Rheological stratification of high-concentration liquid-granular flows

Michele Larcher

CUDAM - Department of Civil and Environmental Engineering, University of Trento
michele.larcher@ing.unitn.it

High concentrated uniform granular flows with water as interstitial fluid are 
analysed, drawing the attention to the relevance of the condition of flow in 
equilibrium with the bed. Four different flow regimes have been observed: (a) 
loose bed, immature debris flow; (b) loose bed, mature debris flow; (c) loose 
bed, plug debris flow; (d) rigid bed debris flow. 

The present work presents detailed experimental measurements resorting to a 
novel recirculatory flume set-up, in combination with recently developed 
Voronoļ imaging methods, used to obtain a detailed characterisation of the 
local flow kinematics and of granular concentration, as seen through the 
flume sidewall. 
Looking at the profiles of the variables of interest in the stress formation 
(velocity, fluctuation energy, and solid concentration), it is observed that 
they change enormously from cases with and without equilibrium. The analysis 
here proposed stepped out from the possibility to lead on experimental 
assessments of the kinetic theories in any position inside the flow domain. 
The results allowed to build a picture of the rheological distribution that 
is rather simple: throughout the flow depth there are layers that are 
collisionally dominated, whereas the complementary domains are essentially 
frictional.