|Budget Amount *help
¥3,500,000 (Direct Cost : ¥3,500,000)
Fiscal Year 2003 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 2002 : ¥2,000,000 (Direct Cost : ¥2,000,000)
Reclamation projects in the form of man-made islands in the bay area have been used for the disposal of the dredged clay generated from the creation and maintenance of navigable waterways and shipping berths, and the dredging river beds. Plastic board drain (PBD) is generally used for the accelerating consolidation of the dredged clay layer Dredged clay shows high water content and low strength, and is consolidated by only its self-weight in the natural condition. However, the efficiency of PBD on the self-weight consolidation process is unknown, and the applicability of Barron's solution, which used generally in order to analyze the consolidation process for the improved ground, is also unknown. In this paper, a series of centrifuge model tests of cylindrical drain and banded drain, simulating sand drain and plastic board drain, respectively, was conducted to investigate the converted drain diameter of the banded drain, the effect of diameter (width) and pitch of the drain, and the in
fluence of clay thickness on the self-weight consolidation process. These results were interpreted by the existing consolidation theory's solution. Furthermore, the efficiency and mechanism of the method combining vertical drain and dewatering was investigated.
Main conclusions are as follows: 1)effect of the drain is small in case a water content of dredged clay is higher, 2)the method of converting the drain circumference into the diameter can be applied to the converted drain diameter, 3)the consolidation of the deforming type in which the drain deforms by following the settlement of the clay, proceeds slightly faster than that of the fixed type in which the drain doesn't deform, 4)Barron's solution does not explain the experimental values, and 5)the compound solution by Barron's solution and Mikasa's one-dimensional self-weight consolidation solution is sufficient to explain them, therefore the compound solution is considered a practical calculation method.
In the meantime, more large effect of accelerating consolidation was obtained in the method combining vertical drain and dewatering. However, peeling of the side and central collapse phenomenon occurred on the tests as the pore water pressure in the drain decreased, and they did not become one-dimensional consolidated deformation. In present tests, the increase of the effective stress corresponding to the reduction of water level could not be confirmed. Less