Experimental study of uplift pressures underneath slabs with gaps running across flow

Abstract

An analysis was made to determinate if the pressure underneath a slab floor is affected by the flow velocity, the unsealed transverse gaps at the same level, and the separation between slab and floor to avoid level changes between gaps due to non-kinetic energy to pressure energy conversion. The variable was measured with the slab lying at the bottom or when separated from it, studying a flow with Froude numbers from 2.84 to 9.94 and depths with one-centimeter increments from 2.5 to 5.5 cm and separations between slab and bottom of 0, 0.2, 0.5, 1, and 2 mm. Furthermore, it was determined whether the measured pressure is greater than the static pressure, and whether the difference between these results corresponds to the kinetic energy of the flow that is converted into pressure energy inside the back edges of the gaps. In each test the pressure was measured along three longitudinal lines underneath the tile: one central line with 8 pressure transducers and two laterals lines (side by side from the central line), with 4 pressure sensors each. As it was assumed, energy conversion in the gaps increases the measured pressure in the bottom of the slab beyond the static pressure. In addition, the experiments confirmed that the pressure deceases in the direction of flow. Thus, an inestability factor of the floor linings of hydraulic structures was identified, being not previously considered in the failure of floor revetments in several civil engineering projects.