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By Murray W. Grabinsky

The in situ performance of Cemented Paste Backfill (CPB) systems can be monitored to improve understanding of the paste?s behaviour and therefore optimize the geomechanical design of the cemented paste backfill system (i.e., minimize binder content, minimize fill barricade complexity, maximize fill rate-of-rise during backfilling, and minimize cure time before resuming production blasting in proximity). However, undertaking such a monitoring program is inherently complex, because the rate-of-rise and accompanying self-weight induced stresses occur at a time rate that is similar to the rate of hydration and associated increase in the paste?s stiffness and strength. In addition, arching within the stope complicates the overall stress distribution. Therefore, to obtain a complete picture of the CPB?s response, it is necessary to measure several variables (3-D total pressures, water pressures and suctions, hydration rates, and blasting induced vibrations) at a given ?point?, and take all such measurements at many points throughout the fill mass as well as at barricade locations. The overall testing program can therefore be logistically difficult to implement and have an apparent high cost. However, if the program is successful, the benefits arising from improved mine design can significantly outweigh the seemingly high initial capital and labour costs of the monitoring program. A case study involving an instrumented paste fill in a tall and narrow Alimak stope is briefly outlined. Plans for a similar experiment in a large long-hole stope are then considered.

May 1, 2008

By M. Yekich, W. R. Reed, G. Ross, M. Shahan

"Canopy air curtains on roof bolting machines have been proven to protect miners from respirable dust, preventing their overexposure to dust. Another desired application for canopy air curtains is in the compartments of shuttle cars. The challenges faced in developing the design of canopy air curtains for shuttle cars include mine ventilation rates in tandem with the shuttle car tram speeds. The resulting cab airspeeds may exceed 182 m/min (600 fpm), as found in the present study conducted in a central Appalachian underground coal mine by U.S. National Institute for Occupational Safety and Health (NIOSH) researchers. Prior research and laboratory testing had indicated that successfully protecting a miner in high air velocities is difficult, because the clean air from the canopy air curtain is unable to penetrate through the high-velocity mine air. In this study, the dust concentrations to which a shuttle car operator was exposed were measured, and air velocities experienced by the operator were measured as well using a recording vane anemometer. The results indicate that the highest exposure to respirable dust, 2.22 mg/m3, occurred when the shuttle car was loading at the continuous miner, where the average airspeed was 48 m/min (157 fpm). While tramming, the operator was exposed to 0.77 mg/m3 of respirable dust with an average airspeed of 62 m/min (203 fpm). This study indicates that a canopy air curtain system can be designed to greatly reduce an operator’s exposure to respirable dust by providing clean air to the operator, as the majority of the operator’s dust exposure occurs in air velocities slower than 61 m/min (200 fpm). IntroductionThe U.S. National Institute for Occupational Safety and Health (NIOSH) issued contract #200-2015-63485 to develop a canopy air curtain for coal mine shuttle cars with Marshall University and J.H. Fletcher & Co. (Salem, Begley and Ross, 2016). The proposed design maintains a design similar to that of a roof bolter canopy air curtain by providing filtered air through a blower over the operator. The plenum, which will provide uniform airflow over the operator, is anticipated to be built into the shuttle car canopy. One of the main interferences with a canopy air curtain is ventilation airflow perpendicular to the plenum airflow (Engel, Johnson and Raether, 1987). This ventilation airflow can shear the downward flow from the plenum, and this shear can reduce the effectiveness of the canopy air curtain by either disrupting the downward flow or allowing contaminated mine air into the canopy air curtain zone of protection."

Jan 11, 2018

By M. Yekich, W. R. Reed, G. Ross, M. Shahan

"Canopy air curtains (CAC) on roof bolting machines have been proven, through laboratory and field investigations, to protect miners from respirable dust, preventing dust overexposures. Another desired application is to develop a CAC that is mounted in the compartment of a shuttle car to protect the operator from dust. The challenges faced with this design include mine ventilation rates in tandem with the shuttle car tram speeds, causing cab airspeeds that may exceed 600 fpm, as found in this study of a central Appalachian underground coal mine. Prior research and laboratory testing indicate that successfully protecting a miner in high air velocities is difficult to achieve because the clean air from the CAC is unable to penetrate through the high velocity mine air and make it to the breathing zone of the operator. During this investigation by researchers from the National Institute for Occupational Safety and Health (NIOSH), dust concentrations of the shuttle car operator were measured. Also, air velocities experienced by the operator were measured using a recording vane anemometer. Results from the survey indicate that the highest exposure to respirable dust (2.22 mg/m3) occurred when the shuttle car was loading at the continuous miner, where there was an average airspeed of 157 fpm. While tramming, the operator was exposed to 0.77 mg/m3 of respirable dust with an average airspeed of 203 fpm. This study indicates that a CAC system can be designed to greatly reduce an operator’s exposure to respirable dust by providing clean air to the operator, since the majority of the operator’s dust exposure occurs in air velocities less than 200 fpm. INTRODUCTION NIOSH has issued a contract (#200-2015-63485) with Marshall University and J.H. Fletcher & Co. (Salem et al., 2016) to develop a canopy air curtain (CAC) for coal mine shuttle cars. The proposed design maintains a similar design to the roof bolter CAC by providing filtered air via a blower over the operator. The plenum, which will provide the uniform airflow over the operator, is anticipated to be built into the shuttle car canopy. One of the main interferences with a CAC is ventilation airflow perpendicular to the plenum airflow [Engel et al. 1987]. This ventilation airflow, if the velocity is significantly high, can shear the downward flow from the plenum. The shear caused by the ventilating airflow can reduce the effectiveness of the CAC by either disrupting the downward flow or allowing contaminated mine air into the CAC zone of protection."

Jan 1, 2018

By V R. Sastry, D P. Singh, N R. Thote

Rock parameters which are uncontrollable impose restrictions on the procurement of desirable fragmentation. Blast design parameters which are controllable prove to be important tool in blasting operations. An attempt was made by the authors to investigate parameters which causes big oversize boulders in overburden blasting. A case study of coal mine is discussed in this paper.

Jan 1, 1995

By Clive Ellis, Brian Davies, Steven E. Mischler, Jon C. Volkwein

A primary means to reduce environmental levels of diesel particulate matter (DPM) exposure to miners is to reduce the amount of DPM emission from the engine. A quick and economic method to estimate engine particulate emission levels has been developed. The method relies on the measurement of pressure increase across a ?lter element that is brie?y used to collect a DPM sample directly from the engine exhaust. The method has been re?ned with the inclusion of an annular aqueous denuder to the tube which permits dry ?lter samples to be obtained without addition of dilution air. Tailpipe ?lter samples may then be directly collected in hot and water-supersaturated exhaust gas ?ows from water bath-cooled coal mine engines without the need for dilution air. A primary means to reduce environmental levels of diesel particulate matter (DPM) exposure to miners is to reduce the amount of DPM emission from the engine. A quick and economic method to estimate engine particulate emission levels has been developed. The method relies on the measurement of pressure increase across a ?lter element that is brie?y used to collect a DPM sample directly from the engine exhaust. The method has been re?ned with the inclu­sion of an annular aqueous denuder to the tube which permits dry ?lter samples to be obtained without addition of dilution air. Tailpipe ?lter samples may then be directly collected in hot and water-supersaturated exhaust gas ?ows from water bath-cooled coal mine engines without the need for dilution air.

By R Van Laeren, G Langerak, S Fityus, K Koosmen

Co-disposal of partly-dewatered mixed-plant rejects (MPR) from coal processing into spoil dumps is gaining favour amongst Australian coalmine operators in preference to conventional tailings disposal methods which require a tailings dam. Owing to their often low permeabilities and high degrees of saturation, MPR materials may be prone to the development of excess pore pressures when covered by spoil during routine dump advancement. The likelihood of dump failure will increase if these pore pressure regimes and the associated delay of shear strength development are not accounted for during waste dump design. To date however, little is known about these pore pressure regimes due to the complexities associated with their in situ measurement.This paper describes the in situ measurement of pore pressures in a cell of MPR placed within a coalmine spoil dump. Four vibrating wire piezometers (VWPs) were placed within a cell that was then filled with MPR and allowed to consolidate under self-weight before advancing an adjacent tiphead across the cell. The VWPs recorded the transient pore pressures during MPR placement and dump construction, and their interpretations are described within the context of laboratory measured parameters. Following analysis of the measured pore pressures, their implications on shear strength and dump design are also discussed.CITATION:Koosmen, K, Langerak, G, Simmons, J, Fityus, S and Van Laeren, R, 2015. Field measurement of transient pore pressures within co-disposed processing rejects placed in a spoil dump, in Proceedings Tailings and Mine Waste Management for the 21st Century, pp 63–72 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By Christopher Mark

Current longwall pillar design methods are based on many assumptions about pillar and entry response to longwall abutment loads. Knowledge of the magnitude and time-of-arrival of abutment loads is essential for Improving design procedures. The abutment loads are in turn related to the development of yield zones and horizontal confining stresses in pillars. Entry stability, which is the goal of any longwall pillar design, is affected by in situ stresses as well as the interaction between the roof, pillars, and floor. The paper describes a study performed in a longwall panel at a West Virginia coal mine. The behavior of two headgate pillars and the adjacent entries was- monitored as the longwall face approached and moved past. The results provided a detailed picture of the response of long- wall pillars and entries to abutment loadings.

Jan 1, 1986

By Peter Faust, Peter Hubbard, Kenichi Soga

The European Federation of Foundation Contractors (EFFC) and The Deep Foundations Institute (DFI) have set up a task group to compile a Guide for Working Platforms. The first edition of this Guide has been published in January 2020. The aim of the Guide is to provide reliable methods for design, testing and verification of working platforms for construction equipment, especially in the deep foundation industry where track loads can be excessive due to the nature of its operations. The Guide has identified areas where knowledge is limited. Actual track pressure and its distribution along the length of the tracks is still not well researched. Current recommendation provided in EN 16228-1 are believed to be overly simplified and may lead to conservative requirements for working platform thickness. This paper presents results of a series of field tests where the actual track pressure of a large drilling rig during operation was measured in real time together with the deformation of the working platform. Embedded, distributed fiber optic sensing (DFOS) at different depths throughout the platform allowed for a three-dimensional evaluation of the platform deformation throughout the entire operation. Results will help to develop more reliable recommendations for future safety requirements of working platforms for deep foundation equipment.

May 1, 2022

By Daniel W. H. Su

Current longwall pillar design relies heavily upon past experience and many assumptions about pillar and entry response to longwall abutment pressures. Caving characteristics of the immediate and main roof strata are known to play an important role in the overall pressure redistribution, which determines the maximum abutment pressure, abutment pressure at the T-junction, and the width of influence zone. This paper presents the results of an extensive geomechanical study in a longwall panel at a West Virginia coal mine. The response of eight headgate pillars and the adjacent entries was monitored as the longwall face approached and passed by the instrumented locations. Overburden response to longwall mining was also monitored, and height of the highly fractured zone above the gob was determined by postmining drilling. Good agreement was observed between the measured stress changes and those computed using the known height of the highly fractured zone. The results provide a detailed picture of the response of overburden strata and chain pillars to longwall mining.

Jan 1, 1987

By Daniel W. H. Su

This paper presents the results of an extensive geomechanical testing and monitoring program conducted at a longwall panel. The field program included the monitoring of roof caving sequence and mechanism, surface subsidence, change of pillar stress, roof displacement and entry convergence, and strength characterization of the overburden rocks. The response of eight headgate pillars and the adjacent entries was monitored as the longwall face approached and passed the instrumented locations. Overburden response to longwall mining was monitored using time domain reflectometry (TDR) technology; and, the height of the highly fractured zone above the gob was determined by postmining drilling. Good correlation was found between the height of the highly-fractured zone and the TDR, subsidence, and pillar stress data. The results provide a detailed picture of the response of overburden strata and chain pillars to longwall mining. A preliminary model representing the overburden strata behavior at the test site in response to the longwall mining is proposed.

Jan 1, 1987

By Xinzhi (Thomas) Du

"In order to monitor the overburden strata deformation over a longwall mining area in the Pittsburgh Coal Seam, three boreholes were drilled across the longwall panel. Each borehole employed multiple-point borehole extensometers (MBE) to monitor overburden strata movement during and after the longwall face passed under the study area. The longwall face in the study area was 1,428 ft wide and 4,000 ft long. The average mining height was about 7 ft. The overburden depth ranged from 550 ft to 650 ft with an average of 600 ft. The final extensometer readings indicated that overburden strata initially showed sign of movement when the longwall face was 700 ft inby the MBE. The rate of strata movement accelerated when the face was 300 ft inby MBE. When the face was directly under MBE, a sudden anchor displacement occurred, indicating rapid strata movement once under-mined gob. The readings showed insignificant strata movement after the longwall face was 400–700 ft outby MBE.INTRODUCTIONThe longwall mining method is an efficient mining method of underground mining. Surface and subsurface strata are inevitably disturbed above the longwall mined out gob. Figure 1 shows the four zones of disturbance in the overburden strata in response to longwall mining.A longwall shear cuts the coal seam and allows the immediate roof strata to cave into irregular blocky material to fill the void. This is called the caved zone. The caved zone extends from the mining horizon to six or eight times the mining height, depending on the bulk factor of each caving strata layer. The fractured zone is located above the caved zone, in which the strata breaks into regular blocks by vertical or sub-vertical fractures caused by bending forces due to the weight of the underlying strata. The surface soil and rock crack zone extends to approximately 50 ft below the surface. The surface cracking is caused by downward movement of the surface. Between the fractured zone and surface crack zone is the continuous deformation zone. The strata in this zone deforms gently without causing any major cracks that extend long enough to cut through the thickness of the strata, as in the fractured zone (Peng, 2006).The objective of this project is to provide fundamental rock mechanics research about overburden strata movement response to longwall-related activity. The findings aid in better understanding pillar stability, gas well subsidence management, hydraulic impacts, and numerical modeling."

Jan 1, 2018

By J. M. Wetherill

"This paper presents the results of an investigation into the level of radon, as against the natural background, at the Vicary Creek coal mine in Alberta. The concentrations of radon and daughter products detected in the mine were considered to be insignificantly higher than the concentrations of naturally occurring radon and thus do not constitute a health hazard to the miners.INTRODUCTIONTHE HIGH INCIDENCE OF LUNG CANCER among miners exposed to radon was established some thirty years ago. The presence of this gas in mines is primarily associated with pitchblende extraction operations, al-though coal contains detectab`e quantities of U30s. A previous study bas shown that coal from southwestern Alberta (Exshaw and Banff) contains lower than average concentrations of this element (1).As part of a general investigation into the occupational health environment of coal miners in Alberta, field measurements were made to establish the level of radon and to investigate the natural background radiation in the Vicary Creek coal mine, located some 16 miles north of Coleman, Alberta, on the easternmost slopes of the Rocky Mountains."

Jan 1, 1968

By Osamu Shoji, Mamoru Kato

In order to continue improving the quality of telecommunication services to meet the expectations of the people and to increase reliability in the case of emergency such as disasters, Nippon Telegraph and Telephone Public Corporation (NTT) is now constructing cable tunnels which connect main urban telephone offices. However, almost all the large cities in Japan are built in river deltas, so that their chief underground features are low strength fluvial deposit and a high ground water level. In this saturated soft ground, the ground surface at an installation site has occasionally subsided through deep excavations for cable tunneling construction. As these settlements have sometimes caused accidents, especially in densely populated large cities, NTT has made much effort to avoid such accidents. These accidents have occured mainly in flexible sheeting due to its inward movement. Therefore, after the investigation into forecast method of sheeting deflection with accuracy, NTT has reserched a system which forecasts ground surface settlements. This paper describes an outline of the ground settlement forecast system and practical example on the site.

Jan 1, 1979

By Dale Marcy, Pamela L. Drake, Kevin Ashley, Kyle J. Hazelwood

National Institute for Occupational Safety and Health method 7703 is a portable field procedure for the analysis of workplace air filter samples for hexavalent chromium (CrVI) content immediately after the samples are collected. The field method prescribes CrVI extraction from air filter samples with an ammonium sulfate/ammonium hydroxide extraction buffer using ultrasonic extraction (UE). Strong anion-exchange solidphase extraction (SAE-SPE) is then used to separate CrVI from trivalent chromium and other interferences. Portable spectrophotometric measurement of CrVI is then conducted using the 1,5-diphenylcarbazide (DPC) method. However, it has been found that the ammonium extraction buffer does not dequately bring insoluble CrVI compounds into solution during the UE process. Thus, it was deemed necessary to modify the field method so that it would provide acceptable recoveries for insoluble CrVI compounds. To this end, a more alkaline extraction solution—sodium carbonate/sodium bicarbonate buffer—was investigated. The modified procedure using the highly alkaline extraction solution was demonstrated to be compatible with SAE-SPE cartridges when determining insoluble CrVI in air filter samples. It was found that the carbonate/bicarbonate buffer was equally effective for complete dissolution of both insoluble and soluble forms of CrVI. Furthermore, the modified procedure met desired performance criteria established for air sampling and analytical methods. Keywords: field method, hexavalent chromium, insoluble chromates, on-site analysis, sample preparation,workplace air

By Shannon Seitz, Qingwen Shi, Junfeng Pan, Shuwen Wang, Brijes Mishra, Shaohong Liu

Delayed coal bursts in deep coal mines have caused significant fatalities and economic losses in recent years. Instead of occurring right around the advancing face, this particular type of coal burst is characterized by its occurrence at a certain distance behind the advancing face. To better understand the mechanism of a delayed coal burst, we used borehole camera, electromagnetic CT, and borehole deformation monitoring device to observe the fracturing and deformation process of an advancing entry’s surrounding coal in the field. Borehole camera detection showed a zonal disintegration phenomenon in the advancing entry’s surrounding coal. Electromagnetic CT detection showed that zonal disintegration developed within 14 days of excavation. Borehole deformation monitoring indicated a deformation rate difference between the intact zone and fractured zones. The deformation rate difference was observed to increase with time and cause increasing elastic energy accumulation in the intact zone. The cumulative elastic energy in the intact zone finally caused a delayed coal burst in the entry. Sensitivity analysis of the cumulative elastic energy was conducted based on a thick-walled model deduced from field detection. The model shows that the smaller thickness of the intact zone brings higher elastic energy in the intact zone. This investigation provides an improved understanding of delayed coal bursts in deep coal mines.

Oct 19, 2021

By Yang Ruilin

Bulk gassing technology is a growing trend in the commercial explosive industry. The gassed bulk products produced differ from microballooned bulk products or cartridged products. It is easy to know the loaded or in-hole density for microballooned bulk products or cartridged products, whereas it is not as straight forward to know the m-hole density for gassed bulk emulsions. The loaded density is one of the key parameters affecting explosive performance and therefore it is important to have a field technique to monitor the in-hole properties of gassed bulk products in order to accurately predict the blast performance and to ensure efficient use of the products.

Jan 1, 1999

By Tingkan Lu

To understand the reinforcing mechanisms of the fully grouted resin bolt and clarify its performance in weak roof strata, the field monitoring investigation using instrumented bolts has been conducted in a coal mine. The total time of monitoring was around ten months. In the first 8 month period, the rock bolt performance relates to the initial development of the gateroad and subsequent time dependent strata response. After 8 months, the rock bolt performance relates to the effect of the approaching longwall mining operation, up to the point where the measuring station was destroyed due to the mining operation.

Jan 1, 1998

By D. R. Dolinar, A. T. Iannacchione

Limestone formations in the United States can be subject to relatively high horizontal stresses owing to the existence of tectonic loading of the limestone strata. Underground limestone mines use the room-and-pillar method, in which 12- to 18-m-wide rooms are typically excavated. The stability of these excavations can be compromised by the horizontal stress, resulting in a rock fall hazard. Rock falls are the cause of 15% of all reportable injuries in underground limestone mines. Horizontal stress related damage can occur in the form of guttering along one or more sides of an excavation, roof beam buckling or oval shaped roof falls, with the long axis perpendicular to the major horizontal stress. Numerical analyses show that the pillar layout and orientation of the mine workings has an effect on the horizontal stress distribution within the roof. The effects of high horizontal stresses can be mitigated by orienting the heading development direction parallel to the maximum horizontal stress, reducing the number of cross-cuts and off-setting the cross-cuts to limit the potential lateral extent of horizontal stress related roof falls. The modeling approach described in this paper can be used as a tool to evaluate potential roof failure and optimize the stability of room and pillar layouts.

Limestone formations in the United States can be subject to relatively high horizontal stresses due to the existence of tectonic loading of the limestone strata. Underground limestone mines use the room-and-pillar method, in which 12- to 18-m-wide rooms are typically excavated. The stability of these excavations can be compromised by the horizontal stress, resulting in a rockfall hazard. Rockfalls are the cause of 15% of all reportable injuries in underground limestone mines. Horizontal stress related damage can occur in the form of guttering along one or more sides of an excavation, roof beam buckling or oval shaped roof falls, with the long axis perpendicular to the major horizontal stress. Numerical analyses show that the pillar layout and orientation of the mine workings have an effect on the horizontal stress distribution within the roof. The effects of high horizontal stresses can be mitigated by orientating the heading development direction parallel to the maximum horizontal stress, reducing the number of cross-cuts and offsetting the cross-cuts to limit the potential lateral extent of horizontal stress related roof falls. The modeling approach described in this paper can be used as a tool to evaluate potential roof failure and optimize the stability of room and pillar layouts.

Jan 1, 2008

Limestone formations in the United States can be subject to relatively high horizontal stresses due to the existence of tectonic loading of the limestone strata. Underground limestone mines use the room-and-pillar method, in which 12- to 18-m-wide rooms are typically excavated. The stability of these excavations can be compromised by the horizontal stress, resulting in a rockfall hazard. Rockfalls are the cause of 15% of all reportable injuries in underground limestone mines. Horizontal stress related damage can occur in the form of guttering along one or more sides of an excavation, roof beam buckling or oval shaped roof falls, with the long axis perpendicular to the major horizontal stress. Numerical analyses show that the pillar layout and orientation of the mine workings have an effect on the horizontal stress distribution within the roof. The effects of high horizontal stresses can be mitigated by orientating the heading development direction parallel to the maximum horizontal stress, reducing the number of cross-cuts and offsetting the cross-cuts to limit the potential lateral extent of horizontal stress related roof falls. The modeling approach described in this paper can be used as a tool to evaluate potential roof failure and optimize the stability of room and pillar layouts.

Jan 1, 2008