Relationships between size and velocity for particles within debris flows

Abstract

Estimation of the impact forces from boulders within a debris flow is important for the design of structural mitigation elements. Boulder impact force equations are most sensitive to the inputs of particle size and particle velocity. Current guidelines recommend that a design boulder should have a size equal to the depth of flow and a velocity equal to that of the flow. This study used video analysis software to investigate the velocities of different sized particles within debris flows. Particle velocity generally decreased with increasing particle size, but the rate of decrease was found to be dependent on the abilities of particles to rearrange within debris flows.

An Approach to Predict Debris Flow Average Velocity

“…In Table 1, debris flow velocity shows a positive correlation with each of the four independent variables (x 1 , x 2 , x 3 , and x 4 ), but these correlations are weak (R 2 values range between 0.54 and 0.27). According to the previous work [26], we would expect a negative correlation between debris flow velocity and grain size. The positive correlation in this data set is almost certainly because of that these speed values do not depend only on grain size but on several variables at the same time (x 1 , x 2 , x 3 and x 4 ).…”

“…work [26], we would expect a negative correlation between debris flow velocity and grain size. The positive correlation in this data set is almost certainly because of that these speed values do not depend only on grain size but on several variables at the same time (x1, x2, x3 and x4).…”

“…In this study, we took four variables into consideration using the GSA-RBF. Variables influencing debris flow velocity are various [25,26]. In Table 1, debris flow velocity shows a positive correlation with each of the four independent variables (x 1 , x 2 , x 3 , and x 4 ), but these correlations are weak (R 2 values range between 0.54 and 0.27).…”

“…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 .…”

Comparison of measurement methods of the front velocity of small-scale debris flows

“…For these reasons, the front velocity cannot be easily measured through the common hydraulic techniques (Arattano and Marchi, 2005). At real scale, the continuous measurements of surface velocity are possible using spatial filter velocimetry, electromagnetic Doppler speedometers (Itakura et al, 1985;Itakura and Suwa, 1989;Suwa et al, 1993;Inaba et al, 1997) and image processing techniques (Arattano and Marchi, 2000;Prochaska et al, 2008). Measurements of the mean front velocity are possible with ultrasonic (Pierson, 1986;Arattano et al, 1997), seismic and acoustic sensors Arattano and Moia, 1999).…”