Experimental study of steady and unsteady free surface flows with water-clay mixtures

The steady and unsteady free-surface flow of hyperconcentrated water-kaolinite clay mixtures is analysed experimentally. These mixtures exhibit non-Newtonian behaviour if volumetric concentrations of solid particles exceed about 10%. The viscosity-concentration correlations, determined by rotary viscometer, indicate that the Bingham model can be used to describe such fluids. Using the rheological parameters of this model, the water-clay laminar flow friction factors can be determined either by calculating the Reynolds and Hedstrom numbers, or by applying the concept of the extended Reynolds number. A quantitative analysis of the unsteady dam-break type of the free-surface flow is presented, giving a comparison of flow depth profiles and propagation rates between the investigated mixtures and water.