Abstract:

Aim to reveal the intrinsic mechanism of percolation in geotechnical granular media, geotechnical granular media samples were prepared by adjusting the ratio of clay and coarse sand, and their permeability coefficients were measured. With the help of image analysis methods, the distribution parameters of coarse sand in experimental sample images and randomly simulated images were statistically analyzed. Based on this, the percolation law and intrinsic mechanism of geotechnical granular media were analyzed. The results showed that as the mass fraction of coarse sand increased, the number of connected clusters of coarse sand showed a pattern of first increasing and then decreasing. The maximum connected cluster area, average connected cluster area, fractal dimension of coarse sand distribution, and permeability coefficient of experimental samples all showed a monotonic increase. The 30.0% mass fraction of coarse sand is the turning point of the change in the number of connected clusters. When the mass fraction of coarse sand is around 60.0%, the growth rate of the number of connected clusters, the maximum connected cluster area, and the average connected cluster area drops sharply or increases sharply. At the same time, the permeability coefficient of the soil particle media also quickly crosses two orders of magnitude, and percolation occurs. The occurrence of percolation in soil particle media is closely related to the changes in the morphology of connected clusters caused by changes in the proportion of coarse sand. When the mass fraction of coarse sand is below 30.0%, the coarse sand particles are dispersed in an “isolated island” shape in the clay particles. When the mass fraction of coarse sand exceeds 30.0%, the coarse sand begins to connect with each other, and the number of connected clusters decreases, but still appears in a “patchy” shape with poor connectivity. After the mass fraction of coarse sand reaches 60.0%, the probability of coarse sand connecting to each other as a single connected cluster approaches 1.0, and a high permeability channel that runs through the entire seepage path is formed, triggering percolation.

Key words: percolation, binarized image, permeability coefficient, connected clusters, fractal, porous medium