Author(s): Janine Vogele; Robert M. Boes; Ismail Albayrak
Linked Author(s): Robert Boes, Ismail Albayrak
Keywords: Two-phase flow dynamic pressure piezoelectric pressure sensors sensor mounting spectral analysis
Abstract: Spillways are important safety structures of dams. In case of extreme floods, they should ensure the safe discharge of water to the downstream. In the past, multiple failures have been observed due to hydraulic jacking of concrete chute slabs. Some prominent recent examples of this are the spillway failures at Big Sandy Dam in 1983, Oroville Dam in 2017 and Toddbrook Reservoir in 2019. Uplift pressures are generated by water entering through gaps in joints and cracks in the slabs. From below, the water exerts uplift pressures on the slab, especially if the drainage system is inadequately designed. The phenomenon is even more pronounced if a vertical offset is present above the gap. Water will stagnate in front of the offset, leading to higher uplift pressures. An experimental setup has been constructed to investigate mean and fluctuating pressure distributions above and below a slab for different gap width and offset heights at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich, Switzerland. The model spillway has an inclination of 30° which leads to two-phase flow conditions. Prior to conducting experiments in the spillway flume, various pressure sensors are systematically tested in a low-level outlet flume, which is the focus of the present paper. The low-level outlet flume has a quadratic cross-section (0.4 m x 0.4 m) and a length of 20.6 m. In addition to water surface aeration, a bottom aerator is installed to increase the void fraction. The gate and head can be regulated, allowing for different flow conditions. The sensor behaviors in four two-phase flow conditions with contraction flow velocities Uc between 10 m/s and 18 m/s are compared. Two of the sensors are tested mounted flush and with a recess on the flume bed to account for the influence of the mounting. The best performing pressure sensor and mount under two-phase flow conditions will be used for the final design of the spillway model. Since the tests and data analysis are on-going, the results and conclusions of the tests will be presented in the full paper.
Year: 2025