Sheared and un-sheared segregation and settling behavior of fine sand particles in hyperconcentrated homogeneous sand-water mixture flows

Segregation and settling of fine solids particles in hyperconcentrated homogeneous sand-water mixtures were studied for un-sheared and sheared conditions in settling columns in the laboratory. Specific solids percent values were able to be determined as the segregation threshold limit for un-sheared static settling conditions as well as for sheared settling with different rates of shear. Full-scale flume tests were also performed in the field with mine tailings slurry to study the settling and segregation behavior of fine sand particles in the flow of a hyperconcentrated sand-water mixture under equilibrium slope conditions. The solids contents of slurry mixtures were within the range 44 to 58% (by weight). The solids particles in the slurries had D 50 = 10 μm. Experimental results showed that increasing the shear rate in the settling column up to a certain level had the effect of increasing the segregation threshold limit value. Slurry density in hyperconcentrated flow remained constant with depth. Although the flow of the hyperconcentrated mixture under equilibrium slope condition was shown to be total transport flow, further detailed grain size analysis revealed that there was always a slightly higher portion of coarse solids particles that tended to accumulate towards the bottom of the flow.