Relationships Between Starting Motion Of Large-sized Particles In Debris Flow And Hydrodynamic Conditions

Debris flow is a horrible natural geologic hazard.In each year,enormous casualties and property losses caused by debris flow are numerous.It is generally recognized that debris flow is solid-liquid two-phase flow,the liquid phase with high viscosity is composed of water and fine particles,and the solid phase is mainly composed of coarse particles.The impact of the debris flow includes two parts,one from liquid phase,and the another from solid particle.Both experimental and theoretical research finds that the solid phase's impact of the same volume and speed is much larger than the liquid phase's.So in several debris flow's impact reduction engineerings,the most economical way is to cut down the solid phase's impact.The flow condition is the key factor of the disaster eruption,cutting the quantity of flow can significantly cut the scale.In all of the prevention projects for the debris flow,separating water and stone can cut down the flood peak flow effectively,and stop the large-sized particle moving.Researches on the starting conditions of large-sized particles have important theoretical and practical significance to reduce the scale of debris flow.This paper considers the starting conditions of large-sized particles in three typical types of debris flow.First of all,a starting model of large-sized particles in debris flow channel was established.Secondly,according to different types of debris flow,the external forces on the starting particles were analyzed.Probability theory method was used to calculate each external force arm.The hydrodynamic conditions of large-sized particles' starting were obtained by solving the torque equilibrium equations.The effect of slope and liquid phase density on the starting of particles was analyzed.Based on the theoretical analysis,the critical hydrodynamic conditions of the three kinds of debris flow were obtained.For diluent debris flow and viscous debris flow,starting motions of large-sized particles were impacted by the liquid-impact,besides the liquid-impact is closely related to current velocity.So,the paper chose the cross-sectional velocity as the criterion for the starting of the large-sized particles in dilute flow and viscous flow.For water-stone flow,starting motions of large-sized particles were impacted by the solid-impact;the thickness of water stone flow layer is closely related to water depth.Therefore,water depth was used as the criterion for the starting of large-sized particles in water rock flow.The study on the critical hydrodynamic conditions of large-sized particles in debris flow provides a reference for prevention buildings of debris flow designing,especially drainage designing.