Internal erosion of chemically reinforced granular materials: a mathematical modeling approach     

Tony Khalil  Nadia Saiyouri  Bogdan Muresan  Pierre‐Yves Hicher 《国际地质力学数值与分析法杂志》2013,37(5):491-502

Internal erosion (IE) affects the stability of natural and reinforced materials by causing instability within their granular structure. The dislodgement and transport of eroded particles affect both the particulate concentration of eroding fluid and the pore network of eroded material. In this study, we examined these modifications using a transport model with a finite element code. First, IE tests on chemically reinforced sand columns were performed to obtain information about eroded material loss of mass, particulate concentration of effluent, porosity and permeability modifications, and existing IE stages. Second, based on experimental results, a mathematical one‐dimensional model has been formulated to monitor the evolution and spatial distribution of erodible solids, fluidized particles, porosity, permeability, and seepage stresses. The model consists of a set of coupled nonlinear differential equations solved in sequence. It provides valuable information about the extent and the dynamics of structural changes, which can be used to estimate an IE time for the hydraulic work to reach failure. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Oxygen and organic carbon fluxes in sediments of the Bay of Biscay     

Aurélia Mouret  Pierre Anschutz  Bruno Deflandre  Gwénaëlle Chaillou  Christelle Hyacinthe  Jonathan Deborde  Henri Etcheber  Jean-Marie Jouanneau  Antoine Grémare  Pascal Lecroart 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):528-540

The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O₂ consumption and POC burial rates. Benthic O₂ distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O₂ consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O₂ fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O₂ profiles. The rupture in the gradient of O₂ microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O₂ fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O₂ fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O₂ penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment.  相似文献   

Lacustrine sedimentation in a semiarid alpine setting: An example from Ladakh, northwestern Himalaya     

Monique Fort  Douglas W. Burbank  Pierre Freytet 《Quaternary Research》1989,31(3)

The Lamayuru lacustrine strata in Ladakh typify many of the carbonate-rich Pleistocene alpine lakes found in the semiarid environment of the northern Himalaya. Created by a 200-m-thick landslide, the lake was in existence by at least 35,000 yr ago, and may have persisted until 500–1000 yr ago. Represented in the center by thin turbidites and laminated muds, the lacustrine sedimentation along the lake margins and low-relief deltas characteristically displays a marked contrast between (1) clastic lenses representing rapid, sporadic, matrix-poor debris flows and periglacial inputs from the alpine slopes and (2) abundant, diverse, shallow-water, biologically dominated carbonate strata, among which organism-rich, chalky beds and oncolithic and encrusted stem-rich strata predominate. Resemblances of the Lamayuru lacustrine strata and their setting to those of former lakes throughout areas north of the Greater Himalayan crest suggest that the alpine, semi-arid environment would favor diversified, spacially restricted carbonate sedimentation punctuated by occasional clastic influxes. Such a depositional regime contrasts strongly with that found immediately south of the Himalayan crest where more humid conditions promote a more continuous clastic influx into intramontane lakes.  相似文献   

Etude de la couche limite de surface sahelienne — Experience Yantala     

Jean-Pierre Pagès  Jean-Pierre Frangi  Pierre Durand  Claude Estournel  Aimé Druilhet 《Boundary-Layer Meteorology》1988,43(1-2):183-203

This paper presents data concerning the energy budget in the surface layer in the Sahel region (a semi-desert area). The results are drawn from a measurement campaign made in the Niamey region in the Niger, in April–May 1984 (the Yantala Campaign). The sensible heat flux is computed with the profile method, the ground heat flux is deduced from measurement of the temperature field, and the radiative net flux is measured directly with a balancemeter. The latent heat flux, which is deduced from the energy budget balance is very weak and within the accuracy limit of the method. The diurnal variation of the net flux is symmetrical, with a maximum at noon. On the other hand, the sensible heat flux variation is asymmetrical, with an afternoon decrease much slower than the morning increase. After 3.30 pm, it becomes higher than the net flux. This is compensated for by the sign change of the ground heat flux, whose maximum is found in the morning at 11 am. The second part of this paper shows the importance of one term in the surface-layer energy budget: the long-wave radiative divergence between the ground and the top of the surface layer in high superadiabatic conditions. We show, with a radiative model on the one hand and direct measurement of the radiative divergence on the other hand, that this term reaches several tens of W m^-2 in the superadiabatic conditions found in the Sahel region.   相似文献   

Energy budget for the Sahel surface layer during the ECLATS experiment     

Pierre Durand  Jean-Pierre Frangi  Aime Druilhet 《Boundary-Layer Meteorology》1988,42(1-2):27-42

The measurements obtained during the ECLATS experiment were used in order to determine the surface energy budget of the Sahel region (Niamey, Niger). This expedition was carried out from November 15 to December 10, 1980, during the dry period. Some data were collected by an instrumented aircraft, from which the turbulent fluxes were obtained in the boundary layer around midday; data were also collected at a surface station in order to estimate the surface energy budget continuously by the profile method. The aircraft measurements show the homogeneity of the vertical fluxes over large areas, allowing generalization to the bushy steppe of the Sahel region. The mean diurnal cycle of the energy budget is characterized by high values of ground heat flux and weak values of latent heat flux (deduced from the balance of the energy budget). This cycle is compared with that of the Koorin expedition, performed in similar conditions (tropical savanna in the dry period). We compare the three midday budgets: during Koorin; during ECLATS, at the ground station, and with the aircraft. The important differences that appear in the net radiative flux are explained by the difference in surface albedo.Ecole des Sciences, Université de Niamey, B.P. 10662 Niamey, Niger.  相似文献   

Penetration of bomb radiocarbon in the tropical Indian Ocean measured by means of accelerator mass spectrometry     

Edouard Bard  Maurice Arnold  H. Gte stlund  Pierre Maurice  Patrick Monfray  Jean-Claude Duplessy 《Earth and Planetary Science Letters》1988,87(4)

Radiocarbon measurements performed on seawater samples by means of accelerator mass spectrometry (AMS) enable to reduce by a factor of 2000 the water sample size needed for the¹⁴C measurements. Therefore no chemical treatment on board the oceanographic vessel is required. Seventy-four AMS¹⁴C determinations on samples collected in the tropical-equatorial Indian Ocean during the second leg of the INDIGO program (1986) are presented and compared with the β-counting results obtained during the same campaign and the GEOSECS program (1978). A pronounced reduction of the equatorial¹⁴C deficit suggests that substantial amounts of bomb-¹⁴C are associated with the westward flowing Pacific water which enters the Indian Ocean via passages through the Indonesia archipelago and/or to meridional mixing with¹⁴C-rich water of the southern subtropical gyre.  相似文献   

Inverse magnetic fabric in carbonate-bearing rocks     

Pierre Rochette 《Earth and Planetary Science Letters》1988,90(2)

The observation of a magnetic susceptibility ellipsoid whose maximum axis corresponds to the minimum axis of petrofabric (pole of bedding or schistosity) is referred to as an inverse magnetic fabric. The investigation of the magnetic properties of some ferroan carbonate monocrystals and paramagnetic limestones demonstrates thatc-axis preferred orientation of paramagnetic carbonates results in a maximum susceptibility parallel to the flattening direction.Inverse magnetic fabrics due to magnetite are also encountered in weakly deformed limestones. A mineralogical model based on the property of single-domain grains to have a zero susceptibility parallel to their long axis is proposed. However, more complex cases are also encountered.  相似文献   

Evaluation of magmatic processes for the products of the Nevado del Ruiz Volcano, Colombia from geochemical and petrological data     

Nicole Vatin-Prignon  Pierre Goemans  Richard A. Oliver  Eduardo Parra Palacio 《Journal of Volcanology and Geothermal Research》1990,41(1-4)

Trace-element concentrations of the eruptive products from the Nevado del Ruiz volcano indicate that at least for the last 1 Ma, the major controlling factor in the evolution of the magma has been a simple fractional crystallization.The Zr/Hf ratios suggest that the source material is mantle-like in origin and whilst subduction-related contamination of the source material has taken place, there is no evidence that assimilation of continental crust has affected the series.No convincing geochemical evidence for magma mixing was found, and data on banded pumices of Pleistocene, Historic and the 1985 eruptions strongly support a crystal fractionation model to explain the compositional variation of their glasses. Therefore, if mixing has taken place it can only be a mixing of layers within a stratified or partially stratified magma chamber.Modeling of fractional crystallization using a stepwise program has been undertaken and least-squares approximations with small residuals are commensurate with analyzed samples. Crystal fractionation models with plagioclase dominating two-pyroxenes and iron oxides give good fits for all calculations. We conclude that simple crystal fractionation is the process most consistent with major- and trace-element variations in the Ruiz series. This closed-system model requires at least 77% crystal fractionation of a basaltic parent to generate the observed compositions of dacites.  相似文献   

Evidence of an early alteration process driven by magmatic fluid in Mururoa volcano     

Christine Destrigneville  Jacques Schott  Yves Caristan  Pierre Agrinier 《Earth and Planetary Science Letters》1991,104(2-4)

Evidence for a deuteric alteration process induced by a magmatic fluid has been found in the feeder zone of the Mururoa volcano (French Polynesia). Within the dikes, where basaltic glass does not show any evidence of pervasive alteration, vesicles are filled with dioctahedral smectites and calcite, while olivine phenocrysts are replaced by dioctahedral smectites, ankerite and calcite.The ¹³C signature of carbonates, the carbon and H₂O content of the whole rocks and their impoverishment in deuterium are compatible with the presence of magmatic CO₂ during the crystallization of intruding lavas and exclude contamination by seawater. Mass balance calculations on selected thin sections photographs of partly filled up vesicles and replaced olivine crystals, constrain, assuming a closed system interaction, the chemical composition of the initial fluid and the respective amounts of the initial solid phases involved in the alteration process. Thermodynamic modelings using the EQ3/6 software package correctly predict the mineralogic, chemical and isotopic exchanges accompanying alteration, thus validating the closed system assumption. The model which allows prediction of the influence of CO₂ on the alteration products, shows that, above a 0.25 CO₂ mole fraction in the initial fluid, the alteration is entirely controlled by the chemical composition of the initial solid phases. The presence of CO₂ implies the precipitation of dioctahedral smectites and carbonates instead of the magnesian smectites commonly observed in CO₂-free systems.The Mururoa feeder zone shows alteration features typical of a closed system interaction between the basaltic rock and a magmatic fluid in which seawater did not take part.  相似文献   

SrNdPb geochemical morphology between 10° and 17°N on the Mid-Atlantic Ridge: A new MORB isotope signature     

Laure Dosso  Barry B. Hanan  Henri Bougault  Jean-Guy Schilling  Jean-Louis Joron 《Earth and Planetary Science Letters》1991,106(1-4)

Basalts dredged along the Mid-Atlantic Ridge axis between 10°N and 17°N have been studied for their trace element characteristics [1]. To give complementary information on mantle source history and magma genesis, these samples have been analysed for their SrNdPb isotopic compositions. There is a good correlation between the structure of the ridge axis which shows a topographic anomaly centered around 14°N and hygromagmaphile element ratios such as Rb/Sr, (Nb/Zr)_N or Sm/Nd as well as isotopic ratios plotted as a function of latitude. The samples coming from the 14°N topographic high show new MORB SrNd isotopic characteristics which pictured in a classical mantle array diagram, put their representative points close to HIMU sources of ocean islands such as St. Helena, Tubuaïand Mangaia. The 14°N mantle source presents geochemical characteristics which indicate mantle differentiation processes and a mantle history that are more distinct than so far envisaged from typical MORB data. Pb data indicates that the 14°N mantle source cannot be the result of binary mixing between a depleted mantle and a HIMU-type source. Rather, the enriched endmember could itself be a mixture of Walvis-like and HIMU-like materials. The geochimical observations presented favour the model of an incipient ridge-centered plume, in agreement with [1].  相似文献