Abstract: In order to reveal the distribution law and shape characteristics of the macropore structure of granite residual soil, we quantified the round ratio, flatness, overall silhouette coefficient and fractal dimension of undisturbed granite residual soil in Fuzhou by using industrial CT scanning and ImageJ software. Our findings revealed that 1) over 80% of the macropores ranged 0.15-1 mm in diameter, and less than 20% of the macropores had a diameter greater than 1 mm. Ranging between 5.8%-22.7%, the macroporosity of granite residual soil first augmented and then reduced with the increase of soil depth. 2) Larger diameter of macropore resulted in a smaller round ratio. 3) The overall silhouette coefficient of four samples changed within 0.81-0.87, and such change attenuated with the increase of soil depth. 4) The macroporosity of granite residual soil is correlated with the fractal dimension; but the coefficients of such correlation of different samples varied distinctly. In summary, granite residual soil is of large porosity, small toughness, wide distribution of macropores, large difference in pore structure, and large dispersion of local pore flatness.

Key words: granite residual soil, CT scan, macropores, meso-scale, fractal dimension