Interface settling property of clay floc suspension

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The settling velocity of flocculated suspensions is determined as a function of effective floc volume fraction that is believed to be proportional to the solid volume fraction. However, flocs are very fragile and have an extended structure in suspensions so the effective volume changes easily. Therefore, a new method to determine effective volume from sediment volume was proposed and the effective volume was found to not be proportional to the solid volume. By using the measured effective volume, network formation was clarified to occur at an effective volume fraction over 0.25-0.30. Self-similar properties of floc structure were introduced for the analysis of settling velocity, and with the help of the relationship between settling velocity and effective volume fraction, fractal dimension was determined to be 2.35. On the other hand, at high volume fractions, many vertical channels were formed through the sediment and settling velocity tremendously increased. The flow rate in the channel was comparative to the computed maximum viscous-flow rate.