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ABSTRACT ABSTRACT: Mining at Mine Gaspe is carried out via longitudinal blasthole open stoping with delayed backfill. Increasing seismic activity was observed as mining progressed into the second panel. An integrated study of mine induced seismicity occurring over roughly eight months following system installation, seismic velocity, stress and geomechanical data, indicated that the majority of microseismic activity was related to the development of a large stress arch over the mined out panels. During extraction of the 400 panel a back failure in previously cable bolt supported ground occurred in the 400-10 stope. Analysis suggests a significant mine induced stress decrease occurred with extraction of the 400-10 stope. It is believed that this resulted in the observed back failure. The overall integrated analysis was critical to ultimately understanding the interaction of mine induced stresses, mine structure and cable bolt capacity. This technique shows promise as a tool for enhanced design of underground mine openings.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.35)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Anstey (1991) discussed the large effects contact properties can have on seismic velocities. Kowallis et al (1984) noted that framework cementation in a sandstone, partially due to authigenic clay, had an important influence on observed seismic velocities. Suarez Rivera (1992) showed that S-wave attenuation across a single, clay-coated planar interface changed in response to different fluid types and amounts. Attenuation increased as the water content increased, but was less in the presence of non-polar fluids. These studies suggest that clay and fluids at contacts in granular materials may have notable effects on seismic wave propagation.
- Research Report > New Finding (0.87)
- Research Report > Experimental Study (0.69)
ABSTRACT ABSTRACT: Laboratory healing tests were conducted on specimens of intact WIPP salt that were predamaged by straining under constant strain-rate triaxial stress conditions at low confining pressure (0.5 MPa) and near room temperature (25ยฐC). Introduction of dilatant damage caused specimen volumes to increase and ultrasonic compressional wave velocities and amplitudes to decrease. Specimens were then loaded hydrostatically to 15 MPa at temperatures up to 70ยฐC. Under these conditions, damage was partially recovered and specimen volume and compressional wave characteristics approached the values of the undamaged state. From these data, time constants and an activation energy were determined for the damage recovery process. The results have significant implications for sealing systems because they demonstrate that the healing process is quite rapid compared to the creep closure process.
When waves of seismic or other origin are propagated through fractured rock mass not only will the reflection and transmission coefficients depend on the acoustic impedance mismatch and the nature of the interface layer, but also the physico-mechanical behaviour of the interface will change as a function of time. Degradation and aging processes of the interface material, which may quantitatively be formulated by means of continuum damage mechanics principles, may be made responsible in part. Elastic wave behaviour across imperfectly bonded linear slip interfaces separating two elastic media is investigated in Schoenberg (1980), where the displacement discontinuity, or slip, is taken to be linearly related to the stress traction which is continuous across the interface for both the normal and tangential direction. Applying the theoretical results of Schoenberg (1980) to seismic wave propagation model experiments in a jointed columnar basaltic rock formation, acceptable agreement between observed and predicted results has been found by Myer et al (1990). A proper constitutive model for rock joints must be able to predict the deformation behaviour involving aging effects on a long time scale as well as deterioration effects due to repeated loading and unloading. In percussion drilling, the interface is dynamically loaded at high intensity and the interface characteristics will change with each consecutive percussive blow ofthe tool. Improved knowledge about the impact-induced time-variation of the mechanical behaviour of the rock joints appears to be instrumental and vital for the improvement of drill efficiency and the development of smart mining machinery.
ABSTRACT ABSTRACT: Fracture traces and seismic event location data were examined and numerical experiments performed to test whether scale-invariant fracture trace patterns can be represented by point patterns generated at discrete trace sites. Point pattern data censored in different ways were examined with respect to the effects on fractality. A sparse fractal point data set remains fractal, but the scale range of fractality decreases as sparseness increases. Thus, a seismic event location point pattern may not adequately represent the full scale over which the parent faults are fractal. An example of the inverse problem of determining the fractal nature of unknown fault traces from seismicity is given.
- Energy > Oil & Gas > Upstream (0.48)
- Law > Civil Rights & Constitutional Law (0.35)
- North America > United States > Utah > Book Cliffs Field (0.89)
- North America > United States > Colorado > Piceance Basin > Plateau Field > Williams Fork Formation (0.89)
- North America > United States > Colorado > Piceance Basin > Plateau Field > Iles Formation (0.89)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (0.71)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.70)
- Reservoir Description and Dynamics > Reservoir Characterization > Faults and fracture characterization (0.48)
ABSTRACT ABSTRACT: Ultrasonic compressional (P) and shear (S) waves were transmitted through the axial and lateral directions of cylindrical samples of a high porosity rock formation subjected to triaxial, hydrostatic and uniaxial strain deformational paths. Triaxial tests which terminate in a brittle shear fracture generate a P-wave anisotropy and a lateral shear wave birefringence in both the elastic and dilatant phases of loading. Post-failure sliding along the shear fracture does not result in changes in anisotropy. Triaxial tests at high confining pressure generate ductile yielding of the limestone. In the initial elastic phase no anisotropies are evident. At yielding significant P-wave and S-wave anisotropies develop which continue to increase until termination of the tests. Uniaxial strain (ko) tests develop initial acoustic anisotropies at the point of ductile yielding. These anisotropies continue to increase after yielding, for about 1 to 2% volumetric strain, at which point the acoustic velocities begin to increase and the velocity anisotropies remain constant for the duration of the test. Hydrostatic compaction tests evidence small acoustic anisotropies which develop during the initial (elastic) phase but begin to decrease after hydrostatic yielding.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.63)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 018 > Block 2/4 > Greater Ekofisk Field > Ekofisk Field > Tor Formation (0.98)
- Europe > Norway > North Sea > Central North Sea > Central Graben > PL 018 > Block 2/4 > Greater Ekofisk Field > Ekofisk Field > Ekofisk Formation (0.98)
ABSTRACT ABSTRACT: There is controversy as to the cause of catastrophic failures occurring when mining coal under strong roof. The U.S. Bureau of Mines presents a hypothesis that catastrophic mine roof failure is due to the formation of a macrocrack (dilatant zone) in the rock mass above a pillar or longwall panel immediately before roof collapse. The macrocrack closes upon itself during roof caving. From appropriate energy calculations, sufficient energy is available from this model to produce tremors whose energy release is equivalent to local earthquake magnitudes between ML = 2.0 ? 3.5. This energy release is applied to a model of damage criterion for propagation of high-amplitude compressive stress waves through the mine workings. Using a particle velocity damage criterion of 0.30 m/s as needed to induce tensile cracking at free surfaces in coal, the area of damage from a ML = 3.6 mine tremor (NEIS) in a Utah coal mine is calculated to be about 10 m, corresponding closely to the area (7.6 x 10 m) of observed damage.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.72)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.52)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.34)
ABSTRACT ABSTRACT: U.S. Bureau of Mines researchers have analyzed full-waveform digital seismic records from moderate-to-large rockburst events at the Lucky Friday Mine, Mullan, ID. The goal of this work is to characterize source mechanisms for rockburst events. Because the seismometer array used for the recordings usually consists of fewer than 10 instruments, a method of obtaining composite source solutions has been developed. These solutions are determined by selecting events with similar arrival pat-terns at the seismometer array and with hypocentral locations in the same general region of the mine. Some events have all-dilatational first arrivals, while others display arrival patterns with both compressional and dilatational arrivals. There are at least three types of events in the mine. Some of the more complex arrival patterns seem to be associated with right-lateral, strike-slip motion, while others seem to be associated with left-lateral or dip-slip movement. The type of event seems to be independent of source location, although geologic conditions in different regions vary. Even though there is a fundamental difference in the geometry of the mining environment, the three types of events are still recognizable. This work is continuing, and data from all large events (Richter magnitude, mL > 2.0) at the mine are being analyzed and added to a database.
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.51)
ABSTRACT ABSTRACT: A detailed geomechanics study was carried out during the mining of two sill pillar stopes at Brunswick Mining. Microseismics, conventional ground control instruments, numerical modelling and visual observations were used to understand the observed failure mechanisms. Severe rock mass failure was initiated in several locations. The complex nature of the failures was unexpected. Only through the use of all the available tools, was it possible to understand some of the rock mass problems.
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Metals & Mining (0.94)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.90)
Programme (aimed at investigating the performance of rock support under rockbursting conditions) in-situ dynamic monitoring of various types of rockbolts loaded by blasts was performed. The aim of the monitoring was to investigate and explain the interaction of the dynamic load with the rock-rockbolt system. The measured strain waves on the bolt and the dynamic movement of the rock surface were successfully simulated numerically using a one dimensional finite difference representation of the mechanical system involving the wave source, the rockmass, the mechanical rockbolt, and the anchor and head connections. The model was calibrated using field data from the blasts, and parametric studies of the influence of various system parameters on the dynamic behaviour of the rockbolt were carried out. It was found that the wave source, rockmass modulus, tensile strength, connections at the rockbolt ends, and rockbolt pre-tension all play important roles in determining the dynamic stress levels in rockbolts.