Importance of the Particle Shape on Mechanical Properties of Soil Materials

Sammanfattning: Particle shape of soil aggregates is known to influence several engineering properties; such as the internal friction angle, the permeability, etc. Even if this is known, there has been only minor progress in explaining the processes behind its performance and has only partly implemented in practical geotechnical analysis. Previously shape classification of aggregates has mainly been performed by ocular inspection and e.g. by sequential sieving. In geotechnical analysis has been a lack of an objective and rational methodology to classify shape properties by quantitative measures. The image analysis, as quantitative methodology, is tested and it is investigated how the results are affected by resolution, magnification level and type of shape describing quantity. Tailings as a part of granular materials need to be stored safely in facilities and for a long time perspective a good knowledge of current and future materials properties is needed. Tailings are site specific and not well investigated compare to natural geological materials. There also is a need of prognosis tools for long term behavior. Based on laboratory test tailings from Aitik mine has been investigated through triaxial test and particle shape (using two dimensions image analysis). The overview has shown that there is no agreement on the usage of the descriptors and is not clear which descriptor is the best. The resolution in the processed image needs to be considered since it influences descriptors such as e.g. the perimeter. Recent development in image analysis processing has opened up for classification of particles by shape. The interpreted results show that image analysis is a promising methodology for particle shape classification. Results are affected by the image acquisition procedure, the image processing, and the choice of quantity, there is a need to establish a methodology to ensure the objectivity in the particle shape classification. A comparison between laboratory shear strength tests of the analysed tailings material and previouslypublished empirical relationships between shape and friction angle indicates that the minimum quantity value have the shortest difference between obtained data and expected results.