Abstract Description: Damage to the main and emergency spillways at Oroville Dam in 2017 triggered inspections and spillway replacements at dams across California. Inspections at Santiago Creek Dam in Orange County showed the spillway has reached the end of its design life and is in poor condition, requiring replacement to improve safety, pass larger flows, and improve access to site facilities during spills. The proposed replacement spillway features a complex design and geometry due to limited space between the embankment dam and adjacent site features. To accommodate the proposed spillway, cut slopes nearly 200-ft high will be required at the left abutment. The geology at the left abutment consists of a thick sequence of marine sandstone and shale, which are intensely weathered in outcrops. The shale unit in particular presents significant engineering challenges due to its relatively low strength, which is exacerbated by the deep weathering profile sometimes more than 40-feet deep in borings. This paper describes the geologic characterization of the left abutment and along the spillway chute, development of material parameters for these units, stability analysis approach, challenging design of the cut slopes, retaining walls, spillway control structure, foundation criteria, foundation treatment, and constructability challenges.
Learning Objectives:
Learn about the development of strength parameters for weak rock.
Learn about the stability analysis approach and other engineering solutions for the project.
