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By M. V. Kurlenya

The experience of application of geomechanical investigations for substantiation of extraction of undermined ore deposit in the north of Siberia is discussed. The finite element method was used for forecasting the state of massif during the development of mining works. The results of calculations were compared with the experimental data of observations in situ for evaluation of authenticity of numerical modelling.

Jan 1, 1990

By Liu Changyou

This paper analyzes experimentally the stress-strain relationship and the characteristics and variation trends of acoustic emission signals of the medium- and high-burst-prone coal/rock fracture process. The precursor and sensitive characteristics of the acoustic emissions when the burst-prone coal/rock fracture occurs were obtained. The characteristic index and the feasibility for predicting rock bursts using acoustic emissions technology were proposed. Keywords: burst-prone coal/rock, acoustic emissions, energy, prediction index

Jan 1, 2003

By Yingxin Zhou

Data from these field studies and previous case study data have been combined to define ultra-dose seam mining environments and relate them to observed failure conditions. A rating system for ultra-close multi- seam design has been developed and field studies have verified the applicability of the design criteria according to geologic structures, lithology and spatial data. This rating system has been combined with design and depth considerations to create a protocol for quantitatively predicting potential damage in ultra-dose seam mining conditions. A brief discussion of the characteristics of ultra-dose seam mining and its related failure mechanisms is also presented

Jan 1, 1990

By Steve Signer

The San Juan Mine and the National Institute for Occupational Safety and Health conducted a study to measure how development mining effected bolt loads. Twelve fully grouted, instrumented roof bolts were installed at two three-way intersections as part of the standard bolting pattern. Newly developed miniature data acquisition systems (MIDAS) were used to measure bolt load changes during initial face advance and cross-cut breakthrough. The effects of cut placement and depth on roof bolt loads were studied This test showed how bolt loads increased at five positions along the bolt length during initial mining. Both entry advance and cross-cut breakthrough produced a similar percentage of increase in bolt loads. Geologic differences between the test sites were probably responsible for the differences in amounts of bolt loading. The test site with more top coal and a higher rock quality designation (RQD) had lower bolt loads.

Jan 1, 2004

By Yanfa Gao

Clusters of underground openings were developed around the shaft bottom of Tangshan Mine. They were deep and located in soft rock strata. After development, those openings have been subjected to considerable deformation and damages. A combined supporting method including grouting and bolting, shotcrete lining and brickwork was used. This paper analyzing the theories on which this supporting method was based. A new theory called "Disturbed Creep" was developed for deformation prediction of openings surrounded by strata subjected to stresses close to limiting or failure strength. Keywords ground pressure, deep mine, soft rock, stability control

Jan 1, 2002

By S. S. Peng

To acquire knowledge on the general trend of primary and supplemental supports used in tailgates of US longwall mines a survey of 76 mines with 86 longwall panels was carried out in the summer of 1993. This paper attempts to provide some insight on most commonly used support types as primary and supplemental supports in tailgates. Analysis of the surveyed data show that fully grouted resin bolts and cribs are the most commonly used primary and supplemental supports in tailgates in longwall mines of USA.

Jan 1, 1994

The properties of coal or rock containing gas are very important both for studying coal and methane outburst mechanism and for controlling underground rock in mining. The theological fracture properties of coal containing gas were studied to obtain its rheological fracture principle both in microscopic scale and in macroscopic scale. The application of this principle is successful in explaining coal and methane outburst mechanism and for putting forward a rheological hypothesis of coal and methane outburst.

Jan 1, 1992

By Ding Xu Chu

There are many methods developed for measuring the crustal stress in China. Among them only two methods have been adopted in practice, i.e., overcoring method (for which the sensors include: Piezo-magnetic stress gauge, steel-ring strain cell, 3-dimensional hollow-inclusion stress ,gauge, and Leeman's-like stress gauge) and hydraulic fracturing method. For the former method, one of those sensors is installed in a borehole, 36 mm in diameter, then prestressed, and finally overcored with a drill bit of 130 mm in diameter. After that the deformation of the borehole wall is measured, from which the in-situ stresses are determined. In order to avoid the errors resulting from the difference in elastic modulus for various kinds of rocks as well as from the installment of the cells, we have developed a technique to calibrate the sensor on-spot using a confining pressure calibrator and produced a very good result. For the later method, the measurements are achieved by isolating a certain section of a borehole and then injecting water to pressurize it till a tensile break is induced. It is identical to the typical technology used internationally. For many years, through field observations and a large number of laboratory experiments, we believe that the most efficient way of stress measurement for engineering purposes is the overcoring method using Piezo-magnetic stress gauge. It is characterized by stable and reliable measurement values, high accuracy and high adaptability. Taking the measurements in the intact rock mass as an example, the measured stress magnitudes are within accuracies of 8% and the errors in orientation are about 5 degrees. It can even be used perfectly in deep water. Up to now, we have performed in-situ stress measurements in more than 70 sites and obtain more than one thousand sets of data. The deepest depth used in the overcoring method is 80 m in vertical borehole and 780 m in tunnels.

Jan 1, 1987

By Vasundhara

Underground coal mining in soft floor environments has often led to strata control problems ranging from small scale issues such as floor heave which disrupts traffic and ventilation, rib spalling and induced fractures in pillars, through to large scale instability and long term subsidence. Past investigations of the problems encountered in Newcastle Coalfields of New South Wales, Australia, have revealed that the soft floor unit comprises of claystone which is very sensitive to moisture. It is prone to swelling, reduction in stiffness and loss of strength in the presence of moisture. Long term stability of mine panels in such an environment is governed by the extent of deterioration of the floor strata. The paper reports the field investigations conducted at Cooranbong Colliery to assess the extent of softened floor zone in the roadway and under a pillar.

Jan 1, 2001

By M. Zaki Rashad

In this paper, if three slant distances are measured from three given points of known coordinates to an unknown point, the position of this point (X, Y, and Z coordinates) can be determined. A computer program was designed for observing the movement of a point in the roof in Abu-Tartour mine (western desert, Egypt) to measure the convergence. This method, for general using, is very fast and can be applied without any restrictions.

Jan 1, 1990

By Andrew P. Schissler

Cyprus Shoshone is an underground coal mine in southern Wyoming owned by Cyprus Coal Company, a subsidiary of Cyprus Minerals Company. To date, seven longwall panels have been extracted from the pitching seam under increasing depth of cover from 150 ft to 1200 ft. The purpose of this paper is to describe the geology, rock mechanics needs identification, design, testing and successful application of the current headgate/tailgate cribbing system. The immediate roof of the Shoshone is unique in that the first 50 ft of lithology is interbedded mudstones. The mudstone is slickensided, highly friable and has characteristics of unconsolidated fill relative to self-spanning and beaming abilities. Finite element modelling analysis of the overall geomechanical environment showed the mudstone to yield under applied longwall abutment stress. Roof bolt system design methodology also pinpointed the relative weakness of the mudstone roof. In-mine entry vertical convergence and weight response from the mudstone identified the need to design a crib which had superior weight capacity over a wide range of convergence. Design of a structure ensued to achieve the superior strength properties of wood parallel to the grain and the displacement properties of wood perpendicular to the grain. Testing of the prototype structure along with other alternative wooden cribs was done at the U.S. Bureau of Reclamation facility in the Denver Federal Center, Colorado. The test results verified the design. Crib placement pattern was chosen to maximize support with a confined core crib under the high convergence area. The design has been successfully installed in over 5,000 ft of headgate entry in the 11 left panel.

Jan 1, 1993

By Zhijie Zhu

In order to determine the overburden failure characteristics of extra-thick seam mining, EH4 electromagnetic image system and borehole televiewer survey were applied to panel 8100, Tongxin coal mine. EH4 electromagnetic imaging system was used to map the overburden strata before and after mining. Analysis of the distribution of the electrical conductivity showed that the fractured zone height was 492-558 ft (150-170m); Observation through the borehole televiewer showed that the fractured zone height of water conductivity (or water flowing fractured zone height) was 110m-142m. The results of the two methods showed that the fractured zone height of water conductivity was 492-558 ft (150- 170m) or 10-11.3 times the mining height.

Jan 1, 2014

By Behdeen Oraee-Mirzamani

Tunnel stability has an important role in the production process of an underground coal mine. There are various methods for analysing tunnel stability, such as numerical methods and analytical methods. In this paper, numerical methods (Phase2 software) have been used to determine tunnel wall displacement in a mining tunnel of the Parvade underground coal mine. The Ground Reaction Curve has also been drawn using analytical methods to determine tunnel wall displacement. The comparison of results from the numerical method and the analytical method show a noteworthy difference in the tunnel wall displacement. The displacement calculated by the numerical method shows a lower value than that of the analytical method because the numerical method is more suited to modeling the various coal and rock layers, as well as the shape of the excavations found in coal mines. The methodology used in this paper together with the results obtained from both methods can serve as useful tools for the coal mine design engineer when determining the ground support requirements.

Jan 1, 2013

By Abdolreza (Reza) Osouli

Determining the roof stability condition of underground coal mines in the Illinois Basin is sometimes very challenging. The roof stability of Illinois mines are mostly affected by two types of shales: Anna Shale and Energy Shale. These layers are sometimes weak in parallel bedding when subjected to horizontal stresses. The roof rocks in the Illinois Basin are are typically more moisture sensitive than the other coal fields. In this study the geotechnical properties of some of the shale units as well as limestone layers will be presented. The geotechnical properties of roof rocks consist of moisture content, unconfined compressive strength, slake durability, indirect tensile strength, and point load tests (Axial and Diametral). The correlation of indirect tensile strength versus diametral point load strength as well as unconfined compressive strength versus axial point load test are explored and discussed. These correlations will help in identifying the roof mass index and planning appropriate roof control measures. This study also evaluates the application of CMRR rock mass index for an Illinois coal mine.

Jan 1, 2014

By Sheng Zhang

The compressive strength of coal in Yanlong mine area of China is less than 3 MPa. Basically, it is powdery. The roof and floor rocks are mudstone. Therefore this coal seam is a typical ?three soft? coal seam. Roof bolting cannot be used due to the very soft strata. When the conventional U-steel support was used, roadways deformation exceeded 30% of its original dimensions in some sections one half month after development. The required repair work was huge, seriously affecting the daily mine production. This paper describes how to support the soft coal roadways. The deformation characteristics of soft coal roadway were investigated. The conventional U-steel support is not subjected to uniform load, so the whole supporting structure must be strengthened. In addition, drilling holes in the coal seam can transfer high stress from near the ribs to the deeper parts of the surrounding strata, which is beneficial to the stability of the roadway. This new support method is to combine the strengthened U-steel support with pressure-relieving drill holes, providing an economic and efficient way to support the very soft coal roadways.

Jan 1, 2013

By Ben Fahrman

The classical approach to engineering design involves the purely deterministic calculation of the factor of safety, the ratio of strength to stress. The factor of safety is an easy calculation to perform in many circumstances, and it is very easy to interpret the results. The simplicity of the method is both a strength and a weakness. The results of the deterministic factor of safety calculation are simple to determine and interpret, but they have no ability to account for the uncertainty present in the inputs or outputs. Uncertainty is prevalent in geotechnical engineering applications. This uncertainty can stem from spatial variability, poor sampling, a dynamically changing environment, etc. Probability analyses allow input parameters to take the form of a distribution rather than a single value, making them uniquely equipped to handle the uncertainty inherent in geotechnical engineering design considerations. A stochastic approach also has the benefit of providing results as a probability of failure, which is more meaningful than a factor of safety. Though stochastic modeling is becoming more common in many geotechnical applications, it is still not widely used for coal pillar design. The objectives of this study are to justify the concept of using a stochastic approach to coal pillar design and to compare the results of a simple stochastic analysis to those of standard industry practice. A simple synthetic study was performed to compare the results of a probabilistic analysis of coal pillar design to the results obtained from running ARMPS, which is published by NIOSH. Normal distributions were assigned to each input parameter that is required to determine the factor of safety of a single coal pillar. The probability of failure resulting from the synthetic study was found to be more conservative than the ARMPS stability factor. A probabilistic approach to coal pillar design is discussed in comparison to the traditional deterministic approach. The greatest strengths of the probabilistic approach were determined to be the effective handling of uncertainty and the increased meaning of the inputs and outputs inherent to a probabilistic approach.

Jan 1, 2013

By Gary Buchan

"Mine-wide ground control stability is essential to any mining operation to prevent catastrophic failure of underground structures. The ability to recognize or indicate the potential for ground control hazards in underground mine operations is highly desirable to reduce or eliminate ground-control-related injuries and fatalities. The acoustic emissions (AE) form of non-destructive testing has been used for decades to determine material or machine deterioration or potential failure. This paper presents the findings of research in AE with the results of laboratory bolt pull tests and comparisons to field experimentation, including AE sensors and bolt load data in an underground stone mine. The goal of the project is to compare laboratory results of AE sensors on roof bolt pull tests with field experimentation to determine the capability of predicting bolt failure or roof deterioration.INTRODUCTIONMine-wide ground control stability is essential to any mining operation to prevent catastrophic failure of underground structures. The ability to recognize or indicate the potential for ground control hazards in underground mining operations is highly desirable to reduce or eliminate ground-control-related injuries and fatalities. Typical ground control monitoring devices involve drilling into roof or rib, grouting or gluing of sensors, and dedicated cabling for data collection. One of the original goals of this research was to develop a methodology for a simple wireless device that could provide an indication or warning of potential roof bolt or roof failure. Various types of nondestructive testing (NDT) have been used for decades to determine material or machine deterioration or the potential failure of either. One type of NDT is acoustic emission (AE) monitoring, which has been studied for use in mining to predict rock bursts and mine failures since the 1940s (Obert, 1941; Obert and Duvall, 1942). The primary goal of the work was to compare laboratory results of AE sensors on roof bolt pull tests with field experimentation to determine the capability of evaluating bolt loading or roof deterioration in an underground stone mine. Bolt pull tests were conducted in the laboratory to establish a repeatable trend of AE activity versus bolt load. The second part of the project was to then install bolt load cells in an underground stone mine and monitor AE activity in the vicinity of mining."

Jan 1, 2018

By Stankusm John C., Xiaoting Li

"Quantitatively identifying the load on a steel king beam set is a complicated issue in designing the king beam structure at the slope bottom area. From an engineering perspective, understanding the nature and support mechanism of the king beam structure as a standing support is critical in identifying the calculation input parameters for the structure design software. Based on design practices in recent years and successful applications in several slope bottom intersections, the authors present a king beam design methodology, including qualitative analysis, quantitative calculation with a structural design software, and computer Finite Element Analysis (FEA) verification.Especially important is the concept of interaction and the confinement effect between the king beam structure and surrounding rocks, which is essential in designing a proper steel structure in terms of maintaining the roof stability, as well as saving the steel materials and costs of manufacture, labor, and delivery. This paper details the design methodology and applications in several underground slope bottom intersection designs, reaching the goals of improving roof stability and reducing costs.INTRODUCTION AND DESIGN METHODOLOGYCurrently, the load on a square or arch set is typically determined by either past empirical design experiences or known heights of roof falls in current or adjacent mines. These methods work but sometimes are too conservative from an engineering perspective. For example, when designing a king beam structure for an intersection, these methods may lead to a design with extremely large and heavy steel beams, which are not convenient for delivery and installation on-site, not to mention, costly. Therefore, accurately identifying the potential maximum load on the king beam structure is important for designing a safet, effective, and cost-efficient steel structure. Based on past several years’ practices and fundamentals of ground control and structural design engineering, the authors propose a design methodology including the following components:The nature and mechanism of effective roof support (qualitative analysis),Ground reaction curve,Interaction and confinement effect between bolts and steel standing support and surrounding rocks,Factors affecting the load conditions of the king beam set"

Jan 1, 2018

By David Miller

Longwall gateroad support can be supplied by a variety of methods. The system of support also needs to be flexible as conditions change. This is especially true in the complex geological conditions of the west Kentucky # 13 seam. Methods of gateroad support used in this seam will be presented along with the successes and failures of the systems as conditions changed Lodestar Energy's gateroad support progression through the seven longwall panels retreated to date will provide an insight into planning for future panels

Jan 1, 1998

By Andrew Hyett

Over the last 30 years, a transition away from end-anchored bolts to fully grouted rock bolt systems has occurred in many underground mines. It seems geomechanically intuitive that the success of such bolts, which interfere with rock movements around underground excavations through a variety of complex interactions, is precisely why they remain challenging to instrument and monitor. Whereas measuring the load profile for an end-anchored mechanical bolt is trivial, for a fully grouted system, the load may vary dramatically due to discrete rock movement at cracks and joints. Despite the challenges, measuring the strain (i.e., load) along fully grouted rock bolts remains very appealing, and a lot of valuable research has been conducted using foil resistance strain gauges, particularly in US coal mines (Signer and Jones, 1990). Despite good intentions, more widespread adoption of this instrumentation remains unlikely for the following reasons: (i) The technology is expensive, partly because Intrinsically Safe (IS) requirements limit the number of suppliers and solutions. (ii) The technology is perceived as challenging to successfully implement except by those who are skilled in the art. (iii) The reliability of the technology is questionable in harsh environments. (iv) The technology relies on discrete pairs of strain gauges that may not capture the complete strain distribution along the bolt. No existing alternative technology can offer a solution to all of these limitations. However, in this paper, we introduce results from a new Distributed Optical Sensing technology that promises significant potential. Since the technology is capable of distributed sensing, our results suggest that this new technology can, for the first time, reveal the detailed strain profile along fully grouted rock bolts.

Jan 1, 2013