Impact of Brittle Faults with Varying Geometrical Structures on Rock Mass Engineering Properties in the North Tehran and Pourkan Verdij Fault Zones, Iran

The impact of a group of parallel or connected faults causes the creation of fault zones. The effect of brittle spots on the region's rocks differs, and the amount of stress in other parts of the fault varies. In addition to the different amounts of stress in other parts of the fault, the fracture rate of the rock mass in the fault area is variable in such a way that the parts that have not been deformed, in the form of blocks surrounded by severely crushed elements that create a weaker matrix and cause Inhomogeneity in the brittle fault zone, which is called bimrock. Bimrock (block-in-matrix rock) includes mélanges, fault rocks, weathered rocks, and other complex geological mixtures in strong blocks surrounded by a weaker matrix. Investigation and research on the geometry of brittle faults and the impact of these faults on the rocks of the region and establishing a relationship between the mechanism of faults and resistance characteristics is necessary. In this research, we did the geometrical analysis of the North Tehran fault and the Pourkan Verdij fault by examining fault branches and s-c structures in the fault zone. Also, the geomechanical properties of the fault rocks and Bimrocks in the area were investigated using two-dimensional analysis of the outcrop images of the fault zone by "Image Analysis" software and rock mechanics tests. As a result, the survey conducted in the cross-section of these two faults from the front side of the fault zone to the end of the fault zone showed that the volume ratio and uniaxial strength of the fault stone blocks of the North Tehran fault zone show regular changes. In such a way that as we move from the front of the site to the end of the fault zone, the amount of rock crushing decreases, and as a result, the volume ratio of the blocks and their resistance increases. While in the Porkan-Verdij fault zone, these changes are not visible in a particular order from the forehead to the end of the site, and the amount of these changes is sudden and less than in the North Tehran fault zone. This is related to the displacement rate created by the fault, the presence of micro-faults, and the distance of the shear planes relative to each other. This study can solve the most severe geotechnical problems related to rock engineering caused by brittle faults.