Shear Properties of Internal Support System (Rock Bridges)

Presence of rock bridges in rock masses would increase the bearing capacity of Non-persistent discontinuities. This increase is because of the cohesion and friction angle of the internal support system rendered by the rock bridges. In this article the effect of the area and configuration of the rock bridges on their shear properties are investigated. A total of 36 various models with dimensions of 30 cm× 30 cm× 30 cm of plaster specimens were fabricated simulating the open joints possessing 1 rock bridge. The introduced rock bridges have various continuities in shear surface. The area of the rock bridge was 300 cm2, 450 cm2, 600 cm2 out of the total fixed area of 900 cm2 respectively. The fabricated specimens were subjected to shear tests under 4 different normal loads (20, 30, 40 and 50 kg/cm2) in order to investigate the shear parameters. The results indicated that the failure pattern and the failure mechanism were affected by two parameters; i.e. the continuity of the rock bridge and the normal loads. So that increasing in the effective joint in front of the rock bridge changes the shear failure mode to tensile failure mode. Also shear failure occurs in the rock bridge at high normal loads. Furthermore, the cohesion strength decreases with the increasing of the effective joint in front of the rock bridges (in fixed area of rock bridges) while the friction angle was behaved constant all through the tests carried out for various models.