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, RFPA2D. 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) [1], 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.

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