Geostatistical Analysis for delineating sterile inclusions in Sidi Chennane' phosphatic series, Morrocco

The anomalies detected in phosphatic series of Sidi Chennane, one of phosphatic basins in Morocco, hinder the proper exploitation of phosphate levels and the assessing phosphate reserves seems incorrect. The purpose of this study was the evaluation of geostatistical methods for delimitation of these disturbances. To cover all the zones being able to be disturbed, we carried out, during the geophysical prospection in a parcel of 50 ha, 5151 resistivity measurements as horizontal profiling using the well-known Schlumberger array, in order to map the spatial distribution of  the sterile hardpan inclusions.Geostatistical tools were used to quantify the spatial correlation between apparent resistivity data. Semivariograms were obtained using a classical Matheron semivariogram estimator and fit to the experimental semivariograms obtained. We have selected those with the best fit in terms of sum of squared residuals (SSR).Geostatistical analysis was performed using the software VESPER 1.63. Spatial distribution maps were made by ordinary kriging, the qualitative interpretation of these maps reflects that the exponential model is found to be the best model representing the spatial variability of our geoelectric data. The qualitative interpretation of the kriged resistivity maps allows defining resistivity contrast, consequently we have delimited the crossing dominate area from a “normal” into a “disturbed” area. Models of the geology were successfully obtained from geostatical method, which help mapping the phosphate deposit inclusions and the estimations of phosphate reserves were improved and better constrained. ResumenLas anomalías detectadas en las series fosfóricas de Sidi Chennane, una de las cuencas fosfóricas de Marruecos, dificultan la explotación apropiada de los niveles de fosfato y hacen parecer incorrectos los cálculos de las reservas. El propósito de este estudio es la evaluación de los métodos geoestadísticos para la delimitación de estas anomalías. Para cubrir todas las zonas donde se pueden presentar estas alteraciones se llevaron a cabo,durante la exploración geofísica en una parcela de 50 hectáreas, 5151 medidas de resistividad con perfileshorizontales a través del conocido sondeo Schlumberger, con el fin de mapear la distribución espacial de las inclusiones estériles de la capa sólida.Se utilizaron herramientas geoestadísticas para cuantificar la correlación espacial entre los datos de resistividad. Se obtuvieron semivariogramas a través del tradicional estimador de semivariogramas Matheron y se adecuaron a los semivariogramas experimentales obtenidos. La selección se basó en aquellos que mejor se acoplaban en términos de la suma de cuadrados residuales (SCE). Los análisis geoestadísticos se realizaron con el programa VESPER 1.63. Los mapas de distribución espacial se hicieron por Kriging regular, y la interpretación cualitativa de estos mapas refleja que el modelo exponencial es el que mejor representa la variablilidad espacial de estos datos geoeléctricos. La interpretación cualitativa de los mapas de resistividad obtenidos por la técnica del Kriging permite definir el contraste de resistencia, lo que fija el área entre los estándares de “normal” y “Con Alteraciones”. Los modelos geológicos fueron obtenidos del método geoestadístico, lo que ayudó a mapear los depósitos de inclusiones de fosfato y mejoró las estimaciones de las reservas a través de una mejor definición de estas

THE EFFECT OF SOIL DENSIFICATION ON THE ATTENUATION OF THE PHENOMENON OF SOIL LIQUEFACTION IN A PORT PROJECT IN MOROCCO

Morocco, which is in a seismically active zone, is currently experiencing a significant development in terms of the realization of development and infrastructure projects. Therefore, reflection on soil liquefaction problems during project design is essential. The densification of soils by vibro compaction is a recent process of soil treatment, its effect is to improve the geo mechanical characteristics of the soil in this case the relative density and subsequently the reduction of the potential for liquefaction, it is a technique soil improvement in the mass, it is closely linked to the grain size of the soil to be treated, its percentage of fines less than 10% (going to 0.08 mm <10%), this technique gives the treated soil sufficient cohesion to avoid large increases in pore pressures during the earthquake. This article aims, through the study of a real case, to evaluate the effectiveness of vibro compaction to improve the relative density of the soil and consequently the reduction of the risk of liquefaction of the treated soil. The work focuses on the analysis of the SPT tests carried out before treatment and on the CPT tests of control of the vibro-compactge works carried out after execution. This study showed that this process generates an effect of improvement of the relative density and reduction of the compaction by inducing a reduction of the risk of liquefactio

Identification Of Collapsible Soils In Deroua (Morocco)

Deroua belongs to the Berrechid plain and it is characterized generally by a flat relief, formations from the quaternary and Pliocene age and unconformably on sedimentary formations of Cretaceous and Permian Triassic on shcists from the primaries. Several anomalies were detected in the buildings and pavement structures in different cities in the territory of the Berrechid plain, such as settlement, cracking or even sudden collapses. The presence of a water table with 1500 square kilometers in area, the climatology of the region and a major urban development are factors favoring collapsing soils. Thus, we conducted a series of geotechnical tests on four samples taken from Deroua, 10 km from the city of Berrechid to identify the nature of the soils of this city in order to study their behavior in unsaturated state. The results of Atterberg limits and the oedometer test, correlated with results of previous studies and bibliographical research confirm the hypothesis of collapsible soils. Therefore, the results will help to quantify and map the collapse of soils in Deroua, in order to establish a local hazards map that can be exploited by the urban agency

Automatic spline-smoothing approach applied to denoise Moroccan resistivity data phosphate deposit “disturbances” map

This paper focuses on presenting a method which is able to filter out noise and suppress outliers of sampled real functions under fairly general conditions. The automatic optimal spline-smoothing approach automatically determi-nes how a cubic spline should be adjusted in a least-squares optimal sense from an a priori selection of the number of points defining an adjusting spline, but not their location on that curve. The method is fast and easily allowed for selecting several knots, thereby adding desirable flexibility to the procedure. As an illustration, we apply the AOSSA method to Moroccan resistivity data phosphate deposit “disturbances” map. The AOSSA smoothing method is an e-fficient tool in interpreting geophysical potential field data which is particularly suitable in denoising, filtering and a-nalysing resistivity data singularities. The AOSSA smoothing and filtering approach was found to be consistently use-ful when applied to modeling surface phosphate “disturbances.”

Lissage automatique par spline fonction applique au “debruitage” de la carte des resistivites des “derangements” des phosphates marocains

Dans le présent travail, nous présentons une nouvelle méthode de “débruitage” et de filtrage utilisant des fonctions analytiques échantillonnées. A partir d’un échantillon de points d’ajustement de la fonction spline utilisée, la métho-de dite «Automatic Optimal Spline Smoothing Approach » ou AOSSA permet de déterminer automatiquement l’ajustement par fonction spline d’ordre 3 au sens des moindres carrés, sans pour autant connaître la localisation des points de l’échantillon sur la courbe. Cette méthode rapide permet facilement de choisir différents points de lissage avec une certaine flexibilité de la procédure. En guise d’illustration nous avons appliqué la méthode AOSSA à la carte des données d’anomalies de résistivités correspondantes aux « dérangements » des phosphates maro-cains. La méthode de lissage et de filtrage AOSSA s’est avérée être un outil potentiellement efficace pour l’optimi-sation des surfaces correspondantes aux zones des « dérangements » des phosphates marocains.This paper focuses on presenting a method which is able to filter out noise and suppress outliers of sampled real functions under fairly general conditions. The automatic optimal spline-smoothing approach automatically determi-nes how a cubic spline should be adjusted in a least-squares optimal sense from an a priori selection of the number of points defining an adjusting spline, but not their location on that curve. The method is fast and easily allowed for selecting several knots, thereby adding desirable flexibility to the procedure. As an illustration, we apply the AOSSA method to Moroccan resistivity data phosphate deposit “disturbances” map. The AOSSA smoothing method is an e-fficient tool in interpreting geophysical potential field data which is particularly suitable in denoising, filtering and a-nalysing resistivity data singularities. The AOSSA smoothing and filtering approach was found to be consistently use-ful when applied to modeling surface phosphate “disturbances.”

Assessment of the Swelling Pressure of the Green Clay of Tangier (Morocco) Compared with the Soil-Moisture Conditions

The swelling phenomenon appears seriously when changing the soil-moisture conditions. The swelling pressure induced by the expansive soil can causes unfavourable problems or instability for the civil structures. So, understanding the soil behavior is considered a valuable work for engineers and consultants in the geotechnical and civil engineering sectors. In reality, the assessment of the swelling pressure of expansive soil depends, first of all, of test conditions related to the change of soil-moisture, as it happens, the influence of the combination “loading-start wetting” and also the unloading process after saturation. To this end, we establish an experimental study on the green clay of Tangier to evaluate the swelling pressure by using oedometer apparatus. Secondly, attention is bore to the combination “initial water content-dry density”, another factor related to the change of the soil-moisture, to show the influence of initial state condition on the swelling pressure

Identification of formations of soil and subsoil using finite elements modeling

The Soil and subsoil survey are performed by direct and indirect methods. The direct methods are the investigations of field and laboratory while indirect methods are the geophysical methods. These allow, from one or more physical properties, to find out the underground's structure nondestructively. Geophysical methods for characterizing subsurface have long been used, in geotechnical, hydrogeological and environmental studies. For our study, we used the electrical resistivity's method. 52 geoelectric soundings VES was performed with a mesh of 500 m and electrodes distance between 1000 m and 3000 m. The interpretation of these VES allows the determination of the vertical succession of formations in place. In order to have a lateral facies variation, we used geostatistical methods for having adequate data that can be used in the input file of inversion's code Res2Dinv. The 2D images of the subsoil obtained confirm and complement the results of the correlations of oil drilling that are in this region. Thus, the study area also has a horst and graben structure. This study also allowed us to locate the sandstone formations that extend in two places along a North-South direction

Acerca de las respuestas de filtrado espacial en el mapa de anomalías de gravedad de Bouguer del norte de Marruecos

This paper reports the results and interpretations of gravity signatures of the transformed map of Bouguer gravity anomalies of the Tangier-Tetuan area according with the data provided by aerial and terrestrial gravimetric surveys carried out in that area. Filtering analysis based on classic signal process was applied. Operators signal process like vertical gradient, horizontal gradient and downward continuation were used. This study also brings the possibility to define other adequate methods under consideration for the analysis of the gravity of the Tangier-Tetuan area.este artículo presenta los resultados y las interpretaciones del mapa transformado de las anomalías de la gravedad de Bouguer de la región de Tanger-Tetuan a partir de ls datos suministrados por sondeos gravimétricos aéreos y terrestres en dicha región. Se aplicó el análisis de filtración basado en los procesos clásicos de tratamiento de señales. Se utilizaron para ello operadores de señales como el gradiente vertical, el gradiente horizontal y la continuación descendente. Este estudio da también la oportunidad de utilizar otros métodos adecuados para el análisis de la gravedad en la region de Tanger-Tetuan