The present article discusses the effect of the change in the continuity and area of the rock bridge on the complete failure behavior of the open rock joints. Forty five models were prepared using plaster with dimensions of 15 cm × 15 cm × 15 cm. The models consisted of 15 different types of rock bridges that occupied 45 cm2, 63cm2 and 90 cm2 out of the total fixed area, respectively. Different continuity configurations were simulated in these models. Three similar samples were prepare for every variation in the continuity configurations of the rock bridges and tested for direct shear strength considering 3 different normal stresses. The results indicated that the failure pattern and the failure mechanism were affected by the continuity configuration of the rock bridge. Furthermore, with the reduction in the continuity of the rock bridge in a fixed area, the shear resistance showed a small reduction. The investigations suggest that the increase in the area of the rock bridge and the normal stress would increase the shear resistance dramatically.
Shear slip is acommonphenomenon in rock engineering fields (Sonmez et al. 1998, Shen et al. 2004, Lin et al. 1998). It is well known that the decrease in strength of rock masses is mainly induced by the presence of rock joints. In some rare cases, it is possible that the failure in the rock mass is limited to a single discontinuity. Generally, several discontinuities exist in various sizes, which constitute a combined shear surface. In this sense, the areas which are located between the neighboring discontinuities are called the Rock Bridges and have the greatest importance for the shear resistance of the failure surface. (Eberhardt 2002, Hatzor et al. 2004, Wong et al. 1998, Li et al. 2005). Therefore, a comprehensive study on the shear failure behavior of Rock Bridges can provide a good understanding of both local and general rock instabilities, leading to an improved design for rock engineering projects. The failure behavior of jointed rock under shear loading has drawn much attention from both researchers and practical engineers over the last 3 decades and some extensive works on the coalescence pattern and shear resistance have been carried out through a large number of experimental and theoretical studies. In one of the pioneering works done by Lajtai (1969), tensile wing cracks were found to first appear at the tips of horizontal joints, followed by the secondary shear cracks propagating towards the opposite joint. Savilahti (1990) did some further study on the specimens of jointed rock under direct shear tests where the joint separation varies in both horizontal and vertical directions and joint arrangement changes from non-overlapping to overlapping using modeling material. The coalescence patterns for the specimens indicated that the jointed rock failed in mixed mode for non-overlapping joint configuration and in tensile mode for overlapping joint form.
