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The applicability of four empirical strength criteria for rock masses, namely, Hoek and Brown, Bieniawski - Yudhbir et al., Rarnamurthy - Arora and Johnston - Sheorey et al. has been tested against the triaxial test data for jointed plaster of Paris of Arora. The following modified Bieniawski criterion shows best agreement with the triaxial test data for jointed plaster of Paris:- where st = axial compressive stress at failure, MPa; s3 = confining pressure, MPa; scm = uniaxial compressive strength of jointed plaster of Paris, MPa; and B = - 3.988 + 9.674 (scm )-0? 185 The modified Bieniawski strength criterion can be used to estimate the strength of a coal pillar, based on a knowledge of stress distribution in it.

Jan 1, 1992

By Kevin J. Ma, John Stankus

"In order to access remote reserve areas, some U.S. coal mines have to maintain aged underground entries for a great distance. However, high humidity, warm temperature, and time dependent deterioration can cause progressive roof deterioration and unexpected roof falls can, pose a great challenge to ground control engineers. With an active belt structure in place and limited space, re-bolting becomes very costly, less effective, and, sometimes, impractical and unfeasible. To gain long-term entry stability and serviceability, operators typically rehabilitate the aged belt entries by installing standing steel set supports. In the last several years, Keystone Mining Services, LLC, (KMS) has assisted many coal mines with their belt entry rehabilitation projects, evaluated the ground condition of various aged belt entries, and designed different standing steel set support systems. This paper presents a case study of a large-scale roof fall that occurred at an aged belt entry in a mine located in an eastern coalfield, analyzes root causes of excessive deformation of square sets that were installed in an adjacent entry, evaluates the adequacy of an existing rehabilitation square set, and develops remedial recommendations for future rehabilitation practice. Based on the case study, the paper outlines design guidelines for rehabilitation steel sets that include field evaluation, engineering considerations, design assumptions, steel structural analysis, and field installation quality control. INTRODUCTION With gradual depletion of shallow coal reserves, some underground coal mines have to maintain long-term entries (belt, track, return airway, etc.) for a great distance in order to access remote coal reserve areas. However, due to high humidity, warm temperature, and aging in the belt entry, roof strata weathering and pillar degradation become more and more severe. Progressive roof deterioration poses a great challenge to ground control engineers. Pillar rib sloughs at certain locations, entry width increases in some areas, immediate roof sags, immediate roof rock falls out between bolts, existing bolts lose functionality due to corrosion, cutters develop deeper in corners, and strata separation develops deeper up into the main roof. As a result, unexpected roof falls occur in a random manner resulting in loss of production, damage of belt structure, and even injuries to underground personnel."

Jan 1, 2017

By Zuoliang Xiu

Experience indicates that rockbolting is the most efficient and cost effective means of supporting gateroads of retreating longwalls. However, gateroads supported solely by rockboltiug currently accounts for less than 16% of the 4500km of annual gatemad drivage in China According to a stated target of the Ministry of Coal Industry, this percentage should be at least 50% by the year 2000. Since the learning stage of the technology which is indicated by low drivage rates and frequent roof falls in rockbolted gateroads must be overcome , strategies for the application of rockbolting to gateroads have become the focus of discussions on this topic. This pap presents the recent development on longwall gateroad rockbolting technology in China The development work has concentrated on understanding the mechanism of rockbolting; establishing new design procedures of bolting parameters fix gateroad support upgrading the consumable; optimizing bolt installation procedures; adopting better roofbolting machines; and developing adequate secondary reinforcement technique. The authors believe that this development work together with the on-going wok in other aspects of gaterosd rockbolting, as discussed in this paper 9 represent the rational strategies for the application of rockbolting technology to a wider range of longwall gateroads in Chinese d mines .

Jan 1, 1997

By L. Mahony

This paper describes the design, construction and commissioning testing program for a laboratory facility at the School of Mining Engineering, UNSW, Australia, aimed at evaluating reinforcement tendon performance when subjected to shear loading. The project has been financially supported through the coal industry ACARP research initiative. The single failure plane design adopted in the test rig has been successful in allowing shear loading to be directly applied to fully installed (and where relevant, pre-tensioned) rock bolts. Initial results are extremely encouraging, and illustrate a significant axial component of load development as shearing takes place - particular in lower strength, softer material types. The paper also outlines future plans for use of this facility.

Jan 1, 2005

By Stephen C. Tadolini, Minova USA Inc., Peter S. Mills, David R. Burkhard

"Fiber-reinforced spayed concrete has been used for several years in civil and tunneling operations. Research conducted to reduce cure times and increase compressive and flexural strengths resulted in the development of Tekcrete Fast®, a cementitious product capable of obtaining 41 MPa (6,000 psi) compressive strength and 8 MPa (1,200 psi) flexural strength in only 3 hours and reaching 7 day strengths of 62 MPa and 11.7 MPa (9,000 and 1,700 psi), respectively. A single bag product that uses conventional shotcrete and gunite application systems make it a natural crossover product for mining applications. The discovery of incredible adhesion properties and high resistance to chloride permeability helps ensure long-term stability and increases the ease of application. Project results from Disaster City® in Texas and the application for rehabilitating a coal mine belt entry are presented. The case study illustrates the effectiveness of the product in stabilizing a coal mine beltway and adjacent cross-cuts that were subjected to progressive sloughage due to humidity and cyclical loading. INTRODUCTION Original research produced a shotcrete formulation that extends beyond stabilization and can be used to restore the structural integrity of damaged infrastructure. The primary challenge was to develop a shotcrete or gunite that had structural strength within a few minutes to prevent parasitic loading, allowing ingress into damaged structures minutes after applying the mix formulation. This also applies to mining conditions where rapid support of progressive failures can minimize failure. An additional benefit was discovering that the product had extremely high adhesion properties in addition to high flexural strengths. The approach to product design was the development of “single bag” dry mixes that are entirely self-contained, can be rapidly transported anywhere in the field or underground, and can be deployed using simple equipment. Dry mix eliminates issues relevant to high shear water mixing because water is added in the form of a mist at the point of delivery; thus a low water-to-cement ratio can be achieved. However, since there is no onsite powder mixing, the product must have a high degree of inherent homogeneity. Minova offers a commercial version of this material, Tekcrete Fast®, a product that has been successfully deployed in the mining industry and is currently being used in civil, construction, and tunneling operations. The material can rapidly stabilize lose ground in metal, nonmetal, and coal mines. This paper described the technology development, product testing results, and applications and describes a case study to stabilize a coal mine beltway."

Jan 1, 2017

By Thomas M. Baraak

This paper evaluates factors which influence longwall support and strata interaction. The longwall system is composed of an immediate and main roof structure and three supporting foundations: 1) longwall panel, 2) powered roof supports, and 3) gob waste. The main roof forms a structure that is generally supported by all three foundations, while the immediate roof acts as a beam that cantilevers from the coal face to the powered support. In most cases, shield loading involves a complex interaction of both main roof and immediate roof behavior and is a combination of loads produced from subsidence of the main roof and displacements of the immediate roof caused by deformations of the cantilevered roof beam. Since the shield stiffness remains constant for all leg pressures and main roof convergence is irresistible in terms of shield capacity, the shield must be able to control the behavior of the immediate roof or floor structure for shield loading to be sensitive to setting pressures. If the goal is to minimize total shield loading, any active setting force must be offset by reduced passive shield loading to justify the active setting loads. Field data suggest that the typical reductions in passive loading do not justify the required increases in setting pressure in some applications.

Jan 1, 1990

By Gregory M. Molinda

The U.S. Bureau of Mines has developed a rock mass classification system for coal mine roof control. The Coal Mine Roof Rating System (CMRR) evaluates the structural competence of mine roof using simple field tests and observations obtained from underground exposures in roof falls or overcasts. The basis of the WRR is a weighing system which converts descriptive geologic roof rock data to a numerical value, facilitating its use in engineering design. A full suite of data collection and hand calculation sheets accompanies the CHRR A data base is currently being collected from all major coal basins in the United States to validate the CMW. To date, CHRR values are available from 96 roof exposures in 59 coal mines representing these basins. The system can be used to help solve many practical ground control problems, including longwall gate road design, roof support selection, and decisions regarding extended cut length.

Jan 1, 1993

By Reha Ozel

The stability in longwall faces depends on the interaction beman the roof strata, face supports and floor strata. The load distribution on the other hand, depends upon relative stiffness of the three supporting elements namely, the coal face, support and gob. Therefore, in defining support requirements, it is particularly important to analyze the strata loading, the face convergence and the controlling mechanism provided by supports. The controlling mechanism however, depends on the type and characteristics of supports used in long- wall faces. The design guidelines presented in this paper have bean developed based on a number of strata control oriented projects carried out in Turkey, load and convergence measurements carried out in 10 longwall faces, in Zonguldak Coal Region, and procedures given in literature. Evaluation of load and convergence measurements, and analyses of face supports were carried out by means of a computer program, called L0NGWAI.L-MEW, developed by the authors. The output of the design analyses include the following: (1) estimation of support capacity for roof supports namely; individual hydraulic props, chock-type power supports and various types of shield supports, and (2) analysis of loading conditions and response of shield support components in terms of stability and structural integrity.

Jan 1, 1990

By Jesse Puller, Ken W. Mills, Owen Salisbury

"An underground coal mine located in New South Wales has a target coal seam located 160-180 m deep directly below a 16-20 m thick conglomerate unit that has been associated with significant periodic weighting events on the longwall face. As part of the investigations to better understand the causes of periodic weighting at the mine, inclinometers capable of measuring horizontal shear movements through the full section of the overburden strata were installed ahead of mining at two locations approximately 1 km apart above the centre of two longwall panels. These inclinometers were monitored as the longwall approached each site. This paper presents the details of the installation, the results of the inclinometer monitoring at both sites, and the insights that these measurements provide for overburden behaviour about longwall panels.Horizontal shear movements were observed to develop on shear horizons that correlate closely across the two sites suggesting a mechanism that is consistent across a large area of the mine. Shear movements were observed to develop on a single horizon near the top of the conglomerate strata that was mobilised almost immediately after initial formation of the longwall goaf at a distance of 425 m ahead of the longwall face. The direction of horizontal movement was consistent with the relief of the major principal horizontal stress. As the longwall face approached each inclinometer, other horizons within the upper part of the overburden strata begin to shear with the upper strata moving toward the approaching goaf more than the lower strata. Within the last 30 m of longwall approach, tilting of the strata associated with the increase in vertical subsidence toward the extracted goaf caused a change in the style of deformation with tilting and reverse shear offsets.INTRODUCTIONLongwall mining is recognised from subsidence monitoring, surface extensometer measurements, and various other observations to cause significant disturbance to the overburden strata directly above the extracted goaf of each longwall panel. Disturbance to the overburden strata beyond the limits of each longwall panel is not so well understood. Subsidence monitoring indicates that horizontal movements beyond the edges of the extracted longwall panel are generally greater in magnitude than vertical subsidence and horizontal movements may extend up to several kilometres from the edge of the panel in some circumstances (Reid 1998, Reid 2001, Hebblewhite et al 2000, Mills 2001, Mills 2014). The mechanics of how these movements are accommodated within the overburden strata is only poorly understood and there are few direct measurements."

Jan 1, 2015

By Lisa Burke

In underground coal mines, concrete block stoppings are widely used to control mine ventilation. Although stoppings are not intended as roof support, they are subjected to roof to floor convergence, and may fail as a result of this loading. Premature failure of stoppings can significantly affect mine ventilation, limiting the amount of fresh air reaching the working faces and increasing the risk for methane explosions. Softening materials are often used in stoppings to reduce the damaging effects of roof to floor convergence. However, to date, research has not focused on the behavior of stopping construction materials subjected to roof or floor loading, leaving the design process to trial and error. A combination of numerical simulations and large scale physical tests were employed to develop a scientific understanding of stopping performance. The first series of physical models were constructed using standard CMU (concrete masonry unit) blocks and tested in a load frame. The behavior of these walls was simulated with a distinct element model. A key finding was that very small variations in block size and irregularities in block shape significantly affect wall performance. These variations, which are inherent to the type of blocks typically used underground, create stress concentrations that initiate the failure of stopping walls. A second series of models employed concrete stoppings that incorporated woos planks, a shredded wood material, and foam planks like those commonly used underground. Numerical models were again able to match the physical test data. Analysis of the softening layers used in stopping construction indicated that the strength and stiffness of the material relative to that of the wall is crucial in determining the amount of roof to floor convergence the wall can withstand prior to failure. The product of this study is a numerical model that can be used to evaluate the performance of stopping materials and different wall geometries in a controlled environment. Testing was done in a laboratory setting with walls constructed on flat, parallel surfaces and subjected to uniform loading at a constant rate. Parametric studies with the model indicate that in this ideal environment it is possible to control the amount of vertical displacement the stopping can withstand by adjusting the number of softening layers built into the wall and the thickness of the layers. Additionally, under these conditions, the position of softening layers within the wall appears to have little effect on the amount of displacement walls can withstand prior to failure.

Jan 1, 2004

By Zbigniew Lubosik, Andrzej Walentek, Stanislaw Prusek, Aleksander Wrana

"The Carboniferous coal measures, mined across Europe including the major European underground coal mining countries of Poland, UK, Germany, and Czech Republic, suffer from increasing extraction depth. This results in major geomechanics problems associated with ground control and support design.With production being concentrated into ever fewer high performance longwalls, located at greater and greater depth, pressure to ensure the roadways’ functionality (required dimensions) continues to increase. Mining in deeper and more highly stressed mining environments creates several problems. The high stress and deterioration in geological and mining conditions in many cases causes problems with gateroads maintenance (due to excess convergence). That leads to costly production gaps, longwall slowing, transport problems, an increase in the methane hazard and in the general health and safety of the workforce, and deterioration in climatic conditions with major economic risk associated with interruption of the revenue stream. Time—and thus production—delays due to maintenance often result from insufficient geological and geotechnical data acquisition and misinterpretation combined with inadequate support for the type of rock mass.longwall face on the gateroad stability (described by the gateroad convergence, support load, and shape and height of the fractured zone around the longwall gateroad) are presented. The investigations were carried out in the longwall panel with roof caving located at the great depth, in conditions of the Upper Silesian Coal Basin in Poland.The measurement results showed that the gateroad fractures in roof strata began to occur at the distance of about 1000 m ahead of the face. Additionally, the load on support and gateroad convergence increased as the longwall face got closer.It is very important for coal mining research institutes and mine operators to investigate and develop practical solutions and apply innovative support technologies at a great depth (particularly for reinforcement and stabilization of roadways and other openings).Underground measurements of stability conditions around the gateroad is of great importance to mining practice, especially in planning and designing supports for longwall gateroads.The influence of the front abutment pressure results in an increase of support load, gateroad convergence, and shape of fractured rock zone."

Jan 1, 2015

By Zbigniew Lubosik, Stanislaw Prusek

"The main elements of hard coal extraction systems in the Polish mining industry, including the characteristics of gateroads, are described, followed by several dozen underground measurements of gateroad roof sag performed in different geological and mining conditions in Upper Silesia Coal Basin.Based on the analysis of the roof sag measurements, an attempt to describe the gateroad roof sag process using a geometrical model was made. To build the model, it was assumed that the roof sag curve could be described by three straight lines. The first line describes the roof sag ahead of the longwall face; the second line, the sag at the longwall-gateroad junction zone; and the last line describes the zone behind the longwall face. Determining the intersection points and inclination angles is essential for the model. These model parameters depend on the geological and mining conditions in the gateroad.Using the statistical computations and analysis, the dependencies between the characteristic points of the gateroad roof sag model and the selected geological and mining parameters were defined. The STATISTICA computer program by StatSoft was used for computation.This paper presents a simple form of the geometrical description of roadway roof sag progression that is very useful during the gateroad support design process.INTRODUCTIONThe longwall system with caving is the dominant method in European mining in cases of hard coal seam extraction. For instance, in Poland, in 2009, 117 longwalls were driven, with total production of 77.5 million tonnes. In roughly 95% of the longwalls, mining operations were conducted using longwalls with roof caving; the remaining 5% used the hydraulic stowing system. The average mining depth was about 700 m (2,297 ft), and average daily output per face was approximately 2,600 tonnes per day. When using the longwall mining system, gateroads play an important role. These principal roadways transport materials, mine crews, and output. In addition, they impact ventilation of the extraction area, affecting, among other things, the climatic conditions or methane hazard. Unfortunately, difficulties often appear in maintaining an adequate size for the gateroads, due to the face line, which causes origination zones with stress concentration around the gateroad, resulting in rock mass movements in the form ofroofsag, floor heave, or horizontal convergence (Figure 1)."

Jan 1, 2010

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 Brian G. D. Smart

A scheme is presented whereby the complexities of design and operation of a hydraulically powered coalmine support are modelled using the finite element method. This enables predictions to be made of the interaction of the support with its environment in a variety of operating conditions. The model is a two dimensional representation. The modelling scheme was applied in two case studies. In the first, the performance of a four leg support was uprated by increasing the front leg force. The finite element model enabled changes in overall support performance to be verified. In the second case study, the change in lateral force developed by a two leg support was assessed with changes in support operating height and floor foundation stiffness. The modelling scheme is capable of further development with the possibility of extending the model into three dimensions and the addition of control elements that would enable an actual mining sequence to be represented.

Jan 1, 1992

By Kray Luxbacher

Three-dimensional time-lapse velocity tomograms were generated to image stress redistribution around a longwall panel to produce a better understanding of the mechanisms that lead to ground failure. Mining-induced microseismic events provided passive sources for the three-dimensional velocity tomography. Surface-mounted geophones monitored microseismic activity for 18 days. Most similar studies have utilized active sources including longwall shearers, controlled explosions, and hammer blows. These active sources generally require a person to initiate and measure the location and time of the source, and are not conducive to continuous monitoring. This method utilizes mining induced microseismic events as passive sources and lends itself well to continuous monitoring. Two event location methods were compared in order to move toward quantification of tomographic results in terms of ground conditions. Additionally, LAMODEL was utilized to determine the expected stress distribution around the longwall panel and compare these images to the velocity tomograms. Eighteen tomograms were generated, one per day, and high velocity regions in the set of tomograms generated from the initial location algorithm correlated with abutment stress redistribution predicted by numerical modeling. This research is significant as it has the potential to improve safety in underground mines and is the only example of long term passive velocity tomography implementation for the purpose of inferring stress redistribution around an area of active mining. Though still immature, this technology has the potential to allow mine personnel to image areas of active mining on a regular basis and detect areas with anomalous velocity distributions indicating potential safety hazards.

Jan 1, 2007

By Phil R. Ames, Anil K. Ray, Murali M. Gadde, John A. Rusnak

"Many factors can be responsible for coal mine roof falls including, mining geometry, stress conditions and local geology. In the Illinois Basin coal mines, roof instability is commonly attributed to the low strength of the immediate roof, which is also moisture sensitive. Recently, in order to understand the mechanisms of roof instability, numerical modeling has often been the preferred ground control analysis tool. Since roof materials can exhibit significant spatial variability, such modeling results may not represent every section of the mine. At the same time, it is not feasible to carry out numerical modeling for the full range of geological and mining conditions possible at a mine. Operationally, it is more convenient and highly practical to have a simple map that depicts the expected roof conditions, determined through either complex numerical models or simple empirical analysis throughout the reserve area. In this paper, a case history is presented that shows how a combination of simple empirical analyses of geologic data and past ground control experiences at a mine can be synthesized into a roof stability map, which can then be used to forecast future ground conditions. The usefulness of such a roof stability map will be examined in terms of the predicted and actual ground conditions encountered over a period of more than a year after the map was created.INTRODUCTIONA roof fall, which can result in fatalities and lost work time, is considered to be one of the most severe ground control hazards in underground coal mines. In general, there are many factors responsible for roof falls, including mining geometry, stress conditions and local geology. In the Illinois Basin, roof falls are commonly attributed to the weak nature of immediate roof rocks, and some superficial falls may be initiated due to moisture sensitivity. Some unstable areas also occur when the immediate roof is highly laminated.Numerical modeling is a useful tool used to understand the mechanism of a roof fall by incorporating site-specific parameters. In the past, numerical modeling has been used to explain the mechanism of roof falls as well as simulate· roof falls and cutter behavior, but such work had been strictly site-specific (Gadde and Peng, 2005; Ray, 2009). Because of the restrictions imposed by the input parameters, numerical modeling results cannot represent the entire mine. In the real world, mining conditions vary from place to place, and even in a single panel, modeling results valid at one site may not apply at another nearby site. At the same time, due to the lack of input data pertaining to rock characteristics and in-situ stress variations, it is not practical to carry out numerical modeling for each local area of the entire mine site. In addition to these difficulties, mine operators prefer simple tools to understand the ground conditions at their mine sites. One simple and commonsense based tool is the roof stability map. A stability map not only synthesizes the geologic and stress analysis data empirically, but it can also be used to predict future ground control issues at that mine. Because of this practical appeal, stability maps are more likely to gain mine operators' acceptance and be used in their planning operations. In this paper, a case study is presented on the development of a 'Roof Stability Map' that was principally used for roof fall prediction for a mine in the Illinois Basin."

Jan 1, 2010

By E. Bane Kroeger

In underground coal mining, there is often a need for supplemental support for mine openings. In the past, one of the most common types of supplemental support was wooden posts that were installed against the roof using opposing wooden wedges. Underground, wood has the tendency to shrink from moisture loss and dislodge if not under load. Another drawback to using wood is the variability in strength between posts. Defects in the wood such as knots can cause weaknesses that often lead to premature failure of supplemental support. Many mines that install large amounts of supplemental support in certain areas of the mine such as bleeder entries in longwall mining have switched to using steel props rather than wood posts or cribbing. The reactions of steel props under loading are well- defined and there is little variability in strength between props. Steel props and can be fabricated so they can be used in a variety of roof heights without modification. Wooden posts often have to be cut to a usable length underground before installation. This adds to the installation time of the wooden posts. Steel props are more compact and can be lighter than their wooden counterparts, depending on the length and carrying capacity. Often times it is desirable to prestress the supplemental support to improve roof stability. This is often problematic and time consuming with some types if supplemental support. With these factors in mind, research was undertaken at Southern Illinois University Carbondale (SIUC) to design a new steel roof prop. Several new clamping designs were developed and prototypes were fabricated and tested in the labs at SIUC in the spring of 2003. The designs were modified and refined and the first full-size prototype roof prop was tested in January 2004. With the success of the full-size prototypes, a cooperative research program was established between SIUC and Excel Mining Systems, Inc. to further develop the new prop. Development went smoothly and the prop has performed as expected. In February 2005, SIUC and Excel entered into an exclusive licensing agreement. The prop design under license, the K-Prop, will be installed using a lightweight portable hydraulic jacking system under design that can be used to prestress the props, applying load to the roof and floor during installation. By varying the installation load, the prestress load can be varied from about 1,000 to 10,000 pounds (4.448 to 44.48 kN) and at the same time, the carrying capacity of the K-Prop can be varied from 10,000 to 100,000 pounds (44.48 to 444.8 kN). The K- Prop is composed of only 3 pieces and laboratory testing has suggested that it can be installed by a pair of workers in less than two minutes. The speed of installation of the K-Prop should significantly reduce the total installed cost for supplemental support and should provide a safer working environment by prestressing the prop, which will add support load to the roof and floor during installation.

Jan 1, 2005

By M. J. Beus

A shaft is truly the "lifelinen of an underground mine. Damage to the shaft lining and guides as a result of ground movement can result in serious loss of production and extensive and continual repair. In some mining districts, annual shaft repair and maintenance costs resulting from high rock stresses and excessive displacement are in the millions of dollars per year. For many years, the Bureau of Mines has conducted research to characterize the rock mass and to develop structural guidelines to improve the design of accessways in deep mines. Much of this work has centered on determining the in situ conditions that affect the structural stability of shafts in the Coeur d'Alene Mining District of northern Idaho. Recent work by Beus and Board (1984) has concentrated on measuring the rock and support behavior during sinking of the Silver Shaft at the Lucky Friday Mine. These results are currently being used as a comparative data base for further basic research as well as to establish structural design criteria. The factors affecting the deign and structural stability of deep mine shafts are numerous. A design approach that use field data as input and directly compares field measurements with numerical models can validate the procedure and provide realistic design criteria. Naturally occurring "fixed? conditions such as magnitude, direction, and ratio of in situ stresses, geologic environment, and physical properties and constitutive relationships of the rock mass ere obviously basic to numerical modeling.

Jan 1, 1989

By Feiya Xu, Syd S. Peng

"As a highly efficient and new surveying and mapping technique, 3D laser scanning technology has been gradually applied to surface subsidence monitoring in mining areas. 3D laser scanning technology was used to monitor the mining subsidence in a coal mining area in this paper. Based on the 3D laser scanning data obtained in March, May, and December 2016 in the studying mining area, the surface subsidence basin and points deformation were acquired. The 3D laser scanning data were compared with that of the conventional surface movement surveying method. The results show that the 3D laser scanning technology could obtain the data of the subsidence basin more efficiently and reflect the true shape of surface subsidence caused by mining. The maximum surface subsidence obtained by 3D laser scanning technology was 3.60m, while the conventional surface movement surveying was 3.56m; the relative observation error between 3D laser scanner and the conventional surface movement surveying was less than 10%. Therefore, it is feasible to apply 3D laser scanning technology to monitor surface subsidence in coal mines.INTRODUCTIONWith the over-exploitation of coal resources, the problem of surface subsidence has become the focus of attention (Peng, 2011; Guo Wenbing, 2012). Setting up observation stations for surface movement was the traditional method to study the characteristic of surface subsidence and its parameters. At present, hundreds of observation stations have been set up in longwall mining, and a large number of measured data have been obtained (Ministry, 2017). However, due to the length of time surveying requires, great workload in the field, the high cost of observation, and difficult protection for monitoring points, conventional observation stations for surface movement have not met the research on surface subsidence. Therefore, as a new surveying and mapping technique, 3D laser scanning technology has been gradually used for surface subsidence monitoring in mining areas (Ma Liguang, 2005). Li Qiu, Qin Yongzhi, and Li Hong (2006) first proposed 3D laser scanning technology in the application of monitoring surface subsidence in 2006. It was showed that the 3D laser scanning technology had obvious advantages in efficiency and accuracy of data acquisition than other methods of deformation monitoring technology of surface subsidence (such as total station, precision level technique, GPS, etc.). Subsequently, Zhang Shu, Wu Kan, and Wang Xiang (2008) and Chen Ranli and Wu Kan (2012) analyzed the feasibility and precision of 3D laser scanning in subsidence monitoring, concluding that the 3D laser scanning can be used to obtain the subsidence basin and the monitoring precision can reach millimeter. Hu Dahe, Wu Kan, and Chen Ranli (2013) introduced the data processing method of 3D laser scanning for surface subsidence in detail. On the basis of a case study, the subsidence basin in subsidence area was obtained, which reflected the shape of mining subsidence basin intuitively and comprehensively. Wang Qisheng, Wu Kan, and Zheng Ruyu (2010) carried out the research on prediction parameters of mining subsidence by using 3D laser scanning data and got the parameters of major influence angle and the offset distance of inflection point. Meng Wanli, Cai Lailiang, and Yang Wangshan. (2017) made a profile analysis for the 3D view of the surface subsidence using 3D laser scanning data and put forward a “Geomagic” method of surface subsidence prediction."

Jan 1, 2018

By Mostafa Sharifzadeh, Ebrahim Ghasemi, Kourosh Shahriar

"The Tabas Central Mine (TCM) is one of the underground coal mines located in the Tabas coal region, in the mid-eastern part of Iran. This mine is the first mechanized coal mine in Iran that uses the room and pillar method. Pillar design is one of the most important issues in underground coal mines, especially in room and pillar mining. In this paper, a new method for coal pillar design in the main panel of TCM is presented. This method is able to estimate the magnitude of the various loads (both development and abutment loads) that pillars might experience throughout the mining process. Also, the method reduces the pillar failure risk. Based on this method, proper pillar sizes in TCM are obtained (11.6 x 11.6 m (38.l x 38.1 ft)).INTRODUCTIONPillar design and stability are two of the most complicated and extensive mining problems related to rock mechanics and ground control subjects. Although these problems have been investigated for a long time, to date only a limited understanding of the subject has been gained. Prior to this, the dimensions of a pillar were largely determined by experience based on trial and error, intuition, or established rules of thumb; any research available tended to be isolated and sporadic. But nowadays, various pillar design formulas have been developed based upon laboratory testing, fullscale pillar testing, and back-analysis of failed and successful case histqries. In 1980, a number of ambitious field studies conducted by the U.S. Bureau of Mines developed the ""classic"" pillar design methodology. It consisted of three steps (Mark, 1999, 2006):1. Estimating the pillar load using tributary area theory2. Estimating the pillar strength using a pillar strength formula3. Calculating the pillar safety factorAlso, Bieniawski (1981) presented a step-by-step method to determine coal pillar dimensions in room and pillar mines. In this method, similar to the classic method, pillar load is estimated by using tributary area theory.Currently, in mqst of the room and pillar mines, remnant pillars in panels are recovered by retreat mining (pillar recovery). Hence, the above mentioned methods are not appropriate for pillar design, because in these methods pillar load is estimated by the tributary area theory, and the effects of abutment loads, which result from retreat mining and the creation of a mined out gob, are ignored. Abutment loads affect the pillars in the adjacent of pillar line and a load greater than what is estimated by tributary area theory is applied on the pillar. So, pillar design without considering the abutment loads leads to pillar failures during retreat mining. Pillar failures continue to be one of the greatest single hazards faced by underground coal miners. Pillar failures are responsible for unsatisfactory conditions, which include the following (Mark et al., 2003):"

Jan 1, 2010