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This article proposes a method based on artificial neural networks (ANN) to predict the time history responses at any point on the ground near a shaking table reaction mass (Earthquake Engineering ...

The natural hazard assessment is hampered by many difficulties due to the complexity of the phenomenon and the need to manage simultaneously several natural and/or technological hazards. Such is the case of most unstable urban sites in Algeria. The paper presents a risk analysis study of landslides and their reactivation in Tigzirt coastal city, located in the north of Algeria, which is classified in a moderate seismic zone. The spatial techniques based on geographic information systems are used to assess landslide susceptibility and hazard. Two qualitative studies of landslide hazard assessment are conducted using parameters defining the Algerian landslides context. The hazard is evaluated by performing a combination of the landslide susceptibility and the urban density. Earthquake-induced landslide hazard is assessed taking into account the Algerian seismicity. The study led to determination and mapping of the hazard induced by Tigzirt landslides.

In the assessment of slopes, factor of safety values still remain the primary indexes for determining how close or far slopes are from failure. Limit equilibrium and finite elements methods are among the most popular methods of slope analysis. Both methods were used to analyze homogeneous and inhomogeneous slopes. However, Limit equilibrium methods are relatively simple and suffer from many assumptions compared with finite element analysis. Recently, as computational techniques advance, more and more attention has been paid to the slope stability evaluations using finite element methods (FEM). This article demonstrates a finite element approach to analyze the response of homogeneous and layered slopes. A detailed parametric analysis is presented to study the effect of surcharge (it can be an imposition of building load….etc.) on the stability of the slope. In regard with these results it is seen that the factor of safety increases with increase in soil properties, groundwater depth, slope length, distance from the crest of slope. However, it decreases with increase in surcharge intensity, increase of weak soil layer thickness and increase of slope angle and slope height.

The behaviour of saturated clays under undrained conditions around pressuremeter path is studied by means of a theoretical and a numerical analysis based on the generalised elastoplastic Prager’s model with the Von Mises Criterion which is suitable for these cases of soils and gives a realistic response when unloading is considered. The soil constitutive model is described depending only on three parameters. The model response on pressuremeter path and its identification from experimental data lead to the determination of the undrained cohesion and the initial Young modulus of clays. Comparisons between the undrained cohesions determined with the proposed method and those obtained by other means illustrate the applicability of the method. An application to predict the bearing capacity and the settlement of bored piles using parameters derived from the proposed approach is also presented with a comparison to the measured data. Le comportement des argiles saturees en conditions non drainees sur un chemin pr...

The purpose of this paper is to present a stochastical approach, which analyse the torsional ground motion, induced by the spatial variability of seismic motions. For this purpose, a torsional ground motion analytical model is proposed and a normalised differential motion parameter is introduced. The approach regards the seismic motion as the combination of a travelling wave on the site (coherent component) and a zero mean randomizing factor that introduces a loss of correlation effect. The soil parameters as fundamental frequency and damping coefficient are integrating by modeling the coherent component with the commonly used Kanai-Tajimi power spectral density. The parametric analysis of the model shows an increase of the induced torsion with both the soil frequency and the motion scattering parameter, and a decrease with the separation distance, the apparent wave velocity and the correlation length. Finally, in order to test the proposed torsional ground motion model prediction, it is compared to the experimental results recorded by the EPRI LSST array in Lotung, Taiwan (Laouami and Labbe, 2002). The comparison leads to the identification of the model parameters for the Lotung soft site.

This paper reports on the assessment study conducted by the authors on the new Algiers airport building. The evaluation approach included visual inspection of the concrete, seismic parallel method for piles testing and non-destructive testing of concrete with Schmidt hammer, ultrasonic pulse velocity measurements, cores testing, carbonation tests and also ambient vibrations of the structure. The diagnostic confirmed that the concrete was of low strength and showed many shortcomings such as inappropriate mix design with respect to coarse aggregate size of concrete resulting in honeycombing, construction errors such as lack of cover and the use of low slump concrete, poor placement and inadequate vibration. The repair work involved the application of ready mixed cement based polymer modified sprayed mortar with and without fibers on more than ten thousand square meters of honeycomb concrete, the injection of about five hundred linear meters of cracks and the repair of about one hundred square meters of corrosion damaged concrete at a cost of more than three millions US dollars.

The management of major landslides faces several difficulties especially when important stakes are exposed to risk. The landslide of the city Azazga is one of the most extensive cases observed in Algeria. This is an instability reactivated by specific climate events such as floods of 1974 and snow of 2012. Landslides affect the center town of the region of Azazga situated 20 Km East of Tizi-Ouzou (northern Algeria). They affect a highly urbanized area and endanger vital structures such as the regional hospital. Managing this risk requires the development of an effective management methodology as well as a good knowledge of site conditions, the causes and the extent of the landslide. To better characterize this extensive instability, a geographic information system was created for the study site. This GIS greatly facilitates the interpretation of spatial data.

International audience; This paper describes an efficient methodology for the identification of soil parameters using the combination of the finite element method and the in situ pressuremeter test (PMT). The objective of the procedure applied here is to identify the parameters of generalized Prager model associated with the Drucker and Prager failure criterion from a pressuremeter expansion curve. The approach consists of minimizing the function representing the difference between the experimental curve and the curve obtained by integrating the model along the loading path in the in situ testing. First, both analytical expressions governing the problem of cavity expansion and those related to the finite element modeling are given in detail. Then, a Fortran computer program called "Press-Sim" along with the solution strategy are described and clearly explained. The influence of some model parameters as well as the probe geometry on the computed pressuremeter curves is examined. The paper finishes by presenting some identification examples drawn from real experimental tests for which the targeted parameters are compared with those of other experimental procedures. Results of comparison show a very good agreement.

This paper presents a new method proposed for the prediction of long term settlement of very heavy structures based on a numerical interpretation of long term pressuremeter creep tests. The constitutive model used for the modelling of the soil creep is described. The constants of the constitutive model are determined by fitting a simulated curve, given by a simple Finite Element Method, to the results of a long term pressuremeter creep test. The calculation of long term settlement under nuclear power plants, using the soil parameters defined by this method, is presented and compared with the in situ measured values.

The morphology of the North Algerian basins characterized by precarious stability constitutes an important issue for the development and the economy of many cities in the region. The landslide affecting the city of Azazga represents one of the most active and dramatic land movements experienced by the region in recent years. The city affected by the movement is situated at about 20 Kms in the East of the Wilaya of Tizi - Ouzou (in northern Algeria); the instability is located in a slope, composed of flysch (Azazga flysch are compounds of two terms of marly clay with small sandstone beds), with an inclination of about 13 °. Several factors have acted to activate this instability. Furthermore, water factor and geological conditions of this region are the main parameters of the susceptibility of the site to landslides.The Geographic Information Systems (GIS) are an effective alternative for the analysis of large-scale instabilities (such as Azazga landslides). GIS made for the site of Azazga allowed better management and interpretation of spatial data as well as good understanding of deformation mechanisms and the extent of this landslide. Geological profile has been defined for this slope using the results of spatial data analysis. Numerical modeling of this slope was then carried out, using the finite element software PLAXIS 2D , with taking in consideration the effect of the water level. Those studies show the important influence of the position of water table on the activity of the landslide and the safety factor.