Vulnerability and fate of a coastal sand dune complex,Rosetta-Idku,northwestern Nile Delta,Egypt

Types, distribution, and origin of recent sand dunes between Rosetta and Idku, in the western sector of the Nile Delta, Egypt were investigated. Sand samples from the dunes, beach, and seafloor were studied for grain size distribution and mineralogical composition. It has been found that most of the dunes in the study area have been subjected to deterioration and removal due to the construction of buildings and the International Coastal Highway. The remnant constitutes a damaged belt of foredunes that extends from El Bouseily village to the west of Idku town. The dune’s origin is interpreted to be the result of coastal drifting and the subsequent transport of sediments of the former Canopic Nile branch eastward by the predominant longshore current and by aeolian processes. The blown sand grains accumulated to form a belt of coastal sand dunes of original longitudinal and crescentic forms. Urbanization of the coast has severely altered the landscape. The study area is considered vulnerable to the impacts of climate change and the expected rise in sea level. The outcome of potential sea level rise is serious; erosion problems are expected to be exacerbated and vast areas from land and property would be lost. Thus, protection and preservation the remaining dunes in the study area are vital requirements for shore protection.     

Structure de socle,sismostratigraphie et héritage structural au cours du rifting au niveau de la marge d'Ifni/Tan-Tan (Maroc sud-occidental)

Seismic reflection profiles from the Ifni/Tan-Tan Atlantic margin of southern Morocco, interpreted in the light of well data and field geology from the Western Anti-Atlas, allowed us to establish the seismostratigraphic framework of the syn-rift series and to reveal (i) a compressional structural style in the pre-Triassic basement similar to that established in the adjacent outcropping onshore basement but with an opposed western vergence, (ii) the importance of inherited anterior structures in the formation of Triassic-Liassic rift structures and (iii) an east–west propagation of these rift structures. To cite this article: N. AbouAli et al., C. R. Geoscience 337 (2005).     

Pseudostatic approach for seismic analysis of pile group

This paper evaluates a simple approximate pseudostatic method for estimating the maximum internal forces and horizontal displacements of pile group subjected to lateral seismic excitation. The method involves two main steps: (1) computation of the free-field soil movements caused by the earthquake, and (2) the analysis of the response of the pile group based on the maximum free-field soil movements (considered as static movements) as well as a static loading at the pile head, which depends on the computed spectral acceleration of the structure being supported. The methodology takes into account the effects of group interaction and soil yielding at pile–soil interface. The applicability of this approach has been validated by a similar approach for single piles and then verified by both experimental centrifuge models of pile-supported structures and field measurements of Ohba-Ohashi Bridge in Japan. It is demonstrated that the proposed method yields reasonable estimates of the pile maximum moment, shear, and horizontal displacement for many practical cases despite of its simplicity. Limitations and reliability of the methodology are discussed and some practical conclusions on the performance of the proposed approach are presented.     

Behavior of Shallow Strip Footing on Twin Voids

This paper numerically examines the bearing capacity and failure mechanism of a shallow strip foundation constructed above twin voids. The voids may refer to caves, caverns, underground aqueduct or tunnels due to water seepage, chemical reaction or deliberately excavated in soil deposit. The ability of numerical model to accurately predict the system behavior is evaluated by performing verification analyses on existing researches. Subsequently, a parametric study carried out to reveal the influence of size of footing/voids and their location (i.e. depth, spacing, eccentricity) on the bearing capacity of footing. To clarify the failure mechanism, the distribution of shear strain in the soil for different scenarios is assessed. The parametric study provided a new framework to determine the bearing capacity and the mode of failure for footings on voids. Based on the results, a criterion can be issued to avoid collapse of footing/voids regarding the shape, location and size of voids. The results can also be used to design construction of a footing on existing voids while the acquired failure mechanisms can be appointed to develop analytical solutions for this problem. Results demonstrated that a critical depth for voids and a critical distance between them exist where the influence on the ultimate bearing capacity of footing disappears.     

Late Cretaceous–Early Paleogene tectonic events at Farafra-Abu Minqar Stretch,Western Desert,Egypt: results from calcareous plankton

This work depends on integrated high-resolution calcareous plankton nannofossil and foraminiferal biostratigraphic analyses for three Upper Cretaceous-Lower Paleogene successions at Farafra-Abu Minqar area, Western Desert, Egypt. These sections are distributed in a north-south geologic profile as follows: El Aqabat, North Gunna, and Abu Minqar. Lithostratigraphically, four formations are recorded in the study area, namely, Khoman (at base), Dakhla, Tarawan, and Esna (at top). In the north at El Aqabat section, Khoman Formation (carbonate facies) is only represented which changes partially toward the south to Dakhla Formation (siliciclastic facies). In the extreme south at Abu Minqar section, it changes completely into siliciclastic facies of Dakhla Formation. Biostratigraphically, seven calcareous nannofossil and eleven planktonic foraminiferal zones represent the Late Cretaceous-Early Paleogene are identified. Based on the occurrence or missing of these zones accompanied with the field criteria resulted in detecting four tectonic events. These tectonic events took place at the Cretaceous/Paleogene (K/Pg), the Danian/Selandian (D/S), the Selandian/Thanetian (S/T), and the Paleocene/Eocene (P/E) boundaries. These tectonic events are related to the impact of the Syrian Arc System. Four sequence boundaries (SB1, SB2, SB3, and SB4) are defined in the Late Cretaceous-Early Paleogene sequence in the Farafra-Abu Minqar area.