“5. 12”Wenchuan earthquake generated a lot Slumping Mass,the angular coarse particles on slope are easy to start forming debris flow Under water erosion. This article is on the basis of the Geological research model of the earthquake debris flow on slope,established the basic model of the cube as the coarse particle of the lean debris flow on slope,combined with a wide size distribution characteristics of the debris flow on slope,the cube model contain the slip,flip( including around the edge flip,flip around and embedded solid fulcrum around the edge flip)and other start-up mode,and the theory are based on the hydraulics,sediment dynamics,deducing the start-ing average velocity formula of the coarse particles in the slip. Referring Chen Qibo experimental data,we calculate the starting velocity when the diameter of particles is 5~10 mm at different slope conditions,the comparison of the data showed good agreement between the two,indicating that the cube as a starter model of debris flow on slope di-lute coarse particles is reasonable. The results also show that,under the same gradient conditions,the Stimulate the flow rate of coarse starting slip is the minimum,followed by winding start side,the flow rate of solid particles embedded in the excitation required for starting is the maximum. For examples,the gradient is 30° under the con-ditions of starting the slip velocity of the flow excitation 0. 349 m/s,about the starting edge of 0. 430 m /s,embed-ded solid starter is 0. 473 m / s. As we can infer from this,when the water reaches a certain velocity(such as flow velocity below 30° slope of 0. 349 m/s),the coarse particles initially start to slip;as the flow rate increases,the gradual emergence of flip start;when the flow velocity increases sharply,most embedded solid coarse particles to flip instant way to start to form a dilute of debris flow on slope,thereby forming a dilute of debris flow on slope. The achievement has some theoretical significance for thinning of debris flow on slope starting conditions study,debris flow disaster warning has a guiding role.%“5.12”汶川地震产生了大量崩滑堆积体，这些棱角状粗颗粒体在水流激发下易起动形成坡面泥石流。在对汶川地震区坡面泥石流地质模型调研基础上，建立以立方体为稀性坡面泥石流粗颗粒的基本模型，结合坡面泥石流的宽级配特性，提出立方体模型的滑移、翻转（包括绕边翻转、绕支点翻转及嵌固绕边翻转）等起动方式。并以水力学、泥沙动力学为理论基础，推导得出粗颗粒在滑移、翻转起动方式下的起动平均流速公式。参照陈伯奇的实验数据，计算粒径为5~10 mm颗粒在不同坡度条件下的起动流速，并对比显示两者具有较好的吻合性，表明立方体作为稀性坡面泥石流粗颗粒的起动模型是合理的。计算结果也表明，在同一坡度条件下，粗颗粒滑移起动所需的水流激发流速最低，绕边起动次之，颗粒嵌固起动所需的激发流速最大，如坡度为30°条件下，滑移起动的水流激发流速为0.349 m/s，绕边起动为0.430 m/s，嵌固起动为0.473 m/s。据此推断，当水流达到一定流速（如30°坡度下、流速为0.349 m/s）时，粗颗粒的最初起动以滑移为主；随着流速增大，逐渐出现翻转起动；当水流流速急剧增大时，大部分嵌固粗颗粒会以翻转的方式瞬间起动，从而形成稀性坡面泥石流。成果对稀性坡面泥石流起动条件研究具有一定的理论意义，对泥石流灾害预警具有一定的指导作用。
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