FLOW CHARACTERISTICS OF GRANULAR BULK MATERIALS

The paper discusses the interest in conventional triaxial tests widely used in soil mechanics for a better understanding of both the mechani cal behaviour and flow characteristics of granular bulk materials. It proposes a rheological characterization of granular foodstuffs on dive rse types of stress path using a conventional triaxial cell. The chara cteristic state concept, defining the disaggregation threshold of the granular structure, is found to be suitable and even indispensible for examining the mechanical behaviour and the flowability of stored bulk materials. The experimental results readily suggest, as an indicator of the arching effect, a rheological index that characterizes the part icle interlocking breakdown and hence the flowability of the stored ma terials. In addition, this study offers a realistic physical meaning f or parameters in use in constitutive models (yield conditions and flow rules) when describing granular flow in various hopper geometries. Th e case of silos equipped with vibrating hoppers necessitates additiona lly the study of the rheological behaviour of materials under cyclic a nd vibratory loadings in order to analyse the processes of densificati on or disaggregation conditioning the flowability of the stored materi als during emptying operations.