UC Berkeley

Scourof rock is a complex process and can be very problematic for dams when excessive scour threatens dam stability. Removal of individual rock blocks is one of the principal mechanisms by which scour can occur, particularlyin unlined spillways and on dam abutments/foundations. To alleviate some of the complexity,commonlyused methods for scour prediction tend to simplify the rock mass using rectangular block geometries or incorporate empirical relationships for the rock mass and do not actually model the physical scour process. Such simplifications can be problematic,particularlyfor block analysis,wherethe 3D orientation of discontinuities within the rock mass largely influence block removability. To better represent the 3D structure of the rock mass,blocktheory is used to evaluate stability of removable rock blocks subject to hydraulic forces. Block theory provides a rigorous methodology to identify removable blocks,determine potential failure modes,andassess block stability. An actively eroding unlined spillway at a dam site in Northern California is used to demonstrate the use of this approach for the evaluation of the scour potential at the site. Copyright 2013 ARMA, American Rock Mechanics Association.