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Collaborating Authors
The 27th U.S. Symposium on Rock Mechanics (USRMS)
ABSTRACT ABSTRACT During 1982 and 1983, it became increasingly clear that North River No. I Mine would have to buy a set of replacement longwall shields. Despite extensive efforts to make improvements, the shields that were in place at that time were incapable of holding the roof. North River Energy had limited experience in specifying and acquiring longwall roof supports, but a great deal of experience with our conditions and needs. We there- fore compiled a shield evaluation method that uniquely responded to our situation. The resulting system emphasized teamwork among operating, maintenance and engineering personnel. The charge from management was threefold: select shields to support maximum expected loads, optimize face operations, and pay attention to detail. Final selection was made objectively, based on all available information. We chose a 5516 KN (620 tons)support with a minimum yield load density of 760 KN/m (7.9 tons/ft). This paper reviews our process of specification, design, prototype testing, and fabrication, and offers some relevant suggestions. INTRODUCTION Volumes of material have been written about longwall mining and roof control. Little, however, is directed toward helping the mining company choose and test the roof support that optimizes both roof control and operational efficiency. This is probably because every mine is unique in its combination of roof and operating conditions. The process of successfully choosing roof supports is dependent on roof and equipment analysis. Both of these come largely from the mining company engineers and the roof support vendors. There is no standard method of comparing analyses and proposals, so great care must be exercised in choosing one roof support over another. Such critical parameters as canopy ratio, support capacity, and roof support density can be calculated by different methods. For accurate comparisons, one method must be chosen to recalculate these and other parameters from proposal drawing measurements. When design and specification are complete, the prototype shields must be carefully tested for compatibility and durability. Finally, once the prototype shields have passed every test, the series fabrications must be manufactured to the required standards. SUPPORT SPECIFICATIONS Support Capacity The first question is: How much support is necessary to hold the roof? We used every available resource including books, articles, government agencies, other mines, consultants, and vendors, as well as the "laboratory" of our own longwall. To calculate necessary support capacity, we determined the weight of the roof block that would rest on the support (Figure 1). The width of that block is easy to figure. It is the distance from the center of one shield to the center of the next. The length and height are a little more difficult. The length of the roof block equals the length of the shield canopy, plus the distance from the tip of the shield to the face, plus the roof rock overhang behind the shield. Generally the rear over- hang is not broken off square with the face. In our case, many observations behind the operating longwall indicated that the rear of the roof block usually breaks at about a 35 degree angle.
ABSTRACT ABSTRACT The Bureau of Mines, in cooperation with the Illinois Mine Subsidence Insurance Fund, is monitoring the response of two foundations to ground movements induced by subsidence from a high-extraction retreat room-and-pillar operation in southern Illinois. The objective of this monitoring program is to study the interaction between the ground surface and a structure during a subsidence event. Data from such a study should enhance the understanding of the mechanisms that produce structural damage and aid in the design of structures that resist such damage. This paper describes the monitoring instrumentation and techniques as they relate to the mining and site conditions. The capability of a tiltmeter to detect and follow the tilt of the foundations caused by the mining subsidence sequence is demonstrated. Using data from this tiltmeter, the development of curvature in the foundations as they conformed to the displaced ground surface is shown. This curvature is represented by differences in tilt at various points on the foundations, indicating a change in tilt over a horizontal distance. Also, even though subsidence damage has not been fully analyzed, preliminary observations of the cracks that formed in the foundations are reported. These cracks resulted in the separation of one footing into distinct pieces; therefore, their effect on the tilt readings is cited. INTRODUCTION The investigation of subsidence and its effects is an active area of research within the Bureau of Mines. The objective of this particular project is to study the interaction between the ground surface and a structure during a subsidence event and, as a corollary, to determine the effectiveness of commonly recommended damage mitigating techniques. Data from such a study should enhance the understanding of the mechanisms that produce structural damage and aid in the design of structures that resist such damage. It should be noted that this project was not an attempt to completely delineate the subsidence event. rather, in order to study the ground surface-structure interaction, two foundations were built and instrumented above an active mine, and a survey net was designed to accurately measure the subsidence around the structures. One of these structures was built to simulate foundations of homes in southern Illinois. The second foundation was built to weather the subsidence event by incorporating commonly recommended damage-mitigating techniques (NCB, l975; Brauner, 1973). The footing was reinforced with steel rebar to increase its resistance to tension and poured on top of a compacted sand layer covered with polyethylene sheeting to reduce the friction between the soil and footing. Also, a trench around the structure was filled with vermiculite to reduce lateral pressure on the foundation. The structures were built during the late summer of 1984. Monitoring was initiated in December 1984, and is continuing. At this time, it is possible to show that a tiltmeter can detect and follow the deflections of the foundations caused by mining subsidence. Also, the development of curvature in the foundations as they conformed to the displaced ground surface can be demonstrated. Finally, observations of the cracks that formed in the foundations can be reported and related to the tilt readings.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.68)
ABSTRACT ABSTRACT The concepts of conditional probability and geometrical probability are used to establish a relation between the probability density of the trace length and the probability density of the discontinuity diameter. The discontinuity is represented as a thin circular disc. A numerical solution scheme is used to obtain the probability density of the disc diameter from the probability density of the trace length. An example was used to illustrate the possibly large difference between the mean discontinuity diameter and the mean trace length. Introduction The engineering properties of most rock masses are controlled to a large extent by the characteristics of the discontinuities. To predict the behavior of structures in and on such rock masses, it is necessary to characterize the discontinuity geometry, the geomechanical properties of the discontinuities, and the geomechanical properties of the intact rock. The discontinuity geometry in three-dimensional space can be modeled by the number of discontinuities per unit volume and the location, orientation, shape and size of the discontinuities. The parameters that describe these characteristics need to be estimated from the data obtained from the discontinuity surveys. In discontinuity surveys, observations are usually made on intersections of discontinuities with lines, as in boreholes, or with planes as in exposures. Hence, the field data are in one or two dimensions, such as spacing between traces, trace lengths, or orientation of discontinuities. An important geometric property of discontinuities is the size. This paper describes a mathematical model which relates the trace length to the size of the discontinuities. In discontinuity modeling, joints have been represented as thin circular discs (Baecher et al., 1977; Bridges, 1976) and as Poisson planes {Glynn et al., 1978). Robertson (1970) reported that strike length and dip length of discontinuities were approximately equal. In this model, the assumption of circular discs is retained. Then the mean disc diameter provides a measure of discontinuity extent. The sampling domain is a vertical exposure of finite size. The concepts of conditional probability and geometrical probability are used to establish a relationship between the probability density of the trace length and the probability density of the disc diameter, D. A numerical solution scheme is developed. It allows one to obtain the probability distribution of D for any probability density function of the trace length. An example is given for trace lengths that have an exponential distribution. It is assumed here that sampling biases have been corrected (Bacher et al., 1977; Kulatilake and Wu, 1984). Mathematical Model Let f(x,I) be the probability density function of the corrected trace length (Kulatilake and Wu, 1984) on the infinite vertical plane, where I : event that the discontinuity intersects the plane and x = resulting trace length. The model discontinuity is a circular disc, whose diameter is represented by the probability density function, g{D), and g(D) is related to f(x,I) through(mathematical equation) (available in full paper)
ABSTRACT ABSTRACT High voltage electrical discharge in water causes instantaneous release of accumulated energy into water, The experiment described in this paper regards the utilization of the electric discharge phenomenon in rock splitting. The pressure in the shock waves created by the discharge inside a small volume of water enclosed in solid rock causes stresses which can result in breakage of rock. Holes drilled in tested samples were notched in order to weaken the tensile strength of the rock and achieve a uniformly directed split. The influence of the notches was theoretically analysed and compared with experimental data. Results of the tests have been statistically elaborated in order to correlate the newly-created surface to the energy supplied. INTRODUCTION Most technologies of mining and quarrying hard rocks are based on energy accumulated in explosives, In some cases of quarrying valuable rocks, the use of explosives gives rise to such problems as waste of material due to fracturing of the brittle rock and difficulties in controlling the splitting process. The search for new, more efficient and economical methods of quarrying rocks by dividing the beds on cubical blocks has drawn attention to electric discharge as a substitute for explosives in some applications of quarrying technology. A direct conversion of electrical energy into rapidly released mechanical energy eliminates many links in the typical electro-mechanical chain of power conversion. This leads to better overall efficiency in energy transformation. Very high pressure generated in the process of electro-hydraulic discharge creates opportunities for breaking or splitting rocks. This process produces only a small amount of compressed gasses so it can be controlled and maintained in a high level of mining safety. Precise engineering of the discharge energy and pressure in EHD ( Electro- Hydrodynamic ) discharge opens the field of application where valuable rocks should be mined without damaging the whole bed. BASIC PRINCIPLES An expanding plasma channel is created as the result of high voltage electric discharge in water (Naugolnykh, 1968). High energy ( up to 200 kJ ) is discharged into water and consequently in the form of high pressure waves propagates through water into the rock. The pressure wave becomes a shock wave when the plasma channel expands with a speed equal to or higher than the speed of sound in water. The wave is partially transfered to the rock and partially reflected from the water-rock interface. This refraction of the shock waves creates a varying stress field in the rock. The destructive action of the shock waves depends on the dynamic strength of the rock, intensity and duration of the pressure waves and characteristics of the stresses induced in the rock There are similarities between electrohydraulic discharge and the discharge of regular explosives when applied to rock breaking. In both cases the breakage of a rock is initiated by shock waves. Explosives additionally discharge a large volume of gasses which crush the broken rock and disperse its particles. The electrohydraulic discharge does not produce gasses in such vast amounts so that the crushing action and dangerous expansion of the rock particles are diminished significantly.
- Europe (0.49)
- North America > Canada (0.29)
- Geology > Mineral (0.69)
- Geology > Geological Subdiscipline > Geomechanics (0.49)
ABSTRACT INTRODUCTION The most important information required for the engineering design of structures in rock is its inherent rock properties. Without providing adequate parameters on the rock property, high quality of the engineering design cannot be expected. Many laboratory rock testing methods have been developed, but they are mostly for testing intact homogeneous rock without appreciable discontinuities. In reality, the intact rock properties do not represent the behavior of rock masses because rock masses include irregularities such as joints, cracks, interlayers, variations in mineral composition, etc. In general the type and intensity of the rock defects may be much more important than the type of rock which will be encountered (Terzaghi, 1977; Bieniawski, 1984). In-situ rock testing can provide better information on rock parameters, but it takes a tremendous amount of effort, time and cost. In recent years, numerical modeling techniques are gaining popularity as a design tool for structures in rock bodies due to the enormous progress in computer technology (Wang, 1985; Kripakov and Melvin, 1983; Park and Ash, 1985), but it is quite dangerous to use numerical techniques without having proper input data. Bieniawski (1984) states as follows: Some design methods such as numerical techniques have outpaced our ability to provide the input data necessary for the application of these methods. In order to provide an adequate amount of input data, an extensive testing program may be required, thus major efforts in time and expenses are commonly spent. In this paper, a new rock testing method, which utilizes the principles of laser holographic interferometry, is introduced. This method requires only a few minutes to measure the modulus of elasticity and quality of a rock core sample, which does not have to be cut or ground. The Poisson's ratio can also be measured in a few minutes from a sliced rock specimen. HOLOGRAPHIC INTERFEROMETRY Principles of Holographic Interferometry In 1948, Gabor invented holography, which is the technique of reviving three dimensional images using a monochromatic light source. A full demonstration was not made then because a clean monochromatic light source was not available. Later, in the early 1960's, the laser was adopted as a monochromatic and coherent light source (Leith and Upatnieks, 1963). Since then, applications have been made in many different fields ranging from crime prevention to three dimensional television. In this technique, an image is usually recorded by means of constructing a hologram which is a record of the interference pattern formed on a high resolution photographic system as shown in Figure 1. A beam splitter divides the laser beam into two beams: (1) an object beam which is expanded while passing through beam expander and illuminates the object, and (2) a reference beam which is expanded and illuminates the holographic plate. Subsequent to an exposure, the holographic plate is developed and illuminated by the expanded reference beam. The original scene of the object is revived in a three-dimensional image. The entire instrument should be placed on a vibration free environment.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Energy > Oil & Gas > Upstream (0.51)
- Materials > Metals & Mining (0.48)
A Nonlinear Rheological Model For Time-Dependent Behavior Of Geologic Materials
Hardy, H. Reginald (Geornechanics Section, Department of Mineral Engineering, The Pennsylvania State University) | Sun, Xiaoqing (Geornechanics Section, Department of Mineral Engineering, The Pennsylvania State University)
Abstract Rheological models are widely accepted as a means of describing the mechanical behavior of geologic materials. It has been found, however, that rheological models developed for a specific stress level on the basis of linear visco-elasticity generally are not satisfactory at other stress levels. It has been suggested that the parameters of such models should be functions of stress level (Hardy, 1965; Kim, 1971). In this paper, continuous functions of stress have been utilized to obtain the required variation of Burgers model parameters with stress level. The model developed using these functions provides a constitutive relation which reflects the real time-dependent behavior of rock materials. The new model is capable of predicting the creep behavior over a wide range of stress levels and also predicts mechanical behavior under different loading condition (e.g. constant stress rate). It is also interesting to note that the mechanical behavior of individual elements in the model appear to reflect the different stages of brittle fracture in rocks (Bienlawski, 1967), namely; crack closure, elastic deformation, stable fracture propagation and unstable fracture propagation. Nomenclature (mathematical equation) (available in full paper) Introduction The subject of time-dependent behavior of rocks has been studied now for over sixty years, and a wide range of methods for such studies have been developed. The study of time-dependent behavior of rocks have been undertaken in many areas such as mining, civil engineering, geology and seismology; and has involved various loading forms including tension, compression, torsion and bending both in the laboratory and in the field. Generally, the methods can roughly be divided into three categories, namely: empirical method, physical theory method and, theological (or mechanical model) method. The empirical method involves selection of a curve to fit a set of experimental data. Fitting curves to a set of data can assist in establishing certain relationships between the data. This is useful especially when the mechanism of the physical process is vague or unknown. Because this approach is based on interpolation, extrapolation from the laws developed using this method is hazardous (Price, 1969), especially where the deformation mode changes. The physical theory method starts from the analysis of the microscopic structural variation of the material observed under loading, and produces a theoretical explanation of the basis of the time-dependent behavior. The method originated in metallurgy and was later introduced into rock mechanics. Rock, however, is a much more complex material than a metal. For example, the atomic bond in natural rock is always a chemical bond rather than a metallic bond; furthermore most rocks are multigranular-structured in contrast to the relatively homogeneous structure of metals. These factors make the microscopic characteristics of rocks, such as dislocations (Mott, 1956; Cotttell, 1963), activation energy (Cruden, 1971), etc., different from those of metals. Since there is still a lot of work required in order to understand the microscopic characteristics of rock, physical theories are not widely used in rock mechanics. In the theological or mechanical model method the actual mechanism of deformation is ignored. When materials are deformed, two basic characteristics are clearly observed, namely: elasticity and viscosity.
Elastomeric Borehole Pressure Cells For Measurement Of Stress States And Their Time-Dependent Changes In Salt
Blzler, D. (Domtar Chemicals Group, Sifto Salt Division, Goderich Mine) | Gardner, B.H. (Serata Geomechanlcs, Inc) | Serata, S. (Serata Geomechanlcs, Inc) | Wang, Y.P. (Serata Geomechanlcs, Inc)
ABSTRACT ABSTRACT As part of an ongoing effort to develop more cost-effective and "user friendly" hardware for geomechanical measurements required for underground mine design, Serata Geomechanics, Inc. (SGI) has investigated the potential of borehole pressure cells (BPCs) for in situ measurement of stress states and continuous monitoring of changes in ground stress. In particular, because of certain advantages gained thereby, BPCs utilizing an elastomer, instead of metal (e.g., copper), for the skin of the pressure cell have been developed. A data analysis technique for determining ground stress state directly from BPC data has been developed. This technique has been tested for salt ground through both in situ applications and computer simulation analysis of the BPC/borehole boundary interaction. This paper discusses the data analysis technique, the results of field and computer simulation testing of its validity, and evaluates the advantages of elastomeric BPCs in relation thereto. It utilizes field data from recent elastomeric BPC applications in the salt mine at Goderich, Ontario operated by the Sifto Division of Domtar, Inc. INTRODUCTION In sltu measurement of ground stresses forms an essential part of the methodology for geological engineering practiced by Serata Geomechanics, Inc. (SGI). This methdology is known as the "integrated" or "SPDM Method" in its general form, and as the "Stress Control Method" in its particular application to underground mine design (1). SGI has developed a new method of stress measurement, the borehole dilatometer, diametral deformation method. Its development was motivated by the need to overcome the difficulties which beset conventional methods, such as overcoring and hydrofracturing, in complex ground, e.g., ground characterized by pre-existing fractures, predominantly non-elastic behavior, etc. (2,3). However, the Stressmeter which implements this method is a sophisticated, state-of-the-art tool whose proper application requires some degree of training, skill, and expense. For these reasons, this tool is not normally applied as a station instrument, to monitor ground stress changes over extended durations by repeated testing at a single measuring position along a given borehole. Rather, it is used as a "traveling" probe testing device, moved from one measuring position to another along a borehole, and normally testing each measuring position for only one time point, or at most over short periods of time. This paper describes a new kind of borehole pressure cell (BPC) which utilizes an elastomeric material for its outer pressure-transmitting membrane. This BPC has been effectively and conveniently applied as a station type instrument for monitoring ground stress changes in salt and coal pillars. This BPC utilizes the high pressure elastomer technology developed for the borehole dllatometer Stressmeter, thereby realizing a number of advantages over conventional metal-skinned BPCs. A data analysis technique has been developed which determines the magnitudes of the principal maximum and minimum stresses, P and O, respectively, perpendicular to the applied borehole direction, directly from the pressure readout of paired BPCs. This technique is delineated through presentations of field data from elastomeric BPC installations in the Sifto Salt mine, Goderich, Ontario, and of results from computer simulation analyses of the BPC/borehole boundary interaction, using the REM finite element program.
- North America > United States (0.47)
- North America > Canada > Ontario (0.45)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral > Halide > Halite (0.69)
ABSTRACT Abstract. Data analysis is one of the most important steps required for the successful application of the acoustic emission/ microseismic (AE/MS) technique. A dedicated computer software package to analyze acoustic emission/ microseismic data associated with field applications in the geotechnical area has been developed recently at Penn State University. This paper addresses the major features and applications of this computer software package. INTRODUCTION For nearly two decades, the Penn State Rock Mechanics Laboratory has been actively involved in the development of acoustic emission/ microseismic (AE/MS) monitoring techniques for geotechnical applications. One of the major achievements of this ongoing work has been the development of a computer software package for rapid and accurate processing and analysis of a variety of AE/MS field data. The first version of this software package was developed by Hardy and Mowrey in the late 1970s (Hardy and Mowrey, 1981). The primary application of this software at that time was to process AE/MS data associated with an underground natural gas storage reservoir (New Haven project), under study on behalf of the American Gas Association (AGA). After successfully completing the AGA- sponsored project, it was decided in 1984 to further modify this software package in order to meet the rapidly growing applications of the AE/MS technique. This current paper outlines the major features of the recently modified version of this computer software package. The current version was designed for general purpose use in the sense that it can rapidly be applied to a variety of field applications and can effectively perform the required analysis. For this purpose, the current version encompasses the major computational algorithms essential to successful analysis of AE/MS field data. However, the package is not merely a simple collection of programs; rather it incorporates only those routines which, over a period of time have been found to be the most versatile and useful for specific processing and analysis of AE/MS data. All of the routines contained in the package have been tested extensively and, in many cases, implemented successfully. Probably the most important aspect of this software package is the fact that it is a result of the broad-based AE/MS research efforts carried out at Penn State since 1970. In particular the extensive experience gained in a wide variety of field studies has shaped the software package in a unique manner. Usually AE/MS data analysis involves a number of approaches which may vary from one application to another. It appears, however, that for most field applications four particular aspects are necessary and essential, namely; individual-event analysis, continuous-data analysis, source location analysis and optimum transducer array geometry analysis. These four aspects are not only distinguished by the subject under study, but also by the theoretical background and the methods utilized in the study. As a result, the material in the software package is divided into four parts, each part consisting of a number of programs. The major functions of these four parts are illustrated in Figure 1. The software package is currently installed in the Computer Based Microseismic Analysis System (CBAS) developed by Hardy and Mowrey (1981) during the time the first version of this software package was developed.
ABSTRACT ABSTRACT The in situ elastic moduli of rock are measured holographically by a borehole instrument in marble and oil shale. A point force induced displacement field is recorded with double exposure holography. Data consists of a fringe pattern on the viewed hologram. The elastic moduli are determined by modeling of the fringe pattern. Only Young's modulus is fairly constrained by the present data reduction. For an applied force of 520 ± 50 Newtons, a marble was found to have a Young's modulus of 56 ± 8 GPa, near an ultrasonically determined value of 48 ± 6 GPa. In an oil shale, an applied force of 295 ± 10 Newtons indicates a Young's modulus of 25 ± 1GPa. INTRODUCTION Accurate knowledge of the in situ elastic moduli is required by most conventional stress measurement techniques (.McGarr and Gay, 1978). The holographic in situ stressmeter, which records a micron scale stress-relief dis- placement field (Bass, Schmitt, and Ahrens, 1986), requires values of Young's modulus and Poisson's ratio for a volume of rock with dimensions 10 cm square by 1 cm deep adjacent to s. borehole wall surface. Other stress measurement techniques: the C.S.I.R. "doorstopper" cell, (Leemah, 1969), the C.S.I.R. triaxial strain cell, (Leemah and Hayes, 1966), and the direct strain-gauge technique, (Swolfs, Handin, and Pratt, 1974) would benefit from small scale elastic moduli magnitudes. With this primary motivation in mind, double exposure holography is applied to the measurement of the in situ elastic moduli. In situ elastic moduli are difficult to measure due to problems in reproducing the original rock properties such as the state of stress, fluid saturation, jointing, and microfractures (Cheng and Johnson, 1981; Jaeger, 1979). Conventional in situ testing methods: compression tests, plate bearing tests, fiat jack tests, dilatometer tests, the "petite seismique" test, and the borehole jack tests (Bieniawski, 1978; Jaeger, 1979), measure the rock elastic moduli on varying length scales, force levels, and strain magnitudes. The rock modulus is dependent upon the sample scale and the density of discontinuities (Bieniawski and Van Heerdeen, 1975). For example, the N-X borehole jack method applies a uni-directional force of up to 703 KNewtons via two 20.3 cm long platens to the walls of a 7.62 cm diameter borehole (Goodman, Van, and Heuze, 1970). Changes in the hydraulic fluid pressure and the borehole wall diameter are measured; typical displacements are on the order of 0.2 into (Meyer and McVey, 1974) resulting in strain magnitudes near 1000 µstrains. The test is affected by the tensional properties of the rock surrounding the borehole (Heuze and Amadei, 1985). In a plate bearing test, compressional forces of up to 11.8 MNewtons are applied to areas on the order of I m(Jaeger, 1979). Induced displacements are 0.25 to 2.5 mm and are measured with dial gauges; strain levels encountered are also approximately 1000 µStrains. The holographic test, described in this paper, is on a much smaller scale. The test, similar in principle to plate bearing tests, requires application of a normal point force to the borehole wall of 50 Newtons to 5 KNewtons.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.46)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Oil Shale (0.45)
ABSTRACT INTRODUCTION The studied coal mine is an underground coal mine located in the northern Wasatch Plateau of central Utah (Figure 1). Since operation began in 1981, in situ stress conditions have been encountered which differ from the assumed conditions utilized during early mine design efforts. Geologic structures also varied some- what from those projected during initial geologic interpretations of the area. The encountered geologic conditions combined with the unusual stress conditions prompted a combined study of in situ stress and stress-related geologic structures. The study was conducted in two phases, with phase 1 consisting of detailed underground mapping and analysis of stress-related geologic structures to determine stress orientations from which they originated; and phase 2, consisting of over- coring two sites within the mine to determine present in situ stress orientations and magnitudes. GEOLOGICANALYSIS Three types of geologic structures have been encountered in the mine that act as indicators of stress orientations of the geologic past. Two of these structures, faulting, and igneous dikes, are directly measureable in the mine. A third type of structure, photolineation, was detected through remote sensing methods and shows good correlation to roof conditions in certain areas of the mine. Faults Two major orientations of faulting have been encountered in the studied coal mine, including a system of N 80 W striking normal faults and a system of N 55 to 70 W striking oblique-slip faults. Only data collected from the oblique-slip faults were used for this study due to the fact that these faults offset the N 80 W faults wherever the two systems intersect, indicating that the N 55 to 70 W system was created by a more recent stress field. Figure 2 shows locations within the mine where data were collected from seven locations along oblique-slip faults. Data collection consisted of measurement of fault plane strike and dip, fault slickenside trend and plunge, and slip direction. The data are tabulated in Table 1. The fault data were then plotted on stereo nets to determine the stress orientations present at the time of faulting (Figure 3). The determined stress orientations are also included in Table 1. The stereo net plots show average principal stress orientations of: 1) s1= S 88 E, plunge 36 degrees, 2) s2= N 90 W, plunge 54 degrees, and 3) s3= N 00 E, plunge 1 degree. These data suggest that the N 55 to 70 W oblique-slip faults were produced by a nearly horizontal principal stress created by east-west compression. Figure 2. Generalized mine map showing faults, igneous dikes, and photolineations, as well as fault data collection points and overcore site locations.(available in full paper) Igneous Dikes Igneous dikes are common in the mine area and are a good indicator of regional stress orientations at the time of their emplacement. Parker (1973) indicated that veins (or in our case, dikes) are commonly emplaced parallel to 'the maximum compressive stress. In other words, as dikes are intruded into a rock mass, they naturally follow the path of least resistance. Nearly all of the dikes in the mine area have a N 80 W orientation and were injected along previously existing N 80 W trending joints and faults (Figure 2).
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Fault > Oblique-Slip Fault (0.99)