A model of capillary cohesion for numerical simulations of 3D polydisperse granular media

We present a 3D discrete‐element approach for numerical investigation of wet granular media. This approach relies on the basic laws of contact and Coulomb friction enriched by a capillary force law between particles. We show that the latter can be expressed as a simple explicit function of the gap and volume of the liquid bridge connecting a pair of spherical particles. The length scales involved in this expression are analyzed by comparing with direct integration of the Laplace–Young equation. We illustrate and validate this approach by application to direct shear and simple compression loadings. The shear and compression strengths obtained from simulations reproduce well the experimental measurements under similar material and boundary conditions. Our findings clearly show that the number density of liquid bonds in the bulk is a decisive parameter for the overall cohesion of wet granular materials. A homogeneous distribution of the liquid within the bridge debonding distance, even at low volume contents, leads to the highest cohesion. The latter is independent of the liquid content as far as the liquid remains in the pendular state and the number density of liquid bonds remains constant. Copyright © 2007 John Wiley & Sons, Ltd.     

Fluoride contents in groundwaters and the main consumed foods (dates and tea) in Southern Algeria region

In the Algeria South, the dental fluorosis is a “silent” epidemic spreading within the populations. The present study was aimed to determine the fluoride content in water, dates and tea that are widely consumed. The results reveal that 35% of water wells had excessive fluoride levels (>1.5 mg/L). The eastern areas where dental decay is the most widespread pathology present the highest contents. Dates, tea and water are considerable sources of fluoride, with a daily contribution of 10, 20 and up to 70%, respectively. For these three sources, the daily intake of fluoride ingested by an adult exceeds the proposed safe threshold of 0.05–0.07 mg/kg day.     

Modeling the attenuated total reflectance infrared (ATR-FTIR) spectrum of apatite

Attenuated total reflectance (ATR) infrared spectra were measured on a synthetic and a natural fluorapatite sample. A modeling approach based on the computation of the Fresnel reflection coefficient between the ATR crystal and the powder sample was used to analyze the line shape of the spectra. The dielectric properties of the samples were related to those of pure fluorapatite using an effective medium approach, based on Maxwell–Garnett and Bruggeman models. The Bruggeman effective medium model leads to a very good agreement with the experimental data recorded on the synthetic fluorapatite sample. The poorer agreement observed on the natural sample suggests a more significant heterogeneity of the sample at a characteristic length scale larger than the mid-infrared characteristic wavelength, i.e., about 10 micrometers. The results demonstrate the prominent role of macroscopic electrostatic effects over fine details of the microscopic structure in determining the line shape of strong ATR bands.     

Seismicity of Morocco for the Period 1987–1994

— A seismic data file of 3,740 earthquakes from January 1987 to December 1994 has been elaborated for Morocco and the border regions, with 10 main events registering magnitudes from 5 to 5.6. Such seismicity is particularly important for Morocco as the released seismic energy constitutes a considerable part of the total energy radiated during the 20th century. Relative seismicity maps confirm the persistence of the major features of the seismicity of Morocco. An important seismic activity is observed in the Alboran region continental crust, which absorbs the maximum deformation resulting from the convergence of the African and Iberian plates. However, in the longitude window 3.5°– 6° W at depths of 25 to 50 km, a seismic gap zone seems to take place. An explanation of this phenomenon may be provided by the slab breakoff model. Even if the seismicity of Morocco remains moderate, heavy damage is observed when the magnitude of earthquakes exceeds 4.5, especially in the case of traditional buildings.     

Investigation of active faults in Morocco using morphometric methods and drainage pattern analysis

A survey has been done of recently active faults in Morocco. In addition to field observations, morphometric methods were applied and an analysis was made of the drainage pattern. In the morphometric analysis, a map of vertical deformation was established from the elevations of summit level surfaces. This enables the recognition of neotectonic discontinuities and lithological contrasts; the actual discrimination of different rock-types can only be achieved by comparison with field observations. The analysis of drainage patterns — including their perturbations and anomalies — can also reveal the presence of features due to neotectonics, structural control or lithological variation. Certain faults can be detected which correspond to structures known from field geology or remote sensing (NE-SW and NW-SE oriented sets). Some new faults are observed which belong to these sets, as well as others which define a new N-S trending set. The present analysis leads to a distinction between ancient faults and currently active faults. The results of this study are shown on a map of recently active faults where the respective vertical displacements are also indicated.

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Zusammenfassung Bei einer Untersuchung der heute aktiven Störungen in Marokko wurden zusätzlich zu Feldbeobachtungen morphometrische Untersuchungen sowie eine Analyse des Entwässerungsnetzes durchgeführt. Bei der morphometrischen Analyse wurde eine Karte der vertikalen Deformationen von Aufragungen aus den Gipfelfluren abgeleitet. Dadurch können neotektonische Diskontinuitäten sowie lithologische Kontraste erkannt werden; die wirkliche Unterscheidung verschiedener Gesteinstypen kann aber nur im Vergleich mit Feldbeobachtungen erreicht werden. Die Analyse des Gewässernetzes — auch seiner Komplikationen und Anomalien — kann gleichfalls Elemente aufdecken, welche neotektonischen Ursprungs bzw. strukturell bedingt oder aber auf lithologische Unterschiede zurückzuführen sind. Bestimmte Störungen korrespondieren mit Strukturen, die aus der Feldgeologie oder der Fernerkundung bekannt sind (NE/ SW- und NW/SE-gerichtete Scharen). Einige neu entdeckte Störungen gehören zu diesen Scharen, während andere ein neues, N/S-streichendes System deutlich machen. Die vorgelegte Analyse erlaubt, zwischen älteren und noch heute aktiven Störungen zu unterscheiden. Unsere Ergebnisse sind in einer Karte der aktiven Störungen zusammengefaßt, in die die vertikalen Versätze gleichfalls eingetragen wurden.

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Résumé Un recensement des failles à jeu récent (néotectonique) a été fait sur l'ensemble du Maroc. Outre les observations de terrain, les méthodes de la morphométrie et celles de l'analyse du réseau hydrographique sont appliquées. En morphométrie, l'établissement d'une carte de la déformation verticale d'après la situation altimétrique de la surface sommitale permet la reconnaisance de structures (discontinuités) néotectoniques et d'alternances lithologiques (la discrimination ne peut être faite que sur le terrain). De même l'analyse du réseau hydrographique, de ses perturbations et de ses anomalies (cf. infra) met en évidence des discontinuités dues à la néotectonique, à la structure des terrains et à la lithologie. Les ensembles morphostructuraux marocains (Meseta, Rif, Atlas), ressortent nettement de la carte de synthèse. On y retrouve les failles connues par la géologie de terrain et par l'analyse des images satellitaires (ensembles de direction NE-SW et NW-SE), de nouvelles failles appartenant à ces deux familles, ainsi qu'un nouvel ensemble de failles de direction N-S. Cette analyse permet de distinguer failles actives et failles anciennes. Les résultats sont portés sur la carte des principales failles à jeu récent avec leurs rejets verticaux respectifs.

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Spatial distribution of stream sediment pollution by toxic trace elements at Tourtit and Ichoumellal abandoned mining areas (central Morocco)

This study presents a diagnostic of the current state of 114 stream sediment samples by their elemental concentrations (Sb, Cd, Pb, As, Cu, Zn, Ni, Cr, and Hg), collected from Ighardayane upstream on an area of 15 km² located at the SE part of central Morocco where Tourtit and Ichoumellal, two abandoned mining sites of Stibnite, are located. Several approaches were used to model the analysis (i) enrichment factor (EF), (ii) sediment pollution index (IPS), (iii) probable effect concentration-quotients (PEC-Qs), and (iv) potential ecological risk index (PERI). Results show highly contaminated areas around the old mining sites by Sb As, Pb, and Cd. Cadmium and lead show 86.9 and 12.29% (respectively) of trace element pollution according to sediment pollution index. Twenty-eight percent of the sampled area is potentially highly toxic because of the presence of Hg, Pb, and Cd. The very similar distribution of pollution and toxicity of most analyzed trace elements may originate from the same source, which corresponds to mining wastes where we recorded the highest pollution and toxicity degrees. This environmental issue represents the combination of Tourtit and Ichoumellal anthropic sources responsible of Sb, As, Pb, and Cd release and a probable natural source of Hg “that needs a further study,” which contribute in the degradation of an aquatic ecosystem of the same area. Therefore, both ecotoxicological analysis and stream sediment quality management should be carried out to control this aquatic ecosystem toxication.     

Geochemical characterization of the salinity of irrigated soils in arid regions (Biskra,SE Algeria)

Acta Geochimica - The agriculture in Biskra, southeastern Algeria, is based on traditional practices and characterized by small irrigated fields. In the last decades, the increasing demand in water...     

Estimation of aboveground biomass and carbon in a tropical rain forest in Gabon using remote sensing and GPS data

The knowledge of biomass stocks in tropical forests is critical for climate change and ecosystem services studies. This research was conducted in a tropical rain forest located near the city of Libreville (the capital of Gabon), in the Akanda Peninsula. The forest cover was stratified in terms of mature, secondary and mangrove forests using Landsat-ETM data. A field inventory was conducted to measure the required basic forest parameters and estimate the aboveground biomass (AGB) and carbon over the different forest classes. The Shuttle Radar Topography Mission (SRTM) data were used in combination with ground-based GPS measurements to derive forest heights. Finally, the relationships between the estimated heights and AGB were established and validated. Highest biomass stocks were found in the mature stands (223 ± 37 MgC/ha), followed by the secondary forests (116 ± 17 MgC/ha) and finally the mangrove forests (36 ± 19 MgC/ha). Strong relationships were found between AGB and forest heights (R² > 0.85).