This paper presents a new experimental procedure aimed at defining the global instantaneous uplift force, acting on slabs at the bottom of stilling basins. The global uplift force on slabs of different dimensions is measured for Froude numbers of the incident flow ranging from 5 to 12. The measurements were made in the zone of hydraulic jump, where high turbulence yields the maximum uplift force. The fluctuating force per unit area is shown to depend on the slab shape and on the statistical structure of the instantaneous spatial distribution of turbulent pressures at the bottom of the hydraulic jump. This paper provides direct experimental evaluation of a criterion for the design of the protection slabs in spillway stilling basins. It is shown that rectangular slabs with the longer side placed along the flow direction (where the transverse direction is maintained to a technically minimum length) are most suitable for the design of the lining of spillway stilling basins.
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