Premelting effects in gehlenite (Ca2Al2SiO7) have been studied by Raman spectroscopy and calorimetry, and in gehlenite and pseudowollastonite (CaSiO3) by electrical conductivity. The enthalpy of premelting of gehlenite is 17.3 kJ mol−1 and represents 9% of the reported enthalpy of fusion, which is in the range of the reported fraction of other minerals. The
Raman and electrical conductivity experiments at high temperatures, for gehlenite and pseudowollastonite, show that the premelting
effects of both compositions are associated with enhanced dynamics of calcium atoms near the melting point. This conclusion
agrees with the results obtained for other minerals like diopside, but contrasts with those found for sodium metasilicate
in which the weaker bonding of sodium allows the silicate framework to distort near the melting temperature and deform in
such a way to prefigure the silicate entities present in the melt.
Received: 30 April 2002 / Accepted: 7 August 2002
Acknowledgements We thank Y. Linard for help with DSC measurements and two anonymous reviewers for their constructive comments. This work
has been partly supported by the EU Marie-Curie fellowship contract no. HPMF-CT-1999-00329, the CNRS-Carnegie Institution
of Washington program PICS no.192, and the NSF grants EAR-9614432 and EAR-9901886 to B.O.M. 相似文献
The permeability of sedimentary rocks during triaxial compression tests was investigated to relate it to the complete strain–stress process. It was found that the permeability was not constant, but varied with the stress and strain states in the rocks. Prior to the peak strength, the permeability decreases with increasing load. A dramatic increase in permeability occurs during the strain softening period. In the present study, in situ measurements of fluid flow and pressure in floor strata was carried out in a double longwall mining face in the Yangzhuang colliery. These measurements show that both the strata pressure and the position with respect to the mining face influence the hydrogeologic properties. The permeability increased in the floor strata behind the mining face because those mining induced fractures opened as the strata pressure decreased. To better understand this change in hydraulic behavior around the mining faces, 3-D numerical modeling was carried out. The model provides the general picture of the stress distribution and failure zone both in the floor and roof strata. The field and model results demonstrate the importance of changes in the stress and strain states on the hydrogeology of a site. 相似文献
Field observations on ground motions from recent earthquakes imply that current knowledge is limited with regard to relating vertical and horizontal motions at liquefiable sites. This paper describes a study with the purpose of clarifying this emerging issue to some extent. A series of numerical analyses is carried out on a liquefiable soil deposit with a verified, fully coupled, nonlinear procedure. It is shown that the transformation of vertical motions in the deposit differs considerably from the transformation of horizontal motions. Both the amplitude and frequency content of the horizontal motions are strongly dependent on the shaking level or the associated nonlinear soil behavior. The transfer function for vertical motions is however likely to be independent of the intensity of input motions; no reduction in the amplitude occurs even in the case of strong shaking. The results are shown to be in consistence with the laboratory observations on shaking table tests and recent field observations that less nonlinearity exists for vertical motions. It is also shown that the possibility exists for using information on spectral ratios between the horizontal and vertical surface motions to quickly identify in situ soil behavior and liquefaction that are not readily covered by conventional field or laboratory experimentation procedures. 相似文献
Under seismic excitation, liquefied clean medium to dense cohesionless soils may regain a high level of shear resistance at large shear strain excursions. This pattern of response, known as a form of cyclic mobility, has been documented by a large body of laboratory sample tests and centrifuge experiments. A plasticity-based constitutive model is developed with emphasis on simulating the cyclic mobility response mechanism and associated pattern of shear strain accumulation. This constitutive model is incorporated into a two-phase (solid–fluid), fully coupled finite element code. Calibration of the constitutive model is described, based on a unique set of laboratory triaxial tests (monotonic and cyclic) and dynamic centrifuge experiments. In this experimental series, Nevada sand at a relative density of about 40% is employed. The calibration effort focused on reproducing the salient characteristics of dynamic site response as dictated by the cyclic mobility mechanism. Finally, using the calibrated model, a numerical simulation is conducted to highlight the effect of excitation frequency content on post-liquefaction ground deformations. 相似文献
Spatial variation of earthquake ground motion is an important phenomenon that cannot be ignored in the design and safety of strategic structures. Several models have been developed to describe this variation using statistical, mathematical or physical approaches. The latter approach is not specific to an event. A recent contribution, which uses such an approach and called complete stochastic deamplification approach (CSDA), was developed [1]. The aim of this paper is to analyze the spatial variation of earthquake motion induced by the propagation of body waves using the CSDA. Coherency functions are evaluated for the cases of SH–SV–P waves propagating through stratified soil. Results obtained show that the variation of the coherency function is not the same for vertical and horizontal components and that the motion is more coherent at depth than at the free surface. In fact, we found that the rate of decrease with frequency and distance is not the same if P–SV waves propagate through stratified soil. 相似文献
A field test and analysis method has been developed to estimate the vertical distribution of hydraulic conductivity in shallow unconsolidated aquifers. The field method uses fluid injection ports and pressure transducers in a hollow auger that measure the hydraulic head outside the auger at several distances from the injection point. A constant injection rate is maintained for a duration time sufficient for the system to become steady state. Exploiting the analogy between electrical resistivity in geophysics and hydraulic flow two methods are used to estimate conductivity with depth: a half-space model based on spherical flow from a point injection at each measurement site, and a one-dimensional inversion of an entire dataset.
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Introduction The measurements of the compressional wave velocity and electrical conductivity of minerals and rocks are of fundamental importance to look into the earths interior, including composition, geotherm, generation and distribution of fluids and melts. Hydrous minerals formed by metamatu-siom are abundant within the earth. Previous studies have been carried out on the dehydration effect on the electrical conductivity and wave velocity of rocks such as serpentine, amphibole, most of whi… 相似文献