Recently, debris flow hazards are the problem for many countries in the world. Awareness of danger of debris flow and their deposits on land surface and under water is essential. This topic aims to measure the flow behaviour of debris mixtures under different conditions using slump tests. Two groups of sediment samples with different sizes are employed to conduct experiments in three different conditions, namely, dry, wetted and underwater. The slump test is the primary equipment to measure the slump height and spreading diameter of sediment materials. Each experiment is repeated three times to minimize the errors. The results show that the slump behaviour is influenced mainly by factors such as particle size, size distribution and test condition.
The result of experiment showed that the size of sediment greatly affected slump behavior. In particular, the larger size sediments leads to a higher spreading diameter and the slump height. We also know that, in the distribution of the sediment after sliding, the largest size sediment layer stay on outer ring position, next is the smaller size in the middle and the last one is the smallest at the top of the sediment shape. However, comparing the slump behavior of sediment in dry and water conditions, shows that sediment in dry condition has greater slump height and slump diameter, than sediment in underwater condition because of the existence of dragging effect by water on sediment.

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