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The basic objectives of mine roadways are to provide sufficient cross sections in order to meet the needs of accommodation of equipment, transport, personnel travel and ventilation. However, many roadways become damaged to the extent of needing maintenance, generally dinting, and in some cases requiring re-ripping. The damaging of a roadway is a result of several factors including geological properties of surrounding strata, method of roadway formation, type and spacing of support and so on. Among these factors, strata conditions play an important effect on the stability of roadway. Weak rocks cause excessive roadway closures and water softens some rocks and promotes the closure problem. In this paper, a scientific discussion on the effect of water on the stability of roadways is given on the basis of results obtained by means of in-situ investigation and laboratory rock tests.

Jan 1, 1996

By Guorui Feng, Min Zhang, Yi Luo, Jian Yang, Yujiang Zhang, Junwen Bai

"Safe mining of coal seam sandwiched between abandoned upper and lower room-and-pillared mines (ULPM) ·is increasingly becoming the focus of attention in recent years, which is closely related to the damage intensity of the upper and lower interburdens. The #7 seam with ULPM in Baijiazhuang coal mine was selected for this research. According to the mining and geological conditions, the vertical stress and plastic zone distributions were determined first by numerical simulation. Then, a theoretical model based on the elasti-plasticity theory was developed. The stress distribution and failure zone created in the interburden by mining the upper and lower seams were determined. Finally the feasibility of mining #7 seam between the abandoned upper and a lower seam was evaluated. The results show that: (1) the distributions of abutment pressure and plastic zone coincide, both of which can be used to evaluate the failure zone in ULPM. The failure zone penetrates the whole upper interburden, while only parts of the lower interburden fail. (2) the theoretical failure zone coincides with the maximum distribution zone of abutment pressure and plastic zone obtained by numerical simulation: the failure zone height in the lower interburden is less than its thickness, while that in the upper interburden is larger than its thickness. (3) the #7 seam is located in the failure zone created by the upper seam room-and-pillar mining, which leads to well-development fractures and blocky fragments in the roof, thereby it is unstabled. (4) when mining the #7 seam in the interburden, the key is to control the roof strata and proper support measures should be taken timely to ensure safe mining.INTRODUCTIONMany coal mines in China mine the thick, superior and easily mineable resources preferentially, while the thin, inferior and difficult-to-mine resources were abandoned (Chappells and Trentrnann, 2015; Zhenfu, 2012; Xu, et al., 2015; Guorui, 2009). As the results of deficient geological data and shortage of investment capital, the residual coal resources distributes in many mining areas in China.In recent years, many residual coal seams sandwiched between the abandoned upper and lower room-and-pillar mines (ULPM) were explored in Shanxi Province, especially in the mining area of Datang, Xishan and Luan (Figure.1). The reserves of residual coal seams in ULPM are considerable, increasingly becomes the focus of attention among scholars and engineers."

Jan 1, 2016

By Nikzad Oraee, Parham Khajehpour, Kazam Oraee, Arash Goodarzi

"Rock fall related accidents continue to occur in coal mines, although artificial support mechanisms have been used extensively [1]. Roof stability is primarily determined in many underground mines by a limited number of methods that often resort to subjective criteria. It is argued in this paper that stability conditions of mine roof strata, as a key factor in coal mines, must be determined by a survey which proactively investigates fundamental aspects.Failure of rock around the opening happens as a result of both high rock stress conditions and the presence of structural discontinuities. The properties of such discontinuities affect the engineering behavior of rock masses causing wedges or blocks to fall from the roof or slide out of the walls [2]. A practical rule based approach to assess the risk of a roof fall is proposed in the paper. The method is based on the analysis of structural data and the geometry and stability of wedges in underground coal mines. In this regard, an accident causing a huge collapse in a coal mine leading to four fatalities is illustrated by way of a case study. A comprehensive investigation of the hanging wall has been gathered through a systematic collection of evidence. The investigation results are then analyzed, and an interpretation of the evidence gathered is provided.For this purpose, horizontal and vertical profiles are prepared by geophysical methods to define the falling zone and its boundaries. The collapse is then modeled by the use of sophisticated computer programs in order to identify the causes of the accident and hence recommend corrective actions to prevent or minimize reoccurrence probability of similar accidents. The corrective measures are placed into a rule-based framework for the benefit of the mine operators.INTRODUCTIONRoof rock failure has generally been the most dangerous hazard for underground coal mining in the world. Failure of rock around shallow coal mine openings often results from loosening of blocks of rock on the weakened planes under the influence of gravity. This condition is not typically seen in large deep coal mines. There are a number of differences between large mechanized mines and small mines related to ground control [3]."

Jan 1, 2015

By William J. Conrad, Ryan J. Molka, Erik C. Westman

"In order to study pillar and overburden response to retreat mining, a ground control program was conducted at a Central Appalachian mine. The program consisted of several monitoring methods including a seismic monitoring system, borehole pressure cells in the pillars, and time-lapse photogrammetry of the pillar ribs. Two parallel geophone arrays were installed, one on each side of the panel with the sensors mounted 3m (IO ft) into the roof. A total of fourteen geophones recorded more than 5,000 events during the panel retreat. A MIDAS datalogger was used to record pressure from borehole pressure cells (BPCs) located in two adjacent pillars that were not mined during retreat. A series of photographs were taken of the pillars that had the BPCs as the face approached so that deformation of the entire rib could be monitored using photogrammetry.Results showed that pillar stability and cave development were as expected. The BPCs showed an increase in loading when the face was 115 m (380 ft) inby and a clear onset of the forward abutment at 30 m (100 ft). The photogrammetry results displayed pillar deformation corresponding to the increased loading. The microseismic monitoring results showed the overburden caving inby the face, again as expected. The significance of these results lies in two points, I) we can quantify the safe manner in which this mine is conducting retreating operations, and 2) we can use volumetric technologies (photogrammetry and microseismic) to monitor entire volumes of the mine in addition to the traditional point-location geotechnical measurements (BPCs).INTRODUCTION AND BACKGROUNDExcavation of underground openings is a difficult job in a challenging environment. The rigor of the process is compounded by the lack of a method that allows quantification of changes within the rock mass as excavation progresses. Statistics kept by the Department of Labor, Mine Safety and Health Administration show that 16% of fatalities and lost time incidents in the underground mining industry are due to unexpected rock mass failure (MSHA, 2015). A recent example is the Crandall Canyon, Utah, coal mine accident caused by the vertical collapse of a longwall coal mine on August 6, 2007 (Dreger, Ford, Walter, 2008)."

Jan 1, 2016

By V. Bondarenko

The forecasting of floating earth inrush into the working is to a great extent connected with the investigation of the rock mass stressed-deformed state around the working. The aim of such investigations is to estimate the carrier ability of the protective layer (which is stabilized by the physico-chemical mode of fixing) and to determine it's thickness, which is to be sufficient to present the floating earth inrush into the working. We consider the protective layer to have exhausted it's carrier ability if the rocks of this layer reached the overlimit phase of deformation and it's greater part (section), which adjoins the working. is destroyed up to the limit of the remaining strength. So, the aim of investigations is to determine the size of the rocks inelastic deformation zone in the roof of the working. It is necessary to take into account the presence of water saturated seam in the roof and the overlimit characteristics of the rocks, their ability to lower the carrier capacity up to the level of the remaining strength.

Jan 1, 1996

By Guo Wenbing

"INTRODUCTIONThere is a great amount of coal (about 140 billions tons) left unmined under the surface structures, water bodies, railways (referred to as the “three-body”). Coal mining under “threebody” especially that under surface structures has become a major problem in the mining area. The key problem of mining under surface structures is to control overburden strata and surface movements. At present, the major surface subsidence control methods are strip pillar mining, backfilling mining method, room and pillar mining, grouting of bed separations, harmonic mining, and so on. Wongawilli mining method is a high-efficient shortwall mining method developed based on the room and pillar mining, and named after the first successful trial in Australia “Wongawilli” coal seam. The room and pillar mining equipment such as continuous miner is employed in this method. Its major advantage is flexible face layout. It can be used to mine the small wedge coal blocks and those that are difficult to be mined with retreat longwall mining method. It requires less capital investment, short lead time for production, flexible equipment operation and face move and high productivity. It has been applied in some China’s coal mines.The “Wongawilli strip coal mining technology” is a new coal mining method for mining under surface structures. It combines the strip mining longwall layout and Wongawilli high efficient mining technology. This technology can fully utilize the advantages of both the strip pillar and Wongawilli mining methods, and overcomes the disadvantages such as frequent face move, and low mining efficiency in strip pillar mining, and poor ventilation condition and poor long-term stability problems of coal pillars. In this paper, the Wongawilli strip mining method was designed for Wangtaipu mine and its feasibility was studied using numerical modeling and surface subsidence prediction.Geological and mining conditionsAt present, most of the No.15 coal seam reserves totaling 377.07 million tons in Wangtaipu mine are located under surface structures. In order to mine the coal under the surface structures, the Wongawilli strip mining method was employed. An appropriate panel was selected for trial and the surface movement monitoring lines were set up. The trial area is located in panel XV2214 (East) ( re 1). In this area, the floor elevation of coal seam is +634~646m, the surface elevation is +810~817.5m, and the average depth of coal seam is about 174m.The average panel length is 282m and average panel width is 73.5m. The seam dips 1~3° and is 1.8~2.5m thick with an average of 2.15m. The roof and floor rock characteristics are shown in Table 1."

Jan 1, 2015

By William R. Kohl, Craig B. Clemmens

"Since 2010, North Central Resources, Bridgeport, WV, has been using the sonic log to estimate the rockmechanics properties of the coal and adjacent strata in their exploration drilling program. In 68 out of the 85 boreholes they have drilled since 2010, they have conducted shear wave analysis on sonic logs run in these boreholes. By incorporating the rock mechanics logs into the geological model of the coal seam, the engineers can develop a better understanding of the support requirements for the mine.WellCAD Borehole processing software provides vastly improved efficiency in analyzing shear waves from borehole sonic data than previously available methods. The calculation of most rock mechanics parameters requires knowledge of the density and both the compressional wave velocity and the shear wave velocity. Density logs are well known and an industry standard. Sonic logging is equally well known, although less frequently used, as an accurate source of compressional wave velocity. Shear wave velocity is difficult to measure in a geophysical log, but can be estimated from digitally recorded wave form records. This is a time consuming manual procedure which requires the visual examination of thousands of individual wave forms.WellCAD allows the viewing all the wave forms on a VDL display. The observer can create a pair of false logs by manually tracing the interference points on the display for each receiver. He can check himself by observing wave forms in the traditional format. He can then create a shear wave transit time log or “Delta-S” log by subtracting the false log from the near receiver from that of the far receiver. This can be plugged into standard formulae to generate curves for most standard rock mechanic parameters, including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio.While these parameters do not entirely substitute for destructive testing, they are extremely cost effective. An entire borehole can be analyzed for the cost of a single destructive test. This allows for a more judicious use of destructive testing while permitting the extension of test data into the rock mass with much greater confidence."

Jan 1, 2015

By David Bigby, Tim Ross, David Conover

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

Jan 1, 2010

By Brent A. Slaker, Michael Murphy, John Ellenberger, Erik Westman

"Photogrammetry, as a tool for monitoring underground mine deformation, is an alternative to traditional point measurement devices, and may be capable of accurate measurements in situations where technologies such as laser scanning are unsuited, undesired or cost-prohibitive. An underground limestone mine in Ohio is used as a test case for monitoring of structurally unstable pillars. Seven pillars were photographed during four visits over a 63- day period. Using photogrammetry, point clouds of the mine geometry were obtained and triangulated surfaces were generated to determine volumes of change over time. Pillar spalling in the range of 0.29–4.03 m3 of rock on individual rib faces was detected. Isolated incidents of rock expansion prior to failure, and the isolated failure of a weak shale band, were also observed. Much of the pillars remained unchanged during the monitoring period, which is indicative of proper alignment in the triangulated surfaces. The photographs of some ribs were of either too poor quality or had insufficient overlap, and were not included. However, photogrammetry was successfully applied to multiple ribs in quantifying the pillar geometry change over time.IntroductionAdequately measuring underground rock mass movements is integral to understanding how rock masses behave and how to interact with them safely and efficiently. Many modern measurement techniques employed in underground mining environments rely on point measurements, such as through extensometers or borehole relief methods (Christiansson, 2006). These techniques, while commonplace, do not provide a comprehensive view of how the rock mass is behaving. The dynamic changes in stress states underground, coupled with the mechanical uncertainty of rock masses, near active excavations, creates a need for measurement systems which better capture the behavior of the rock mass. Photogrammetry is a technology capable of producing the wide-area displacement measurements required for a comprehensive understanding of rock mass movements.Digital photogrammetry is a means of obtaining threedimensional point clouds from digital photographs. By finding the same point across multiple images, all viewing an object from different angles, the location of that point in three-dimensional space can be inferred. Close range digital photogrammetry (CRDP) is photogrammetry applied to measuring objects or scenes less than 100 meters away (Atkinson, 1996), and is used for various functions in underground mining environments. These uses include, but are not limited to, mapping fracture networks (Kim, Kim, & Won, 2005)(Somervuori & Lamberg, 2010), characterizing fractures (Styles et al., 2010) and measuring volumes of blast rock (Heal, Hudyma, & Potvin, 2004)."

Jan 1, 2015

By Filippo Vallianatos, Michael Verigakis, Vasili Saltas, Kosta Kaklis, Stelio Mavrigiannakis, Zach Agioutantis

"Development of failure in brittle materials is associated with microcracks, which release energy in the form of elastic waves called acoustic emissions. This paper presents results from acoustic emission measurements obtained during three-point bending tests on Nestos marble under laboratory conditions. Acoustic emission activity was monitored using piezoelectric acoustic emission sensors, and the potential for accurate prediction of rock damage based on acoustic emission data was investigated. Damage localization determined based on acoustic emissions evident in the critically stressed region in the form of scattered events or stresses below and close to the strength of the material.IntroductionNon-destructive testing (NDT) has gained popularity in recent years due to commonly available sensors, devices and software tools. Although the majority of such testing still occurs under laboratory conditions, the ultimate goal is a direct field application, especially in the case of underground mining. NDT, if properly applied, may be used to directly provide material property values and characteristics that can be used to determine rock mass or soil mass behavior, with a direct impact to mine design (Iannacchione et al., 2003).AE is generally defined as the high-frequency transient elastic waves originating from the sudden release of energy at localized points within a loaded material (Nomikos et al., 2010). The field of Acoustic Emissions (AE) due to compressive, tensile or other types of loads is a promising research area due to its wide application. The accurate identification of failure precursors stemming from AE is still an open research topic (Lei et al., 2004).Rock is a typically inhomogeneous and anisotropic material that contains several natural defects with various scales such as grain boundaries, microcracks, pores and joint inclusions (Jing, 2003; Read, 2004). Damage induced by microcracks is an essential mechanism in many brittle rocks subjected to stresses. An applied stress induces microcrack growth and damage is distributed uniformly throughout the sample. Finally, the microcracks coalesce and the damage is localized to a shear band, leading to strain softening and macro-scoping failure (Dragon et al, 2000)."

Jan 1, 2015

By Nengxiong Xu

The WTZ coal mine is located adjacent to an auxiliary dam in P. R. China. The mining-induced ground movements are calculated using a 3-D numerical procedure based on the finite difference method (FDM) to judge whether the extraction of the coal seam will have a negative impact on the dam. First, the values of the rock mass mechanical parameters in the numerical model are estimated using the available literature that relates intact rock and discontinuity properties to rock mass parameters. Then, based on available surface subsidence monitoring data for an area in WTZ mine, the main mechanical parameters of coal and rock masses are calibrated by a back analysis procedure that combines an experimental design technique with numerical simulations. Then the reliability of these rock mass parameters is verified. Finally, according to the planned mining sequence, predictions of mining induced surface subsidence are computed in steps, and the boundary of the ground movement area of each step is determined. The nearest distance from the boundary of the surface movement area to the edge of the dam foundation was found to be about 1347 m. The maximum surface subsidence within the mining area turned out to be 2.7 m, and the maximum settlement point was found to be close to west-south corner of A2 mined area. These findings led to the conclusion that the coal seam mining would not cause dam damage.

Jan 1, 2013

By David W. Evans

"Induced hydraulic fracture of strata during roof bolt installation is a potentially prevalent, but masked phenomenon within the underground coal industry. Previously reported resin testing programs (McTyer et al., 2014) examined the relationship between resin mixing effectiveness and varying bore hole diameter. The methodology employed within this earlier test program facilitated a further critical area of research – the measurement of back pressures generated within the bore hole during standard rock bolt installation practices. Experimental data has indicated that fluid resin can be pressurised to levels where it exceeds the compressive strength of the strata, inducing hydraulic fracture within the immediate area of the bolting horizon. The routine cycle of roof bolting serves to propagate this effect, progressively fracturing and delaminating the roof during mine advancement. This masked phenomenon can lead to a perception of difficult ground conditions - mining efficiencies and costs are therefore affected, with increased needs for additional support subsequently required to restabilise the inadvertently damaged roof.Further analysis of the parameters associated with resin bolt installation has now been conducted, assisting in the development of an empirical relationship between bore hole pressure, bore hole diameter and bolt insertion times. This relationship has been analysed for 15:1 ratio resins and 2:1 ratioresins, within 28mm and 30mm boreholes. Further to this, load transfer performance has been comparatively assessed for both 28mm and 30mm boreholes, suggesting that for 2:1 resins, acceptable resin mixing and load transfer can be obtained within a 30mm bore hole. The combination of 2:1 resins, utilised within a 30mm bore hole, may well provide the optimal solution to reduce the risk of hydraulic fracture in weaker strata during resin bolt installation.INTRODUCTIONA growing number of industry papers have previously investigated areas of concern associated with the performance of cartridge style resins in roof bolting, predominantly focussing on the effects of plastic film gloving, inadequate resin mixing and the pressurisation of resin within the bore hole. These three effects have a critical influence on the load transfer of the steel bolt element, through the cured resin and into the surrounding strata.Gloving occurs due to the plastic film of the resin cartridge partially encasing or wrapping around the steel roof bolt element – a known phenomenon over many years (Pettibone, 1987). The plastic film creates regions of discontinuity between the bolt, cured resin and borehole, reducing effective load transfer into the strata. Experimentation conducted into the effects of bolt ends fully encased by plastic film (Pastars and MacGregor, 2005) revealed that load transfer can be reduced by 85 to 90% in worstcase occurrences. It is also known that the aggregate filler size used within the resin can assist in shredding and breaking up the plastic film – this effect was observed in a previous study on resin mixing effectiveness (McTyer et al., 2014)."

Jan 1, 2015

By Muhammad Zaka Emad, Rangzeb Goraya, Muhammad Usman Khan

"Numerical modeling has been used extensively to assess the stability of surface and underground mines. Tabular, steeply dipping ore bodies are generally mined out by open stoping methods with delayed backfill. Cemented rockfill (CRF) is employed as a backfill material for narrow vein deposits with low production rates. Sublevel stoping methods with delayed backfill are employed to mine out steeply dipping ore bodies. Backfill is exposed to blast-induced vibrations and dynamic loading due to loss of confinement, which could lead to backfill failures. Backfill failures could influence the operating cost of a mining stope and the productivity of the entire mining project. This work shows a detailed overview of the factors contributing to backfill failure. A detailed literature review is presented along with case studies of longhole stoping operations from the Canadian Shield region for this work. The backfilled stopes are analyzed with the finite difference code FLAC3D. The literature review shows that the factors primarily responsible for fill failure are the strength of backfill, stope geometry, mining sequence, and blast-induced vibrations. INTRODUCTION Sublevel stoping methods with delayed backfill are popular in Canadian hardrock and metal mines. Backfill facilitates ground control and greater recovery of ore with pillar mining. It reduces wall slough, thus decreasing ore dilution from adjacent walls. The production of cemented rockfill (CRF) is simple; rock aggregates are mixed together with cement slurry and then placed in a mined-out stope. CRF has a low water content, thus it requires no additional drainage unlike some other backfill. Low water-to-cement ratio enables faster curing rate, hence a faster mining cycle can be achieved (Annor, 1999; Hassani and Archibald, 1998; McKay and Duke, 1989). CRF is generally placed in stopes from the upper sill drift using a truck or a load haul dump machine. Some of the problems associated with CRF are the moderate to high operational cost, the difficulty to get a tight filling, and segregation. Backfill failure is a product of many factors, such as cementation, particle size distribution, placement method employed, water quality, segregation, and blast-induced vibrations. The problem of segregation in aggregates has been observed when aggregate is dumped from a backfill raise (Meech, 2012; Indiana DOT, 2013). Segregation becomes unavoidable when the aggregates are not properly sized (Yu and Counter, 1983; Stone, 2007; Yu, 1989). The exposed backfill zones will contribute to ore dilution due to backfill when subjected to dynamic loading due to fill failures. This paper presents a detailed literature review and numerical modeling results of a mine backfill, along with case studies from longhole stoping operations. The backfilled stopes are analyzed with the finite difference code FLAC3D (Itasca, 2017). The literature review shows that the primary factors responsible for fill failure are the strength of backfill, geometry of stope, sequence of mining, and the vibrations induced by blasting operations."

Jan 1, 2017

By B. Macdonald

In 1991, roofbolts were introduced as a primary support for inseam retreat longwall entries at CBDC's Phalen Colliery. Increasing mine depth (+550 m) necessitated replacing conventional inseam steel sets in these entries because they were being severely damaged during wall retreat and subsequently causing gate end problems. Roofbolts had been used in the Sydney coalfield between 1949 and 1963 in room and pillar working, however, some concerns arose with using roofbolts as a primary support in long (2.2 - 3.4 km) single entry roadways. In order to alleviate these concerns, a phased approach was adopted whereby conventional steel densities remained along with roofbolts. The roofbolt design was such that the roofbolts would be the primary support and the steel sets would experience little or no loading. A detailed geotechnical monitoring program was developed by both CBDC and the Cape Breton Coal Research Laboratories technical staffs. The results of this monitoring were used to build-up confidence in roofbolts and subsequently reduce the steel set densities until eventually only roofbolts were used as a primary support. This paper will discuss briefly the phased introduction of rootbolts at Phalen Colliery and more specifically the development of geotechnical data collection and interpretation.

Jan 1, 1994

By Bob Coutts, Matt Martin, Dan Lynch, Dan Payne

"The Broadmeadow punch longwall coal mine in Central Queensland Australia has experienced significant highwall movement associated with the effect of longwall subsidence when the longwalls approach their final position close to the open-cut highwall. In response to this movement, Broadmeadow employed two types of broadscale highwall monitoring (radar and laser scanners) to provide full coverage measurement throughout three consecutive longwalls approaching the highwall. This was to attain a better understanding of the mechanism causing the movement and potentially enable prediction of instability. Results from the monitoring found the highwall is displaced to magnitudes unlike those typically measured in open-cut mining and in direct contrast with typical longwall subsidence behaviour.This paper discusses the ground movements measured, monitoring methods used, safety measures established, as well as theorising the failure mechanism. Recommendations are made for mine and pit designs for future punch longwall layouts. The paper shows how the movements measured are more aligned to some measurements made during stream valley closure studies previously presented at the ICGCM and challenge the mechanisms suggested by previous literature.BACKGROUNDThe mining of longwalls under or adjacent to large voids (e.g., stream valleys, escarpments, or cliffs) is commonly associated with heavily vegetated or steep surface areas. In areas of extreme topographic variance, access to traditional survey pegs and stations or even new radar or laser technologies is limited. In addition, seldom have the longwall layouts aligned themselves parallel or perpendicular to the surface feature, making interpretation of any available surface movement data more complicated.The punch longwall layout (Figure 1) is also quite uncommon (only undertaken at a small number of longwall mines in Australia) but creates the perfect configuration to enable a somewhat controlled study of the effect of longwall subsidence on a steeply dipping surface feature (an un-vegetated, evenly excavated open-cut highwall). The relatively recently developed radar and laser scanning technology has also enabled near continuous, real-time, sub-millimetre monitoring of a full 500m wide x 100m high highwall. Because the punch longwall enables access and a clear view, the technology could be easily deployed as compared to the highly vegetated and variable topography of stream valleys."

Jan 1, 2018

By V. M. Shick

With gentle bedding within the zone of support pressure the delamination in roof rocks may occur only on those stratification planes where cohesiveness of rock is close to zero. Unlike this, at dip angles of more than 30-35° disintegration of rock occurs on the surfaces with cohesion up to 5 MPa. Therefore, the delamination in roof rocks at inclined beds is greater than at gently dipping ones. The original disintegration along the pressure fissures with the formation of block structure at inclined strata is not typical, and it may be observed only in roofs with included thick rocks; in this case, the orientation of fractures depends on the angle of seam inclination. Deformation of roof roocks above the mined-out space is determined by anisotropy of layers stiffness (hardness). With the increase of dip angle the own bearing capacity of layers will rise in the direction of strike. It was emphasized that the natural and technological factors are of great importance for rock pressure manifestation in longwalls.

Jan 1, 1996

By Mike Watts

Since the first longwall panel development started in the new mining, (Southern) area, a number of roof falls have occurred in L1 and L2 gate-entries. The longwall was delayed for a total of two months due to roof falls in the gate-entries. To prevent roof falls in future gate-entries, an extensive ground control analysis has been conducted which incorporated regional horizontal stress and panel orientation, tectonic stress, roof strata, surface stream valleys, etc. Results of the analysis indicate that a combination of these factors caused the roof falls. Therefore, a Roof Instability Rating (RIR) system was constructed to predict the roof condition and identify areas where supplemental support should be implemented. The L3 gate-entries, supported by the prediction using the RIR system, have not experienced any roof problems.

Jan 1, 2000

By David Conover

Technological advancements in electronic sensors and mine-wide monitoring systems have improved remote monitoring and analysis of underground mining information. The effective use of . these systems for ground control applications, however, remains a challenge facing the mining industry. The U.S. Department of Interior, Bureau of Mines is conducting research, utilizing real-time acquisition of rock mechanics data, to provide mine operators the means to rapidly identify and manage potentially hazardous ground conditions. The Bureau has installed a remote monitoring network in a Colorado coal mine to record Pressures from instruments installed in the roof and pi1lars of gateroads and from transducers on shield-legs along the face. The field data are being monitored at the Denver Research Center, 150 mi from the mine. A computer at the Center analyzes the field data and generates graphic displays, which permit detailed examination of mine-wide ground conditions in real-time. For the first time, Bureau researchers are able to perform real-time monitoring and analysis of rock mechanics data while mining is in progress. The data collection and display capabilities of the system were effectively used to identify and evaluate face stability problems at the mine.

Jan 1, 1990

By S. P. Singh

Drifts are an integral component of underground mining. They provide access for men and material, means for transporting ore and rock and serve as air passageways. In view of their importance on the overall safety, economy and productivity of mines, empirical guidelines for controlled blasting design in drifts have been developed in this study. The application of the proposed concept was described by generating blast hole patterns for a mine with the help of a computer program. The mechanism of blast damage and the need for controlled blasting to alleviate ground control problems in underground mines have been outlined in this paper. The economic analysis between normal-and controlled blasting was performed based on the information from an operating mine. In addition, the review of drift blasting practices and problems in Canadian mines was also carried out in this study.

Jan 1, 1990

By Lou Gaozhong, Guo Wenbing, Zhao Gaobo, Wang Shuren

"The height of a fractured zone due to high-intensity mining (HIM) plays a vital role in the safety analysis of coal mining under bodies of water. This paper described the characteristics of HIM. The processes of overburden failure transfer (OFT) are analyzed. The state of destruction transfers from a certain stratum to the upper stratum as face advance distance increases, and the processes of OFT are divided into two stages: transmission development stage and transmission termination stage. Through theoretical analysis, the limited suspension-distance and limited overhanging distance of each stratum are proposed to judge the damage of each layer. Based on this, the OFT criteria of fractured zone development are obtained. The mechanical model of strata suspended integrity and overhanging stability are established. Finally, a new method to predict the height of fractured zone due to HIM is put forward based on the processes of OFT, the limited suspension-distance, and the limited overhanging distance. Further, a HIM panel in the Datong coal mine is taken as an example. Theoretical methods are proposed, and engineering analogy is used to predict the height of the fractured zone, which is compared with in-situ measurements reported in the literature. The results show that the in-situ measurements for the height of the fractured zone are in close agreement with the theoretical calculation result. Therefore, the rationality and reliability of the theoretical method proposed to predict the height of fractured zone is verified.INTRODUCTIONThe height of the fractured zone (HFZ) due to the exploitation of coal is a key parameter for the safety analysis of coal mining under a body of water (Wenbing, Youfeng, and Hou, 2012). Accordingly, it is necessary to predict HFZ under the corresponding mining conditions before coal mining."

Jan 1, 2018