00518538

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タメイケ テイタイ ノ イホウ トウスイセイ ト シントウリュウ トクセイ

Anisotropic Permeability of Fill-Type Dams for Irrigation Ponds

Japanese (日本語)

神戸大学都市安全研究センター研究報告

11

329-338

神戸大学都市安全研究センター

2007-03

2008-07-09

Typhoon No.23 struck Awaji Island, Japan, in 2004, and caused extensive damage to a number of fill-type dams for irrigation ponds. The soil was sampled from the remaining parts of damaged fill-type dams, and physical properties and permeability coefficients kh and k„ were tested, where kh and if, are the coefficients of permeability in horizontal and vertical directions, respectively. The value of anisotropy of soil (kh/k,) was discussed, and the following results were obtained: (1) The larger the uniformity coefficient U, becomes, the larger the value of anisotropy (kh/k„). (2) The smaller the representative grain size (e.g., D15 or D20) becomes, the larger the value of anisotropy (kh/k,). D15 and D20 are the 15 and 20 percent diameters, respectively. (3) The permeability of soil in the vertical direction k, is directly proportional to the 20 percent diameter to the second power D202. The cross section of the A-dam was also measured using the pole (or ranging rod) surveying method. The seepage flow through soil of the A-dam was analyzed using the finite element method for isotropic (assumed) and anisotropic (actual) cases. The following conclusions were obtained: (4) The ratio of the increase in discharge due to anisotropy (Q1a,0) is almost equal to the value of anisotropy (WO, and the A-dam has the same property of seepage flow as the trapezoidal dam shape. Q and Q,,0 are the discharges through soil of anisotropic (actual, kh and k,) and isotropic (assumed, k=k,) permeability, respectively. (5) The line of seepage has a 0.34m higher maximum in the anisotropic than in the isotropic case. (6) The shape of the A-dam has a marked effect on the increase in discharge through soil due to anisotropic permeability.

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