Conference Paper 曲がったPVDの通水性能に関する実験

北詰, 昌樹  ,  Kitazume, Masaki

The vacuum consolidation method with prefabricated vertical drains (PVD) is one of the most effec-tive methods to improve the soft ground. In this method, the PVD installed in soft ground was bended along with the consolidation settlement. As a result, the drainage performance of the PVD might be de-creased. A series of laboratory tests were performed to evaluate the bending effect on the consolidation behavior in PVD. First, the large scale model tests were performed to measure the bending shape of PVD by the vacuum consolidation. In these tests, the clay slurry at a water content of 150 % was consolidated under the vacuum pressure of 60 kPa in the consolidation cells, which were 5 m in height and 30 cm or 76 cm in diameter. Second, the permeability tests for PVD were carried out under a given constant water head difference. In these tests, three types of PVD were used as samples, i.e., the straight PVD, the mod-erately-bended PVD whose shape was observed in the large scale consolidation test and the sharp-ly-bended PVD. It was confirmed, based on all the test results, that the consolidation speed was not de-layed even by the bended PVD on usual site.
軟弱な粘土地盤にPVDを打設して圧密改良を行うと,PVDは沈下にともなって曲がり,曲がりが大きくなると,PVDの通水性能が大きく低下する可能性がある.そこで,高含水比に調整した粘土の真空圧密土槽実験(直径30 cmあるいは76 cm×高さ5 m)の圧密終了後にPVDの曲がり形状を測定した.次にPVDの通水実験を実施した.通水実験は直線状のPVD,圧密土槽実験とほぼ同様に曲げたPVD,および強制的に大きく曲げたPVDを対象とし,PVDの面内方向の漏水を防止するために遮水シートを巻きつけたPVDに水頭差を与えて曲がり形状と通水量の関係を求めた.これらの結果を考察すると,現場で使用されているPVDは十分な通水性能を保持していると考えられる.

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