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By Bret E. Leisemann

The geomechanical environment in which highwall mining must operate represents a hybrid between surface and underground operations. Mine design must take into consideration the complexities associated with unsupported spans, pillars with extreme aspect ratios and the instability related to the interaction between coal extraction and the highwall stability. The rock mass adjacent to the highwall, and for a significant distance in, is affected by lateral stress relief and blast damage. This paper describes a rigorous site investigation program aimed at providing some of the input parameters for the design of highwall mining layouts at the Moura Mine and focuses upon defining the nature and extent of the relaxed zone behind the highwall. The combination of borehole imaging and C factor analysis allows delineation of blast damage and relaxation of the rock mass immediately adjacent to the highwall excavation, as well as the more subtle relaxation effects deeper into the rock mass. This has led to the formulation of a proposed geomechanical model for the relaxed zone for direct input into highwall instability analysis and mine design.

Jan 1, 1993

By William Monaghan

Over the period 2000 to 2003, roof falls have accounted for 4 to 14% of the fatalities in underground mining operations. The National Institute for Occupational Safety and Health (NIOSH) is conducting research to reduce the frequency, exposure, and risk of these events through an ongoing program of field and laboratory studies. One area of research involves the evaluation of polyurethane grouting technology that is commonly used to stabilize fractured mine roof strata. Concurrently, NIOSH is conducting work to evaluate the application of ground penetrating radar for advanced delineation of problematic mining areas. In this study, NIOSH partnered with Sub-Technical, Inc. who injected a polyurethane grout (also known as glue) into a roof area of NIOSH's Safety Research Coal Mine. The mine roof area was scanned using ground penetrating radar technology before and after grout injection in an attempt to determine the extent of grout infiltration. A comparison of the pre-and post-grouting radar records showed a significant change at a mine roof depth of about four to five feet. The interpreted radar records were then compared with drill core information, borescope evaluation of roof-bolt holes in the study area, and underground observations. At this site, the interpretations of the radar records correlated with data obtained from the core holes, borescope evaluations and underground observations. This study showed that ground penetrating radar technology can be a useful tool for detecting changes in mine roof due to the injection of the grout.

Jan 1, 2004

By C. J. H. Brest van Kempen

The techniques developed should provide a useful tool, not only during the initial formulation of a suitable bolting plan for a new section, but also for periodic check¬ing on the utilization factor of hardware installed in the roof. Indications are that with present practice, utilization seldom exceeds 507.. Retro-fittable bolter equipment now available (FCBS?) allows doubling of the utilization factor in many cases. We are also introducing a computer pro¬gram based on the material outlined in this paper. This program can save a great deal of time in examining the real effect of implementing alternate bolting plans or using different installation techniques. It allows fine-tuning of bolt lengths, spacing and installation tension to mini¬mize roof support cost, while maximizing safe life of the mine opening. We have developed a procedure which allows easy, site-specific quantification of the need for reinforcement of a mine roof. The concept is based on the forma¬tion of a direct link between theory and empirical data to custom-fit each mine section. In its simplest form, the proce¬dure requires only recording of roof bolt torques in a sample working place (16 to 25 bolts) several times during the first week or so after initial bolting. The way in which the torque pattern changes during this time can reveal whether or not the bolts carry enough tension to maintain stability in that specific roof. From the same data, the nature of the anchorage horizon is derived. Specifically, shale or limestone can be distinguished from sandstone. If the procedure is repeated a few times (within the same mine section) with different bolt installation tensions, we can numerically characterize the roof in terms of one single value: an "effective angle of internal friction". This number can then serve to calculate trade-offs in bolting plan design, such as bolt length, bolt spacing and optimum bolt tension. Additional refinement is possible if a sagmeter is installed in the sample work¬ing place being monitored and if bolt anchorage capacity is determined. The lat¬ter can be done automatically on each bolt as it is being installed, using a system we developed and patented. Alternately, a number of pull tests could be performed. Using the sagmeter, bolt torque and anchor¬age data, it is possible to project the safe life of the supported opening. The details of the procedures described apply specifically to tensioned roof bolting, but a brief discussion paints the way for a similar analysis of full-column resin bolting also.

Jan 1, 1986

By Karl Jr. Zipf

The famous Homestake gold mine in Lead, SD. closed recently alter 125 years of operation. However, the mine may receive a new lease on life as a National Underground Science Laboratory (NUSL) supported by the National Science Foundation (NSF) and dedicated to high-energy physics experiments involving neutrinos. These experiments require the construction of many large underground chambers tells of meters wide at depths of over 21 18 m. Construction of such large openings at such extreme depths has few precedents m civil-engineering-type construction. The Spokane Research Laboratory has a long history of ground control research at the Homestake Mine and has supported NSF and the physics community in their efforts to develop a NUSL at I Homestake or other suitable location. This paper will summarize underground science and describe proposed underground science laboratories ill the United States, in particular tile proposed NUSL at Homestake. Next, the paper describes an empirical design approach using the Q system of rock mass classification for these large Openings. .M initial site investigation that produced three good case histories is described. The actual support system used at the three sites agrees well with support recommendations from current support design charts, giving credibility to estimates of the classification parameters and Q. Feasibility of, and support requirements for, 25-, 50-, and 100-m spans arc estimated in the anticipated rock mass. This analysis indicates that 25- and 50-m spans are probably feasible, but a stable 100-nn span may be unachievable. The empirical predictions are then compared to detailed numerical analyses. The paper concludes with preliminary support recommendations and necessary site investigations needed to make a proposed NUSL a successful reality. These studies have been important input to NSF for their decisions on the technical feasibility of developing the proposed NUSL. If NUSL is developed, it could enable scientific experiments in areas beyond high-energy physics. 'the laboratory could also enable research in rock mechanics. ground water hydrology. mining engineering, nine safety and health, and ground control.

Jan 1, 2002

By Syd Peng

It is necessary to fully understand roof geological features in order to design a proper roof support system for underground coal mines. These geological features include: rock type, rock strength. rock layer interfaces, voids, cracks, and bed separations. Traditionally, engineers have relied heavily on the use of surface borehole log data to identify geological features. Since surface boreholes very expensive to be drilled in close spacing, log data are often insufficient to provide detailed information on the roof geology. Recent advances in control technology have made a large amount of roof bolter drilling data available to mine personnel. These data can be obtained during normal roof bolt installation cycle with little or no interruption in mining operations. This research project has developed several methods to identify geological features in a mine roof from measured drilling parameters. Power trend line analysis can be used to locate discontinuities and interfaces in mine roof. Power averaging can be applied to determine the relative strength of roof strata. Thrust trend line analysis can be used to locate fractures in mine roof. The results of these methods are combined to produce a mapped roof geology In a production environment, manually interpreting and managing collected drilling parameters is not practical since hundreds of holes will be drilled during a production day. A new software package, MRGIS, has been developed to allow mine engineers to make use of the large amount of roof drilling parameters for roof support design. An actual underground test site is presented to demonstrate the analysis and display capabilities of MRGIS.

Jan 1, 2003

By Joseph Hirschi, Naga S. Y. Tirumalaraju, Aditya Mishra, Anthony (Sam) J. S. Spearing

"Primary roof support in underground coal mines in the USA consists mostly of fully grouted passive rebar or grouted (partially or fully) tensioned rebar. Research conducted at two room-and pillar coal mines in the Illinois Basin and one longwall mine in Colorado monitored the performance of these passive and active rock bolts under similar geologic and mining conditions and found no significant initial loads in either passive or active rock bolts (Spearing et al., 2011). Active rock bolts showed significant loss of initial pre-load, although the exact reasons for this were not fully investigated. Subsequent laboratory testing has also shown that in weak rock, resin creep occurs, caused by slippage of the mechanical key between resin column and rock interface. These creep tests were studied in the laboratory in an effort to quantifythis phenomenon.INTRODUCTIONResin-grouted rock bolts are the first and main line of defense to counter roof and rib falls in underground coal mines of the United States. Rock bolts are categorized as active or passive. Active bolts are tensioned during installation whilst no (or limited) tension is applied to passive bolts, which need subsequent strata movement to generate reactive loads. During installation of passive bolts, some reactive pre-load may be generated by a significant up-thrust from the rock bolter boom.The selection of active or passive bolts is critical and is mostly dependent on the conditions and properties of the immediate roof (Unrug, 2009). This decision is frequently made based on personal experience, bias, and most recently cost. Active bolts are generally used in cases of highly laminated roof rock. When active bolts are tensioned, they develop compressive forces between these layers forming a beam, which helps to stabilize weak individual layers thereby increasing frictional forces between layers and decreasing effects of horizontal stresses. The fully grouted tensioned rebar system is high in stiffness as compared to mechanical bolts and provides higher surface area of contact along the length of the bolt due to the grout, which permits it to develop a strong anchorage mechanism."

Jan 1, 2015

By Douglas Morrison

Hardrock mines in Ontario generally operate at between 3,000 and 7,500 ft below surface and generally experience significant rockburst activity below 5,000 ft. Since the introduction of bulk mining techniques around 1980, the safety record of Canadian hardrock mines has improved dramatically. However, the process of improvement was not a smooth one and, in the early years, the number of accidents and fatalities actually increased. One incident in 1984 that resulted in 4 fatalities in Ontario initiated a complete re-examination of mining practice and by the mid 1980s many changes had been introduced, driven by new non-prescriptive mining legislation. These changes affected not only the technical discipline of mining engineering but also the management of operational procedures and, together, they resulted in the significant improvements that have continued to this day. The analysis of the rock-fall related fatalities showed 5 major causes (loose, scaling, installing support, collapse and rockburst) and by the mid 1990s fatalities in all of these categories, except rockbursting, had been eliminated and even then, all these rockburst fatalities occurred in one mine which was closed shortly afterward. This paper discusses both the technical and social reasons for the initial failure and the ultimate success in improving the safety of these mines, with implications for mines in other major mining jurisdictions.

Jan 1, 2003

By Thomas Barczak

A new generation of hydraulic mine support prestressing devices has been developed. These thin-walled steel shells are machine-welded and can be inflated with water or any liquid to provide prestressing for a wide variety of roof support products ranging from Can supports to props and cable bolts. With an expansion capability of several inches, depending on the geometry and size of the unit, they can also establish roof contact eliminating the need for wooden wedges or crib blocks that are commonly employed with several standing roof support products. Capable of withstanding pressures from 1,000 to 6,000 psi, these cells are able to transfer roof loading into the support structure without rupturing. A recent development has been the addition of an inexpensive yield valve that provides control of the maximum pressure and load development on the support. This paper examines the performance capabilities of these inflatable prestressing units and the impact they have on the performance of various support systems, including an evaluation of the overall stiffness of the support system and the load control during yielding of the prestressing unit. Recommendations are made regarding the design requirements of the prestressing unit to optimize the support performance. A summary of mine applications using this technology is provided with general comments regarding their impact on ground control.

Jan 1, 2004

Effective strata control, utilising fully encapsulated roof bolts, is dependent on the installed quality of the reinforcement elements. One mechanism by which fully encapsulated roof bolts may become less than fully effective is by gloving (glove fingering) and un-mixing of the resin. Following some small roof failures containing gloved bolts, investigations have been undertaken in some New Zealand coal mines to determine the extent of, and mechanisms involved in, the gloving of fully encapsulated roof bolts for a range of roof types and installation methods. Gloving, in this context, refers to the resin cartridge partially or completely enveloping a length of the bolt, typically with unmixed resin filler and catalyst/hardener remaining within the cartridge. Results have shown that gloving and un-mixing is a systematic and widespread phenomena, occurring across a range of resin and/or bolt manufacturers, and across a variety of roof types. Gloving was found in bolts installed using: hand held pneumatic and continuous miner mounted hydraulic methods, under run of mine (ROM) conditions by mine workers, and under controlled "best practice" conditions. The roofs bolts investigated are all 1800mm (6ft) long, and have shown that, on average, 485mm (-19") of the bolt length is gloved and/or unmixed. This equates to a 27 percent reduction in effective bolt length. The effected length of bolt is sufficient to impact on the load transfer/reinforcement capabilities of the bolt system, and hence impacts on the design assumptions and subsequent stability assessments. Furthermore, there is a direct relationship between the mechanism for the gloving of bolts and an increased occurrence of resin loss and reduction in encapsulations length in soft (less than 10 MPa) and/or highly fractured rock. Investigations have concentrated on developing an understanding of the mechanisms involved. This has been undertaken using both field installations and recovered bolts, as well as test bench trials. The mechanisms involved have been confirmed as being: the development of a pressure front as the bolt encounters the resin and is spun up the hole, which, in turn, leads to over-pressurisation and radial expansion of the resin cartridge, resulting in an increase in diameter of the plastic resin cartridge, which allows the bolt to be spun up into the cartridge without making sufficient contact to shred the cartridge or the hardener tube, resulting in an unmixed portion of resin.

Jan 1, 2003

By David Bigby, Tim Ross, David Conover

"Extensive arrays of telltale roof monitoring instruments were recently installed in a Mexican copper mine and a large underground mined storage facility in the eastern U.S. The data were used to evaluate roof stability during development and retreat mining and after installation of supplemental supports. Both manual-reading and automated systems were employed and consisted of up to 64 instruments. This paper will discuss the practical issues involved with installation and monitoring, including reliability and maintenance. Examples will be given for telltale response in relation to known events affecting roof stability, including nearby pillar extraction roof caving, installation of supplemental cable bolts, and separation of the immediate roof layer. The strategy for processing the large quantity of data, presenting the data for review, monitoring the system remotely, and identifying and reporting critical events will be described.INTRODUCTIONTelltales have been used for many years with many varied applications. They are relatively inexpensive, easy to install and interpret, robust, and adaptable. The term ""telltale"" generally denotes a strata extensometer that incorporates a visual indication (and warning) of strata movement. The most common dual-height telltale (Figure 1) was developed by British Coal in the early 1990s as roof bolting was replacing steel arch support (Bigby, 2001). Dual-height telltales provide immediately visible measurements, distinguish between movements above and below the bolted height, and are an established means for providing preemptive warnings of roof falls.Many improvements and modifications on the basic design have been developed to adapt to different mining conditions. For example, triple-height telltales are commonly used where roof bolts of different lengths are installed. The standard manuallyread telltales are limited by the difficulty of obtaining frequent, consistent, and accurate readings, especially in high openings. The instruments may also be located in unstable or inaccessible areas. Consequently, an intrinsically safe electronic telltale system was developed that combines high accuracy and both local and remote reading options. The system supports a network of up to 100 dualheight telltales on each of four separate branches. The instruments are connected with a two-conductor cable and can be read both underground, using a portable readout, and on a surface computer (Figure 2). The automated system still provides the visual warning indication underground."

Jan 1, 2010

By Jeffrey K. Whyatt

Estimation of the initial vertical stress carried in a coal seam is an important first step in virtually all methods of evaluating the required size of pillars in coal mines. Such estimates are a trivial exercise in coal fields overlain by gently undulating topography. The LaModel program is easily and routinely applied in such cases to efficiently estimate mining-induced stresses throughout the coal seam. However, application of LaModel to coal mines operating under rugged topography and/or in tectonically disturbed regions is more difficult. LaModel estimates stresses in a twostep process. Topographic and multi-seam mining effects on insitu stresses are estimated in an initial step, and then mininginduced stresses are estimated in an independent second step. A LaModel program function has recently been introduced that decouples these two steps, allowing in-situ stresses to be directly entered from a file rather than calculated. One application of this function is to streamline sensitivity studies by avoiding repeated recalculation of in-situ stress. The function also allows importation of in-situ stress estimates developed by other means. There are no constraints on the imported stress field, which may include significant stress perturbations due to topography, faults, etc. Hence, the range of geologic environments that can be examined by LaModel is significantly increased. This study uses the new decoupling function in an exploration of in-situ stress estimation in mountainous terrain. One option is to use the topographic stress estimation feature included within the LaModel program, and the influence of important parameters in this routine is explored. Another option explored is importation of results from a detailed volume element model. Results of this study suggest that the method used to estimate in-situ stress, and the details of its execution, can have a significant impact for mines in mountainous terrain with strong overburden. More generally, decoupling is an efficient and flexible function that should be considered for most design studies.

Jan 1, 2011

By Karl H. Brandt

In the Auguste Victoria mine a bolted rectangular roadway has been kept open for the first time in the seam D/C after retreat. The target of the project was to gain a basis for planning and experience for future mining layouts in the same scam in view of the reuse of boated rectangular roadways. For this the roadway was additionally secured in sections with longbolts before the influence of the retreating panel had taken place. On retreat a concrete sidepack was concurrently put in place on the face side. The installed monitoring systems consisted of endoscopic devices, multiple extensometers (Tell-Tales), shear-tales, extensometers and convergence measurements. The experience that was gained was carried over into a physical and numerical model.

Jan 1, 2001

By Stephen C. Tadolini, John Bolton, Bre-Anne Sainsbury, Tom Meikle

"The capacity of ground support components which have been affected by corrosion is reduced and may ultimately lead to dynamic failure of the component and the strata. In order to maintain an effective, long-term ground support system, significant campaigns of rehabilitation are often required in corrosion affected areas which also expose the workers to hazardous conditions. The most common corrosion protection for steel ground support utilises sacrificial systems such as galvanising. Galvanising has previously been proven to be susceptible to some corrosion processes. Stainless steel is the most effective in resistance to corrosion, but can be cost prohibitive, and its mechanical properties often make it unsuited to use in ground support components.Providing an outer protective plastic coating to bolts has proven to be an effective means of protecting the inner steel bar from corrosion. However, these support systems tend to be susceptible to coating damage, and require post cement grouting to provide full encapsulation. In comparison to a standard bolt/resin system, they can be slow to install and expensive. These systems have also been shown to reduce overall load transfer performance of the bolting system.In order provide a higher level of corrosion protection whilst maintaining current installation practices and bolting cycle times, Minova has developed the Enduro™ Steel Ground Support Range. The Enduro™ range consists of standard Minova steel ground support components which have been treated with a unique coating process. The Enduro™ coating has been tested in the harshest of conditions, in laboratory controlled conditions and in underground trials. It has been proven to effectively resist or completely eliminate the formation of corrosion, even in the most aggressive environments. This paper explains the process and provides the details of the laboratory and underground corrosion performance testing carried out on Enduro™ ground support products.INTRODUCTIONTraditionally, the most common form of corrosion protection in steel ground support consists of a sacrificial protective coating such as galvanising (Aziz, et al., 2013). Such coatings have proven to be ineffective in extreme high and low pH conditions with corrosion of the support system commonly encountered. There is also evidence that common forms of galvanising may actually increase the rate of corrosion in certain pH environments. Figure 1 shows typical corrosion and failure of a standard re-bar roof bolt."

Jan 1, 2016

By Francis Kendorski

A longwall coal mine in Appalachia about 1,500 ft deep encountered a fault while developing a new longwall panel. The fault extended from mining depth to the surface near a secondary road and drainage. The fault was located inside the anticipated angle of draw within the mined panel and gob. The fault extended vertically out and up, away from the panel, caved zone, and gob at nearly the angle of draw: the fault very nearly following the angle of draw. It was initially thought that "fault reactivation" could possibly occur. Fault reactivation is the phenomenon of having mining subsidence localized along a fault leading to a "reactivation" of the fault and shearing and displacement along the fault. Such fault reactivation would disrupt and deform the fault plane beyond the normal angle of influence of the subsidence trough, and may provide a conduit for any ground and surface waters to reach the mine. We contacted all operators of longwall mines in Appalachia to determine if any Appalachian longwall mines had ever experienced fault reactivation, and teamed that none had experienced the phenomenon. After studies of possible water intrusion quantities and rates based upon in-fault pump tests, which indicated that water intrusion rates should be manageable, and the prior experience that faults in this particular area were usually barriers to water flow, mining proceeded with caution and monitoring. Mining was successful with no noticeable increase in water inflow rates, and no measurable off-setting of the fault exposure on the surface. It can be concluded that the fault did not reactivate due to its relationship to the mining sequence.

Jan 1, 2003

By Zach G. Agioutantis

The prediction of ground movements due to underground mining using the influence function method is a mature technology, widely used by researchers and planning engineers around the world. Surface strain, either tensile or compressive, is an important indicator of potential impacts on structures such as buildings, bodies of water, pipelines, railway and power lines, and tailings dams. Calculation of static or dynamic surface strains, for varying surface terrains and slopes, should be accurately predicted and be independent of the methodology applied for the calculation. This paper discusses and compares the development of horizontal and ground strains on the surface due to underground mining for different surface topologies (sloping terrain, monitoring lines, etc.) and presents the steps needed to ensure accurate calculations. Examples are given to demonstrate how ground strains can be calculated for one- and two-dimensional gridded surfaces.

Jan 1, 2013

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 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 Stankusm John C., Xiaoting Li

"Quantitatively identifying the load on a steel king beam set is a complicated issue in designing the king beam structure at the slope bottom area. From an engineering perspective, understanding the nature and support mechanism of the king beam structure as a standing support is critical in identifying the calculation input parameters for the structure design software. Based on design practices in recent years and successful applications in several slope bottom intersections, the authors present a king beam design methodology, including qualitative analysis, quantitative calculation with a structural design software, and computer Finite Element Analysis (FEA) verification.Especially important is the concept of interaction and the confinement effect between the king beam structure and surrounding rocks, which is essential in designing a proper steel structure in terms of maintaining the roof stability, as well as saving the steel materials and costs of manufacture, labor, and delivery. This paper details the design methodology and applications in several underground slope bottom intersection designs, reaching the goals of improving roof stability and reducing costs.INTRODUCTION AND DESIGN METHODOLOGYCurrently, the load on a square or arch set is typically determined by either past empirical design experiences or known heights of roof falls in current or adjacent mines. These methods work but sometimes are too conservative from an engineering perspective. For example, when designing a king beam structure for an intersection, these methods may lead to a design with extremely large and heavy steel beams, which are not convenient for delivery and installation on-site, not to mention, costly. Therefore, accurately identifying the potential maximum load on the king beam structure is important for designing a safet, effective, and cost-efficient steel structure. Based on past several years’ practices and fundamentals of ground control and structural design engineering, the authors propose a design methodology including the following components:The nature and mechanism of effective roof support (qualitative analysis),Ground reaction curve,Interaction and confinement effect between bolts and steel standing support and surrounding rocks,Factors affecting the load conditions of the king beam set"

Jan 1, 2018

By Rossen A. Halatchev

This study introduces a new probabilistic approach to seismic stability analysis of embankments and slopes. The approach is based on Sarma's solution, which is modified through presentation of the seismic force by its horizontal and vertical components; i.e. the force may have an arbitrary inclination. The probabilistic modelling includes Monte Carlo simulation of the shear strength parameters of the soil mass, which are assumed to have a normal distribution. The probability of failure is determined based on the seismic co-efficient, which is treated as a random quantity. The probabilistic approach is illustrated through a solution of a numerical example from an opencast coal mine.

Jan 1, 1992

By Keith Heasley

In this paper, a state-of-the-art, three-dimensional, full waveform, microseismic system was used to analyze the rock failure around a deep (> 750 in (2500 ft) of cover) bump-prone longwall panel. The microseismic system consisted of both underground and surface geophones coupled through radio telemetry and a fiber-optic network to produce pseudo real-time detection and location of seismic events surrounding the coal seam. This was the first microseismic installation of this scope at a U.S. coal mine, and the system was intended to help determine the exact strata mechanics associated with the redistribution of stress and the associated gob formation at one of the U.S.'s deepest longwall mines. Overall, 5,000 calibrated seismic events were recorded during the mining of one panel, including a Richter magnitude 4.2 event which occurred inside of the array. Analysts of these events provides a number of notable insights into the rock mass behavior. For instance, the longwall panel was widened during the retreat process, and the mining-induced seismicity shows a distinctly different behavior between the start of the panel, the mining of the narrow part of the panel and the mining of the wider part of the panel. Also, in itself, the acquisition of the ML 4.2 event was a major milestone in geomechanical and bump research. This is the first time that such an event has been recorded with this detail and accuracy at a bump-prone coal mine in the U.S. `The analysis of this single event has set distinct new limits on the relationship between mining seismicity and coal bumps.

Jan 1, 2001