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By R. B. Alke

Request to Mine Beneath Bridge The Jabs Run Bridge is a reinforced portland concrete arch filled bridge located on WV Bouts 7 near Pentress, WV. The bridge has a span of 22.9 m (meters) and a height of 4 m above normal pool elevation to the underside of the center of the arch (See Pig 1). The bridge is a two lane structure with a width of 6.86 m. The structure is over 50 years old Wing been built in 1929 and is owned by the Department (WV Department of Highways).

Jan 1, 1984

By Carl Tom Blevins

Resin was first introduced to U. S. mines in 1971 and first produced in 1973. The original polyester roof bolt resin was very expensive and limited to a single cartridge size and a single slow gel time. Early resin applications were limited to very difficult ground conditions. Today approximately 80% of the over 100 million roof bolts installed in U.S. mines, tunnels, and construction projects employ polyester roof bolt resin. The industry has evolved from hand packing samples for trial testing to producing enough resin, if converted to a .9 inch (22.9mm) diameter cartridge, to encircle the world at the equator approximately three (3) times each year. Manufacturing and design improvements allow for a more consistent product with a wide range of applications at a price that is approximately 30% below our 1974 sales price. An inflation adjusted dollar buys six (6) times more resin in 2006 than in 1974. Modern gel times range from a few seconds to over 15 minutes. Viscosity is matched to bolt type and drilling machine characteristics. Multiple cartridge diameters and a wide range of cartridge lengths are offered by two operating companies. Resin manufacturers have also gone through a period of restructuring and change to meet the challenges of the mining industry. DuPont Fasloc has become Fasloc, Inc., a stand-alone company. Celtite became Fosroc then Minova, as it is known today. During this transformation, several manufacturers have either discontinued production or were absorbed. The industry led the development of the chemical grouting materials specifications contained in ASTM F432-95, Standard Specifications for Roof and Rock Bolts and Accessories. A history of the industry will be presented within a discussion of the evolution of the strength index, speed index, cartridge volume, class designation, and product marking requirements of ASTM F432-95.

Jan 1, 2006

By Jiulong Cheng

Underground coal mining causes overburden deformation and failure, one major form of which is bed separation in the overburden. Surface subsidence can be controlled by injecting grout into the bed separations. For a long time, the grouting results of bed separation can not be validated. This is the problem in the application of this technique. This paper analyzes the conditions leading to bed separation, develops mathematical models for seismic wave fields generated before and after bed separation, and bed separations grouted with different materials, and computes the seismic wave field characteristics using the finite difference method. The results show that the existence of bed separation causes changes in the characteristics of seismic wave field, and that different grouting materials generate different seismic wave field characteristics. Intact strata, bed separation, and bed separation filled with air or water all display distinctive seismic wave field in amplitude and frequency spectra. After mining, the original location that provides strong seismic reflection wave no long exists. It is replaced by a weak and syncline-shaped reflection wave. The area, where the seam wave disappears, is larger than that of the mined area. The location, where a bed separation occurs, generates a set of reflection waves stronger than the normal one. The energy of the reflection waves varies with the materials filling the separations. Bed separations filled with air generate stronger reflection waves than those filled with water. The major frequencies for those filled with air are lower than those filled with water. Therefore, it is possible to determine the property of filling materials by analyzing and comparing the amplitude and frequency spectra of the reflection waves. Case studies of application of seismic method for exploring bed separations and grouting were analyzed. The results show that it is feasible to use seismic technique for exploring bed separations and grouting.

Jan 1, 2006

By Luis Giraldo

The installation procedure of fully grouted rebar bolts requires that the bolt be pushed through the resin grout until it is fully inserted in the borehole. Resin grout is a highly viscous fluid that is forced to flow through the annulus between the bolt and the borehole as the bolt advances. Variables such as bolt insertion speed, bolt vs. borehole diameter and grout viscosity determine the magnitude of the pressure generated ahead of the bolt tip. Under weak rock conditions, the magnitude of the pressure of bolt insertion is often sufficient to initiate hydraulic fracturing along joints or bedding planes that allow injection of grout into the strata leading to significant loss of bolt encapsulation. The grout pressure front has also been linked to gloving, a bolt installation problem that reduces bolt effectiveness. A series of tests were conducted to characterize the pressure of bolt insertion during bolt installation under various conditions. Analysis of the data shows three distinct stages of pressure build up during bolt installation. Understanding of the mechanisms involved may allow development of strategies for controlling the pressure buildup and its negative impact during roof bolting under weak rock conditions.

Jan 1, 2006

By Changsheng Song

With increasing depth of coal mining in China, the number of coal and gas outbursts has been increasing for years. By means of destressing the protective seam, the gas in the protected seam is drained to reduce gas concentration in the high gassy seams, thus ultimately attaining simultaneous extraction of coal and gas. Base on the simulated material scale modeling and numerical simulation, the protective seam mining method was practiced at No. 8 coal mine in Pingdingshan city. After extracting the No. 15 seam, the overlying strata movement and the deformation of No. 9-10 protected seam were studied. The experiments showed that it was feasible to destress the protected seams with large interburden thickness. As the protective seam was being mined, the protected seam experienced dynamic movement process and the change in vertical stress in the No. 9-10 seam assumed ?W? shape. When the face had advanced 656 ft (200m) from the setup room, the No. 9-10 seam was fully destressed, resulting in easy gas drainage in the destressed zone. Recommendations on mining sequence of multiple seams mining in the Pingdingshan coal areas were made.

Jan 1, 2008

By A. MacG. Robertson

A cone penetrometer has been used to assess the level of stress existing in hydraulically placed mine backill. The test apparatus was fabricated at the mine and consisted of a steel cone, connector rods and a hydraulic jack. Testing was carried out from a manway passing through the centre of the stope. The cone was pushed horizontally into the fill, both at right angles and parallel to the orientation of the stope walls, and the resistance to penetration was measured. Corrections were made to allow for friction along the rods. In a cohesionless sand, such as mine fill, the point resistance should be directly related to the in situ stress. The stresses in mine backfill are due to o the self weight of the fill o convergence of the footwall and hangingwall of the stope. Silo theory was used to estimate that component of the in situ stress due to the self weight of the fill. The difference between the stress predicted by silo theory and the stress estimated from the cone resistance was assumed to be due to convergence of the stope walls.

Jan 1, 1986

By Jeffrey K. Whyatt

The Crandall Canyon accident investigation included an interesting and unexplained observation by rescuers that the ?barrier rib had shifted northward as a unit, as much as 10 feet.? This is not the first mention of such a movement, although such reports are rare. Historical accounts describe unusual movement and displacement of intact coal, cribs and timbers. Two movements of particular interest are the creation of gaps above coal pillars and falling of standing support elements without apparent damage. A dynamic boundary element program was used to explore movements induced by slip on geologic features removed from the affected panel. While the resulting models are much too simple to fully replicate these observations, they do show that the types of phenomena observed are possible. They can also provide insight into the types of motions that ground support elements are subjected to during large bump events. This was demonstrated for the case of a large bump in a Book Cliffs coal mine. Seismic information suggested the source mechanism to be normal slip on a fault. A model of that source showed initial dilation of the panel followed by dynamic compression and rebound ? consistent with underground observations. The initial dilation is important as it may allow slender standing support to shift or fall.

Jan 1, 2009

By Dennis Dolinar

In this National Institute for Occupational Safety and Health (NIOSH) investigation, numerical modeling is used to evaluate the degree the pillar strength is increased with a rectangular pillar over a square pillar. Three-dimensional models are developed with pillar sizes and geometries typical of underground limestone mines in the United States. Physical properties for the models are based on geotechnical surveys of nearly 30 underground limestone mines. To examine the effects of pillar length on pillar strength with the modeling, a parametric study was conducted where the pillar width was held constant while the length and height were varied resulting in width-to-height ratios ranging from 0.5 to 1.5 and width to length ratios ranging from 1 to 6. There are two aspects to pillar strength and failure. At relatively low stresses, pillars can fail as a result of geologic structure. At greater depths and sufficient extraction ratios, the pillars can also fail as a result of the vertical stresses exceeding the pillar strength. The effects of increasing pillar length regarding both strength aspects are presented in this study. Equations were developed for the increase in pillar strength with both height and length based on the model results. The results from these equations were compared to those from previously developed empirical equations for rectangular pillars. For the more slender limestone pillars with a width-to-height ratio below one, there is little increase in pillar strength for length-to-width ratios above 2 and almost no increase with length for a width-to-height ratio of 0.5. Only with the more squat pillars is there a significant improvement in strength with length. The gain in pillar strength with length for the pillars is explained by the change in the ratio of the area of the pillar affected by the ends to the area of the pillar. For the squattest pillar, the change in strength is also affected by an increase in pillar confinement along the central length of the pillar as the pillar transitions from a square to a long rectangular pillar. With geologic structure, added pillar length can significantly improve the pillar strength, depending on the strike of that structure with respect to the long pillar axis.

Jan 1, 2007

By Stephen Iverson

The National Institute for Occupational Safety and Health (NIOSH) is currently performing research to help mine operators minimize the amount of loose or damaged rock surrounding a blasted opening. Improperly designed blast rounds can result in excessive wall rock damage that may reduce the rock mass competency and increase ground support requirements. Unnecessary blast damage can cause many safety and operational concerns including an increased potential for injury from rock falls and other hazards resulting from sub-optimal blast designs. This paper focuses on the ground control and safety implications of blast damage in underground mines. A reduction in rock quality due to blasting can increase the amount of ground support required. Case study data collected by NIOSH in underground metal mines during standard drill and blast production rounds included blast vibration monitoring, detailed three-dimensional laser scanning of the as-built excavation, and geotechnical mapping of development headings.

Jan 1, 2007

By Miklos D. G. Salamon

If all stratifications are horizontal, the computation of surface deformation induced by coal mining involves the prediction of roof and floor convergence and then the transfer of the effects of this relative displacement to the surface through the use of the appropriate influence functions. A laminated model, in the form of a quasi- continuum, provides a simple means of computing the approximate convergence distribution and leads to the Gaussian distribution as the influence function. The ideas presented in this paper represent a subtle but fundamental generalization of the influence function Method. It is postulated that the influence of a small area of extraction is proportional to the roof and floor convergence and not to the thickness extracted. This difference in definition removes many conceptual difficulties associated with the influence function method. To demonstrate the utility of the model, the surface disturbances induced by the extraction of a parallel sided long panel are derived. Formulae giving subsidence, tilt, horizontal displacement and strain are given.

Jan 1, 1989

By Haile Manteqi

In longwall coal mines, estimation of roof strata condition, sequence of loading, and supporting requirements are of a high degree of importance, and they are directly related to production and safety. Also, a prediction of the initial caving distance is rather complicated to calculate, because there are many parameters that effect caving process?roof and floor strata conditions, thickness of immediate roof, depth of cover, excavation geometry, and magnitude, and direction of principal stresses. This paper presents the results of 3D numerical modeling of the initial caving mechanism using the finite difference code FLAC3D at the E1 longwall panel of the Parvade 1 underground mine located in the Tabas area in the central part of Iran. The initial caving distance obtained was 10.4 m. Also, the results of numerical modeling have been compared to the analytical methods, such as Peng?s method. The results show good agreement with each other.

Jan 1, 2012

By Xinzhi Du

Coal strength is essential to analyze the stability of excavation in coal. It is well known that the strength of coal tested in the laboratory is size-dependent, and different size specimens will produce different strength. Many researchers have studied the uniaxial compressive strength of coal and developed a number of empirical formulae to describe the strength variation with specimen size. According to a comprehensive data base that includes most of the laboratory testing results in the last century in U.S. and South Africa, the size effect and shape effect were reviewed and analyzed. The results show that different groups of coal specimens have different size effect on the compressive strength. The critical size for the size effect from the data analysis is about 40 in. The shape (W/H) of the specimens has a large effect on the compressive strength. The pillar strength formulae obtained from the data regression have a larger strength than all other existing formulae. Most pillar strength formulae have their own place in coal pillar design field. In order to analyze the difference of those formulae, twelve design formulae have been selected to compare using the Pittsburgh coal seam. The intention is not to determine the preferred formulae, but only to compare them, and see how do the W/H ratio, width, length, angle, cross-section area and effective width affect different pillar strength formulae?

Jan 1, 2008

By Yoginder P. Chugh

The characteristics of weak floor strata associated with actively mined coal seams in Illinois are very important from ground stability point of view and, in many cases, are the governing factors in determining the size of pillars and mine openings. Laboratory and field getotechnical characterization studies of weak floor strata were conducted at six mines during the period 1985-1988. Correlation analysis among engineering index properties, and laboratory, and field determined strength-deformation properties were conducted to identify simple tests which can be used to estimate ultimate bearing capacity and deformation properties of immediate floor strata. It was concluded that the ultimate bearing capacity (UBC) and strength- deformation properties of the weak floor strata can be estimated from simple tests such as, natural moisture content, atterberg limits, and axial swelling strain. Indirect tensile strength was found to be a better estimator of UBC than unconfined compressive strength.

Jan 1, 1989

By Youzhen Zhang

The drilling boom is the key component of a roof bolter, and it has significant impact on the performance, safety, and reliability of the overall working device. In this paper, the experimental modal parameters of a drilling boom at low frequencies are identified with the Laplace wavelet correlation filtering method. Based on the obtained experimental parameters, a finite element model of the drilling boom is revised using an optimization algorithm to improve its accuracy. The dynamics of the drilling boom are analyzed through its modal and harmonic response. As a result, an improvement for the drilling boom is proposed to fix the weak links and enhance the dynamic performance.

Jan 1, 2012

By Kazem Oraee

Falls of ground have historically been the main cause for fatalities in underground mines. Although recent advances in technology have reduced the number of such accidents, when failures occur they usually result in severe consequences. Risks of rock falls, use of heavy machinery and electrical apparatus, entry to confined spaces, working in noisy and dusty environments, and working on unstable platforms are some of the hazards in ground control operations. Managing these risks requires a management regime involving strict adherence to operational codes of practice and an enshrined culture of safety. These should be subsequently reinforced through active participation of management, systematic training, and stringent internal and third party auditing. Accident reports show that the major contributing factor in most rock fall accidents is the failure to adequately manage known risks due to the lack of a systematic process. OHSAS 18001 (Occupational Health and Safety Assessment Series) is an international occupational health and safety management standard specification to develop occupational health and safety at the workplace. This standard is intended to help mine operators control occupational health and safety risks. Addressing the requirements of OHSAS 18001 can be a complex and demanding task. A comprehensive guide for efficient and accurate implementation of this standard is provided in this paper. The discipline can be used to establish an accountable management system foreground control activities in underground coal mines. The paper also provides guidelines for preparing necessary documents, devising safety policies, procedures, performing risk assessment, and handling instructions. Finally, the paper concludes by providing a sound analytical basis in terms of the creation of a robust safety management system foreground control operations in underground mines. Full benefits of implementing an effective and systematic operational health and safety management system are illustrated. The procedure adopted and prescribed in this paper can be used in all underground coal mines where lack of appropriate ground control practices can create deficiencies in both safety and productivity.

Jan 1, 2012

By Kevin M. Connor, Malcolm J. McPhersqn

Examples are presented in which Time Domain Reflectometry (TDR) was employed to locate deformation of rock masses induced by mining. The first example involved motoring the propagation of overburden fractures above a longwall coal panel and the second example involved the we of a)R to monitor rock mass deformation in the vicinity of a strip mine highwall. Bock mass deformation, strata separation and large block movement generated strains and failure along coaxial cables which were installed in drill holes and the TDR reflections generated by these strains and failures were monitored. Analysis of field data and a preliminary laboratory test indicate that it may be possible not only to locate rock mass movements but also to quantify these movements with TDR data.

Jan 1, 1984

By Sandin E. Phillipson

The Mine Safety and Health Administration?s Roof Control Division responded to a massive ground failure at an underground marble mine in northern Georgia. The ground failure occurred in a benched area that had been abandoned in the early 1990s. It involved the failure of an estimated 19 pillars, in conjunction with a massive roof fall of an undetermined extent that was at least 60 ft high. Pillars in the benched area had been mined nominally 40 x 40 feet to a height of 50 feet ft, with 40-ft mining widths, although it seems likely from measurements and accounts from mining personnel that pillars were even smaller than intended. Average overburden depth was 500 ft, and the rock mass was characterized by three sets of intersecting geological discontinuities that not only defined very blocky conditions that were conducive to pillar spalling and volume loss, but they were also adversely oriented in such a way as to cut diagonally through pillars at a high angle. The recently released S-Pillar software from NIOSH was used to determine pillar safety factors in the failure area and indicated that pillars were undersized for the conditions. S-Pillar was used to assess pillar stability in active areas to evaluate the likelihood of experiencing similar collapses in the future. S-Pillar correctly identified the pillars in the bench area as having been at risk for instability, in light of their ultimate failure. A two-dimensional finite element model was used to evaluate the possible stages of failure and to assess the likelihood of continued failure in the benched area that might affect more distal mine openings. Although stone mines are generally characterized as having more forgiving conditions than those found in softer sedimentary rocks, the failure shares some characteristics with domino-style massive pillar collapses experienced in coal and trona mines. First, the minimum dimension of the benched area approached 350 ft; second, the pillars defined by benching had small width-to-height ratios (0.8), and; third, the pillar failure area was slightly greater than 4 acres. The massive pillar collapse and associated roof fall illustrate the importance of incorporating pillars that have been properly sized for depth and for the final bench height. Furthermore, the designed dimensions must be adhered to during the actual mining process. Finally, the importance of understanding the geological conditions and their effect on the rock mass is critical.

Jan 1, 2012

By Erik Westman

Coal bumps remain one of the industry?s most devastating but least understood phenomena. If changes to the internal conditions of the rock mass could be observed there is hope that bumps could be forecasted. Seismic tomography has been used over the past 25 years in an attempt to image these changing conditions in the vicinity of the longwall face. This paper describes the history and practical considerations of using seismic tomography in bump-prone coal mines. The implementation of seismic tomography at six different longwall mines will be described along with lessons learned. Early studies used mining independent sources of seismic energy, including explosives and sledgehammers. Subsequently more operator friendly sources, such as the mining equipment itself and mining-induced seismicity, were used. Seismic energy sensors have been placed in gateroads and on the surface above the mine. Each of these configurations has associated advantages and disadvantages. Although the results obtained have been encouraging, the application of seismic tomography to monitoring a bump-prone longwall face is still immature. The ultimate goal of clearly imaging changing stress conditions in the longwall panel in a manner that does not inhibit mining operation is still distant, yet drawing nearer. When this goal is achieved, the industry will have a capable tool for identifying locations where bumps are imminent.

Jan 1, 2008

By Bill Stormes

This paper will discuss implementation of the Hilti OneStep rock anchor technology to improve face bolting operations during the May 2008 longwall move; increase rock anchor installation capacity; and improve safety by reducing employee exposure periods by utilizing the Hilti OneStep rock anchors.

Jan 1, 2008

By Archie Richardson

The trona mines in the Green River Basin, commonly known as the "trona patch," present an interesting set of rock mechanics issues stemming from mining in a unique underground environment. Like other minerals occurring in tabular deposits, trona is mined using high-productivity room-and-pillar and longwall methods. However, trona does not behave quite like other evaporites and behaves far differently than coal. In this paper, the following key issues in trona patch rock mechanics are discussed: material properties, in situ stress field, water and gas pressure effects, creep characteristics, pillar behavior, roof span stability, floor stability, underground tailings storage, longwall mining, two-seam mining. and solution mining. Many of the existing trona producers are entering potentially more difficult mining conditions, and much consideration is being given to "new" technologies such as longwall mining and solution mining. In analyzing 20 years of experience with trona patch rock mechanics issues the authors have identified key comparisons and contrasts with conventional tabular deposit rock mechanics that will help illuminate what has been learned as the trona patch enters the 21" century.

Jan 1, 1999