Automated Determination of the Distribution of Local Void Ratio from Digital Images
The frequency distribution of local void ratio is believed to be an important parameter, in addition to the void ratio, for describing the mechanical behavior of granular materials. Oda proposed a method to determine experimentally the distribution of local void ratio from 2-D plane sections. To date, implementations of Oda´s method have depended to varying extents on operator judgment to form polygons by joining the centers of gravity of all particles that surround a void. Furthermore, the studies have involved a significant amount of manual work in making the required measurements. This paper describes a fully automated implementation of the method, which uses high-level, image-processing techniques. The proposed method eliminates operator judgment and manual work and makes the determination of the distribution of local void ratio from 2-D plane sections both repeatable and efficient. The method is illustrated with measurements performed on synthetic and real images. The importance of correcting the images to account for factors such as thickness of segmentation lines is demonstrated. Measurements that confirm the stability of the proposed polygon network generation procedure are also presented.