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Materials
ABSTRACT The granitoid rocks of Sharm El Sheikh are in south Sinai include alkali feldspar granite. Petrographically, the alkali feldspar granite characterized by the predominance of alkali feldspar, quartz, amphibole, biotite and plagioclase, the secondary minerals are Kaolinite, chlorite and sericite. The hydrothermal solutions are responsible for the formation of muscovite after feldspars and biotite, as well as increasing the cracks in the granite. K-metasomatism changed the physical properties of the granite, increasing their porosity, brittle extent, and providing the storage space for mineralization. Progressive alteration of the rocks has been marked by gradual transformation of the fresh granite to altered rocks. With increasing intensity of alteration, newly formed cracks connect with and intersect preexisting tectonic cracks, providing an isotropic permeability structure for solutions to flow. Polarizing microscope used to elucidate the optical properties and abundance of mica (biotite and muscovite) in the groundmass of granite asserts an important role in the formation of cracks. The influences degree of alteration on the granite consistency is studied numerically with a rock failure process analysis code, RFPA. Microscopic investigation and Numerical simulation results showed that alteration minerals have a negative effect on the strength and elastic modulus of rocks. On the other hand the influence of alteration in disintegrating the rock is greater than any other constituents like quartz and feldspars due to physical, mineralogical, and structural reasons. Therefore the choice of fresh granite (without alteration minerals) for construction projects is a key decision in order to avoid subsequent granite decay. 1. Introduction The Sinai Peninsula is an area of triangle shape, 60,000 Km2 in size, bordered in the southwest by the Suez Gulf and the line of the Suez Canal, in the southeast by the gulf of Aqapa, (Fig. 1A). The alkaline granites under consedration cover about 165 Km2, (Fig. 1B) , and are bounded between longitudes 33° 3 and 34° 24 E and latitudes 27° 47 and 28° 5 N. Collected samples represented the alkaline rocks of G. Al Att, G. Umm Markha, G. Hedmaiah, G. Al. Khoshby and G. Mdsosss This research aim to study the petrological controls effect on the reduction of mechanical properties, also to gain a better understanding of the influence of the alteration process on the granite failure to apply a numerical model based on mechanics that can be used for analysis. Alkaline rocks are most briefly defined as igneous rocks carrying feldspathoids and /or alkalis/pyroxene/amphiboles, and having a surplus of alkalis when compared to petrographically related rocks. The study of alteration effects, on strength and deformational behavior of rock under uniaxial compression environment is of vital necessary; most engineering works are confined to shallow depths where weathering and alteration have a dominant role to play and affects almost all chemical and physical properties of rocks. In this study, the hydrothermal alteration and weathering events in the Sharm El Sheikh granite have been studied, since they caused the most important solution actions through the fractures and cracks that affected the consistency of the rocks.
- Africa > Middle East > Egypt (0.24)
- Europe > Ukraine (0.15)
- Geology > Rock Type > Igneous Rock > Granite (1.00)
- Geology > Mineral > Silicate > Tectosilicate > Feldspar (1.00)
- Geology > Mineral > Silicate > Phyllosilicate > Biotite (0.64)
ABSTRACT One of the difficulties in describing the rock mass behavior is assigning the appropriate constitutive model. This limitation may be overcome with the progress in discrete element software such as PFC, which does not need the user to prescribe a constitutive model for rock mass. In this paper, the model size of 30m × 30m was analyzed by using the fracture geometry from two tunnel sites. PFC simulations were carried out to examine the mechanical behavior of rock masses. From the numerical tests, it can be concluded that as the number of joint sets increased, the values of mechanical properties of rock masses were decreased to about 50% of those values of rock mass without joints. And the behavior of the rock mass changed from brittle to perfectly plastic with increase in the number of joints. Also the values of Young's modulus, Poisson's ratio and peak strength are almost similar from PFC model and empirical methods. As expected, the presence of joints had a pronounced effect on mechanical properties of the rock mass. More importantly, the mechanical response of the PFC model was not determined by a user specified constitutive model. So the discrete element model gives very contrasting results compared to the traditional model. 1 INTRODUCTION Although the evaluation of the mechanical properties and behavior of discontinuous rock masses is very important for the design of underground openings, it has always been considered the most difficult problem. The reason is that it is often impossible to carry out large-scale in situ tests and, although widely used, the correlations between strength parameters and quality indexes (for instance GSI or Q index) are still affected by considerable uncertainties (Ribacchi 2000). The evaluation of rock mechanical properties such as deformation and strength properties can be achieved through the application of empirical relationships or by a theoretical approach based on numerical modeling. Both methodologies imply some assumptions and uncertainties that need to be considered. Deformation properties and rock mass strength are not only dependent on the intact rock, but also on the fracture network (number and orientation of fracture sets, intensity, mineralization, and so on) and the presence of deformation zones. Therefore, characterization of both the intact rock and of the fractures is required to define the mechanical behavior of the rock mass. Discontinuous rock masses are usually weaker and more deformable and are highly anisotropic when compared with intact rocks. So constitutive modeling of discontinuous rock masses has long been a subject of interest and numerous models have been developed in attempt to simulate their mechanical responses (Staub et al. 2002). Recent developments in numerical modeling that allow study of the overall response of a synthetic material containing discrete heterogeneities and discontinuities both at the micro (particle) scale and at the larger scale of jointed rock masses can greatly aid the interpretation and application of laboratory test results on these materials (Potyondy & Fairhurst 1999). The methodology for the rock mechanical descriptive model was developed in Sweden.