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Transport properties of rocks from statistics and percolation 总被引:7,自引:0,他引:7
Two simplified microstructural models that account for permeability and conductivity of low-porosity rocks are compared. Both models result from statistics and percolation theory. The first model assumes that transport results from the connection of 1D objects or pipes; the second model assumes that transport results from the connection of 2D objects or cracks. In both cases, statistical methods permit calculation of permeability k and conductivity , which are dependent on three independent microvariables: average pipe (crack) length, average pipe radius (crack aperture), and average pipe (crack) spacing. The degree of connection is one aspect of percolation theory. Results show that use of the mathematical concept of percolation and use of the rock physics concept of tortuosity are equivalent. Percolation is used to discuss k and near the threshold where these parameters vanish. Relations between bulk parameters (permeability, conductivity, porosity) are calculated and discussed in terms of microvariables. 相似文献
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On the basis of two assumptions i.e. (1) plastic and anelastic behaviour of the upper mantle can be approximated by the behaviour of the dominant mineral olivine, and (2) the behaviour of natural olivine and synthetic forsterite are similar, we have investigated the flow laws and the flow microstructures of forsterite single crystals. The results obtained between 1400–1650°C and 10–100 MPa suggest a model of climb controlled creep in which the a edge dislocations are dominant. The activation energy measured in that regime is 4.7 eV, close to that of Si self-diffusion and the flow law is , where σ is in MPa. Extrapolation of these results to the upper mantle would imply very low stresses (i.e. ?10 MPa) in the asthenosphere. However the effect of pressure and grain size are unknown and extrapolation to very low stresses is not straightforward. 相似文献
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Spectra of internal friction between 2 and 8 Hz were studied in a single crystal of enstatite, in a polycrystal of synthetic forsterite and in several samples of natural peridotite. Measurements of Q?1 and μ were performed in vacuum (10?6 torr), from room temperature up to 1100°C. For these experimental conditions no peak was observed in the polycrystalline undeformed forsterite, but the background attenuation irregularly increased from 5 · 10?3 to 10?2.A peak Q?1 = 7 · 10?2 appears in a deformed peridotite at 930°C. It is reduced of 60% after 5 h of annealing at 1100°C. But the background attenuation persists. In the single crystal of enstatite, a peak is observed at 760°C (Q?1 = 6 · 10?2). A mechanism involving dislocations is suggested as a possible explanation for the peak obtained with the peridotite samples. If this hypothesis is right, the observed effect would be diffusion controlled so that one can expect pressure to translate it towards higher temperature. This mechanism could therefore appear in the upper mantle. Background attenuation could be the result of intergranular thermal losses. 相似文献
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Philippe Gueguen Véronique Jolivet Clotaire Michel Anne-Sophie Schveitzer 《Bulletin of Earthquake Engineering》2010,8(2):327-338
Over recent years there has been a growing interest in the building frequency analysis for earthquake and structural engineering
fields using ambient vibrations. Simultaneously, velocity measurements with LASER remote sensing techniques have gained more
interest for several applications. This paper details the comparison of the frequency analysis obtained using sensitive velocimeter
sensor and coherent LIDAR (Light Detection and Ranging) sensor, and applied to one RC existing building. Ambient vibrations
recordings were processed using the Frequency Domain Decomposition method for defining the frequencies and mode shapes of
the building target, while LASER remote sensing approach used coherent LIDAR method for velocity and frequency measurement.
The results of the two systems are discussed. A good agreement is observed, which let us conclude on the ability of the coherent
LIDAR to assess the frequency of existing buildings for structural and earthquake engineering fields at long range and without
any retroreflector on the structure. 相似文献
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Using experimental data to reduce the single-building sigma of fragility curves: case study of the BRD tower in Bucharest, Romania 总被引:1,自引:0,他引:1
Matthieu Perrault Philippe Gueguen Alexandru Aldea Sorin Demetriu 《地震工程与工程振动(英文版)》2013,12(4):643-658
The lack of knowledge concerning modelling existing buildings leads to significant variability in fragility curves for single or grouped existing buildings. This study aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest, Romania, a RC building with permanent instrumentation. A three-step methodology is applied: (1) adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson's criteria, (2) computation of the structure's response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements (IM), and (3) construction of the fragility curves by comparing numerical interstory drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering Sd ) as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology. 相似文献
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Philippe Gueguen 《Bulletin of Earthquake Engineering》2012,10(4):1285-1298
In recent years, many studies have been focused on the use and effectiveness of passive islotaing devices for reducing the effect of seismic ground motion on buildings. Among the available methods, one consists in isolating the structure using rubber bearings, the solution certainly the most accomplished and having the most feedback. In this study, we focused on the case of Martinique earthquake (Mw=7.4) of 29 November 2007, recorded by accelerometric stations installed at the Centre de Découverte des Sciences de la Terre (Martinique), a base-isolation building with rubber bearings. Several earthquakes are used in this paper, from moderate to strong ground motion. Ambient vibration modal analysis is first described in order to understand the elastic response of the building. The earthquake data are then interpreted, in particular to understand the mechanism of vibration of the structure and its comparison with the experimental modes previously estimated using ambient vibrations. 相似文献