Determination of Sliding Path in Rock Slopes Containing Coplanar Non-Persistent Open Discontinuity

In 3-D analyses of rock slopes there’re can be numerous sliding paths a long a coplanar nonpersistent discontinuity with a known strike. This paper describes an approach for the determination of a most probable sliding path. For this particular study, several blocks of gypsum with the dimensions of 15×15×15 cm containing coplanar non-persistent open joints were fabricated. The models have various configurations of rock bridges occupying 45, 90 and 135 cm of total shear surface (225cm) respectively. In order to study the complete failure behavior in the discontinuous joint, from each model, two similar blocks were prepared and were subjected to shear tests under two different normal stresses of 3.33 kg cm and 7.77 kg cm. The failure mechanisms were monitored by visual inspection and a low power microscope to detect crack initiation and propagation. For each test, the failure surfaces were investigated to determine the characteristics of each surface. Two types of newborn cracks were observed: wing (tensile) cracks and secondary (shear) cracks. Both types of cracks initiate from the tips of the joints and propagate in a stable manner. Based on the change in the configuration of rock-bridges, a factor called the Effective Joint Coefficient (EJC) was formulated, that is the ratio of the effective joint surface that is in front of the rock-bridge and the total shear surface. In general, the failure pattern is mostly influenced by the EJC while shear strength is closely related to the failure pattern and its failure mechanism. It is observed that the propagation of wing cracks or shear cracks depends on the EJC and the connection of wing cracks or shear cracks dominates the eventual failure pattern and determines the peak shear load of the rock specimens. So the EJC is a key factor in determination of sliding path. Key word: Coplanar non-persistent discontinuity • rock bridge • Effective Joint Coefficient (EJC) • tensile and shear cracks