Dégradation des eaux de rejets issues d’une raffinerie d’huile de coton par plasma d’arc électrique rampant à pression atmosphérique

Wastewater samples from liquid effluents of cotton oil refinery in Far-Northern Cameroon were exposed to a gliding arc discharge for various exposure times in a cold plasma reactor. The analysed results showed high levels of organic pollution parameters (TOC = 4635 mg/L, COD = 6943, 98 mg/L) before treatment. More than 56% TOC and 75% COD abatement were obtained after 30 min treatment in batch conditions with a laboratory reactor. The resultant pollution abatement is attributed both to strong oxidizing effects of °OH and NO° radicals formed in the plasma and their derivatives (H₂O₂, ONO₂H and NO₃H). The conductivity and TDS increase linearly and the pH, TOC and COD decrease with increasing exposure time to the discharge. The oxidation obeys a pseudo first-order kinetics law (kinetic rate: k_1DCO = 0, 0381 min^?1 and k_1COT = 0, 0245 min^?1).     

Définition d'une typologie des dépôts de laves torrentielles et identification de critères granulométriques et géotechniques concernant les zones sources

The paper discusses viscous and saturated flows which can propagate at high velocity in torrent channels, referred to here as debris flows. Specific morphological, textural and sedimentological criteria have been identified, on which to distinguish debris flows from other torrent deposits. From a study of numerous debris flows sampled in 11 torrential catchment environments in the French Alps, two types of debris flows have been determined: those with a granular matrix and those with a cohesive matrix. Their typology is based mainly on the fraction of soil smaller than 20?mm although several discriminating particle size criteria have also been considered on the fraction between 20 and 200?μm. The author has selected five criteria for study, that relative to the fractions <50?μm being the most convenient. Geotechnical tests have also been used as a complementary criterion for this typology. The values of the Atterberg limits and blue methylene tests are generally lower for the debris flows with a granular matrix (Fig.?8a and Table?5). In most situations, the plasticity index of debris flow deposits is low. Both the soils sampled in the source areas and those mobilised as debris flows generally have particle size distributions and geotechnical characteristics similar to those of debris flow deposits reported in the literature. The paper concludes that source materials with a granular matrix are more likely to result in debris flows (as defined here) while the source materials with a higher fine fraction are more likely to move as mud flows.     

Caractéristiques des masses et marnes du gypse et de leurs faciès d'altération dans la région parisienne méthodologie des études géotechniques

The author presents the principal results of a research project concerning a geological formation widely represented in the natural region of Parisis, North of Paris, which is dreaded by geotechnicians: masses and interstratified marls of ludian gypsum. The impossibility of making ground observations essential to a thorough study of the phenomena of weathering of the gypsum, and notably its substitution, led to the work being undertaken along the following lines:

-Modelling of the geological infractructure of the gypseous slopes.

-The quest for indicators of the lithology and distribution of the residual masses and interstratified marls of gypsum, and the valuable role of diagraphs of natural radioactivity.

-The incidence of the weathering of the gypsum on the mechanical (pressiometric) characteristics of the gypseous areas.

-A methodology of geotechnical surveys on gypseous sites.

A progressive approach is proposed, beginning with a feasibility study, followed by a detailed study of the evolutive nature of the site, essential to the establishment of a suitably adapted project, and concluding with a mechanical characterisation necessary for the structural design of foundations.     

Caractérisation minéralogique et géotechnique des argiles marneuses gonflantes de la région de Médéa,Algérie

This paper presents the approach followed for the geological, mineralogical, and geotechnical characterization of swelling marly clays in the Médéa region. This investigation is conducted in order to estimate the swelling potential of this marly clay layer. The studied sites, located at about 80 km south of Algiers, Algeria, cover an area of approximatively 400 hectares. Five sites are considered. In the first step, the geological, tectonic, climatic, and hydrological contexts of the region are described. According to the geological map of Médéa, most of the formations encountered in the area are composed of Miocene layers represented by marly clays (Fig. 2). This region is characterized by its high and low temperature in summer and winter, respectively, and variable humidity (Fig. 3). In a second step, the results of geotechnical studies, X-ray diffraction tests, chemical analyses, and scanning electron microscope (SEM) observations are presented (Figs. 3, 4, 5, 6, 7, 8, 9). The soils contain quartz (20–26 %), calcium carbonates (11–55 %), kaolinite (8–13 %), illite (6–14 %) and Montmorillonite (18–26 %). The study of their microstructure by means of SEM indicates that these soils are formed by a compact marly clay matrix that is relatively homogeneous and oriented in the dip direction of bedding. A grain size analysis shows that the clay content varies between 17 and 70 %. The water content of all samples varies between 8 and 30 %. The values of the liquidity limit (LL) and plasticity index (PI) vary between 28–76 % and 16–36 % respectively, indicating a highly plastic soil; this is also confirmed by a specific surface varying between 99 and 179 m²/g. The dry density γ _d varies between 15 and 19 kN/m³. The swelling potential of the marly clay samples is evaluated firstly using various indirect methods. In literature, a number of empirical classifications are proposed by different authors (BRE 1980; Chen 1988; Komornik and David 1969; Seed et al. 1962; Snethen 1984; Vijayvergiya et Ghazzaly 1973 et Williams and Donaldson 1980). The swelling potential is related to certain physical properties of soils, such as consistency limits, clay content, methylene blue value, etc. In general, these methods indicate that all the tested soils have a high swelling potential, which confirms the results of mineralogical analysis. Secondly, direct measurements of swelling parameters are performed. Swelling tests are carried out using a standard slaved one-dimensional odometer using two methods: free swell and constant volume, according to standard ASTM D 4546-90 and AFNOR (1995). The swell pressure, the swell percentage and the swell index are given in Fig. 16. It is noted that the soils develop very significant swell pressures which vary between 25 and 900 kPa. This is in agreement with the results obtained by empirical methods. This investigation clearly shows that the marly clays of the Médéa region have a high swelling potential. Therefore, taking into account the phenomenon of soil swelling in structure design is essential.     

Traitements et analyse des mesures de diagraphies différées pour la reconnaissance géotechnique

Résumé Les diagraphies différées, essentiellement employées, à l'origine, dans le domaine pétrolier, sont de plus en plus utilisées en hydrogéologie pour la recherche d'aquifère et en reconnaissance géotechnique. En effet, les informations qu'elles apportent sur les caractéristiques physiques des sols et des roches, in situ, sont particulièrement riches. Cet apport est à deux échelles: l'échelle de l'unité lithologique et l'échelle de l'intercalation ou de la discontinuité dans cette unité. Toutefois, pour un apport d'information optimal, il convient de traiter les mesures diagraphiques. Nous montrons qu'une transformation de la structure des supports de mesure (volumes investis) des diagraphies différées permet d'obtenir, par rapport à une interprétation classique de ces mesures, une détermination plus précise des caractéristiques mesurées, un meilleur positionnement des limites de couches en profondeur et une meilleure estimation de la variabilité de la caractéristique mesurée. Nous montrons également que la définition verticale d'un outil de diagraphie peut être directement définie par le pas d'échantillonnage de la mesure le long du forage. La recherche d'un transfert d'information entre les mesures diagraphiques et les paramètres géotechniques de calculs permettrait aux diagraphies différées de devenir un complément indispensable aux forages destructifs dans toute reconnaissance géotechnique. Received: 11 May 1999 · Accepted: 27 November 1999     

Apport d’une base de données d’éboulements rocheux obtenue par scanner laser dans la caractérisation des conditions de rupture et processus associés

Using laser scanner data, an exhaustive rockfall database has been established for a rockwall located near the town of Grenoble (France). The study site is a long double cliff, on the eastern border of the Chartreuse Massif. The two cliffs consist respectively of thinly bedded and massive limestone, which show different structures, morphologies and rockfall activities. The 3D point clouds obtained by laser scanner allow to detect and model the fallen compartments in 3D. Information about cliff surface, and localization, dimensions, failure mechanism for each compartment were obtained and analyzed in order to characterize the morphological evolutions of the cliffs. It appears that the morphology and the slope of the lower cliff is related to fracturing and torrential erosion which occurs in the marls below the cliff, showing a rockfall frequency 22 times higher than for the upper cliff. These results show that the erosion process in the lower cliff is in a transient state, whereas it could be in a steady state in the upper cliff. Rockfalls have been dated by a near-continuous photographic survey (1 photo each 10 mn) and a monthly survey during 2.5 years. The analysis of the two data bases shows that the rockfall frequency is 7 times higher during freeze-thaw episodes than without meteorological event, and 4.5 times higher during rainfall episodes. Moreover, it becomes 26 times higher when the mean rainfall intensity is higher than 5 mm/h. Based on these results, a 3-level hazard scale has been proposed for hazard prediction.

     

Pompage d��une nappe libre recharg��e: solutions pour la charge hydraulique et le temps de transfert

Using the Dupuit assumptions, a new closed-form solution is established for steady-state pumping of an ideal unconfined aquifer that is recharged by infiltration. This new solution is complete for the two-part mathematical domain, which was not the case for previously partial solutions. A second new solution is then provided for the travel time of a non-reactive tracer to the pumping well, under steady-state conditions. The travel time integral has no known closed-form solution, but is easy to calculate, either numerically or using a simplified equation. The numerical calculation and the simplified equation give travel times very close to those obtained using finite element codes for saturated and unsaturated groundwater flow and particle tracking.     

Comportement à l’eau des roches argilo-marneuses, suivi du gonflement, importance de la minéralogie et des textures

In the presence of water, clayey-calcareous rocks display behaviours which are often significantly different. Through the study of four materials which are representative of the marly formations commonly met on the occasion of road construction, the authors show how this behaviour depend on the mineralogical and textural characteristics of rocks. After reminding the main mechanisms of swelling phenomena the authors characterize the selected materials on the one hand through the measured physical and physico-chemical parameters and on the second hand through the mineralogical and textural characteristics obtained from X-ray diffractometry and scanning electron microscopy. The materials are then studied firstly in “free swelling” conditions submitted to cycles and secondly in “stress swelling” conditions. These studies lead to the determination of their swelling capacity and of resulting swelling pressures. Afterwards, the materials are examined from the textural point of view. The study with the help of the S.E.M. allowed to point out:

—the evolution of textures and their role in the initiation of the changes which affected the materials.

—the role of minor minerals such as pyrite, which contribute after oxidation to the degradation of clayey minerals and consequently to the evolution of textures which finally lead to a decay of mechanical characteristics.

     

Les formations plio-quaternaires de la région de Casablanca (Maroc): aspects sédimentologique et géotechnique

The Plio-Quaternary formations of the Casablanca area consist of a sequence of cross-bedded strata. They frequently begin with a lumachelle conglomerate occasionally associated with gravels and marine calcarenite. The marine deposits are overlain by yellow and grey dune sandstones, locally oxidized at depositional horizons. These dunal calcarenites have been extensively exploited and hence their sedimentological and geotechnical parameters have been determined from numerous samples taken from the quarries in the region. The sedimentological study results show that these generally homogeneous materials consist mainly of well-graded fine to coarse carbonate sands (98%) containing both bioclasts and calcareous cements. It is clear that at the time of deposition there was little detrital material, with the marine deposits formed mainly of shell debris. Study shows that the marine deposits underwent early lithification in a shallow marine environment which then continued in a continental environment by the movement of meteoric water. The marine deposits are well cemented. They have a low degree of dissolution but quite a high degree of recrystallization, notably towards the bottom of the individual horizons. The dunal deposits which underwent lithification in a continental environment are characterized by a very low cementation, mainly at point contact, a high dissolution and a weak recrystallization. The difference in diagenesis affects both the physical and mechanical features of these Plio-Quaternary calcarenites. From a geotechnical point of view, the consolidated marine and dunal deposits have a weak to medium compressive strength (502), a very weak resistance to shocks (453. 8.?Density and percentage CaCO₃. 9.?Compression resistance and percentage CaCO₃. In view of the graph relationships, it is possible to estimate the other parameters from the determination of a single physical or mechanical feature of the calcarenite. However, the sedimentological and petrographical analyses show that the following factors can be subject to quantitative variations: (1) the carbonate content; (2) the nature of the bioclastic elements; (3) the grain size of the detrital elements; (4) the cement percentage and its grain size; and (5) the importance of dissolution and the vacuum percentage. These factors control the physical and mechanical features of the Plio-Quaternary formations of the Casablanca area. As a consequence, it is suggested that when considering the sedimentological features and physical and mechanical characteristics of the Plio-Quaternary formations of the Casablanca area, the particular deposits must first be categorized into one of the four following facies: lumachelle; marine calcarenite; yellowish dunal calcarenite; or grey dunal calcarenite.     

Essais d’altération chimique accélérée au laboratoire par le double extracteur Soxhlet. Application à des roches granitiques de Corée du Sud

A double Soxhlet extractor was used in the laboratory to perform accelerated chemical weathering tests in order to simulate the leaching of granitic rocks under tropical climate. Several types of granitic rocks corresponding to various initial weathering grades were sampled on two test sites in South Korea. They were subjected to leaching with hot and pure water in the double soxhlet extractor in order to measure the evolution of some of their physical and mechanical properties. Tests showed a decrease of the physical characteristics, more particularly the P-wave velocity and quick water absorption ratio. This decrease mainly occurred during the first leaching cycles. Uniaxial compressive strength also decreased during the leaching test, and the fresher the granitic rock, the most important the UCS decrease. This kind of test allows the evaluation of the chemical weathering effects and also the estimation of the long-term mechanical properties of the rock.     

Instabilités gravitaires dans la région de Béjaïa (Algérie): Inventaire et appréciation de l’importance relative des différents paramètres conduisant au déclenchement,au maintien ou à l’activation des instabilités

Bulletin of Engineering Geology and the Environment - This article contributes to the analysis of the various factors that interact in triggering and reactivating of landslides in Béjaïa...     

Étude Rétro-analytique du glissement du bord Nord de la mine à ciel ouvert de Kef Essenoun (Djebel Onk), Algérie

On September 8th 2007, a few minutes before sunrise, a spectacular event occurred in the phosphate kef Essenoun open pit mine related to the mining field of Jebel Onk, located in Northeastern part of Algeria. It is a major landslide by volume (7–8 million m³) which had completely filled the pit of the mine and led to the temporary cessation of mining work over an extended period. This paper, presents a retro-analysis of this phenomenon for which, we draw the morphological, geological, hydro-geological and geotechnical characteristics of the deposit and the principal factors liable to be the triggering factors of this landslide.     

Diversité floristique des mares temporaires de la région d’Annaba (Nord-Est Algérien)

Nine wetlands in Annaba region (North East of Algeria) were the subject of floristic inventories during three years (2014–2016). We have revealed the presence of five types of temporary ponds in which Ranunculus aquatilis L is dominant. The studied flora is rich and diversified. It comprises 190 species and 143 genera belonging to 58 botanical families. These species were either strictly subservient to humid zones or transgressive from terrestrial environments. This flora is characterized by a big proportion of rare and / or threatened taxa (11.05%). The composition of global biological spectra shows the dominance of therophytes, with 99 taxa (52.11%). The majority of the listed species belong to the Mediterranean phytochronic species. Eighteen taxa belonged to the endemic category. The preservation of this exceptional biodiversity, threatened in the short term, urgently requires phytoecological studies and relevant protection measures.