Abstract
In order to investigate the mechanism of the occurrence of the sediment flow under the influence of ground water, it was to tried to keep the ground water pressure nearly constant throughout the sand layer. In these experiments, three kinds of materials were used; that is to say, one is (A) which average grain diameter dm is 0.65mm, another is (B) which dm is 3.20mm, the third is (C) which dm is 6.20mm. It was made clear experimentally that the equation of the equilibrium with (H0/H)≤1 could be applied to (A), (B), on the other hand the equilibrium with (H0/H)>1 could be applied to (C). It was shown that the type with (H0/H)<1, (H0/H)=1 and (H0/H)>1 corresponded to the ype with (θ/θc)>1, (θ/θc)=1 and (θ/θc)<1 respectively, where θ is the gradient of the flume, θc is the critical slope of the occurrence of sediment flow, Furthermore it was found the following facts; the sediment flow with (H0/H)≤1 and (θ/θc)≥1 always occurs under the influence of the ground water itself, the one with (H0/H)>1 and (θ/θc)<1 occurs under the influence of urface water which is caused after the ground water got to the surface of the sand layer.
