Experimental results on arching structures in sedimentary deposits are presented. Polydisperse mixtures of rough non-spherical natural calcite particles (ground limestone) settled collectively in a liquid, in a lab-scale experimental cylinder. At the bottom, layers of sediment were produced. The morphology of the deposit layers was studied with the help of visualization and image analysis. Families of inter-connected arching patterns in the form of voids or cavities were identified, of highly complex geometry. The effect of the mixture composition on the deposit structure was investigated. It was found that arches tend to form under specific conditions. Large and small grains promoted the arch formation, while the medium grains tended to inhibit arching. (C) 2013 Elsevier B.V. All rights reserved.