Fluctuating Uplift and Lining Design in Spillway Stilling Basins

Abstract

The paper deals with the characterization and the control of transient uplift generated by turbulent pressure fluctuations in spillway stilling basins. Theoretical and experimental analyses are presented, defining the maximum instantaneous uplift acting on the linings, which lead to a design criterion for suitable floor slabs. The thickness of concrete linings (not accounting for the possible contribution of anchors) required for stability is defined in this paper as a function of (1) The incoming kinetic head and/or Froude number; (2) a dimensionless function of the longitudinal and transversal dimensions of the lining slabs, the areal extent of extreme turbulent pressure fluctuations, and the anisotropic integral scales of the instantaneous spatial correlation of pressure fluctuations; (3) the ratio of specific weights of water and immersed concrete; and (4) a dimensionless pressure coefficient qualifying the maximum difference of positive and negative pressure fluctuations about the (stationary) mean value. It is concluded that safe design of protection works is significantly affected by the structure of instantaneous spatial distribution of pressures at the bottom of hydraulic jumps. Consideration of this factor leads to recommendations for the design of slabs in stilling basins.