Search

The closure and shear behaviors of 3D self-affine rock joints are simulated by the Discrete Element Method using PFC3D. First, a methodology to produce rough self-affine rock joints using DEM is presented then eight self-affine rough joints, having low and high values of roughness exponent, self-affine correlation length, and height variance, are considered. After the calibration of the elastic and fracture behaviors of an elementary volume formed from spherical discrete elements bonded by elastic beams, the numerical rock joints are submitted to closure tests at 14 and 21 MPa followed by a shear test at constant velocity and under constant normal load. Each DEM joint is tested using three different mechanical models: rigid, ideally elastic and elastic-fracturing. The use of these three models allows highlighting the distinct influences of the morphology, the joint stiffness and the micro-fracturing on the closure and shear behaviors of the joints. [ABSTRACT FROM AUTHOR]

A global modelling approach for estimating the climate influence on corrosion activity in reinforced concrete is developed. It combines: (a) the identification of statistical properties of climates in various temperate regions, and the development of a synthetic simulator able to reproduce its dominant patterns, (b) the identification of an empirical corrosion activity model, based on the analysis of experimental data, highlighting the respective influence of temperature and humidity. Synthetic simulations combining these two models are carried out. They show the complexity of the interactions, since the influence of temperature and humidity may be adverse, and the interest to describe both random fluctuations at daily scale and at seasonal scale. They confirm that monitoring of corrosion must account for this time variability and propose a way to estimate average corrosion even with measurements which would remain limited to a short period. Synthetic simulations are also used for estimating the influence of a global warming scenario on the corrosion activity. A global increase of about 38% of corrosion activity has been estimated in response to an average temperature elevation of 3°C. [ABSTRACT FROM AUTHOR]

We demonstrated a simple methodology for the reinterpretaion of sets of electrical vertical soundings and the production of 2D resistivity models. The method is applied to the northern central part of the subsiding Saiss basin (Morocco) where a series of vertical electrical soundings (VES) were acquired in 1982 and 1984, using the Schlumberger array with current electrodes semispacings between 3 and 3000 m. We describe a methodology used to estimate and sample apparent resistivities collected from traditional single soundings acquired by using a Schlumberger configuration. We then construe! a resistivity pseudosec-tion in a format compatible with a Wenner-Schlumberger array to perform 2D electrical tomography. The methodology takes into account the lateral and vertical spatial correlations shown by the apparent resistivities. The tomographic inversions are performed using a commercial inversion software commonly used in industry. Geostatistical tools are used to quantify the spatial correlation between apparent resistivity data. The resuli is a series of estimated pseudosections that are inverted to produce 2D resistivity models of the basin along geophysical profiles. We focus our attention on one of these profiles (i.e.. one 2D resistivity model). The inverted geoelectrical model allows us to propose a geologic model of the basin. Our methodology allows historical and current data carried out using the Schlumberger configuration, to be rapidly reinterpreted in countries where only low-cost methods, such as VES soundings, can be used due to technology and economic constraints. It can also be applied to cases where continuous or pulled-array continuous vertical soundings method, where a tail of electrodes is towed behind a small vehicle while continuously and simultaneously measuring several electrode configurations, is inoperative clue lo field conditions (survey length, deep layers, and local environmental conditions). [ABSTRACT FROM AUTHOR]

The Riou Mort River watershed (SW France), representative of a heavily polluted, small, heterogeneous watershed, represents a major source for the polymetallic pollution of the Lot-Garonne-Gironde fluvial-estuarine system due to former mining and ore-treatment activities. In order to assess spatial distribution of the metal/metalloid contamination in the watershed, a high resolution hydrological and geochemical monitoring were performed during one year at four permanent observation stations. Additionally, thirty-five stream sediment samples were collected at representative key sites and analyzed for metal/metalloid (Cd, Zn, Cu, Pb, As, Sb, Mo, V, Cr, Co, Ni, Th, U and Hg) concentrations. The particulate concentrations in water and stream sediments show high spatial differences for most of the studied elements suggesting strong anthropogenic and/or lithogenic influences; for stream sediments, the sequence of the highest variability, ranging from 100% to 300%, is the following: Mo < Cu < Hg < As < Sb < Cd < Zn < Pb. Multidimensional statistical analyses combined with metal/metalloid maps generated by GIS tool were used to establish relationships between elements, to identify metal/metalloid sources and localize geochemical anomalies attributed to local geochemical background, urban and industrial activities. Finally, this study presents an approach to assess anthropogenic trace metal inputs within this watershed by combining lithology-dependent geochemical background values, metal/metalloid concentrations in stream sediments and mass balances of element fluxes at four key sites. The strongest anthropogenic contributions to particulate element fluxes are 90-95% for Cd, Zn and Hg in downstream sub-catchments. The localisation of anthropogenic metal/metalloid sources in restricted areas offers a great opportunity to further significantly reduce metal emissions and restore the Lot-Garonne-Gironde fluvial-estuarine ecosystem.