Automating particle size and shape measurement in soil mechanics

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It is well established that the geometry (size and shape) of the individual particles influences the overall response of a granular material to applied loads and deformations. Traditionally in soil mechanics we measured the size of soil particles by passing the particles through a succession of sieves with different aperture sizes. Shape was measured qualitatively, by comparing the shape of a small number of particles with standard (2D) charts. These methods have some disadvantages. Considering sieving, we have no information about the distribution of particle sizes between the standard sieve intervals. The results of a sieve analysis are not always consistent, especially when long platy particles are involved. Changes in particle size distribution are used to assess damage to the individual particles, and the small changes we need to measure cannot be reliably detected using a sieve analysis. Regarding shape analysis, we know that particles in granular materials are three-dimensional. We also know that to get a statistically valid assessment of particle shape and particle shape variation in a granular material, the shape of thousands of particles should be considered. The traditional simple, visual description of particle geometry does not allow objective, quantitative, three-dimensional shape analysis of statistically meaningful numbers of particles. A new technology, the QicPic apparatus manufactured by Sympatec, includes a system for dispersing particles, a high speed camera and sophisticated image analysis software to measure particles sizes and shapes. This apparatus overcomes the limitations of the traditional low tech approaches, allowing 3D assessment of size and shape for large numbers of particles. We have had access to this apparatus, it was installed in our laboratory for a one-week trial period. During this period we established that the apparatus can produce valid measurements for the particles we are interested in, it can easily be used by our research students, and the degree of sophistication of the output (including black and white images of individual particles) makes it a good tool for fundamental research on particle morphology.This apparatus would provide us with improved capabilities for quality control for a range of experimental work involving granular materials in the department. These materials include natural and artificial sands used in soil mechanics research, morsellised bone used in biomedical engineering research and artificial aggregates that are being developed from waste by-products as environmental engineering research. The apparatus can also be used to better understand how the individual particles are damaged when a granular material is loaded and deformed, and this understanding is important for developing numerical models of the material. The apparatus would also be useful to support ongoing research that will develop a relationship between the overall material response and the characteristics of the constituent particles.The applicants are already collaborating to develop methods to quantify both particle strength and particle geometry and relate these characteristics to the overall material response. Our current facilities include an optical microscope,a surface mapping microscope, and single particle mechanical apparatii. This apparatus would complement these tools, and strengthen our expertise in this area.