Recent studies have pointed out the importance of the basal friction on the dynamics of
rock avalanches, landslides, and debris flows, which consist in large-scale flows of grains in different sizes. In this paper, we proposed an innovative method to measure the dynamic basal friction coefficient of granular assembles, and also developed new relationships between the dynamic basal friction angle, the velocity, the displacement, and the time. A trajectory tracking system was designed to capture the timedisplacement
of granular assemblies during their sliding. The acceleration functions, which were used to calculate the dynamic friction angle, were then deduced based on the measured displacement. It is found that power law described well the time-displacement curve of the granular assemblies. Logarithm laws that related dynamic friction angle to displacement and time were both in a descending trend, which indicates the velocity-weakening feature of dynamic friction for granular assembles. A cyclical quick-slow
pattern in the increment of velocity is shown in the velocity-time curve. The duration of slow period was shorter. This cyclical pattern indicates that there existed intermittent fast-rearrangement which resulted in smaller dynamic friction and faster acceleration. The differences between static and dynamic friction angles were measured for different granular assembles, which were up to about 20 % at the early sliding highlighted
the difference between static and dynamic friction of granular assembles, and also revealed the sharp decrease of dynamic friction angle at the early sliding. The proposed method would contribute to develop space-time evolution of dynamic friction of granular assembles, and also provide a basis to understand the mechanism of long run-out geophysical flows.