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By Christopher Phillips

In light of recent events in the mining industry, there has been an increasing demand for technology to detect underground voids and abandoned mine workings. This paper summarizes the use of geophysical methods for this application. Geophysical methods have been successfully employed in the detection of underground voids in several disciplines, including foundation analysis, road and infrastructure analysis, and darn analysis, but is not yet being widely employed by the mining industry. The principal reasons are that the combination of the complex geological setting of a mine, mine design, surface conditions, and improper choice of geophysical method often makes the task of locating abandoned mine workings with geophysics a frustrating, time consuming, and often unsuccessful venture. While there are several geophysical methods that have been demonstrated for the successful detection of abandoned mine workings, there is still no 'silver bullet' to solve the problem in every case. The choice of geophysical method to detect abandoned mine workings should be made on a site specific, and sometimes target specific, level. This paper reviews current methods, and introduces recently developed methods, for the detection of underground voids and abandoned mine workings.

Jan 1, 2003

By D. Reddish

The combination of free standing steel supports, such as arches, and rock bolts (mixed support) has Frequently been in used in UK coal mine roadways when it is considered that the strata and/or environmental conditions would not be suitable for rock bolts solely. However, how such mixed support systems operate is not fully understood. Due to the differences in the support method provided by rock bolts and free standing steel, the total support generated is not simply a case of adding the contribution to the support of the roadway given by the two systems. This paper describes a numerical investigation into mixed support systems when used in coal mine roadways. A series of 2D and 3D geomechanical models are described and the method of modelling the rock bolts and steel supports in coal mine tunnels is discussed. The numerical models described include rock boltd only roadways, steel supported roadways and mixed supported roadways in a variety of geological and in-situ stress conditions. Conclusions are formed that allow an insight into mechanisms of strata reinforcement provided by the support systems modelled. Further to this, a review of the numerical modelling of pre-tensioned rock bolted systems is described identifying the contribution to support efficiency given by the adoption of tensioning in full column resin anchors. The results obtained highlight that the effectiveness of the pre-tensioned load is dependant on the rock mass quality and in- situ stress level at the site where it is to be used.

Jan 1, 2004

By S. Y. Liu

Based on the underground measurements, physical model test of simulated materials in the laboratory and finite element analysis, this paper demonstrates the pattern and process of roof fall over the tip-to-face area in the fully mechanized coalfaces. The main factors that affect the stability of the immediate roof are thoroughly studied including the fracture position and tilt angle of the main roof, the tensile strength (Rt) and cohesive force (c) of the immediate roof, and type and resistance of the powered support. Based on these factors, this paper proposes the basic process of immediate roof breakage a. follows: As the longwall farm advances, the main roof breaks and then rotates. A tensile fracture zone will be formed in the immediate roof under the fracture line of the main roof. A caving zone (plastic zone) will be formed in unsupported area between coalface and canopy tip. If these two zones overlap the immediate roof will be completely unstable. Under this condition, powered support will have difficulties lo control the rod. Therefore it is necessary to study the process of immediate roof breakage and look for effective methods for controlling the roof.

Jan 1, 1990

By Jay Keng

During the construction of shaft on the fractured and weak rock strata, the stability of construction plays an important role. This study includes earth stress estimation, support method, and stability analysis. Stresses on the site of three shafts include structural residual stresses, earth pressures, and hydrostatic pressures were determined. The basic method of estimating the support strength is dependent upon the' size of the plastic ring after rock excavation. During the construction of the shaft, geotechnical measurements, physical properties of the rock, and the change after excavation have to be evaluated again. Geology and construction methods need further consideration.

Jan 1, 1988

By Rao Pothini

Measurement of pressure distribution under the base plate of the Hemscheidt 2-leg 800-ton shield was performed underground for two shifts using 12 pressure cells installed in two rows, one each under each split base plate. Pressure distribution was uneven depending on contact condition. In general the highest base pressure occurred at 1/3 of the base plate contact length from the rear edge. The resultant was near vertical, and the pressure under the tail side split base plate was always higher than the head side. For comparison, pressure distribution on the canopy and under the base plate was also measured under controlled conditions at the USBM's Mine Simulator Testing Facilities in Pittsburgh, PA. A total of 45 tests were conducted under several simulated contact conditions. The results showed that the actual contact area is highly dependent on the compliance of the immediate roof and floor due to the sloped canopy tip and a base lifting device under the base tip. The loading distribution tends to change in magnitude and profile as the leg pressure increases. The base lifting device exaggerates the high toe loading on the base plate characteristics of this type of shield support. This paper describes in detail the testing methods, data analysis results obtained, and recommended changes.

Jan 1, 1992

By J. Riefenberg

U.S. Bureau of Mines (USBM) researchers are developing a personal computer-based hazard mapping system for use in underground coal mines. Hazard mapping is rapidly gaining interest as delineating areas of possible instability is becoming more complex. The development of a hazard map is based on the consensus that combined effects of local and regional stresses, roof, floor, and rib quality, geology, faulting, presence of ground water, etc., all contribute to stability of the ground. In order to demonstrate the concept, a hazard map was developed that combined stresses anticipated to occur in a multiseam setting using numerical modeling, and the newly developed Coal Mine Roof Rating (CMRR) where roof quality ratings in untested areas were modeled using geostatistical methods. Ten borescope readings from an underground mine were used to compute CMRR's for the geostatistical analysis. CMRR's for the mine ranged from 57 to 77, and are considered in the moderate to strong range. A hazard map was developed by combining the stress effects of interseam mining, scaled to weigh equally with CMRR's, and CMRR geostatistical analysis results. This hazard map demonstrates a synergistic effect between the mining-induced stress fields and the roof quality ratings, indicating, as expected, a greater hazard index in areas of high stress and lesser roof quality.

Jan 1, 1994

By A. Wahab Khair

This paper presents an analysis of surface ground movements recorded from two longwall mines in Northern West Virginia which operate in the Pittsburgh Seam. The instrumentation areas consisted of four panels, two at each mine, covering various sections with unique topographic features. Instrumentation consisted of survey monuments on 25 to 120 ft. spacing. Vertical and horizontal ground movements were measured at specified intervals to determine subsidence rate, developing and final subsidence profiles, angle of draw, horizontal displacements and associated strain profiles. A relationship between panel depth and width and the subsidence factor was also developed.

Jan 1, 1988

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 John L. Ellenberger

The National Institute for Occupational Safety and Health (NIOSH) has continued the research role of the former U.S. Bureau of Mines to develop techniques that will reduce the hazards in the mining work place associated with coal bumps. Current research focuses on both analyzing historical seismic data from bump-prone operations and utilizing a mine-wide seismic network to investigate the exact strata failure mechanics associated with bump-prone geology. The anticipated outcome of this research will be reduced bump incidences through advanced engineering concepts and designs which implement the new understanding of strata behavior. The analysis of the historic seismic data consists of correlating observed mining seismicity with the geologic and geometric parameters at the sites. The primary seismic parameters are the timing, location and magnitude of a recorded seismic event. These parameters are correlated with such mining parameters as: the overburden, the size of the immediate gob, the size of the district gob area, etc. This detailed analysis of historical seismic data has provided an informative quantifiable relationship between many of the specific mining parameters and the induced seismicity. The second aspect of the coal bump research is the instrumentation of an appropriate field site to determine the main roof, floor, and gob behavior associated with hump behavior. The chosen field site is a deep-cover longwall mine with competent geology in a historically bump-prone area. The primary field instrumentation is a three-dimensional, full-waveform, seismic array with both surface and underground sensors surrounding an active multi-panel district. The purpose of this seismic array is to determine the timing, the exact location, and the mechanism (tensile fracture, bedding plane slip. etc.) of the failure of the strata surrounding the active and multi¬panel gobs. The preliminary results presented in this paper help to define the strata failure areas around the longwall panel.

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 D. Newman

An underground limestone quarry, developed in the 1940's, transitioned from a surface quarry to an underground room-and-pillar operation. The quarry expanded to a second underground level when the reserves on the first level reached the property boundaries. The historical basis for the sill pillar thickness between the first and second level, pillar dimensions, and mining height was lost during the course of several changes in ownership. When reserves on the second level reached a five-year life, and plans were initiated for a third level, quarry management embarked upon a thorough evaluation of i. current ground control practices for the support of the immediate roof, ii. roof support in the declines between the surface, Level 1, and Level II, iii. pillar centers and pillar safety factors, iv. pillar alignment between levels, v. mining height within a level, and vi. the locations of declines to access future reserves on level three. The evaluation began with detailed mapping of the location and orientation of calcite veins, joints, fractures, and ground conditions in the immediate roof of Level II. The orientation and location of calcite veins, joints, and fractures on Level II were compared with similar mapping on Level 1, completed in the 1970's to establish whether these features were continuous and would be expected to affect conditions on Level III. Rock strength, physical properties, and fracture spacing were obtained from two (2) diamond core holes drilled from Level I to Level II and two (2) holes drilled from Level II to define the vertical extent of future reserves on Level III. The effort to characterize geological conditions was expanded to a rock mechanics investigation of the: i. performance of the current roof support, ii. optimization of roof and rib scaling, iii. calculation of safety factors for 416 pillars on Level II, iv. evaluation of future pillar centers and mining height within a level based upon pillar strength and pillar geometry, v. development of beam safety factors for the immediate roof on Level II, vi. identification of the most suitable strata for the roof in the future level three, and vii. use of LAMODEL to develop a large numerical model of overburden, inter-level, and total stress on the pillars in levels one and Level II with a stress "footprint" on the proposed level three. The characterization of engineering parameters and geological conditions resulted in changes to the: ? active operations in Level II regarding scaling ? equipment and scaling practices, ? pillar centers, ? mining height, ? raising the immediate roof horizon to avoid ? laminated strata in the current roof, and ? a change in rock bolts from a friction based system ? to active tensioned rebar. The planning and design of level three is ongoing and relies heavily upon the geological and engineering investigations conducted during the past year and one-half.

Jan 1, 2001

By C. A. Vining, J. R. Nopola

"Evaporites, such as salt and potash, pose unique problems to ground-support designs not encountered in other rock types. Evaporites are subject to continual creep and no amount of ground support can successfully arrest this process. Common ground-support techniques that are useful for most rock types may reduce the effective life of bolts in evaporite mines and can create unseen hazards. A different approach to ground support must be applied to provide long-term support in areas where high creep rates are present. The goal of effective ground-support designs in these situations is not to contain the rock and prevent it from moving; rather, the ground-support design must be able to move along with the rock and contain any fully detached slabs until additional remediation measures can be undertaken. The most appropriate ground-support designs will consider both the expected movement of the rock and the duration that the area needs to remain accessible.INTRODUCTIONEvaporites, such as salt and potash, pose unique problems to ground-support designs not encountered in other rock types. The factors that must be considered in design stem from the deformation behavior of salt, which can fail in a brittle manner, akin to most rocks, but can also deform in a slow, ductile manner, resembling the stretching and elongation of steel. The deformation behavior of salt has been well established in technical circles where it has been studied for decades (Hardy and Langer, 1984). Much of the research in salt mechanics is related to repository science, specifically at the Waste Isolation Pilot Plant (WIPP) in southwest New Mexico. RESPEC has been continually involved in the WIPP from the initial design considerations (Gnirk, Grams, and Zeller, 1977) to the current day (Keffeler, 2016) and has been able to leverage cutting-edge research of salt mechanics into practical solutions for mining operators. While a detailed description of salt mechanics is not provided in this document, Fossum and Fredrich (2002) include a fine overview of salt mechanics. The following list paraphrases their chapter on basic facts about salt to provide some context for the reader unfamiliar with salt mechanics:"

Jan 1, 2018

By R. Quentin Eades, Kyle Perry

"Surface mines continue to implement highwalls for several reasons, such as increasing recovery, improving margins, and justifying higher stripping ratios. Highwall stability is a complex issue that is dependent upon a variety of mining and geologic factors, and a safe design is necessary for a successful surface operation. To improve highwall stability, it is important to understand the connection between local geology and blasting.Explosives are employed throughout the mining industry for primary rock breakage. There are a number of controlled blasting techniques that can be implemented to improve highwall stability. These include line drilling, smooth wall blasting, trim blasting, buffer blasting, air decking, and presplitting. Each of these techniques have associated advantages and disadvantages. Understanding local geology is necessary for selecting the appropriate controlled blasting technique. Furthermore, understanding the limitations and conditions for successful implementation of each technique is necessary. A discussion of the impact of geologic conditions on highwall stability is provided. Additionally, discussion is provided for the successful incorporation of the controlled blasting techniques listed above, and the associated mining and geologic factors that influence the selection and design of controlled blasting plans. Finally, a new methodology is proposed.INTRODUCTIONExplosives are used throughout the mining industry as the standard for primary rock breakage, a critical part of the mining cycle. In 2015, the U.S.. consumed 2.2 million tons of explosives (Apodaca, 2015). The coal mining industry accounted for the majority of explosive consumption, accounting for approximately 63% of total explosives. The quarrying and nonmetal mining industries accounted for 12% of explosive consumption, and the metal mining industry accounted for 9% (Apodaca, 2015). This constitutes 84% of the explosives used in the U.S. However, the energy released during the detonation process is often in excess of that required to adequately fragment the surrounding rock (Jhanwar and Jethwa, 2000). This excessive energy, along with over confinement and poor blast geometry, will cause damage to the undisturbed rock mass beyond the intended boundary of the blast. This event is known as overbreak or back-break (ISEE, 2011)."

Jan 1, 2018

By Axel Preusse

This paper shows basic considerations about the prognosis and prediction of surface subsidence and other ground movements in the German hardcoal industry. The following case studies describe experiences collected in projects between university and industry.

Jan 1, 2000

By Anthony Lannacchione

There has been a persistent need to forecast roof falls so that miner's exposure to hazardous underground environments can be minimized. Several monitoring techniques have been developed and are used today with varying levels of acceptance in the mining industry. This paper examines the potential for monitoring microseismic emissions activity as a means of forecasting roof falls. The use of this activity to forecast roof falls has drawn only limited attention, resulting in a lack of published field performance data. This deficiency is being partially addressed by analyzing data obtained during longwall mining at Moonee Colliery in 1998. The Moonee data base contains a wealth of information concerning roof fall forecast parameters and the seismic alarm criteria used to develop these forecasts. Four seismic alarm criteria were developed and used by Moonee with varying degrees of success. Roof falls were forecasted 73% of the time with average forecast times of 54 minutes. Ninety percent of the predicted roof falls had a warning time, i.e., the time between warning and roof fall event, of greater than 1 minute. The fraction of forecasted roof falls decayed logarithmically as a function of warning time, until only 20% of events were predicted more than 100 minutes prior to roof falls. False alarms occurred in 50% of the warnings. Many of the false alarms were quickly followed by a cessation in mining which could have temporarily halted the on-going failure process. If mining had continued immediately after the false alarms, a roof fall may have occurred soon after. The microseismic activity collected .from Moonee Colliery demonstrates that techniques to forecast roof rock instabilities in underground mines are possible.

Jan 1, 2005

By M. V. Kurlenya

The experience of application of geomechanical investigations for substantiation of extraction of undermined ore deposit in the north of Siberia is discussed. The finite element method was used for forecasting the state of massif during the development of mining works. The results of calculations were compared with the experimental data of observations in situ for evaluation of authenticity of numerical modelling.

Jan 1, 1990

By Binchuan Zhang

The combined reinforcement system (CRS) combines the strengths of roof' bolting, resin-anchored cable bolt, and chemical grouting to effectively control the deformation of the strata surrounding an extremely poor entry. It is easy to implement and fast in installation. It is one of the systems that are suitable for the reinforcement and maintenance of extremely poor entries.

Jan 1, 2001

By G. Bucelluni

An essential element of truss bolt installation requires machines to angle a hole in the top of approximately 39° to 45° from its vertical axis. Parameter which inherently effect the drill position are: height, width of truss, physical size of mast, and whether single or dual mast bolting is utilized. The combination of these facets govern the installation procedures required for the bolting cycle. The following illustration with written explanation will demonstrate this concept. See Figure #1. [ ] This model assumes certain fixed criteria which corresponds to a dual mast drill design and a set 41° drill angle. Using the derived formula, the maximum possible seam height for both masts to touch the bottom can be calculated for any given condition by substituting by the appropriate bolt spread distance. [ ] In a high seam application where the mast touching the bottom was considered a requirement, the proposed model demonstrates the advantage of single mast drilling. See Figure #2. [ ]

Jan 1, 1982

By Li-min Liu

The Semi-Analytical method can be used to solve a variety of problems in geomechanics and civil engineering. When it comes to layered rock strata and rock masses, it is superior to all other analytical methods. This paper presents the application of a 3-D semi- analytical method to 3-D surface subsidence and stress analysis caused by mining. In this semi-analytical method the layered elements and triangular elements ate used alternatively. Their displacement pattern, strain mahix, elastic matrix, stiffiness matrix, load matrix and stress matrix are presented. A numerical simulation program based on the semi-analytical method bas been developed using Fortran 90. This program is suitable for subsidence prediction and stress analysis of mom and pillar mining, strip longwall and mechanized longwall mining methods. It is applicable to all geological conditions and mining methods. Comparing with the finite method, this method reduces significantly the number of simultaneous equations to be solved and the amount of data preparation. It not only reduces the computer memory, but also runs faster and cost less. Key Words Semi-analytical method, surface subsidence, stress analysis, layered element, triangular prism element

Jan 1, 2002

By David L. Kuck

This paper describes a system for providing structural, support in underground mines, employing water ice for pillars. packwalls and brattices. It consists of a refrigeration brine chiller, brine circulation system, and disposable plastic containers. The system provides for the timely freezing of uniform ice pillars, and for ice maintainance and/or melting on demand. Unique, useful ice properties include: expansion upon freezing, resilience to dynamic loads, and plasticity. Ice will not dilute or contaminate coal or ore. Economic advantages include: 1) lower labor and material costs (water can be piped to the ice pillar site through mine-water, spray-water, or drill-water lines); 2) replacement or supplementation of timber. concrete or other roof support equipment; and 3) potential use of ice brattices as ventillation control; and 4) conversion of ice bratices to ice pillars upon retreat. See Figure . A safety advantage for personnel and equipment is that ice pillars can be placed in hazardous sites, by remote control, if neccessary, without human entry. All filling, freezing and melting operations can be controlled from a safe distance.

Jan 1, 1987