The method of dynamical numerical analysis is used to analyse the movement of grains on slope; and the research is based on in-situ observation and model tests. First

there are two main movement patterns

slide and roll. And these two movement patterns can converse each other. The movement can be caused by pull or push forces. On the pull-surface

most of grains move in rolling pattern and the roll will be driven by the movement of sands on the top or in front of them. On the push-surface

most of grains move in slide pattern and the slide will be driven from the top or back of them. Then

based on the driven force conditions of a grain of sand

the movement parameters and dynamical model of sand in sliding

rolling and crash are derived.