Prediction of impact force of debris flows based on distribution and size of particles

A debris flow is a solid–liquid two-phase flow; the composition and gradation of the particles within have a significant influence on its impact force. This paper proposes a new method for studying the impact force according to the composition of a debris flow based on analysis of existing calculation methods. The impact force is divided into three parts: (1) the dynamic pressure provided by the debris flow slurry, which is composed of fine particles and water; (2) the impact force of coarse particles; and (3) the impact force of boulders. This paper analyzes the established formulations used to calculate the impact force by using hydrodynamic theory and contact mechanics to propose a debris flow impact model according to the debris flow type. The results show that the impact force is closely related to the solid volume fraction, composition of particle materials, motion velocity, and depth of a debris flow. Among all the components of the impact force, the boulder impact force is the largest followed by the impact force of coarse particles; the dynamic pressure is minimal.