On the Permeability of the Coarse Materials at the Low Hyraulic Gradient.

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In this study, the experiment about the permeability of the coarse materials was carried out at the low hydraulic gradient. (Hydraulic gradient : i=0.005-0.1) It is not clear that the permeability of the coarse materials is valid to Darcy's Law or not especially at the low hydraulic gradient. This permeability is the important value when the drain system in the earth structure is one of important factors for the safety of structure.The materials used in this experiment were three kinds of glass beads with the diameter D=30mm,15mm and 5mm.The results obtained are as follows:1) The unconfined flow through the coarse materials is not valid to Darcy's Law between above mentioned hydraulic gradient.2) Similary, the confined flow through the coarse materials is not valid to Darcy's Law, too3) The exponent law as follows is valid to the flow through the coarse materials.v=a*i^b where v : velocity, i : hydraulic gradient and a , b : coefficients.4) As the results of analysys of the data obtained from experiments, the value of b is about 0.7. This is not valid to Darcy's Law.