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.

     

Le Pont Vasco de Gama – la démarche durabilité

From the concrete example of a large construction, this paper aims to show how the results obtained from the research work carried out on transfer in cement pastes were applied both on site during the concrete construction and in the laboratory to predict the durability of the concrete structure. This unique process, carried out in close collaboration with the constructor, is based on a new concept of High Performance Concrete. The construction concerned is the Vasco da Gama Bridge in Lisbon, which is one of the most important bridges ever constructed in Europe: it is more than 17?km long, built in the maritime zone on the Tagus river estuary. It was opened in April 1998. A guarantee of life duration of 120?years, without major maintenance, has been demanded. In addition to the criteria relative to the concrete constituents (non-reactive aggregates with regard to the alkalireaction, the nature of the cement and a formulation adapted to the direct environmental effects on the different construction parts), one of the main life duration criteria selected is a chloride concentration limit value of 0.4%, compared to the mass of the cement, measured directly at the reinforcement steel position. This value determines the initiation threshold of the corrosion process of steel. Specifications are both a diffusivity coefficient of chloride of less than 1×10^–12?m²?s^–1 determined by the TANG Luping method and an oxygen permeability of less than 1×10^–17?m². These basic criteria have been perfected by measures of porosity to water, tests of resistance to chloride penetration, chloride migration tests and also by extensive examinations of the concrete microstructure. All the measurements and tests have been undertaken both on concrete samples made in the laboratory and on samples made on site and concrete cores from parts of the structure built in 1995. Coefficients of chloride diffusivity measured or calculated from profiles of concentration in concrete cores have been used in a predictive model, using a finite element method integrating the interaction ions with cement paste and the evolution of the diffusivity coefficient in time. The various computing simulations, improved progressively with controls and after comparison with the real bridge, tend to confirm, on the one hand, the validity of the model used and, on the other hand, the accuracy of the chosen formulations. These formulations, having mechanical properties close to those of High Performance Concrete, also have special microstructural properties of diffusivity and permeability, answering the requirements of the durability of this bridge.     

Différentes déclinaisons de l'aléa liquéfaction: de la cartographie préventive au projet

As part of its Public Service, Applied Research, and Client Service activities, BRGM's Thematic Centre for Natural Geological Risks (NGR) has recently undertaken studies in order to characterize "liquefaction hazard". The paper considers definitions and presents several approaches to liquefaction hazard assessment, demonstrated by several examples. The first approach is a naturalistic one: Hazard assessment is considered in a structured manner by undertaking: – a regional inventory of historic events – mapping of formations susceptible to liquefaction in homogeneous risk areas subject to seimic activity – preventive mapping of the phenomena at local scale The second approach is a semi-deterministic one: It allows to produce a seismic microzonation, considering parametric calculations and charts (Seed's reverse method). This approach can be used also to recommend soil improvements when liquefaction hazard does exist. The third approach is a deterministic approach: It takes into account a 3D geotechnical model of the analysed area, as well as specific charts to produce a liquefaction hazard assessment of soils and an advanced seismic microzonation. This method was used in Guadeloupe and Martinique districts (French Lesser Antilles) ad for the design of a new TGV railway track in the south of France. The proposed methodology relies on the French Association for Earthquake Engineering recommendations and brings some innovative aspects: combined naturalistic and geotechnical analyses for liquefaction hazard assessment, combined chart use and 3D geotechnical modelling for liquefaction hazard microzonation. Apart from the complete analysis of the liquefaction hazard not always being useful, it also demands major resources, and is consequently sometimes broken down into several less-detailed stages. The various examples considered thus form a continuum and are simply variations of a same definition of the liquefaction hazard: where: X, Y and Z=coordinates t=time Δu=interstitial over-pressure σ'_vo=initial effective stress I_L=Iwasaki's liquefaction index     

Erosion d’une vase de l’estuaire de la Loire sous l’action du courant

This research work deals with an experimental study on the erosion phenomenon of a mud under the action of a water current. It is observed from research works carried out by Partheniades (J Hydraul Div ASCE 91(HY1):105–139, 1965), Migniot (La Houille Blanche 1&2:11–29, 95–111, 1989), Ockenden and Delo (GeoMar Lett 11:138–142, 1991), Aberle et al. (Mar Geol 207:83–93, 2004), among others, that mud erosion process by an hydrodynamic action depends mainly on sediment properties. Based on a literature study, this critical stress is assumed to be proportional either to the effective cohesion (Eq. 2) or to the yield stress (Eq. 4) of the sediment bed. Six erosion test series have been performed at six different concentrations of a mud from the Loire estuary. Some properties of the tested sediments are: a solid particles density ρ _s = 2,550 kg m^?3, a liquidity and plasticity limit at 140 and 70% of the water content, respectively, a mean size of the dispersed mineral fraction determined by laser techniques of 10 μm, and a volatile matters content of 11.86% by total dry weight burned at 550°C. As the rheological behaviour is difficult to describe, the sediment strength is characterized by only a parameter, namely, the yield stress τ _y . It is measured with a coaxial cylinder Brookfield LVT viscosimeter following a defined procedure (Hosseini in Liaison entre la rigidité initiale et la cohésion non drainée dans les vases molles—Relation avec la dynamique sédimentaire. Thèse, Université de Nantes, 167 p, 1999). For each studied concentration, three successive erosion tests are carried out, and for every erosion test, 15 successive measurements of τ _y are made. The mean values and the standard deviations of τ _y are shown in Table 1 as a function of the bed sediment concentration C. A confined flume has been conceived and built to characterize the erosion rates. With this device, a current-induced shear stress is generated above an homogeneous deposited sediment (Fig. 1). The bed shear stress τ _o is calculated from the measured mean velocity V by Eq. 5. The friction coefficient c _f involved in Eq. 5 has been evaluated from measurements of the hydraulic pressure loss. Finally, the validity of Eq. 5 has been confirmed by five calibration tests on the incipient of the movement of sands for which results are compared with Shields diagram in Fig. 2. The observed erosion mechanisms affecting cohesive sediments depend mainly on the value of the yield stress. For a fluid mud (τ _y less than 3 N m^?2), the bed shear stress produces at first a wavy motion on the bed surface with a progressive undulation. When the shear stress increases, resuspension produces a diluted sediment cloud which is entrained and dispersed by the flow. For a plastic mud (τ _y greater than 3 N m^?2), erosion occurs by a wrenching of aggregates which are transported near the bottom. Initially, the eroded aggregates measure several millimetres in size; but, once transported, aggregates break into very rigid and compact aggregates of maximum size close to 1 mm in all the cases. During erosion tests, erosion volumetric rates E _v have been evaluated under steady-state bed shear stress τ _o from the observed variation in time of suspended sediment concentration. A generalized erosion is assumed for E _v ≥ E _vo = 3 × 10^?7 m s^?1 (that is the equivalent of 1 mm sediment layer eroded per hour). The generalized erosion occurs above a critical bed shear stress τ _oe which is linked to τ _y and mud density through Eq. 7. A phenomenological law defined by Eq. 8 is proposed to calculate the erosion rate as a function of yield stress and hydrodynamic shear stress at the bottom. For τ _o < τ _oe , a small erosion is observed, which is described by a formulation given by Cerco et al. (Water quality model of Florida Bay. U.S. Army Engineer Research and Development Center, ERDC/EL TR?00-10, Vicksburg, USA, 260 p, 2000). Above τ _oe , a small increase in τ _o produces an important erosion rate rise which is described by a formulation suggested by Mehta and Partheniades (Resuspension of deposited cohesive sediment beds. In: Proceedings of the 18th coastal engineering conference, Cape Town, South Africa, 2:1569–1588, 1982). Figure 3 shows as a function of τ _o the observed values of E _v (discrete symbols) as well as the proposed model (in solid lines) for the six concentrations. For the theoretically maximum value of E _v , the hydrodynamic shear stress is very high with regard to the sediment cohesion; and then, the water flux produces an entrainment of underlying fluid mud layers. The asymptotic law obtained from the model of Kranenburg and Winterwerp (1997) plotted in dashed lines in Fig. 3, is expressed by E _v = 0.3 u _* . A sediment trap inserted in the experimental system allows a sample of eroded mud aggregates to be obtained. It is observed that the maximum value of the diameter D _M of the eroded aggregates depends on the density and yield stress of the initially deposited mud according to Eq. 10. In the same way, the density of the aggregates issued from plastic mud erosion is measured following an original experimental method and procedure (Table 3). The erosion of plastic muds with a concentration from 310 to 420 kg m^?3 produces aggregates with a concentration close to 400 kg m^?3 and yield stress a little greater than 100 N m^?2.     

Impact d’une galerie étanche peu profonde sur l’écoulement d’une nappe

While many studies have been achieved on the interactions between groundwater and deep tunnels, in order to identify the evolution of pore pressure around the structure and to characterize the flow to its leaky parts, few studies have dealt with the impact of the carrying out of an impervious gallery in a shallow aquifer. The induced change in the piezometric level of the aquifer and the one in the hydraulic gradient of the flow however can, in this case, have significant consequences, in particular when the linear structure is located in an urban environment. This paper investigates, in steady state, the case of a straight tunnel having a horizontal axis perpendicular to the direction of the regional groundwater flow and a circular or square cross section. The aim is to determine the additional lost head Δh _s due to the tunnel (i.e. additional to that resulting from the regional flow, supposed to be uniform with a hydraulic gradient i ₀). In the context of a horizontal confined aquifer having a thickness 2B and of a tunnel of radius R located in the middle part of the aquifer, an analogy can be established with the flow above a hydraulic threshold resulting from a local rise of the elevation of the base of an aquifer, having a thickness B, on a width 2R and with a vertical maximum amplitude R. When neglecting the vertical component of the hydraulic gradient compared to its horizontal component, analytical solutions are developed for various hydraulic threshold shapes (rectangular, triangular and circular), based on the equivalence with a local change in the transmissivity of an aquifer keeping a constant thickness. The corresponding formulas take the form: $ {\frac{{\Updelta h_{s} - \Updelta h_{0} }}{{\Updelta h_{0} }}} = f(a) $ , with $ a = {\frac{R}{B}} $ and Δh ₀ = 2Ri ₀. The use of these formulas shows that the additional lost head Δh _s due to the hydraulic threshold is proportional to i ₀ and that, for values of the ratio a < 0.5, the change in the piezometric surface is small. These conclusions are therefore limited by the fact that the vertical conductivity is supposed to be very large. In order to remove this hypothesis, numerical simulations are achieved using the MODFLOW code. It is considered a confined aquifer of length 2L = 110 m and thickness B = 10 m, a ratio $ a = {\frac{R}{B}} = 0.25 $ and a horizontal hydraulic conductivity $ K_{H} = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . In the case of an isotropic medium ( $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} = 1 $ ), the simulations allow to check the linearity of the relationship between Δh _s and i ₀, with therefore a homogeneous variation in the proportionality coefficient compared to analytical solutions. Simulations also reveal that, in the case considered, the width of influence upstream and downstream L _i , corresponding to a value of the vertical component of the hydraulic gradient <1% of i ₀, is below 5.5R for the three hydraulic threshold shapes, and that it was few influenced by the hydraulic gradient i ₀. In the case of an anisotropy of the horizontal and vertical hydraulic conductivities, simulations reveal the significant importance of the anisotropy ratio $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} $ when it is more than 1, the most common case, and indicate that the proposed analytical solutions give an asymptotic value of $ {\frac{{\Updelta h_{s} }}{{\Updelta h_{0} }}} $ for the isotropic case and for the values of the component α < 1. In the context of an unconfined aquifer, the hydraulic threshold model is not directly applicable. The model studied, using the Dupuit-Forchheimer assumption, is the one of a water table aquifer with a sloped base (slope value: p ₀). The simulations focus on an aquifer of length 2L = 85 m, with a tunnel of circular cross section having a diameter 2R = 5 m, bottom of which is located 5 m above the base of the aquifer, the isotropic hydraulic conductivity being equal to $ K = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . The definitions of water heights d ₀ and d between the water table and the top of the tunnel are given in Fig. 7. The water table can be located above (fully submerged tunnel) or below (partially emerged tunnel) the top of the tunnel. The difference d ₀ ? d represents the half of the additional lost head Δh _s due to the tunnel. Simulations are performed for various values of p ₀ and d ₀. They provide the values of i ₀, d and Δh _s . In the case of a fully submerged tunnel (d > 0), a significant rise of the water table upstream of the tunnel is obtained only for high values of the hydraulic gradient (5 and 10%), but, even in this case, it remains less than the tenth of the wetted height of the aquifer h _m . It is also highlighted that the ratio $ {\frac{{\Updelta h_{s} }}{{i_{0} }}} $ varies as a linear function of (R + d) and that, in the studied case, there is no influence of the tunnel for d ≥ 4R. In the case of a partially emerged tunnel (d < 0), the aquifer is locally confined under the tunnel. It is suggested that an equivalence is possible with the case of a confined aquifer having a thickness equal to the wetted height in the unconfined aquifer. This is verified with one of the simulations. In the case of a partially emerged tunnel, the change in the water table due to the tunnel remains low.     

Technologie de Traitement de la Fondation pour l’Exécution des Ponts de l’Autoroute

Sommaire: Le présent texte se concentre principalement sur la recherche des problèmes relatifs à la fondation des ponts de l’autoroute, qui a pour objet d’améliorer la technologie de traitement de la f...     

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.     

Contribution à l’étude du mouvement de terrain de la ville de Tigzirt (Algérie)

This article is a contribution to the study of the causes, characterization, and numerical modeling, using finite elements, of the landslide affecting the coastal slope at the edge of the Mediterranean Sea near the city center of Tigzirt (Algeria). This slope is characterized by a relatively low inclination (13°–15°) and composed of two main geological formations (marly bedrock overlain by recent Quaternary deposits). Several factors have acted jointly and explain the activity of Tigzirt landslide: it is the effect of geological, morphological, and hydrogeological site contexts combined to triggering factors of various origins (human, climatic, and seismic). The landslide is characterized by a planar failure surface, which involves a global translational deformation towards the sea.     

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.     

Essais systématiques de validation de formulations de sable sénégalais pour l'élaboration d'un sable normalisé

Résumé. Au Sénégal, pays en voie de développement, le sable normalisé employé pour la détermination des classes de résistance des ciments est importé. Un inventaire des ressources locales en sable a été conduit pour rechercher un produit de substitution au sable de Leucate. La première phase de l'étude a permis sur la base d'essais d'orientation, de mettre au point un mélange ternaire composé de deux sables roulés et d'un sable de concassage qui remplit les critères requis pour un "sable normalisé CEN". Dans la deuxième phase de l'étude, des essais systématiques croisés ont été menés à Rennes et à Dakar, ils confirment les résultats des essais d'orientation et les valident d'un point de vue statistique. Electronic Publication     

Impact de la décharge publique de Marrakech (Maroc) sur les ressources en eau

Résumé. Les lixiviats de la décharge publique de Marrakech, qui ne sont ni collectés ni traités, pourraient constituer une source potentielle de pollution des eaux de la nappe phréatique et de celles de l'oued Tensift situé près de la décharge. Le but de cette étude est de caractériser ces lixiviats et de déterminer le degré de pollution des eaux à proximité de la décharge. Les analyses physico-chimiques des lixiviats ont montré qu'ils présentent des concentrations élevées en Cl^–, HCO₃ ^–, Na⁺, K⁺, SO₄ ^2–, Ca²⁺, Mg²⁺, NH₄ ⁺, Cu et Pb. La pollution organique est également importante; la DCO peut atteindre 138.000 mg/l O₂. Les concentrations en certains polluants sont nettement supérieures à celles généralement rencontrées dans d'autres décharges d'ordures ménagères. Le suivi de la qualité des eaux durant l'année 1999, a montré que les eaux souterraines et celles de l'oued Tensift sont de mauvaise qualité pour les besoins domestiques et pour l'irrigation. L'Analyse en Composantes Principales a montré que la pollution des eaux, par les lixiviats, est essentiellement due à la matière organique, HCO₃ ^–, NH₄ ⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^– et SO₄ ^2–. Electronic Publication     

Un détail de ce qui change: Function of a Function

Why should computation be leading to a bifurcation in architectural detailing, resulting in a simultaneous, and opposing, tendency towards either greater precision in fabrication or increasing plasticity? Architectural designer and theorist Peter Macapia asks what is driving these propensities in computation, and what in turn historically might be the relation between the detail and force. What comes into play now, though, when architectural style is no longer identified by a taxonomy of parts, or a vocabulary of orders, but rather by a network of forces and functions correlating actions? How might economic and political power be interacting with force, the diagram and function in contemporary design?     

Les dépôts morainiques holocènes de la zone axiale pyrénéenne: approche déterministe de leur instabilitéà Verdun sur Ariège, (Pyrénées centrales, France)

This paper reports a study of the historic instability of the till deposits in an area of the central Pyrenees between France and Spain upslope of the town of Verdun. The object of the work was to create a model based on the geomorphological and geological mapping of landslides and a geotechnical survey of the instability of the whole of the mountainous slopes of the Domanial Verdun area. The detailed mapping allows the historic landslides to be distinguished from the more recent/active movements which involve volumes of 100,000 to 400,000?m³ of material. In addition, it was possible to assess the areal percentage of the actively slipping zones (5%) compared to the historic slide zones (12%) and the stable areas (78%). Following the European classification, two types of slides were identified in the Verdun study area: (1) historic rotational slides and (2) active translational slides located in the Verdun area at between 1000 and 1250?m altitude. The stability was calculated using the classic "method of slices", subdividing the slipped zone into vertical slices along a suitable cross section. The so-called factor of safety (F) was determined by dividing the moments of resisting forces (M_R) by the moments of driving forces (M_D). The state of limiting equilibrium has a "factor of safety" of 1. The physical parameters of the till deposits of Verdun were established as: unit weight γ=24.9?kN/m³ (calculated using the percentage of gneissic blocks contained in the tills) and porosity n=0.24. The results of 15 triaxial tests in a gravelly sand matrix were plotted in a Lambe diagram following a linear regression model [x=(σ₁+σ₃)/2 and y=(σ₁–σ₃)/2 with sin?φ′ =tan?θ]. From this the friction angle φ′=33°±3 and c′=45±5?kPa were established. The factor of safety calculated for the moraine deposits in the historic slides was 1.44 without water (Hw=0). With a height of water of 7?m, representing 85% of the till thickness, this was reduced to F=1. To achieve a factor of safety of 1.3, the maximum water level within the till should not exceed 2.5?m, representing 65% of the till thickness. Similarly, the factor of safety was calculated for the active slides of another area (shown as section 4 in Fig.?3 in the paper). Using slice number 9 from the middle of the slide, the factor of safety was 1.08 when the height of the water was taken as 90% of the till thickness. This high calculated factor of safety for the height of water is consistent with the slow movement of the actual slides. However, a lower internal cohesion of the till deposits or the presence of a weathered zone would decrease the factor of safety from 1 to 0.8. It is also possible that other parameters, such as the regional seismic activity, could have been sufficient to initiate movement (F<1) during the last 50?years. It is of note that the map of seismic activity shows that more than a 100 earthquakes with magnitudes greater than 3 have occurred in the central Pyrenees since 1660. The paper emphasises the importance of high-quality mapping which identifies and classifies areas of historic and recent instability. From this, a single geotechnical model to calculate the stability can be established. The level of the water is shown to be the critical parameter and of more significance than the variations in the effective friction angle, which itself is more important than variations in the effective cohesion. With this information it is possible to determine those areas where some form of stabilisation and/or drainage of the till deposits is necessary.     

Quantification des matières en suspension et valorisation des sédiments de dragage à l’échelle d’un bassin semi-aride: Cas du barrage du K’sob (Algérie)

Due to the semi-arid climate, scarcity of vegetation, the presence of a sometimes steep slope, Algeria is vulnerable to soil erosion that threatens its socio-economic development. In the watershed of K’sob, transport of suspended sediment by rivers is a disturbing phenomenon due to siltation to 80 % of the dam at the outlet. Data of suspended sediment concentrations are closely related to liquid discharge (Q). Models of solid discharge (Q_s) according to the equation Q_s = aQ^b were used to perform qualitative and quantitative analysis of suspended sediment. Different scales of analysis helped identify and explain conclusively seasonal models. Sediment production is very high in the fall. In the spring, despite the increase in discharge, it is less significant. In summer, during a period of disappearance of vegetation cover, highly loaded floods are sometimes observed. Currently, millions of cubic meters of sediments are dredged each year. This large volume is an economic, environmental and ecological problem. To remedy this, an experimental study of manufacturing brick has been proposed with 65 % of sediment, 25 % of dune sand used as an additive and 10 % water. The shrinkage is minimal for a solid brick fabricated to 800 °C during 6 h of cooking. The mechanical tests carried out on the brick exhibit acceptable values of compression strength, mass density and water absorption. The study of the evolution of these parameters for different pressing intensities (13.2–20–30 and 40 kN) at different ages (4, 14, 21, and 28 days) shows that the solid brick acquires its resistance only after 21 days.     

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.     

Impacts de recouvrements de résidus organiques sur des résidus miniers réactifs

Résumé Les résidus miniers constituent aujourd'hui un problème environmental important. En particulier, les résidus miniers à l'origine du drainage minier acide (DMA) sont les résidus provenant de l'exploitation de minerais tels que l'or, le cuivre, le zinc, le plomb, le nickel, ainsi que le charbon, qui contiennent des minéraux sulfurés généralement associés en formation primaire. L'action intensive et prolongée de l'oxygène atmosphérique et de l'eau de pluie sur les minéraux sulfurés résiduaires contenus dans la zone non saturée des haldes minières conduit à une production d'acide sulfurique. L'une des solutions envisagée pour empêcher la formation de la DMA consiste en un recouvrement des résidus miniers par une couche de matériaux afin de les isoler de l'oxygène atmosphérique. Parmi les matériaux pouvant être utilisés, on trouve ceux composés par des résidus organiques qui peuvent eux-mêmes être composés de différents types. Plusieurs études ont déjà mis en évidence l'efficacité de ces matériaux organiques comme barrière à l'oxygène. Un aspect important qu'il reste à étudier a trait aux interactions entre la couche organique (et ses produits de dégradation) avec les résidus oxydés et non oxydés. Le but de cet article est de présenter les mécanismes théoriques de formation de la DMA et l'utilisation de couches de résidus organiques comme moyen d'y remédier. L'interaction entre les couches de résidus miniers et les couches de résidus organiques est aussi discutée compte tenu de l'importance de ce sujet dans les domaines miniers, civils et environnementaux.

---

     

巴黎Frédéric Malle香水新店

这间香水店如同一个小小的方形盒子一般,嵌入在巴黎玛黑区一座古老建筑的底层。整个空间由木质家具和镜面组成,充满了未来感。进入“盒子”内部,木质小格子纵横交错,就像一座座漂浮在空中的神秘小岛和岩洞里的钟乳石,构成了香水展示架、桌子、冷藏陈列柜等等。墙面和天花板由反光的不锈钢面打造而成,明暗之间,真实与虚幻交错掩映,仿佛打造了一个无穷变幻的虚拟空间。架子上放置的香水瓶则在时空和灯光的交错中变成了一个个小点,等待着消费者去探索和发现……