Effect of Joint Micro Mechanical Parameters on a Jointed Rock Block Behavior Adjacent to an Underground Excavation: A Particle Flow Approach

Abstract

The particle flow code PFC3D was utilized to investigate mechanical behavior of jointed rock blocks, having non-persistent filled joints, located adjacent to an underground excavation. The focus of this investigation was to study the effect of filled joint micro-mechanical properties on the failure mode and strength of jointed rock blocks by varying the joint orientation. The smooth joint model was incorporated to create non-persistent filled joints having the following micro-mechanical parameters: the joint normal stiffness, joint shear stiffness, bonded joint friction angle, bonded joint cohesion, joint friction coefficient and joint tensile strength. The joint normal and shear stiffness were found to affect the mechanical behavior of jointed rock blocks having joint dip angles less than or equal to 45°. Increase of the bonded joint cohesion increased the strength significantly of jointed blocks having dip angles 30° through 90°. Increase of the bonded joint friction angle increased the strength significantly of jointed blocks having dip angles 30° through 60°. Increase of the joint friction coefficient slightly increased the strength of jointed blocks having dip angles 30° through 60°. Effect of the joint tensile strength on the mechanical behavior of jointed blocks was found to be negligible apart from the jointed block which had 90° dip angle, which showed slight affect. The applied stress path in the conducted study resulted in more shear fractures compared to the tensile fractures in the joint segments. The results indicated the importance of using proper micro-mechanical parameter values to obtain realistic behavior of jointed rock masses in investigating stability of underground excavations using PFC3D.