Pore water pressure distributions of granular mixture flow in a rotating mill

Abstract

We measured the pore water pressure distributions in miniature debris flows to assess the validity of the related constitutive equations. Our experiments used a rotating mill that allowed steady flows to be maintained easily and a Pitot tube to measure pore pressure accurately. Plastic and glass beads with particle sizes of 1–6 mm were used to simulate the debris flows. Since laboratory debris flows within a rotating mill give flow fields that differ from those of in situ debris flows, the flow characteristics in the rotating mill were also investigated. The experimental results showed that the pore water pressure was greater than the hydrostatic pressure. Although Stokes drag also appeared in the excess pore pressure in tests of small particle sizes due to infiltration flow caused by the inherent fluid field of the granular mixture flows in the rotating mill, pore water pressure in the case of 6-mm particles could be induced by Reynolds stress. The observed excess pore water pressure in the debris flows with 6-mm particles corresponded closely to theoretical values, supporting the use of constitutive equations for evaluating shear stress in the pore fluid of debris flows.