Search Documents

By Denise Y. Dizon

The objectives of this study were to document the hydrologic impacts of longwall mining on streams, identify the factors affecting the extent of stream dewatering, and develop empirical trends to predict the extent of dewatering and recovery of streams in advance of mining. This study on stream impacts is a companion to a stud; conducted on ground water impacts from longwall mining, which was done as part of the same research project at the' same locations and times. The study areas are three mine sites in north- central West Virginia. Mine A, located in Upshur County, has relatively thin mine overburden under the valley streams (105-115 feet). Stream monitoring there continued the earlier work of Cifelli and Rauch (1). Stream dewatering was severe with streams often going dry over the longwall panels during baseflow conditions. The lost water was probably flowing to the mine. Dewatering began in streams over the mine entry areas adjacent to the panels and as much as 380 feet from the nearest panel edge. The angles of dewatering influence ranged 22 to 72 degrees with respect to the nearest mined panel edge. Discharge then typically increased as the streams- flowed across the panel edge, but then decreased again over the panels. These streams were often ponded by local reversals in hydraulic gradient caused by land subsidence, and often dried up after flowing a few hundred feet across the panels. This occurred over panels that were previously mined up to eight months before. Mine B, located in Monongalia County, has relatively thick mine overburden (475-485 - feet) under the major stream. Stream dewatering was severe there during warm season baseflows, with complete dewatering occurring then over the longwall panels. This dewatering occurred over mined panels up to five years old, probably in response to a major anticlinal axis lineament and fracture zone in the stream valley. Mine C. located on the West Virginia -Pennsylvania border, has relatively thick mine overburden (about 585-630 feet) under the monitored streams there. stream dewatering was only partial, and these streams typically recovered their lost discharge downstream of the mine, indicating that lost water was not recharging to the mine. Only longwall panels less than one year old were associated with stream dewatering.

Jan 1, 1990

By D. J. Maconochie

This paper describes the investigations and results of monitoring of deformations of houses located within the area of influence of a pillar collapse over the Westfalen No. 3 coal mine near Ipswich, Queensland. The subsidence resulted in minor subsidence of at least 18 modern houses and serious damage to 4 others. The history of the events and the measures taken to deal with the physical problems arising are described. The investigations and results are described and related to the mining methods and geology. The stability of coal pillars up to 9.6 m high was considered and computer modelling undertaken to relate surface subsidence to estimates of the extent of pillar failure. Assessments were made of the likely extent of subsidence during the incident. Measurements of distortion and tilt were obtained as the ground slowly subsided and criteria established to determine when the structures were deemed to be unsafe. Detailed surveys of houses affected or anticipated to become affected were also undertaken. Four houses were condemned and subsequently demolished as a result of excessive tilt. The methods of assessment are described and the implications of the results related to the various house designs.

Jan 1, 1992

By Stephen P. Signer

A field test was conducted by the U.S. Bureau of Mines at the Cyprus Plateau Starpoint No. 2 Mine. near Price. UT. to study the support rock interaction mechanics. Twelve instrumented. fully grouted roof holts and eight sagmeters were installed in the roadway of a two-entry gate road to measure load changes and roof movements. Readings were taken during section development and as each longwall panel passed the test area. Loads that resulted from development of the en- tries were higher than would be expected if simple suspension of the roof rock was the sole cause of loading. When the first longwall face passed the test section massive beam behavior was exhibited over the entry and adjacent pillar. However, no significant localized bending was detected at any of the strain gauge locations. After the first panel passed the test section. all the roof bolts had at least one zone where the steel had yielded. Loading continued to increase. and when the face from the second panel was adjacent to the test section. 70 pct of the strain gauges at the 6-. 1%. and 30-in locations had passed the yield point of the steel roof bolt. However, even at these high load levels, the supporting pattern was sufficient to provide adequate reinforcement to the mine roof.

Jan 1, 1990

By Don Berger

Highwall scaling, bolting and technical blasting are important aspects in the remediation of existing highwall exposures. Proper planning, design and research are important first steps in the development of long term stability. Research into old workings and their influence on highwall stability control the planning and design. These steps are followed by improvements in blasting techniques, highwall monitoring programs and constant evaluation of the results. Recently, due to a number of factors, the highwalls of the Open Cut Mine have started to deteriorate, creating both operational and potential safety problems. Geologic setting, highwall design, mining operations, old workings and weather have combined to create adverse conditions that have allowed sections of the highwalls to become unstable. Homestake Mining Company has developed a program to alleviate the existing ground control problems and to decrease the effect operations has on future highwall stability.

Jan 1, 1996

By Herryal Z. Anwar

In recent years, many both mining and civil engineering projects are developed in the area which may be categorized unstable, such as fractured and jointed rocks or "water sensitive rocks". For example, in underground coal mining, in which the floor strata normally consist of weak shale, the problem that may arise in roadway is floor heaving. In this case cement injection in borehole appears to be an economically effective method in order to make roadway more stable. This method may be also applied in the projects in which the constructions are laid on fractured and jointed rock. Nevertheless, the successful cement injection is much dependent on the water-cement ratio and the injection technique. This paper discusses the application of cement grouting to improve the ground stability in longwall mining, the laboratory experimentation of cement grouting and the method of floor injection.

Jan 1, 2000

By Robert C. Speck

Floor heave or deformation of the mine floor into the mine opening is a problem which has plagued coal mines in this country and others. In mining areas where room and pillar mining is practiced, floor heave generally occurs when the stress applied to the floor material by a coal pillar exceeds the bearing capacity of the floor strata. When the floor strata beneath the coal pillar fail, the pillar moves downward and displaces the material under it. This material, in turn, moves outward and upward into the mine opening (Figure 1). As the underlying materials fail, the load supported by the coal pillar may be transferred to adjacent pillars. If these are marginally stable, they too may become overloaded and push into the floor. Thus, floor heave can spread through a large portion of the mine in a progressive manner. As the pillars push into the floor, differential movement and flexure of the roof strata may cause them to weaken and fail, resulting in subsidence of the ground surface above the mine. This paper describes the problem as it was manifested in the Zeigler Coal Company No. 5 and Murdock room and pillar coal mines near Murdock, Illinois, and reports the results of a U. S. Bureau of Mines- sponsored study conducted by the University of Missouri-Rolla. During the course of the study, floor heave in the two mines hindered the transportation of men, machines, and coal to and from the working mine-face, interrupted ventilation plans, drastically increased roadway maintenance costs, intensified safety and strata control problems, destroyed large pieces of equipment, and, several times, pre- vented access to otherwise minable coal resources. The ultimate objective of the study was to develop one or more simple procedures to allow detection of a potential floor heave problem during the exploration phase of mine design--before initiation of production mining.

Jan 1, 1981

By Weihua Song, Hongwei Zhang, Feng Zhu, Sheng Li, Guoshui Tang

"Rock burst is one of the most serious dynamic disasters in coal mining. Rock burst prevention involves two difficult tasks: systematically evaluating the occurrence conditions and effectively forecast for rock burst. This paper systematically studies the effects of natural geological dynamic conditions and mining engineering on and forecast for rock burst. It establishes the evaluation method and index system of rock burst geological dynamic conditions and proposes a method of forecasting rock bursts by monitoring fault activity with anchor cables. Natural geological dynamic conditions are a necessary condition while mining engineering is a sufficient condition for the occurrence of rock bursts. Rock bursts in mine must have suitable geological dynamic conditions, and mining engineering activity is merely an inducing factor. There is a good correlation between anchor cable stress variation and fault activity, when the anchor cable dynamometer indicates that the fault is active. It can forecast a rock burst a few days in advance. This technique has been successfully applied to Panel 83003 of a coal mine in China, which improved the safety production level of the mine and found a new way of rock burst evaluation and prediction.INTRODUCTIONRock burst is one of the most serious dynamic disasters in coal mining. With the increase of mining depth, rock burst disaster is becoming more and more serious. Systematically evaluation and effective forecasting of the occurrence of rock burst in the coal mines are important and difficult work in the control of rock bursts. Chinese researchers have performed numerous researches on rock bursts, Qi et al., established the rock burst model of frictional sliding instability, explained the occurrence mechanism of rock bursts by stick-slip phenomenon in frictional sliding, gave full consideration to the influence of primary rock stress and mining-induced stress on rock burst occurrence, and proposed the stress controlling theory of rock burst. Pan et al., [3] put forward the criterion of perturbation response, explained and analyzed the problem of rock burst in circular openings, put forward the ratio of coal-rock elastic modulus and reduced modulus is the significant parameters for the determination of stabilization; systematically summarized the rock burst distribution, type, mechanism and control in China. They classified rock bursts into three types: coal compression, roof fracture and fault movement. By applying energy transfer principle and conservation of energy, combined with the analysis of the weakening of rock fabric damage, Zhou and Jiang put forward the theory and equation for the occurrence of coal-rock mass impact effect. They analyzed and discussed the formation mechanism of rock burst by combining impact effect theory and energy equation. Wang et al., recognized that the mechanism of rock burst which induced by fault, fold and phase transition is the superposition of tectonic stress and mining stress and that the axes of syncline and anticline and their flanks are the location where rock bursts mostly occur. To prevent stress superposition is the efficient way to control the structural rock burst [7]. Jiang et al., summarized the research achievement of rock burst mechanism and controlling techniques and existing problems in recent years in China, and pointed out the direction to improve the level of prevention of controlling rock bursts in coal mines."

Jan 1, 2015

By Richard G. Burdick

The Bureau of Mines', Denver Research Center has been conducting research for the past few years on the use of resistivity methods to locate abandoned mine workings. As this work has progressed, it is apparent that in some cases, in addition to detecting the old workings; stoping, precursive to surface subsidence has also been detected. This paper describes the Automated Resistivity method and discusses sites in Colorado. Wyoming. and Illinois where the subsidence phenomenon has been observed.

Jan 1, 1982

By Stephen P. Signer

A method to assist in the evaluation and selection of roof bolts using in situ measurements of roof bolt loading has been developed by researchers of the Spokane Research Center, National Institute of Occupational Safety and Health. Both axial and bending forces are measured by strain gauges at many locations along the length of fully grouted bolts during various stages of mining. This information is then used to ( I) predict bolt loading for variations in bolt spacing, grade, and diameter, (2) calculate the design changes necessary in zones where bending loads are high, and (3) determine if bolt length is adequate. Results from several case studies of full-column bolt loading in coal mine gate roads are used to illustrate the design method. This knowledge will give design engineers a tool for the selection of roof support systems that will improve underground safety by reducing roof bolt failures.

Jan 1, 1997

By Dr. Daniel W. H. Su

t is both an honor and privilege for me to nominate Dr. Daniel W. H. Su for the inaugural Syd S. Peng Ground Control in Mining Award. I can think of no better candidate than Daniel that is deserving of this award ? an award to recognize technical excellence in advancing ground control technologies [and] approaches. Daniel?s education and career spans over three decades. Having graduated from National Cheng Kung University in Taiwan in 1972 with a B.S. degree in Mining and Petroleum Engineering, he spent the next four years in the Taiwanese military and mining industry, before moving to the United States, where he enrolled in West Virginia University?s Mining Engineering Department. He received his M.S degree in Mining Engineering from WVU in 1978; then in 1982 became the first person to ever receive a Ph.D. in Mining from WVU. His thesis was titled, ?Development of Ultrasonic Techniques for the Measurement of In Situ Stresses?.

Jan 1, 2006

By D. W. H. Su

Following a roof fall in the B12 headgate of a CONSOL Pennsylvania Coal Company (CCPC) underground coal mine in February 1998, CONSOL R&D and Exploration initiated an underground roof geology reconnaissance program along the B13 and B14 developments to define potential roof instability areas and to recommend appropriate supplemental headgate support. This reconnaissance program revealed the presence of a thick, massive Pittsburgh sandstone channel overlying the B13 and B14 panels. Surface and underground core holes confirmed the close proximity and the very massive, nonlaminated nature of the sandstone. To mitigate anticipated adverse conditions at the B 13 and B 14 longwall faces due to delayed caving of the massive sandstone behind the shields, a task force consisting of Operations, Exploration, and R&D personnel was formed in May 1998. Several operational adjustments were made by mine management, including repairing damaged lemniscate links, maintaining immediate forward shield support, and implementing measures recommended by the task force intended to boost the shield set load density at the face. After reviewing available geotcchnical information, the task force also recommended fracing of the massive sandstone over the B13 and B14 panels to enhance caving characteristics and further reduce the bending-induced stresses in the sandstone near the face. Horizontal fracs were created at a horizon about 25 feet above the Pittsburgh seam main bench over the two panels in June and November 1998, respectively. To evaluate the effect of sandstone fracing and operational adjustments on the bending-induced stresses in the sandstone, three finite element models were constructed and analyzed. Results from the finite element analyses indicate that one horizontal frac, 25 feet above the Pittsburgh seam, would reduce the bending-induced stresses in the sandstone by approximately 50 percent, maintaining them at a level below the ultimate strength of the sandstone. Operational adjustments to increase the support set load density and support stiffness could reduce the bending-induced stresses in the sandstone by a maximum of an additional 10 percent. Shield pressure monitoring at the B14 midface confirmed the presence of a lower roof pressure zone inby and outby the 1314 frac holes. This lower face pressure significantly contributed to improving the B13 and B14 longwall productivity and safety. The total production downtime due to bad top at the B 12 face within the interval of channel influence was 30,600 minutes compared to about 3,500 minutes each for the B13 and B14 faces. The average longwall advance per machine shift for the B13 and B14 faces within the channel was about 70 percent higher than that for the B 12 face.

Jan 1, 2001

By Kot F. Unrug

The shale response to moisture changes and the major finding of the appropriate research concerning this subject are briefly reported in this paper. Also described are mine ambient atmospheric conditions which are responsible for moisture changes in mines. The need for a quantitative measure of the weathering potential of roof. rock is demonstrated in relation to its influence on safety and the potential for increasing the cost of mine operations. The weatherability test presented in this paper has been developed and used in many mines. It imitates the natural process in a mine by subjecting the rock sample to alternating wet and dry cycles. The natural changes are thus accelerated, but are similar to the natural conditions to which the surrounding excavation rock will be exposed. The measure of the weatherability index is the percentage of the initial sample mass remaining after the test as the largest fragment of the sample. Thus, the index changes, from 100% for rock affected by moisture changes which disintegrates completely, to 0% for rock totally unaffected. In this paper, the apparatus and testing procedures are described. Also presented are examples of test results. with a discussion of the design implication to he considered by mine planners.

Jan 1, 1997

By Hamid Maleki

The U.S. Bureau of Mines implemented a monitoring program in a western U.S. coal mine for the evaluation of both conventional and alternative support systems. The conventional support consisted of 2.5-m-long vertical bolts installed in an 5.5-m-wide entry. The alternative system consisted of 2.5- and 3-m vertical and inclined bolts installed at a higher density during widening of a cut from 3.6 to 5.5 m. Roof deformation, roof stress, rib deformation, and bolt loads were monitored during the 2-month test period. In addition, roof failure patterns and lithology were characterized within the six-entry main test section. Results were analyzed using roof deformation and failure profiles, roof stress profiles. bolt loading and bending moment diagrams, and numerical models. The mechanics of roof deformation, failure, and support reaction in three zones in the mine roof were characterized. Significant improvements were shown in roof stability in the section using the alternative system. Results are encouraging and indicate the effectiveness of alternative support systems and excavation techniques for limiting inelastic deformation of roof in highly stressed underground mines.

Jan 1, 1994

By Styles P.

To determine whether 130 felt earth tremors around Edwinstowe, Nottinghamshire U.K, which also experienced severe surface fissuring, were caused by coal extraction, a surface seismometer array was established around Thoresby Colliery. Over the next year, 785 microseismic events were detected. The spatio-temporal seismicity patterns are clearly associated with the commencement, continuing extraction and closure of faces. Of particular note are events which locate at the surface and appear to be related to the active fissuring. Events occur within days of commencement of production and cease when production finishes, with good correlation between face advance and hypocentral position. Naturally occurring microseismic events have also been detected up to 1 km ahead of active longwall faces in the Midlands using triaxial geophone packages grouted into the seam together with a surface seismometer in the top of the borehole. The quality of these data were very high and guided waves can clearly be seen with the dispersive characteristics associated with seam waves. In one experiment more than 2000 events were detected in only two days of monitoring even in a relatively noisy surface environment. This paper demonstrates how very accurate locations ( 5 10 metres) can be generated using three-component digital data from only one borehole. The surface seismometer and the borehole P-wave onset can give extra precision for the height of the event relative to the seam. The event distributions give a dynamic, three-dimensional image of the developing patterns of fracturing above, below and ahead of the longwall face with important implications for roof control, subsidence prediction and gas migration.

Jan 1, 1992

By Yi Luo

Accurate mechanical and geological information of the roof strata is vital for roof bolting design in underground mines. In order to obtain such information in a timely manner, a research has been under way to develop a technology for mapping the roof geology using the drilling parameters acquired during the roof bolting operations. In this paper, a systematic approach has been proposed for determining the rock strengths using the acquired real-time drilling parameters. A computer simulation program based on the mathematic model has been developed to verify the approach and to study its sensitivity. The method has been used to interpret the acquired drilling data.

Jan 1, 2002

By John Stankus

Seam interaction in multiple seam mining has significant effect on entry stability. The remaining pillar in an old working usually creates a high stress concentration zone while the gob creates a stress release zone. A good panel layout should take advantage of the stress release effect created by old workings. This paper presents two case studies of multiple seam mining. The Jennmar Finite Element Analysis System (JFEA) is utilized to analyze the seam interaction effect and identify the mess concentration and relief zones Panel layouts are designed bad on the results of the finite element analysis Appropriate roof support system are also designed for different seam interaction areas.

Jan 1, 1999

By Lorraine Kent

Mine tunnel support using rockbolts was introduced in UK coal mines over the period 1987- 1992 and is now used in over 70% of all mine tunnels. In every case the reinforcement design has been based on the observational approach. After the initial reinforcement design has been established appropriate action levels are defined for predetermined amounts of movement indicating the onset of instability. If the action levels are exceeded appropriate remedial action is taken usually in the form of additional support or reinforcement to maintain stability. This paper outlines the observational design method as used in UK coal mine tunnels. It discusses the low cost instrumentation which has been developed to monitor roof deformation, dual height telltales, how action levels are defined based on the geotechnical environment and the types of remedial measures typically taken. An alternative approach for dealing with areas of increased deformation involves reacting to early roof movement trends and modifying the support installed at the face of the development accordingly. Installation of additional support at the face of the heading improves ground control in poor geotechnical conditions and has the advantage of potentially reducing later additional support costs. A case study is described to illustrate how 'early' action levels can be incorporated into a roof support plan enabling a flexible roof support strategy. Such a system will be site specific and continued analysis of monitored information will be required to confirm the action levels or to adjust them according to any change in geotechnical environment. More accurate roof deformation monitoring systems, such as the Remote Reading Telltale system recently developed by Rock Mechanics Technology Ltd. (RMT) and currently undergoing Mines Safety and Health Administration (MSHA) approval, are ideally suited to this application. The Remote Reading Telltale system provides accurate mine wide monitoring of roof condition on a surface PC.

Jan 1, 1999

By D. W. Evans

Mine subsidence problems due to coal extraction have occurred in a number of areas throughout the United States. Depending on the local geology, the depth of the mined seam, the type of mining method employed for extraction, and other related factors, subsidence can result in anywhere from slight displacements to a total loss of ground. These conditions can have serious consequences on the health and safety of the people living above the mined areas. A number of methods exist to provide support for the ground overlying mines. All of these methods employ some mechanism for providing additional support to either the roof of the mine or the sides of the pillars. Since failure usually occurs due to overburden stresses which are transmitted to the roof and pillars, these methods employ techniques to counteract stresses induced due to the coal extraction. The applicability of any particular method will depend on the availability of backfill material, the areal extent of the affected area, and of course, the cost. The primary use of coal ash for subsidence control has been as a backfill material for the stabilization of large areas. Large scale backfilling projects for subsidence control have been performed in Rock Springs, Wyoming, Wilkes-Barre and Scranton, Pennsylvania, and in Fairmont, West Virginia. Some of these projects have utilized sand, as well as, coal ash as backfill material. Much of the backfilling work performed in the United States has been done in an effort to control mine subsidence in abandoned mines. South Africa, on the other hand, has used backfilling extensively both for ash disposal and to increase extraction in active mines. The utilization of repetitive fill and mine techniques has resulted in extraction increases of as much as eight percent in shallow mines and as much as twelve percent in deep mines.(1) The coal ash injection system which can be used for backfilling depends largely upon whether the mine voids are dry or submerged. For dry mines, hydraulic or pneumatic conveyance systems can be used, while submerged mines are limited to backfilling by hydraulic methods. The use of coal ash as a backfill material has a number of advantages, such as: 1. Coal ash is available in areas throughout the United States and in many instances is conveniently located near areas requiring backfilling. 2. Coal ash is available in significant quantities since many coals when burned will result in about 15 to 30 percent ash by weight. 3. Coal ash as backfill is, in many instances, the most economical alternative fill material. Due to the costs associated with above ground disposal, power companies will often times give the material away to lower their overall operating expenses. 4. Coal ash is usually pozzolanic in nature, that is, this material results in cementitious bonding within the backfilled matrix of material.

Jan 1, 1982

By John A. Rusnak

Point load testing is used to determine rock strength indexes in geotechnical practice. The point load test apparatus and procedure enables economical testing of core or lump rock samples in either a field or laboratory setting. In order to estimate uniaxial compressive strength, index-to-strength conversion factors are used. These factors have been proposed by various researchers and are dependent upon rock type. This study involved the extensive load France and point load testing of coal measure rocks in six states. More than 10.000 individual test results. From 908 distinct rock units, sere used in the study. Rock lithologies were classified into general categories and conversion factors were determined For each category. This allows for intact rock strength data to he made available through point load testing for numerical geotechnical analysis and empirical rock mass classification systems such as the Coal Mine Roof Rating (CMRR).

Jan 1, 2000

By Jialin Xu

Bed separations position, size, development characteristics and their influence factors have been analyzed in-depth by experimental and theoretical methods. The results show that the key strata determine the creation, development and space-time distribution of the overburden bed separations and fractures. Based on the dynamic growth principle during the two-stage development of bed separations, the theory of section-grouting for the overburden bed separation space and the O-ring theory for the pressure-relieved methane drainage are proposed. The technique has been applied in some coal mines in China to reduce surface subsidence and for methane drainage. Keywords: rock strata movements; key stratum; bed separation; bed separation grouting; pressure-relieved methane drainage

Jan 1, 2003