%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Roche, Olivier
%A Montserrat, S.
%A Nino, Y.
%A Tamburrino, A.
%T Experimental observations of water-like behavior of initially fluidized, dam break granular flows and their relevance for the propagation of ash-rich pyroclastic flows
%D 2008
%L fdi:010046767
%G ENG
%J Journal of Geophysical Research - Solid Earth
%@ 0148-0227
%M ISI:000261687700002
%N B12
%P B12203
%R 10.1029/2008jb005664
%U https://www.documentation.ird.fr/hor/fdi:010046767
%> https://www.documentation.ird.fr/intranet/publi/depot/2009-07-01/010046767.pdf
%V 113
%W Horizon (IRD)
%X The physics of ash-rich pyroclastic flows were investigated through laboratory dam break experiments using both granular material and water. Flows of glass beads of 60-90 mu m in diameter generated from the release of initially fluidized, slightly expanded (2.5-4.5%) columns behave as their inertial water counterparts for most of their emplacement. For a range of initial column height to length ratios of 0.5-3, both types of flows propagate in three stages, controlled by the time scale of column free fall similar to(h(0)/g)(1/2), where h(0) denotes column height and g denotes gravitational acceleration. Flows first accelerate as the column collapses. Transition to a second, constant velocity phase occurs at a time t/(h(0)/g)(1/2) similar to 1.5. The flow velocity is then U similar to root 2(gh(0))(1/2), larger than that for dry (initially nonfluidized) granular flows. Transition to a last, third phase occurs at t/(h(0)/g)(1/2) similar to 4. Granular flow behavior then departs from that of water flows as the former steadily decelerates and the front position varies as t(1/3), as in dry flows. Motion ceases at t/(h(0)/g) 1/2 similar to 6.5 with normalized runout x/h(0) similar to 5.5-6. The equivalent behavior of water and highly concentrated granular flows up to the end of the second phase indicates a similar overall bulk resistance, although mechanisms of energy dissipation in both cases would be different. Interstitial air-particle viscous interactions can be dominant and generate pore fluid pressure sufficient to confer a fluid-inertial behavior to the dense granular flows before they enter a granular-frictional regime at late stages. Efficient gas-particle interactions in dense, ash-rich pyroclastic flows may promote a water-like behavior during most of their propagation.
%$ 066