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By W. Mark Hart

The current Automatic Data Acquisition system developed by some support manufacturers make it possible to monitor and record changes in leg pressure, DA RAM stroke in every shield and shearer position at any moment during mining operation. But how can these massive data (more than 1 MB for every 3 hrs for the current scanning option) be effectively used for improving production and maintenance management as well as providing better roof control at a longwall face? The research currently conducted jointly by WWU and Cyprus Amax Minerals at Emerald Mine and Twentymile Mine attempts to answer this question and make the data, especially leg pressure, more meaningful. A computer software package has been being developed to (1) determine mining cycles, cycle time, face advance rate, production rates, machinery delays, and production delays for each shift; (2) identify defective sensors, check valves, yield valves, by-passing leg and DA RAM cylinders, and other hydraulic and electrical abnormalities; (3) determine the roof weighting period; (4) evaluate the performance of the current shield support design - demand relationships; and (5) predict and overcome ensuing encroaching problems and roof conditions ahead of the face.

Jan 1, 1994

By A. Bortolussi

The paper discusses the state of the progress reached in the development of the diamond wire tool for cutting hard rocks. To the advances of this relatively new technology a substantial contribution has been provided by the research being carried out at the University of Cagliari on samples of granite rocks from different Sardinian stone quarries. On the basis of field experiments and laboratory test data, the mechanism of diamond wire cutting has been assessed. In particular the influence of the rock features and operational variables an tool performance (cutting rate and bead wear) has been elucidated.

Jan 1, 1992

By C. W. Bollier

In recent years, Peabody Coal Company has enjoyed a great amount of success using roof trussing as a secondary support system. Since 1975, over 180,000 trusses have been installed in 12 different Peabody mines with varying geological conditions. Projections from Peabody, and throughout the mining industry, indicate a continuous growth in the trussing principle for roof control. Peabody's primary supplier has sold over 1,000,000 trusses to 50 different mines throughout the country. (1) Roof trusses provide an improved means of controlling difficult roof conditions which, in turn, improves worker safety and mine production. Since the original development of the truss, (2) the only major modification to the trussing procedure has been the addition of the resin point anchor system in the mid-70's. The resin point anchor was the catalyst needed to provide a reliable anchor and create acceptance of the roof truss by both management and labor. Peabody began using trusses in their mines in 1975. For the first few years, most of the truss effort was geared toward determining proper anchorage, spacing, and gathering historical data. In recent years, Peabody's activities have centered on the development of improving trussing procedures. Through monitoring and trussing activities, a number of areas of improvement have been found.

Jan 1, 1982

By A. Wahab Khair

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

Jan 1, 1988

By Larry Stolarczyk

The mining industry would benefit greatly by imaging geologic conditions well in advance of mining. In layered deposits such as coal, trona, quartz, and potash, natural waveguides form and enable electromagnetic seam waves to travel great distances. In the early 1980s, the Radio Imaging Method (RIM) was developed to capitalize on electromagnetic seam wave propagation in the assessments of seam conditions in longwall panels. The initial applications of RIM tomography and comparisons to in-mine mapping of geologic conditions proved that faults, paleochannels, and rapidly thinning coal could be detected and imaged with seam waves. This paper describes the application of electromagnetic seam waves in mapping the margins of a paleochannel crossing a longwall panel and the interesting possibility of adopting the newly developed Full Wave Inversion Code (FWIC) )Newman 1995) to significantly improve imaging resolution. When tomography images are combined with ground control science, a significant reduction in cost, roof fall potential, and waste rock in underground mining may be realized.

Jan 1, 1999

By Uros Bajzelj

When driving mine roadways in the vicinity of tectonic disturbances and fault zones, sudden outbursts of gas, along with ejections of fine coal, occur. Substantial dynamic changes occur around the roadways in the coal and around the support. The problem has several aspects. Studies have been carried out on the technical analyses of the phenomena which occurred in the Velenje Lignite Mine from 1957 to 1988, The second part of the investigation involves systematic laboratory studies of strength and deformability characteristics of lignite samples and "in-situ" measurements of stress changes during the driving of some roadways. Analyses of events (using the model of limit convergence and the finite element method) showed the possibility of gas outbursts, taking into account the deformability conditions when crossing over from compact lignite to the disturbed region. The rate of advance of roadways and the method of support strongly influence the occurrence of the phenomenon. The preventative measures used in driving roadways under such conditions include trial drilling and the use of blasting instead of machine cutting.

Jan 1, 1992

By S. S. Peng

This paper presents a convenient way for the preliminary design of the shield supports. The locus equations which are applicable for all kids of shield supports are derived. These equations facilitate the statics analysis of the shields. An indirect method in determining the coefficient of friction, the external toads and their locations are also developed.

Jan 1, 1982

By H. N. Maleki

The results of five years of geotechnical investigations are presented to develop productive and stable longwall layouts for the Foidel Creek Mine. The program was initiated during the pre-mining stage, and has continuously provided the data required for mine design. From several stress determinations at the mine, the relationship between geologic structure and the stress field/depth was established. The results were used for orienting the entries for improved stability. Cave conditions and load transfer to panel boundaries were evaluated from closely monitored full extraction mining and computer analysis. Back-analyses of ground movements, as compared with the actual measurements, indicated that cave conditions were favorable in spite of the presence of competent, thick-bedded sandstones in the mine roof. Gate pillar design using a yield-rigid concept was developed through computer analyses and underground instrumentation, resulting in 35 and 75 ft wide pillars. The influence of a slickensided bedding plane at the roof contact on pillar yield zones, core confinement, and pillar behavior was evaluated.

Jan 1, 1988

By Kikuo Matsui

Standing supports such as steel arches or square work supports along with the necessary struts and lagging have been traditionally employed in the longwall gateroads of the Japanese underground coal mines. Miike Colliery has newly introduced the interpanel-pillar mining system and the strata bolting system in gateroads to raise productivity levels and reduce operating costs. The Department of Mining Engineering, Kyushu University, in cooperation with the Miike Colliery and the Coal Mining Research Center, Japan (CMRCJ), has been conducting research into the optimum design of strata bolting as a primary support system in longwall gateroads. This paper presents a brief overview of the current state of strata bolting technique being applied in longwall gateroads at the Miike Colliery and discusses some problems in employing bolting.

Jan 1, 1993

By M. G. Schuerger

The United States Steel Mining Company, Inc., (USM) Lynch District, operated the No. 37 Mine in the Harlan coal seam, Harlan County, Kentucky, from 19'2 until its sale to Arch of Kentucky in 1984. Overburden depth varied from 400 to 2000 feet and mining height varied from 8 to 12 feet. In 1981, because of deep overburden, high seam height, and previous pillar stability problems, U. S. Steel Research and the Lynch Mining District entered into a joint project to measure longwall pillar stress. Eight gateroad pillars were instrumented with a total of 86 vibrating-wire stressmeters under overburden depths varying from 500 to 1550 feet. Stress-increase measurements were taken during: (1) pillar development, (2) retreat of longwall panel No. 1, and (3) retreat of longwall panel No. 2. Total average pillar stress was approximately three times the pre-mining stress with total stress at an individual meter reading 5.5 times the pre-mining stress. When maximum, measured average pillar stress was compared to pillar strength predicted by several popular pillar design methods, the pillars were found to be stronger than predicted. This paper will summarize the pillar instrumentation program and present the results. Stress distributions, average measured pillar stress, and comparison of measured pillar stress to predicted pillar strength by several design methods will be given.

Jan 1, 1984

By S. Jayanthu

This paper presents analysis of strata behaviour with special reference to convergence and stress variation during an experimental trial of extraction of pillars with cable bolts as major support system in 6.5 - 8.0 m thick coal seam. Critical span for roof falls was estimated through empirical models and also evaluated by numerical models. In situ strata behaviour studies during 1992-96 for about 70 local/major falls revealed inadequacy of the available literature for interpretation and prediction of the roof falls. Convergence acceleration and variation of induced stress based on continuous monitoring data showed distinct anomalies and potential for better understanding of strata mechanics during pillar extraction.

Jan 1, 1998

By Baisheng Zhang

The definition of Ultra-close multiple seams as defined by the floor disturbance depth, h, due to mining in the upper seam is proposed: it refers to those coal seams that are spaced very closely, i.e. h,, the distance between seams, is small or equal to h, , and mining of any one of the seams will significantly affect the others. Those seams are called the ultra-close multiple seam group. Theoretical formula for defining it and practical examples are given in this paper. Underground measurements and numerical analysis show that in ultra-close multiple seam mining, the characteristics of ground pressure due to lower seam mining is different from that of single seam mining. The major differences is that the roof, as a result of damaged caused by the upper seam mining, is full of factures; the roof broke up in the belt entry and fell down easily; support loading at the face was small without clear periodic weighting phenomenon. Based on these results the roof structure model and roof control theory for ultra-close multiple-seam are established.

Jan 1, 2005

By Axel Preusse

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

Jan 1, 2000

By D. N. Cleaver

Like other influence function methods, the SWIFT subsidence prediction program, developed within the Mineral Resources Engineering Department at the University of Nottingham, requires calibration to regional data in order to produce accurate predictions of ground movements. Previously, this software had been solely calibrated to give results consistent with the Subsidence Engineer's Handbook (NCB, 1975). This approach was satisfactory for the majority of cases based in the United Kingdom, upon which the calibration was based. However, in certain circumstances within the UK and, almost always, in overseas case studies, the predictions did not correspond to observed patterns of ground movement. Therefore, in order that SWIFT, and other subsidence prediction packages, can be considered more universal, an improved and adaptable method of regional calibration must be incorporated. This paper describes the analysis of a large database of case histories from the UK industry and international publications. Observed maximum subsidence, mining geometry and Geological Index for several hundred cases have been statistically analysed in terms of developing prediction models. The models developed can more accurately predict maximum subsidence than previously used systems but also, are capable of indicating the likely range of prediction error to a certain degree of probability. Finally, the paper illustrates how this statistical approach can be incorporated as a calibration system for the influence function program, SWIFT.

Jan 1, 1995

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 David P. Conover

The effects of stress distribution on pillar stability were evaluated through rock mechanics studies conducted in three underground room-and-pillar coal mines. Results of the three field instrumentation programs are presented to illustrate the use of borehole pressure cells to determine vertical stress distribution in coal pillars at various stages of mine development. Vertical stresses and stress changes are determined using methods developed at the Bureau of Mines. Measured stress distributions are compared against theoretical distributions and possible explanations for observed behavior are discussed. Results indicate that stresses and stress changes calculated from pressure cell data are inconsistent with theoretical values; however, the data are useful for qualitative evaluation of trends over time. Calculated values are found to be sensitive to coal properties and initial setting pressures of the cells.

Jan 1, 1989

By Yao Yuping

The strength and deformation of more than two hundred coal samples have been tested in the condition of triaxial compression. The regression equation showing the relationship between coal strength and pressure in the pores as well as confining pressure, was obtained. The appropriate calculation for stress-strain curve was carried out. Further, an analysis shows the variation of coal strength and its modulus of elasticity in methane medium.

Jan 1, 1992

By Mietek Rataj

Installation of pre-tensioned Strand Bolts i.e. resin grouted cable bolts is very common now in Australian coal mines. A short historical development of this type of rock reinforcement is outlined Various systems have been developed to apply 20 to 25 tonnes of pre-load to these bolts but there are still some technical problems which have to be overcome. One of the major problems encountered is bleed off tension which is highly undesirable as required "over loading" rocks the immediate roof thus inducing fractures iii weak strata. The major reason for the loss of tension apart from the design of the tensioning jack, is the design of the conventionally used barrels and wedges. Due to a roof plate tilting during tensioning the cable moves out of the barrel centre which impedes proper positioning of the wedges and subsequent excessive return of the cable once load of the jack is released. This problem has been largely resolved by the design of a special barrel having a centralizing rim allowing for significant reduction of the toss of tension. KEYWORDS: Pre-tensioned Strand Bolts, Cable Bolts, Bleed off Tension, Tensioning Jack, Loss of Tension

Jan 1, 2002

By H. N. Maleki

Tension-torque relationships were investigated *n a coal mine for bath standard 5/8 in. (16 mm) bolts and a vibrating wire instrumented bolt, using conventional and controlled installation techniques. The instrumented bolts differed from the standard bolts by their head size and hole preparation procedures. The controlled installation technique developed by the U. S. Bureau of Nines (USBN) involved using hardened washers and lubrication in the bolt assembly, and maintaining a minimum thrust level during bolt installations. The object of this study was to determine the tension to torque ratio (lb/ft-lbs; for standard bolts and instrumented bolts for both conventional and controlled installation techniques, and to modify the bolt assembly so that the ratios would be equal for the instrumented and standard bolts for both installation techniques. It was shown that the instrumented bolts installed in faced holes had a similar tension torque ratio td that of standard 5/8 in. (16 mm) bolts installed in unfaced holes for each installation technique, and thus they were representative of other uninstrumentea bolts. This was achieved by evaluating the influence of several factors oh the relationship, including: facing the hale surface, introducing washers and lubrication in the bolt assembly, and applying different levels of thrust at installation due to bolter operator practice. The tension to torque ratio fur conventional bolts was only 21 (lb/ft-lb) for the coal mine, resulting in an installation tension of 4000 lbs (17.8 kg) with the typical installation torque of 150 to 400 ft-lb. This tension level was approximately 50 percent of the required bolt tension, and thus, it was concluded that torque standards are not sufficient to assure adequate bolt tension. .he low tension levels were due to the particular wait hardware in use, operator practice, and bolt fencing.

Jan 1, 1984

By P. R. Sheorey

Four case studies of special geomining conditions from Indian coalfields are discuss- ed. These cases relate to (a) pillar extraction in two seams simultaneously under a difficult roof (Satpura I and II). (b) depillaring in an inclined seam resulting in rib instability (Sudamdih), (c) depillaring resulting in floor lift and side spalling (Jarangdih) and (d) contiguous pillar extraction under hard incavable strata. Solutions to these problems are given based on rock mechanics principles involving stress analysis, classification techniques, past experience and engineering judgement.

Jan 1, 1988