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By Clare Offner

In 1998, the Australian Coal Association Research Program (ACARP) awarded funding to the School of Mining Engineering at the University of New South Wales to establish a rockbolt testing facility to research anchorage mechanisms associated with fully encapsulated rock bolts and to develop standardised testing procedures for rockbolts. This facility is still under development but has already been used to evaluate the effect of bolt profile and confinement on the load transfer characteristics of a resin encapsulated rock bolt. This paper describes the test facility and presents some of the results of development testing to date.

Jan 1, 2000

By Sanjay Kumar Singh

This paper presents ground control technology associated with a continuous mining operation for mass exploitation of underground coal deposits in the Indian coal mining Industry It shows that competency of roof strata and performances of continuous miners are safer, than other coal mining method as well as productive and economical. Continuous miners keep playing a major role in the underground coal mining industry for their safety and as well as their productivity. Regarding past experiences in Indian coalfields, Chirimiri and Jhanjara mines have achieved exceptional performances, with a potential for over 500,000 tonnes per year. Tandsi mine has difficult roof conditions and does not typically achieve high production and productivity. Even so, the difficult roof conditions have been controlled with modern ?world best practice? roof bolting systems and an output of up to 1,200 tonnes per day has been achieved. It can further be emphasized that if this technology is implemented properly it will bring an unfathomable change to the Indian mining scenario. There are many mines in India that may have potential and economic viability with ground control technology concepts for installing continuous miner systems and beginning mass exploitation of underground coal deposits.

Jan 1, 2011

By Gregory Hinshaw

Underground mine bolting machines have evolved since inception in the 1940's due to the need for increased safety and productivity. However, major design innovations historically came from changes in the mining plan and the mine environment. During the last ten years, productivity needs have outpaced the evolution of existing designs. J. H. Fletcher & Co. has responded with a commitment to research and development which has fostered several new designs. The most recent machine built is a walk through crawler frame powering four drilling units simultaneously with semiautomatic computer control using two operators. This machine utilizes technology to create a safer yet more productive roofbolter for continuous mining sections utilizing place changing methods.

Jan 1, 1998

By Michael A. Berdine

In early 1997, Twentymile Coal Company took a dramatic departure from traditional longwall recovery methods. Previously, Twentymile's standard longwall meshing procedure included the use of chain link fencing material. Beginning with the 9-Right to 8-Right longwall recovery operation, Twentymile incorporated a polyester geogrid mesh system supplied by DYWIDAG-Systems International. This paper discusses the subsequent utilization of the polyester geogrid mesh system at Twentymile.

Jan 1, 2001

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 D. W. H. Su

A two-year study was conducted by CONSOL in a northern West Virginia coal mine to evaluate pillar design and support requirements to improve roof control in right-hand longwall headgates subject to high in situ horizontal stresses. Horizontal stress measurements conducted within undisturbed areas of the subject mine revealed a pre-existing regional horizontal stress field with a significant difference in magnitude between the east-west maximum and the north-south minimum stresses. Three¬dimensional stress cells installed to monitor horizontal stress concentration in the headgate roof during mining revealed that a narrow (60-foot center) headgate pillar reduces the east-west horizontal stress concentration in the roof ahead of the face such that the headgate is more stable and requires less support. This 60 foot x 140-foot pillar design, which has been employed in subsequent panels, still provides adequate stress attenuation to protect future tailgates under a maximum cover depth of 1000 feet. Roof geology derived from underground roof reconnaissance and underground bolt load and roof displacement measurements confirmed the effectiveness of 12-foot long cable bolts for controlling the headgate roof subject to high horizontal stresses. With the new headgate pillar design and the supplemental cable bolts, headgate roof conditions in the subsequent panels improved significantly, longwall production delay due to adverse headgate roof condition was totally eliminated, and record coal production was achieved by the subject mine in the subsequent years.

Jan 1, 2003

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 Dieter Wittenberg

The use of thc ultrasound technique for monitoring rockbolt support has at last provided support engineers with a measunng system capable of pinpointing fracture failuns in fully-grouted rockbolts. The measurement data are based on the operatmg characteristics of the bolt type, which are determined both under test-bench conditions (DIN 21521) as well as in underground trials. Practical experience acquired to date suggests that this new measuring system is both effective and reliable.

Jan 1, 2001

By W. J. Guo

Overburden movement as a result of longwall mining can be classified into, in ascending order, caving zone, fractured zone, and bending zone. Operation experience and laboratory research have demonstrated that there are bed separations in the bending zone due to differential movement and rock mechanics properties between adjacent strata. In china several coal mines have injected flyash into bed separations to prevent strata movement and control surface subsidence. This method is very effective because it can reduce surface subsidence by 35-55%. Combining the field survey results and laboratory simulation research, the author has investigated bed separation and its mechanisms and effect of backfilling the bed separation and its mechanisms. Finally backfilling application in three mines are introduced, including grout flow chart, grouting pressure, and radius.

Jan 1, 1994

By Wei Wu

A new bench blast design method and its realization with the assistance of the computer is introduced. The basic design principle is to define a rhomb cell, called fully-fractured zone, through a series of full scale bench crater tests and apply this geometric pattern in multi-hole, multi-row blast design. To illustrate the design method, the optimization process and assessment of blast performance are presented in the context of a case study.

Jan 1, 1992

By Vasundhara

A chance detection of a seismic event of unexplained origin in the mining district of Appin in New South Wales. Australia, led to a detailed investigation of recording and analyzing seismic events occurring in the area. Multiple events were recorded each day on the seismometer stations. The larger events were strong enough to be recorded on a number of stations spread out in the district. Background investigation of seismicity stimulated due to engineering activities revealed that similar cases of mining triggered seismicity have been reported previously from many mining districts around the world. If the tectonic stresses are close to failure in a region then a small perturbation of the stress state may lead to instability in the region which may manifest itself as seismicity. The parameters that control the occurrence of such siesmicity include tectonic stress magnitudes and orientations. geological weaknesses or structural features and the amount of stress contribution due to mining. This paper reports on the seismic investigative study conducted in the Appin area and considers its association with the geological layout of the region and the mining activity.

Jan 1, 2001

By J. G. Stewart

Polyurethane injection for the consolidation and control of broken strata is a common practice in the deep mines in Europe. The technology has gained wide acceptance in the coal mines of America since the introduction of RokLok polyurethane binder by Mobay Chemical Corporation in 1977. A popular and growing use for polyurethane consolidation grouting is to control the roof and prevent gob flushing during recovery of longwall face equipment. The technique provides many time and performance-related benefits compared to more conventional methods using wire mesh. Kitt Energy Corporation installed the nation's first 1000-feat longwall face in April and May of 1984. The face completed the first panel in October, 1984, and recovery was begun. Roof Strata consolidation for the recovery was accomplished by a RokLok polyurethane binder infection program designed and supervised by Halbach & Braun Industries. The application provided the most rigorous and demanding test to date of this method's performance and cost-effectiveness relative to bolts and wire screen.

Jan 1, 1984

By Archie Richardson

Periodic weighting of longwall supports occurs during retreat ofthe face under certain geologic conditions. Strong stratain the immediate and main roof tend to cantilever over the gob, weighting the supports periodically. The distance between weighting peaks, as well as the intensity ofperiodic weighting, is determined by the suength and thickness of roof members, their location relative to the seam, the frequency of joinling, and characteristics of the gob. In this paper the effects of varying several of these variables ate investigated using block modeling. The models are calibrated against a published case history of periodic weighting in the Pittsburgh Seam. It is concluded that block modeling is a useful tool for correlating measured support pressure histories with expected modes of strata behavior in the roof, with potential for predicting shield behavior in new geologic enviromnents.

Jan 1, 1998

By John C. Stankus

At the 19th International Conference on Ground Control in Mining, a paper was presented detailing new types of Jennmar INSTáL tensionable cable bolts (Stankus and Taylor, 2000). Since that time, significant testing and trials of the various types of tensionable cable bolts have been conducted. Several MSHA districts and state regulatory agencies have now approved these systems as primary support This paper will detail the use of tensionable cable bolts as primary support at two longwall mines in Virginia (MSHA District 5).

Jan 1, 2001

By Steve Signer

Researchers at the National Institute for Occupational Safety and Health (NIOSH) have developed several new tools for evaluating roof support performance. A miniature data acquisition system (MIDAS) was developed that can collect readings from up to 16 strain gauges at regular time intervals and store the readings for later retrieval. Three LED lights change from green to yellow, then red, based on the reading levels and/or rates of change of rock movement. This feature can be used to warn miners of rock instabilities. The system can be used with any strain-gauged support (resin bolt, friction bolt, cable bolt) or with a newly developed rock strain strip (ROSS) developed by NIOSH to measure rock strain. A ROSS is grouted in a hole drilled adjacent to the rock support to be evaluated; the deformed shape of the ROSS provides anchorage on either side of the strain gauges. Data from both laboratory tests and field evaluations are presented that describe the capabilities of both the MIDAS and ROSS instruments.

Jan 1, 2003

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 Dieter Wittenberg

The successful extension of the applications in which rockbolts can be used in the German coalmining industry is, because of the very great raining depth combined with a high degree of stress in the native rock, only possible on the basis of a comprehensive quality management system. The quality assurance system consists of material tests on the individual component parts of a rockbolt, of test rig trials of installed rockbolts, of suitability tests underground and of measures for quality assurance during roadway drivage. Only on the basis of exact knowledge of the way in which installed rockbolts function in the underground and possible sources of error and faults can quality assurance be guaranteed during roadway drivage.

Jan 1, 2000

By Fred Leighton

Outbursts, or the sudden and sometimes catastrophic expulsion of coal and gas into the working area of a coal mine, are a little understood and growing problem. The AE/MS (Acoustic Emission/Microseismic), or rock talk, activity prior to and associated with several outbursts has been recorded using ultrasonic and micro- seismic equipment and has been analyzed by the Bureau of Mines. Analysis of these data indicates that outbursts are comprised of several failures in rapid succession and that anomalous AE/MS data suitable for providing failure warning are generated 15 to 45 minutes prior to the failure. This paper discusses the techniques for recording and analyzing these data and presents sane case histories.

Jan 1, 1982

By James M. Tennant

In the mid 1970's, American Electric Power significantly expanded its internal coal production. This involved opening several large mines in seams that had never been mined on a large commercial scale before. One of the mines opened was the Martinka No. 1 Mine which is located approximately five miles southeast of Fairmont. The mine was originally designed for room and pillar mining with continuous miners but was later modified to permit the utilization of longwalls and continuous miners for entry development. The coal seam to be mined was the Lower Kittanning which averages fifty-six inches. In order to successfully mine this seam, it required that the mine design recognize the effect caused by the dip of the seam which averages four percent to the Northwest with a maximum of sixteen percent for short distances and a relatively low cover. In fact, seventy-four percent of the reserves have cover of less than four hundred feet. Also, the core hole data indicated that the immediate roof varied from zero to eighteen feet of shale with two to forty-five feet of sandstone overlying the shale.

Jan 1, 1982

By David Hill

Over the last decade, Beltana No.1 Mine has generally been Australia?s most productive longwall operation, with a ROM output of 7.2 Mt in YEJ2007. Characteristically favorable roof conditions and low depths of cover resulted in typically high rates of development drivage and longwall retreat. As a consequence of these high rates of development and extraction, there was a continuing focus on recovering and relocating the longwall face as efficiently as possible to minimize associated production delays and operational costs. This paper presents a comprehensive case study of the conventional longwall recoveries (?take-offs?) at the mine, from Longwall 1 to 14. By examining the take-off monitoring data collected over the life of the mine, the key geotechnical issues are demonstrated, including their relationship to the ground behavior experienced and the issues overcome.

Jan 1, 2011