Trends in the evolution of particle morphology with size in colluvial deposits overlying channel iron deposits

Size limitations of testing equipment often impliy that samples of coarse granular materials must be scalped or scaled, to reduce the size of the constitutive particles, before they can be tested either by triaxial or direct shear in the laboratory. The objective of the investigation is to evaluate the particle shapes in a natural sample of colluvial sediments, to identify potential correlation(s) between shape and size, that could impact shear strength of scaled samples. The material investigated is derived from eroded ancient sedimentary rocks from the Pilbara region of Australia. The fragments have a particle shape ranging from slabs to sub-equant blocks. The observation indicates that there is an increase in the tendency for slabshapes in larger particles. Therefore, scaling inevitably alters the characteristic shapes of the material particles as it implies substituting larger (slabs) particles by smaller (sub-equant) particles. Changes in particle shape distribution may induce changes in material fabric and shear strength and therefore may need to be considered when scaling samples.