An important characteristic of floc formed by fine sediment is its fractal feature,but many researches have been focused on 2-D fractal properties through analyzing SEM image of floc.In order to solve this problem,3-D image of flocs was reconstructed under gray values,and 3-D fractal dimension of flocs was calculated using box-counting method with the help of MATLAB programming.Moreover,a settling formula of interface was derived based on 3-D fractal dimension of flocs and used in the settling calculation of interface of silt in Dianchi Lake,with the calculation error of 5%.The results showed that it is practicable to use grey-scale image to obtain 3-D fractal dimension of flocs,which can avoid man-made error in the image processing,and the formula deduced from 3-D fractal dimension is available to calculate the settling velocity of the interface.
