Author(s): Megh Raj K. C; Brian Crookston

Linked Author(s): Brian Crookston

Keywords: inclined steps; air entrainment; inception point; flow resistance; dam rehabilitation

Abstract: The rehabilitation of spillways at embankment dams regularly involves Roller-Compacted Concrete (RCC). Current RCC mix designs and placement methods include formed (vertical face steps) or unformed (beveled) steps. However, the influence of this bevel on hydraulic and energy dissipation performance in stepped chutes is less explored meriting additional research. This study focuses on the flow characteristics and energy dissipation of a beveled stepped spillway. Research was conducted at the Utah Water Research Laboratory at Utah State University using a field-scale sectional flume with a slope of 3:1 (horizontal to vertical), width of 1 m, and a drop height of 1.8 m. The experiments involved testing step heights of 0.1 m and 0.2 m with the vertical faces inclined at a 45-degree angle for a range of unit discharges (qw) from 0.15 m2/s to 0.55 m2/s. A dual-tip phase detection conductivity probe was utilized to measure air-water flow properties. Data was also collected for steps with vertical faces for direct comparison. Findings indicated multiple significant differences in performance due to the bevels that included a reduced streamwise distance to the inception point; higher mean air concentrations and flow depths at the spillway toe; lower velocities; and slightly more energy dissipation. Flow regimes were also influenced by the bevels, which required slightly larger discharges for the transition to skimming flow.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024