Available online at www.CivileJournal.org Civil Engineering Journal Vol. 2, No. 7, July, 2016 348 Investigation of Separation Non-Persistent Faults in Fracture Mechanism of Rock Bridge N.Nohekhan Hokmabadi a* , V.Sarfarazi b , M.R.Moshrefifar c a M.Sc. Student, Geology Group, Yazd University, Yazd, Iran b Assistant Professor, Mining Engineering Division, Hamedan Industrial University, Hamedan, Iran c Assistant Professor, Geology Group, Yazd University, Yazd, Iran Received 25 May 2016; Accepted 20 July 2016 Abstract Rock mass is a heterogeneous material included joints, fractures and faults. The necessity of rock mechanics studies in conducting constructional issues has become important due to the increase in constructional works and the expansion of the structure’s dimension and especially creating underground spaces in rock masses. Faults are the most important discontinuous fractures in the earth's crust in which the two sides of the fracture have moved relative to each other. The purpose of this research is that if the non-persistent faults were situated adjacent to each other, how would be the shear failure mechanism of Rock Bridge surrounded between the faults. For this purpose, physical model consisting two horizontal edge faults and a surrounded angled fault was built; angularity of the central fault varies from 0° to 60° with increasing the 30°. The central fault places in 3 different positions. Along the lateral faults, 1.5 cm vertically far from the edge faults and 3 cm vertically far from the edge faults. All samples tested by uniaxial test machine so that shear load was distributed in the specimens due to special geometry of specimen. The results show that the failure pattern was mostly influenced by configuration of central joint, while the shear strength was linked to the failure pattern and failure mechanism. Keywords: Discontinuous; Non-Persistent; Rock Bridge; Uniaxial Test; Shear Behavior. 1. Introduction Rock structures are not usually limited to a single discontinuity [1]. In other words, a series of discontinuities are located next to each other and create a combined shear failure surface [2]. Meanwhile, the areas between the adjacent discontinuity areas containing rocks are called Rock Bridge, and are of a high importance regarding shear resistance along the joint fraction plane [3]. The size and exact location of the rock bridge is barely recognizable in the rock mass and is often ignored in designing rock mechanics. The reason for the claim that rock bridges are a resistance source in shear surface is that before the shear occurs across the shear surface, these rock components break at first and the crack made by this fraction spread to the joints of the adjacent sections [4]. Since rock bridges indicate resistance to fracturing, the resistance of the sliding surface is greater than the state that the joint is continuous. Therefore, most of the civil projects, which have been designed assuming the continuity of the joints, suffer high costs to increase reliability coefficient. This is while the identification of the rock bridges along the sliding surface and investigating the resistance of the fracture surface, can increase reliability coefficient and lead to lower costs. Crack propagation and coalescence processes primarily cause rock failure in slopes, foundation and tunnels. Since Griffith (1921) studied the growth of pre-existing two-dimensional crack, many studies performed on the initiation, propagation and coalescence of crack. The studies that performed on jointed rock can help explain the joint propagation mechanism and server as model for the behavior of joint rock masses. Joint propagation and coalescence can reduce the stiffness of jointed rock masses causing the shear failure of rock slopes [5]. Also joint propagation and coalescence can induce earthquakes by * Corresponding author: nasimhokmabadi@gmail.com