Flow properties of simple debris

Sumaryanto Yohanes Martosudarmo, Purdue University


Simple debris, consisting of mixtures of sand and clay-water slurry, has a linear macro-viscous behavior, beyond yield. The dynamic, viscous properties of simple debris can be explained using mixing theory in terms of the coefficient of viscosity of the interstitial slurry and the concentration of the inert granular phase. The ability of debris to remain fluid, even if static, is a result of the slurry and water being practically locked into the structure of the debris. Specifically, the hydraulic conductivity of water through slurries is astonishingly low and the conductivity of slurries into and out of pores in the interstices of the coarser granular solids is extremely low. This explains the slow sedimentation of coarse particles in the debris. A general rheological model is formulated to incorporate, simultaneously, the macro-viscous rheology developed during this research for simple debris flows and the inertial rheology developed by Bagnold (1954) for grain-flows. The combined model largely accounts for the dynamic behavior of mixtures of sand, water and clay, and it predicts the flow curves for sand-fluid mixtures and simple debris with interstitial slurries of various viscosities.




Johnson, Purdue University.

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