Effect of number and configuration of bridges on shear properties of sliding surface

Abstract

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 number, area and configuration of the rock bridges on their shear properties are investigated. A total of 36 various models with dimensions of 30×30×30 cm of plaster specimens were fabricated simulating the open joints possessing 1, 2, 3 rock bridges respectively. The introduced rock bridges were of longitudinal and latitudinal configuration. The area of these rock bridges were 300, 450 and 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 shows that, shear failure occur in longitudinal rock bridge under these normal loads. But tensile failure occur in latitudinal rock bridge when rock bridge continuity was low and shear failure occurs in latitudinal rock bridge when rock bridge area was high. This behavior occurs in each configuration and normal load. The results were indicating that the cohesion of the longitudinal rock bridges is higher than those of the latitudinal rock bridge for similar areas. It was also noticed that in the fixed area of the longitudinal rock bridges the cohesion remains constant with the change in the number of bridges. But the cohesion of the latitudinal rock bridges increase with the increase of the number of rock bridges (under fixed area of the rock bridges). The friction angel was behaved constant all through the tests carried out for various models. In the final section of this article, two equations are introduced for determining the cohesion strength in longitudinal and latitudinal rock bridges.