Granular pressure at the base of dry flows of angular rock fragments as a function of grain size and flow volume: A relationship from laboratory experiments

Abstract

[1] Experiments are carried out by releasing angular rock fragments down a curved chute and by measuring the basal pressures that are exerted by the granular flows on the basal containing surface (the substrate). The purpose of these experiments is to understand the mechanisms of energy dissipation and interaction with the ground of rock avalanches and dense pyroclastic flows. Our data show that collisions due to particle agitation affect significantly the basal interaction of granular flows. In particular, our experiments reveal that particle agitation per unit of flow mass increases as grain size increases or as flow volume decreases (with all the other features the same). This is so because as grain size increases or as flow volume decreases (with all the other features the same), there are fewer particles in the flows and the agitation due to the interaction with the rough containing boundary surfaces penetrates relatively more inside the flows. The analysis of the experimental data generates a linear relationship between particle agitation (expressed as a dimensionless basal pressure deviation) and a parameter which is directly proportional to the square of grain size and inversely proportional to the cube root of flow volume. This relationship shows the intrinsic ability of the granular flows to dissipate more energy (larger particle agitation per unit of flow mass) or less energy (smaller particle agitation per unit of flow mass) as a function of flow volume and grain size.Citation: Cagnoli, B., and G. P. Romano (2012), Granular pressure at the base of dry flows of angular rock fragments as a function of grain size and flow volume: A relationship from laboratory experiments,

Grain size and flow volume effects on granular flow mobility in numerical simulations: 3‐D discrete element modeling of flows of angular rock fragments

“…In both the laboratory experiments [ Cagnoli and Romano , , ] and the numerical simulations, the deposited granular material consists of two portions: a more proximal heap that is much more elongated than thick (the deposit of the flow proper) and a more distal distribution of individual fragments. The distal distribution is formed by fragments, which, bouncing within the chute, traveled individually without interacting and are not part of the flow proper.…”

“…Equation refers to dense flows (i.e., not to turbulent flows) without spurious effects such as those due to electrostatic charges. The density of the flows can span a relatively large range of values as shown by Figure 3 in Cagnoli and Romano []. Coefficients a and b depend on the characteristics of the flow and on those of the slope.…”

“…Particle agitation in granular flows is due to interactions with the asperities of the containing surfaces (both the lateral and the basal ones), and it consists of the acquisition by the particles of speed components in directions different from the downslope one. We measured the variance of particle transversal speeds also in the granular flows of the laboratory experiments [ Cagnoli and Romano, , ]. Average squared deviations are used in the definition of the so‐called granular temperature as well [ Ogawa , ].…”

Grain-Size Analysis of Debris Flow Alluvial Fans in Panxi Area along Jinsha River, China

“…We have examined the degree of sorting of the deposits and because the larger the sorting, the larger the travel distance of the flows [29,30], we have included in Table 6 the potential travel distance that the flows would have had without entering the Jinsha river. However, the correlation we obtain where the mobility of the flows increases as the grain size decreases is confirmed by laboratory experiments [31] and numerical simulations [32].…”

An Approach to Predict Debris Flow Average Velocity

“…Yang also found that average velocity was influenced by the sediment properties represented by clay content and grain size non-uniformity. Prochaska [26] and Cagnoli [27] found that the velocity generally decreased with increasing grain size. Julien and Paris [28] employed the ratio of flow depth to median grain size, h/D 50 .…”