Abstract: The geometry is one of the key factors which can influence the mechanical and hydrological properties of coarse granular soil. In this article, the laboratory test and analysis method are adopted to study the particle appearance characteristic. Two types of coarse granular soil particles with different appearance characteristics are selected in the particle diameters of 10－20 mm, 20－40 mm, 40－60 mm separately. The wax-coated method is used to measure the volume, and the particle surface area is calculated by measuring the thickness of the wax coating. By building the mathematical fitting between the particle volume and the surface area, the correlations between volume and surface area of the two coarse granular soil particles are founded. With analogy, the two fitting equations proposed in this paper are found to be in excellent agreement with that of normative sphere, thus the concept of sphericity-similarity is raised and the coefficient of sphericity-similarity is calculated, which providing a method to describe the appearance characteristic of particle quantitatively.

Key words: sandy gravel coarse granule, appearance character, surface area, volume, coefficient of sphericity-similarity