The effect of fragmentation on the engineering properties of granular materials: Laboratory and fractal analyses.

摘要

Granular materials forming part of engineering structures such as rockfill dams, embankments, the base of flexible pavements and foundations are constantly subjected to harsh environmental conditions and external forces including static and dynamic loads. As a result, these materials experience various levels of fragmentation.; In this study, the levels of fragmentation were analyzed from particle/grain size distribution (PSD) plots before and after fragmentation as well as the fractal dimension concept from fractal theory. The fractal dimension concept was found to evaluate well the fragmentation induced in specimens of sands, gravels and glass beads.; Tests on abrasion as a result of peripheral fragmentation of gravels (5.5 mm.) were produced in the laboratory using the Jar mill apparatus. Applying the area-perimeter method of fractal analysis, it was found that as the profile of the particles becomes more rounded the fractal dimension reduces in value.; Total fragmentation and crushing of granular specimens induced in test apparatus such as the Bromhead Ring Shear, Universal Testing machine and Standard Proctor produces the PSD that evolves from a uniform to a well-graded condition. As a result, the fragmentation fractal dimension increases.; Changes in the engineering properties such as the elastic moduli, hydraulic conductivity and the shear strength were also studied. Tests on the elastic moduli of the fragmented gravels using an ultrasonic velocity Pundit apparatus indicated an increase in the elastic moduli as the levels of fragmentation were increased. Hydraulic conductivity tests indicated that the permeability of the samples decreased as the levels of fragmentation increased. Shearing of Quartz sand (1.6 mm.) in the Ring Shear apparatus indicated a decrease in the angle of internal friction as the fragmentation was increased.; An investigation on the angle of repose of binary mixtures of coarse and fine materials on a smooth glass base as compared to that on rough surface porous stone base was also conducted. A theoretical relationship between the angle of repose, the angle of internal friction and the interface basal friction was developed. It was found that the different compositions of the binary mixture and the basal friction significantly influenced the angle of repose.