times exhibited a wide range of variation due to blasting. Near blast centers below the surficial fractured rock, velocity decreases of about 10% were noted, significantly less than the 50% decrease observed for previously fractured near-surface rock through which the explosive energy was vented. Signal amplitude measurements also varied in magnitude but were less consistent.

Jan 1, 1989

By Kikuo Matsui

In a difficult economic environment, the coal mines in Japan have been making extensive efforts in order to survive by rationalizing the mining operations. Introduction of a new longwall mining system is one of these efforts to establish the rational production structure. In the high production longwall mining system, gateroads should be developed rapidly and maintained effectively during their lifetime. Strata bolting support system has been employed in the gateroads to raise their stability levels and reduce their maintenance cost. However, excessive gatemad closure caused by longwall mining is still occurring, impeding the passage of equipment, personnel transportation, and ventilation air in the longwall panels. This paper describes the development system of gateroads and proposes a new mining method to control the excessive roadway closure problem.

Jan 1, 1995