Bull Run Dam No. 2 and Powerhouse
In response to a Federal Energy Regulatory Commission (FERC) dam safety inspection by others, Cornforth Consultants was retained by the City of Portland Bureau of Water Works, Hydroelectric Power Section to perform seismic stability analyses on Bull Run Dam No. 2 and three adjacent natural slopes surrounding the powerhouse and tailrace. A site-specific seismic hazard analysis incorporating deterministic and probabilistic ground motions was developed for the site. A Becker Hammer drill was used to characterize the density of the sand and gravel drainage blanket under the downstream side of the embankment dam. State-of-the-practice analyses were performed to evaluate static and cyclic shear stresses within the embankment and the potential for generating excess pore-water pressures. Limit-equilibrium stability analyses were performed that incorporated excess pore-water pressure ratios. Post seismic deformations of the embankment were estimated using the Makdisi-Seed approach. Pseudo-static and Newmark-type displacement analyses were performed on the three adjacent natural slopes.