Author(s): Santiago Montserrat; Aldo Tamburrino; Yarko Nino; Olivier Roche
Linked Author(s): Yarko Niño, Aldo Tamburrino
Keywords: Granular flows; Pore-fluid pressure; Aerated flow
Abstract: Results of an experimental study on the movement and deposition of initially aerated granular flows are presented in this paper. Nearly spherical glass beads, with sizes ranging from 45 to 90 um, were placed in a reservoir where they could be aerated by introducing an air flux trough a 10 mm thick porous plate located at the bottom. A sluice gate separated the reservoir from a variable slope, 3 m long and 0. 1 m wide flume. The gate was suddenly opened and a granular flow was generated, which was recorded with two video cameras (one of them a high speed, 90 fps camera). Flow depth and front velocity were obtained from the recordings. A pressure transducer located at the bottom of the reservoir was used to measure and control initial pore-fluid pressure of the granular bed. A dimensional analysis shows that the observed granular flows were dominated mainly by inertia and Coulombic friction, as in many natural geophysical granular flows. Results show that the flow front moves with a nearly constant velocity for most of the flow duration, while initial acceleration and stopping phases occur in shorter times. Flow mobility is importantly enhanced if the initial aeration rate exceeds 70% of the complete fluidized state. This result suggests an important effect of pore-fluid pressure in the flow dynamics when it initially exceeds a certain critical value, in this case about 70% of the fluidized state. An analysis of pore-fluid pressure diffusion in a static bed shows complex nonlinear effects if the aeration rate exceeds the critical state condition. Results show that, for highly aerated conditions (>70% ), the mixture tends to retain pore-fluid pressure for longer periods, thus enhancing its effects in the flow.