Role of particle network in concentrated mud suspensions

Most materials involved in debris flows are made Lip of solid particles in water, covering a large size range. When natural suspensions can be tested with the usual laboratory rheometers, they exhibit a wide range of bulk rheological properties (time-dependent effects, viscoplasticity. etc.) and flow effects (particle migration, shear localization). Such properties are difficult to understand and describe in the framework of continuum mechanics, in which they are most often expressed. A rheophysical approach is ail alternative and fruitful way to describe the dynamics of geosuspensions. This paper reviews tile main notions that are useful for understanding tile rheological properties exhibited by natural mud suspensions. For concentrated suspensions. emphasis is given to the role played by a percolating network of coarse particles and the nature of contact between particles. Through a series of simple laboratory experiments, it is shown that a wide range of rheological behaviors can be observed by merely changing tile particle size distribution.