Determination of the principal axes of elliptic cross sections in strain ellipsoids by a variational method

A method is presented for the determination of the shape and orientation of the ellipse on a central plane section across a triaxial ellipsoid (such as a strain ellipsoid) of known orientation and magnitude. Conditional extremal values of longitudinal strain (λ) are obtained in the plane section and these are the principal axes of the strain ellipse. In solving this variational problem, the arbitrary cosntants (two undetermined Lagrange multipliers) are found to have physical meaning in themselves as proved in a complementary geometric solution. The two roots of the first constant directly determine the magnitude of the principal axes of the strain ellipse in terms of the normal to the cross section. The two arbitrary constants together define shear strains and orientation of these axes.

Strain computation uses simple, single-line equations in either frames of strained or unstrained states.     

Response of fixed offshore platforms to wave and current loading including soil–structure interaction

Fixed offshore platforms supported by pile foundations are required to resist dynamic lateral loading due to wave forces. The response of a jacket offshore tower is affected by the flexibility and nonlinear behaviour of the supporting piles. For offshore towers supported by clusters of piles, the response to environmental loads is strongly affected by the pile–soil–pile interaction. In the present study, the response of fixed offshore platforms supported by clusters of piles is investigated. The soil resistance to the pile movement is modelled using dynamic p–y curves and t–z curves to account for soil nonlinearity and energy dissipation through radiation damping. The load transfer curves for a single pile have been modified to account for the group effect. The wave forces on the tower members and the tower response are calculated in the time domain using a finite element package (ASAS). Several parameters affecting the dynamic characteristics of the platform and the platform response have been investigated.     

Le Carbonifère du Maroc central : les formations de Migoumess,de Tirhela et d'Idmarrach. Lithologie,biostratigraphie et conséquences géodynamiquesThe Carboniferous formations of Migoumess,Tirhela and Idmarrach (central Morocco): lithology,biostratigraphy and geodynamic consequences

New biostratigraphical data based on foraminifers, algae and pseudo-algae indicate that the limestone pebbles of the channelized polygenic conglomerates of the Migoumess formation contain Late Visean (V3bγ–V3c) assemblages. That confirms the Westphalian age attributed to this formation by Hollard [Zdt. Geol. Ges. 129 (1978) 495–512]. The Tournaisian age assigned to it by palynology [C. R. Acad. Sci. Paris, série II 310 (1990) 1573–1576] cannot be retained. The Tirhela formation, Late Visean and Serpukhovian (E1) in age, is coeval with the Akerchi formation [Berkhli, thèse d'État, 1999; Berkhli et al., J. Afr. Earth Sci. (accepté)]. The Idmarrach formation, mapped as a thrust sheet [C. R. Acad. Sci. Paris, série II 310 (1990) 1573–1576], is dated as Serpukhovian (E1) and its thrusting is consequently post-Serpukhovian. Palaeogeographic and geodynamic consequences are listed. To cite this article: M. Berkhli, D. Vachard, C. R. Geoscience 334 (2002) 67–72     

The motion of axisymmetric satellite with drag and radiation pressure

The axisymmetric satellite problem including radiation pressure and drag is treated. The equations of motion of the satellite are derived. The energy-like and Laplace-like invariants of motion have been derived for a general drag force function of the polar angle, and the Laplace-like invariant is used to find the orbit equation in the case of a spherical satellite. Then using the small parameter, the orbit of the satellite is determined for an axisymmetric satellite.     

Investigation of RS and GIS techniques on MPSIAC model to estimate soil erosion

Soil erosion due to surface water is a standout among the serious threat land degradation problem and an hazard environmental destruction. The first stage for every kind of soil conservation planning is recognition of soil erosion status. In this research, the usability of two new techniques remote sensing and geographical information system was assessed to estimate the average annual specific sediments production and the intensity erosion map at two sub-basins of DEZ watershed, southwest of Lorestan Province, Iran, namely Absorkh and Keshvar sub-basins with 19,920 ha, using Modified Pacific Southwest Inter-Agency Committee (MPSIAC) soil erosion model. At the stage of imagery data processing of IRS-P6 satellite, the result showed that an overall accuracy and kappa coefficient were 90.3% and 0.901, respectively, which were considered acceptable or good for imagery data. According to our investigation, the study area can be categorized into three level of severity of erosion: moderate, high, and very high erosion zones. The amount of specific sediments and soil erosion predicted by MPSIAC model was 1374.656 and 2396.574 m³ km^?2 year^?1, respectively. The areas situated at the center and south parts of the watershed were subjected to significant erosion because of the geology formation and ground cover, while the area at the north parts was relatively less eroded due to intensive land cover. Based on effective of nine factors, the driving factors from high to low impact included: Topography > Land use > Upland erosion > Channel erosion > Climate > Ground cover > Soil > Runoff > Surface geology. The measured sediment yield of the watershed in the hydrometric station (Keshvar station) was approximately 2223.178 m³ km^?2 year^?1 and comparison of the amount of total sediment yield predicted by model with the measured sediment yield indicated that the MPSIAC model 38% underestimated the observed value of the watershed.     

Numerical heat and fluid flow modeling of the Hercynian Draa Sfar polymetallic (Zn–Pb–Cu) massive sulfide deposit,Central Jbilets,Morocco

Draa Sfar is a polymetallic (Zn–Pb–Cu) volcanogenic massive sulfide deposit with an actual resource of 13 Mt at 4.0% Zn and 1.3% Pb. It is part of the central Jbilets area known for its several Cu–Zn ore deposits. The ore is hosted in the upper Visean-Namurien sedimentary formation. Owing to the complexity of the geology of the ore deposits, numerical simulation approach was attempted to shed light into the temperature distribution, the circulation of the hydrothermal fluid and the genesis of massive sulfide ore bodies by evaluating the permeability, porosity, and thermal conductivity. On the basis of this simulation approach, the ore is predicted to be deposited at a temperature ranging between 230 and 290 °C. This temperature range is dependent on the pre-existing temperature of the discharge area where a metal-rich fluid precipitated the ore. The duration of the Draa Sfar ore body formation is predicted to be 15, 000 to 50, 000 years. Based on geological studies of Draa Sfar deposit together with the aforementioned results of the simulation approach, an ore genetic model for the massive sulfide ore bodies is proposed. In this model, the supply of ore-forming fluids is ensured by the combination of seawater and magmatic waters. Magma that generated rhyodacite dome acted as the heat source that remobilized the circulation of these ore-bearing fluids. The NW-SE trending faults acted as potential pathways for both the downward and upward migration of the ore-forming fluids. Due to their high permeability, the ignimbritic facies, host rocks of Draa Sfar ore bodies, have favored the circulation of the fluids. The mixing between the ore-forming fluids of magmatic origin and the descending seawaters and/or in situ pore waters led to the formation the ore bodies in 35,000 years. The position and size of the ore body, determined by the simulation approach, is consistent with the actual field geological data.     

Correction to: Imagery of the metamorphic bedrock roof of the Sahel active fault in the Sablettes (Algiers) reclaimed area by ambient vibration HVSR

The original version of this paper was published with incomplete affiliation. Given in this article are the complete affiliations.     

Development of a model for analysis of slope stability for circular mode failure using genetic algorithm

Slope stability estimation is an engineering problem that involves several parameters. The interactions between factors that affect slope instability are complex and multi-factorial, so often it is difficult to describe the slope stability mathematically. This paper, proposes the use of a genetic algorithm (GA) as a heuristic search method to find a regression model for analyzing the slope stability. For this purpose, an evolutionary algorithm based on GA was used to develop a regression model for prediction of factor of safety (FS) for circular mode failure. The proposed GA uses the root mean squared error as the fitness function and searches among a large number of possible regression models to choose the best for estimation of FS from six geotechnical and geometrical parameters. For validation of the model and checking its efficiency, a validation dataset was used to evaluate FS using the proposed model and a previously developed mathematical GA based model in the literature. Results have shown that the presented model in this study was capable of evaluating FS at a higher level of confidence regarding the other model (R = 0.89 for presented model in this study comparing R = 0.78 for the other model) and can be efficient enough to be used as a simple mathematical tool for evaluation of factor of safety for circular mode failure especially in preliminary stages of the designing phase.     

Hydrocarbon source potential of the Jurassic sediments of Salam-3X borehole,Khalda Concession,Northern Western Desert,Egypt

A total of 51 samples, collected from the Jurassic sediments (Ras Qattara, Yakout, Khatatba, Masajid, and Alam El Bueib (member 6) formations) of Salam-3X well, were subjected to organic geochemical analysis. Of the samples, nine have been subjected to palynofacies investigation. Based on the sedimentary organic matter, these sediments show only one palynofacies type, indicating the presence of gas- and oil-prone source rocks and reflecting deposition under marginal dysoxic–anoxic to shelf-to-basin transition conditions. The total organic content of the samples analyzed is characterized by a wide range of content, including fair, good, very good, and excellent. The organic matter quality of these samples is concentrated around types III (gas prone), III–II (gas and oil prone), and II (oil prone), reflecting gas- and oil-prone sediments, with a tendency to generate gas rather than oil; the result matches with the palynological analysis data. The temperature of maximum pyrolytic hydrocarbon generation of analyzed samples are ranging between 440 and 457 °C, reflecting thermally mature organic matter.     

Relationship between geological structures and groundwater flow and groundwater salinity in Al Jaaw Plain,United Arab Emirates; mapping and analysis by means of remote sensing and GIS

Geological structures can be of great influence groundwater movement and accumulation in the surface and subsurface, and should therefore be taken into consideration in studies related to groundwater contamination impact. This study attempts to investigate the influence of geological structures on groundwater flow and groundwater salinity in Al Jaaw Plain, United Arab Emirates. A set of thematic maps derived from digital elevation model (DEM), LANDSAT, and Spaceborn Imagine Radar-C/X-Band Synthetic Aperture Radar were enhanced by applying Soble filter with 10 % threshold and equalization enhancement to reveal and map geological structures crosscut the entire region. Drainage pattern was derived from DEM automatically using D8 algorithm. The algorithm determines in which neighboring pixel any water in a central pixel will flow naturally. The trends of geological structures and drainage pattern extracted from remote sensing data were correlated with the spatial variation of hydraulic head, thickness aquifer, and groundwater salinity in the region. The results of the study reveal that the wadi courses, thickness of the aquifer, and topography are structural controlled by NNW–SSE, NE–SW, and ENE–WSW trending fault zones, significantly influencing the groundwater flow and groundwater contamination in Al Jaaw Plain.