Abdelhamid El-Fakharani

Rock slope stability and design in Arafat-Muzdalifa area, Saudi Arabia

The present contribution is a complete study extending before, during, and after the excavation of the mountain side that lying north of road 7. It includes slope stability analysis, rock cut design, and rockfall modeling for natural slope and rock cut face. Neoproterozoic granodiorite and biotite granite forming the slope body have medium to very high strengths. Mineral compositions and textures of these intact rocks control the strength values. These rocks are intensively dissected by fractures that are filled with montmorillonite and chlorite. The high plasticity and slippery nature of these filling materials represent the main problem that may face a rock cut designer because they damage the mechanical properties of these fractures. The problem begins with the selection of the rock mass classification that deals with the fracture fillings and extends during the stability analysis and the suggestion of mitigation and supporting measures. The rock masses building the natural slope are suffered by plane, wedge, and toppling failures. Therefore, two rock cut designs are suggested to avoid the hazards related to these failures and considering the construction cost as well. Rockfall modeling for the natural slope and rock cut designs was done to assess the hazards related to these falling of the blocks. The kinetic energy of falling blocks is represented on the roadway by the coverage distance and block rebound amplitude. Slope height has a positive effect on the values of these distance and amplitude, whereas the steepness of berm height has a negative effect on them. Coverage distance is a function to the location of rockfall barrier and to the width of road ditch, while the amplitude controls the barrier height.

Editorial: Geology and Tectonic Setting of the Arabian-Nubian Shield

The Arabian-Nubian Shield (ANS) lies at the northern part of the East African Orogen (EAO) or East African Antarctic Orogen (EAAO) and represents the upper crustal equivalent of the high-grade Mozambique Belt (MB). The juxtaposition of the ANS low-grade basement rocks and the MB high-grade rocks is documented in various domains, particularly in southern Ethiopia and Kenya. The ANS itself is considered by some workers as the largest tract of juvenile Neoproterozoic continental crust on Earth, and is regarded by others as a major suture zone separating eastand westGondwanalands. It is dominated by Neoproterozoic juvenile arcs, post-amalgamation depositional basins (≈ forty basins allover the ANS), voluminous granitoid and gabbroic intrusions, and enclaves of pre-Neoproterozoic crust. This collage was evolved during much debatable late Cryogenian–Ediacaran (650-542 Ma) depositional, tectonic, metamorphic and intrusive events. The closing 100 Ma of the Neoproterozoic crustal growth of the ANS has attracted the attention of Precambrian structural geologists and at least four models or paradigms have been proposed; infracrustal-, Turkic-type-, hot-spot-, and arc-assemblyorogenic models. Infracrustal model, whereby ophiolites and island-arc volcanics and volcaniclastics were thrusted over an old craton consisting of highgrade gneisses, migmatites and remobilized equivalents; the contact is Pan-African thrusting. The high-grade rocks are suggested to be exposed in a number of tectonic windows, forming domal-like structures or swells; e.g. Beitan, Hafafit, Meatiq, Sibai and El-Shalul in the Nubian segment of the ANS. However, recent isotopic and geochronologic studies challenge this interpretation. According to the Turkic-type orogenic model, much of the ANS were formed in broad fore-arc complexes. The Hot-spot Model envisaged the evolution of the ANS due to accretion of oceanic plateaux formed by upwelling mantle plumes. The arc assembly model is favored by most ANS