Les blocs en béton à isolation integrée

Research by CERIB (the Research and Study Centre of the Concrete Fabrication Industry) in France has led to the development of three types of concrete block with integral insulation; one type has the expanded polystyrene nearer the inner section, one has the insulation towards the outer section while the inner section is load bearing, and the third type is an insulated hollow block which acts as permanent formwork.     

Utilisation d'arènes granitiques pour la fabrication de béton en terre

Completely weathered granites are abundant materials and, as a first approximation, their composition is such that treatment with lime should be quite satisfactory, whether they are used for road-building or to produce stabilized blocks for low-cost housing. Three types of completely weathered granite were selected. Their mineralogical and geotechnical properties, and the rocks from which they originate, are described. The completely weathered granites studied differ:

- in the particle size distribution;

- in the mineralogy of their clayey fraction;

- in the degree of weathering affecting them.

The aim of the treatment was to obtain a material having sufficient mechanical strength and insensitivity to water. The results reveal differences among the materials. On dry test specimens, the best results are obtained with the completely weathered granites having the highest clay content, while in saturated test specimens, we find that the mineralogy of the clayey fraction is a factor: the test specimen that performed best had the highest clay content, but its clayey fraction contained no smectites. It is shown, however, that the harmful effects appear only above a threshold that varies with the percentage of lime, and the performance of one of the specimens, artificially enriched with its own fines, which contained smectites, was improved. We propose a relation between the saturated strength values and the quantity of binding agents formed, as assessed on the basis of a mild acid attack. To conclude, on the whole, completely weathered granites can benefit from treatment with lime, whether the purpose is road-building or the production of stabilized blocks. But optimization of the treatment product-performance couple depends on a detailed knowledge of the materials.     

Le béton de cosse de riz pour panneaux legers

A project by the Eduardo Torroja Institute in Madrid has focused on the mechanical performance of lightweight panels (= 30 kg) based on concrete made with rice husks treated with lime. The 6 cm thick components measure 90 × 60 cm and are hand‐formed to accord with methods that are suitable for developing countries. The article discusses the results of tests for flexure and axial compression on short series of these components.     

Vision par ordinateur: contribution à l'étude d'un béton durci par traitement d'images

Water content is one of the critical parameters in the composition of concrete. When deficient, handling the concrete during placement is very difficult and when released from the mould the concrete frequently has air voids which adversely affect its performance. In contrast, excess water can lead to segregation between the denser and finer materials, hence it is important the water content remains within the defined range. This study was undertaken to establish a method of accurately determining the optimum water content when preparing a concrete. The literature reports many tests to assess concrete workability, monitoring particularly the ratio of water content (E) to cement (C) for a cubic metre of concrete – see, for example, the Slump Test and the "maniabilimeter" LCPC. The object of the research presented in this paper was to provide laboratories with a methodology by which to characterise the heterogeneity of the coarse fraction and thus establish the segregation threshold. The method presented is based on image processing. A cylindrical test tube of hardened concrete is cut diametrically. After polishing, a digital camera is used to capture the image of the section. The grey scale picture of a concrete cross section is binarised in order to underscore the gravels. Then the picture is divided into six images. On each image, the ratio between the total area of the gravels and the total area of the image is measured. It is proposed that the standard deviation of the six ratios can be used as an indicator of segregation.     

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     

Les pompes de chaleur manquent encore d'intérêt du point de vue coût

Lors d'une réunion ayant eu lieu il y a quelques mois, un sous-groupe technique de la commission de travail CIB W 67 sur la conservation de l'énergie a passé en revue les possibilités et les problémes des pompes de chaleur. La réunion a confirmé que les possibilités des pompes de chaleur sont considérables quant à la conservation de l'énergie et tous les pays sont tellement intéressés que le besoin d'une collaboration dans les recherches s'est intensifié.     

Cartographie des zones de risque de feux de forêt dans la commune de Doui Thabet,Saïda,Algérie

Forest fires have become a supremely topical subject and the year 2017 is considered to be exceptional in terms of burned areas. Thus, nationally more than 32,000 Ha have been ravaged by the flames, but above all, there has been a loss of life. The objective of this study is to implement a methodological approach for the mapping of forest fire risk areas. A model integrating GIS and remote sensing is used. It is based on the evaluation of several parameters that influence the initiation and propagation of a forest fire. These are vegetation, topography and anthropogenic factors. Imagery from the new SENTINEL2 satellite is used for vegetation mapping. GIS is use for the capture, processing, analysis and rendering of various images and maps. An application was carried out on the forest area of Doui Thabet (Saida/Algeria), often the target of fires. This study has two objectives. The first is to provide documents for potential users to help them in their planning and decision-making studies. The second objective is to provide managers with a tool that has made further progress in the management of geographic information.     

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.     

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.

     

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.     

Évaluation et cartographie des risques géotechniques de dégradation des ouvrages d'assainissement une aide à la gestion des eéseaux

A sewage collector can be considered as a composite structure, comprising the collector itself and its geological envelope both sticking together. Its durability is directly linked with the geotechnical behaviour of the soil, as testified by the analysis of numerous pathological cases observed in structures which it is possible to inspect in the Paris urban area. The author proposes a methodology enabling these parameters of influence to be taken into account without recourses to costly procedures of investigation. Based on the principles of mapping risks of soil movements, the method involves two stages:

-The geotechnical classification of soils in terms of their vulnerability to stresses to which they may be subjected.

-The establishments of maps or profiles predictive of risks. in accordance with qualitative criteria derived from the interpretation of existing geological information.

Tested and applied to the inspectable sewage system of the Val-de-Marne and Seine-Saint-Denis Departments, this procedure can be extended to urban systems where sufficient geotechnical documentation is available to obviate the need for any in situ investigation.     

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.