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J. Kozák T. Lokajíček J. Šílený Reviewer V. Rudajev 《Studia Geophysica et Geodaetica》1989,33(4):322-337
Summary The results of laboratory measurements on square perspex models with a stress concentrator under uniaxial compression are presented. An attempt was made to interpret these results in order to determine the mutual relations between the mechanical parameters characterizing the treated models, including their focal zones, parameters of model loading, parameters of seismogenic displacement and parameters of radiated elastic pulses. Particular attention was given to the study of slip displacement, slip velocity, rupture velocity, nucleation points of rupture propagation, nucleation points of elastic radiation and to the frequency analysis of radiated pulses. Measurements of the displacement in the focal zone enabled us to determine the source function, to construct theoretical seismograms in a far field and to compare them with the real pulses from ultrasonic transducers located there. This allowed testing theoretical and experimental approaches to the study of how slip displacement, slip velocity and rupture velocity are related to the parameters of radiated pulses. 相似文献
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Studia Geophysica et Geodaetica - 相似文献
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Jan Vilhelm Vladimír Rudajev Roman Živor Tomáš Lokajíček Zdeněk Pros 《Geophysical Prospecting》2010,58(6):1099-1110
The purpose of this paper is the comparison of P‐wave velocity and velocity anisotropy, measured at different scales under laboratory and field conditions. A shallow seismic refraction survey with shot/receiver spacing of up to 10 m was carried out on a flat outcrop of lhertzolite in the southern part of the Balmuccia massif. Oriented rock samples were also obtained from the locality. The particular advantage of the laboratory method used is the possibility of measuring velocity in any direction under controlled conditions. Laboratory tests were made on spherical peridotite samples, 50 mm in diameter, by ultrasonic velocity measurements in 132 directions (meridian and parallel networks) under confining stress ranging from atmospheric to 400 MPa. The mean P‐wave velocity of the field and laboratory data differed by between 20–30%. In addition, P‐wave velocity anisotropy of 25% was detected in the field data. Whereas the anisotropy in the laboratory samples in the same orientation as the field surveys was less than 2%. This observed scaling factor is related to the different sampling sizes and the difference in frequencies of applied elastic waves. With an ultrasonic wavelength of 10 mm, laboratory samples represent a continuum. The field velocities and velocity anisotropy reflect the presence of cracks, which the laboratory rock samples do not contain. Three sub‐vertical fracture sets with differing strikes were observed in the field outcrop. Estimates of fracture stiffness from the velocity anisotropy data are consistent with other published values. These results highlight the difficulty of using laboratory velocity estimates to interpret field data. 相似文献
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Possible mechanism of rockbursts in coal mines 总被引：1，自引：0，他引：1
One of the important questions of rockburst prevention is the understanding of the mechanism of rockburst source. This question can be effectively studied by direct seismic observations in the rockburst regions. For this purpose, the distribution ofP-wave onset signs and the inversion of first motion amplitudes were utilized as the basic method. In such a way the coal mine regions in Poland (Upper Silesia) and in Czechoslovakia (Kladno coal mine district) were studied as part of the Polish-Czechoslovak rockburst investigation project. More than 250 rockburst events were recorded here in the decade 1977–1983, and analyzed. The results of the statistical analysis of these data allow us to formulate and introduce a model of the rockburst source with an implosion component. The suitability of this conception was verified by laboratory simulation conditions; it was confirmed that the seismoactive displacements with a clear implosive component were recorded in the neighbourhood of a stress concentrator weakened by holes. The results of both the field observations and laboratory tests were in good agreement with the theoretically derived radiation patterns for a combined shear-implosive source and also with the theoretical conception of such a source based on real geometrical configurations of mine excavations and tectonic dislocations.The rockbursts treated exhibit a dominant shear component, the magnitude of the additional implosive component not exceeding 10 percent of the shear component. 相似文献
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Seismic events with non-shear component: II. Rock bursts with implosive source component 总被引：2，自引：0，他引：2
The rock burst mechanism of an implosive character is introduced and discussed; it is based on the idea that the compressional component of the stress field around the loaded stress concentrator can participate in the rock burst event. For easier classification of the rock burst from this viewpoint, a set of P-wave radiation patterns of the rock burst with a varying portion of the implosive component and varying propagation velocity of the displacements is presented and discussed. To support the credibility of the rock burst mechanism of an implosive character the seismic signals of the rock bursts from the mid-Bohemian coal district with negative signs of the P-wave first onsets are presented. 相似文献
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J. Vilhelm V. Rudajev T. Lokajíček J. Veverka 《Rock Mechanics and Rock Engineering》2008,41(5):695-714
Summary. The locations of fractures within loaded rock samples are distributed irregularly because of the presence of inhomogeneities
in the rock sample, the existence of primary microcracks and non-uniformly distributed stress. In the case of brittle fracture,
the positions of these fractures can be determined by locating the foci of ultrasonic events that occur during fracturing.
In some cases, the foci cluster into clouds that are restricted spatially and are referred to as nucleation centres. The purpose
of this research was to determine the mutual relationship between the various nucleation centres, by cross-correlating the
time-series of ultrasonic events produced by microcracking in the individual, separate nucleation centres. An additional goal
was to assess the effect of the existence of such nucleation centres on the autocorrelation parameters. This study showed
that the separate nucleation centres did not appear to influence one another even during the final stages of fracturing. Until
now, autocorrelation analysis of acoustic emission time sequences has been applied to evaluate the mutual influence of individual
events that occur in the whole sample volume, regardless of their location. In a previous study, it was found that before
the total fracturing of the sample, the autocorrelation parameters changed significantly due to the increase in mutual relationship
between successive events. In this study the separated nucleation centres determined by locating the ultrasonic events were
subjected to autocorrelation analysis. It was demonstrated that, in the case of critical loading of the sample, the mutual
influence between the events of a given nucleation centre can be observed. The experiments have demonstrated that the autocorrelation
has a precursory nature and have shown that there is a significant difference in the autocorrelation parameters calculated
between the set of all recorded events, and the specific sub-set. These differences must be taken into account when applying
statistical predictions, for example, in the study of rock bursts.
Author’s address: Jan Vilhelm, Charles University in Prague, Albertov 6, 128 43 Prague, Czech Republic 相似文献
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Lucie Novakova Milan Broz Jiri Zaruba Karel Sosna Jan Najser Lenka Rukavickova Jan Franek Vladimir Rudajev 《应用地球物理》2016,13(2):315-325
Underground storage systems are currently being used worldwide for the geological storage of natural gas (CH4), the geological disposal of CO2, in geothermal energy, or radioactive waste disposal. We introduce a complex approach to the risks posed by induced bedrock instabilities in deep geological underground storage sites. Bedrock instability owing to underground openings has been studied and discussed for many years. The Bohemian Massif in the Czech Republic (Central Europe) is geologically and tectonically complex. However, this setting is ideal for learning about the instability state of rock masses. Longterm geological and mining studies, natural and induced seismicity, radon emanations, and granite properties as potential storage sites for disposal of radioactive waste in the Czech Republic have provided useful information. In addition, the Czech Republic, with an average concentration radon of 140 Bq m?3, has the highest average radon concentrations in the world. Bedrock instabilities might emerge from microscale features, such as grain size and mineral orientation, and microfracturing. Any underground storage facility construction has to consider the stored substance and the geological settings. In the Czech Republic, granites and granitoids are the best underground storage sites. Microcrack networks and migration properties are rock specific and vary considerably. Moreover, the matrix porosity also affects the mechanical properties of the rocks. Any underground storage site has to be selected carefully. The authors suggest to study the complex set of parameters from micro to macroscale for a particular place and type of rock to ensure that the storage remains safe and stable during construction, operation, and after closure. 相似文献
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