Modeling of Entrainment in Debris Flow Analysis for Dry Granular Material

Abstract

Debris flows that entrain sediment by undermining channel beds or scouring channel banks can become exceptionally mobile and destructive. Therefore, the calculation of entrainment plays an important role in debris flow runout analysis. An entrainment model is proposed that takes into account surface erosional effects by considering progressive scouring and shear failure on the channel surface. By considering simple geometry and particle configurations, the equations for the progressive scouring are developed. In deriving the equations for the progressive-scouring mode of erosion, two types of motions are considered: rolling motion and sliding motion. Newton’s law of motion is applied to calculate the acceleration, velocity, and displacement of the particles. A probability-density function (PDF) is used in the calculation of the entrainment rate for different configurations of particle contact. Measurements from flume experiments were used for model verification. It was found that the entrainment rate can be calculated using a normal-distribution PDF. The proposed entrainment model has been shown to be effective in calculating debris flow entrainment.