Evaluation Of Breakstone Grain Shape And Preliminary Studies Of Its Influence On The Permeability

The porous medium is a kind of skeleton constituted by solid material which forming complex pore system, and the fluid can move in the inter-connected pore system of porous medium. Generally the most common solid materials used widely are artificial crushed ballast or sand gravel which is transported through a long distance. Therefore, a study on the influence of particle shape on the pore system and permeability characteristic of porous medium is of great significance. The measurement and evaluation method for particle shape has been studied. Image measuring instrument and special fixture were used to achieve the measurement and evaluation of particle shape for three groups of different sizes by using five shape parameters. Cross-sectional views obtained by CT scanner were used to analyze pore size distributions for filled samples of crushed grain and glass ball, and to achieve fractal characteristics of pore shape for two kinds of opening-degree threshold. By conducting seepage experiments for filled samples of crushed grain and glass ball, the preliminary analysis of the influence of particle shape on the permeability of porous medium was discussed.In this paper, the main researches and conclusions are listed as follows:(1) With image measuring instrument and special fixture to measure the particle shape of crushed grain, multi-angle measurement enriched the measurement information of particles and laid a foundation for an accurate assessment for particle shape.(2) Five shape parameters were used to evaluate the particle shape. The distribution rule of five shape parameters were analyzed statistically for 3 groups of different sizes. The differences between crushed grain and standard sphere were discussed. The comparisons indicated that the parameters of length breadth ratio, flatness and sphericity could sensitively reflect the degree of deviation of particle from sphere. Compared with flatness, length breadth ratio and sphericity could be obtained more conveniently and directly, and were superior to others on the operability and efficiency.(3) Cross-sectional images of filled samples of crushed grains and glass balls were obtained by CT scanner. The images showed that the characteristic of the inner pores were complex and rather connective system for the studied particle groups. Appropriate threshold values of pore opening were used to disconnect the pores at narrow paths in order to carry out statistical analysis of pore size distribution and the research of fractal characteristics.(4) The comparison of seepage experiments were carried out to analyze the permeability coefficient of filled samples of crushed grains and glass balls with the same size distribution and porosity. The preliminary result showed that the more irregular particles would result in the bigger permeability for the porous media.