Overflow pressure characterization in lined plunge pools for slab sizing

This study presents an experimental work on dynamic pressures at the bottom of a lined plunge pool that receives overflow rectangular impinging jets and aims at improving the design criteria for pool slabs. The experiments were conducted in a fairly large-scale facility, designed for the analysis of turbulent jets and the energy dissipation in overflow structures. The paper present new insights on the pressure distribution generated by overflow plunging jets, with various trajectories and stagnation points. Different longitudinal pressure statistics show how the interplay between the overflow rate and downstream tailwater levels leads to different flow features and dynamic load conditions at the pool bottom. In the tested set-up, higher pressures are recorded at the bottom of the pool for higher flow rates, leading to higher mean dynamic pressure coefficients. However, smaller fluctuations are recorded. Therefore, in such conditions the dimensions of the slabs must be larger than for lower discharges, since large average pressures affects a larger surface of the pool bottom around the stagnation point (accentuated upstream). In addition, it has been determined that the presence of an effective cushion imposed by a control section further downstream attenuates the impact pressures between 16-38% (depending on the flow rate). And as the depth of the water cushion increases, the more energy dissipation takes place inside the cushion.