Effect of grain shapes in coordination number from micro-CT image analysis of an unconsolidated sand

Abstract

Coordination number (CN, average number of contacts a grain has with its neighbours inside a granular medium) appears to be one of the important parameters in contact based modelling of elastic properties including seismic velocities in unconsolidated sands. We analyse micro-CT images of two different resolutions of the same unconsolidated quartz sand, in order to find CN and morphology of the grains. Both of the image sets give similar results in CN and size distribution whereas grain morphology differs slightly. We find that the number of grains, to be considered for calculations in the lower resolution image, is sufficient enough to provide a better normal distribution data. However, a decreasing of sphericity and roundness on the grains show a very gentle increasing trend in CNs. Therefore, for modelling of elastic properties, not only CN, but grain morphology should also be considered along with other factors such as pressure, initial porosity, loading unloading history, and prepacking conditions.