Abstract: Featured with long stroke and wide range, debris flow cannot be effectively predicted and prevented. Grain size distribution is an important factor affecting the movement distance of debris flow. Physical model tests are carried out to study the collapse movement of granular columns with single free face varying with different particle gradations. After the collapse of granular column, particles move obliquely towards the outside of the box. The particle motion on horizontal plate is radial, and the depositing plane is in the form of a circle. The deposit profile of particles can be well fitted by parabola and circle equations. Given the same particle type, as the granular column becomes higher, the position of the center of the circle in which particles deposit after collapse moves forward along the y-axis. When the height of granular column is fixed, fine particles move farther than large particles. The range of loosely deposited area of small particles is correspondingly small, and the small particles affect only the densely deposited area;large particles affect not only the densely deposited area,but also the loosely deposited area.

Key words: granular column, collapse model experiment, velocity field, deposited range, shape of circle, grain size distribution