Applicable one-dimensional frozen method for obtaining undisturbed natural sand material containing fine particles

为了评估沙地的液化潜力和设计防止土壤液化的对策，有必要对未受干扰的天然砂样进行实验室试验。在野外采砂前，有时会采用地面冻结技术。然而，众所周知，这种技术非常昂贵。另一方面，管道取样技术比地面冻结技术成本低得多。然而，人们发现，试管取样技术所获得的样品质量低于地面冻结技术。本研究为提高取心管取样技术的砂样质量，对取心管进行了重新设计，并在取心管之前使用防冻液对砂粒和地下水进行了固化。所提出的采样技术在大阪岸和田市的复垦场地进行了试验。采用大直径试样对采用该方法提取的未扰动试样进行了三轴压缩试验。实验结果与重建试件的结果进行了比较。结果表明，原状试件比原状试件具有更高的刚度。此外，本署亦在赤洲及六甲岛进行沙土取样，以比较两座填海岛屿的液化潜力。对未受扰动的粘土试样进行了室内试验，研究了粘土的循环强度和固结历史。在两个岛屿也进行了PS采伐。根据实验室和现场调查，解释了1995年小古根-南部地震期间两个岛屿出现的液化灾害的差异。

Laboratory tests on undisturbed natural sand samples are necessary to assess the liquefaction potential of the sandy ground and to design countermeasures against soil liquefaction. The ground freezing technique has been sometimes used before sand sampling at the field. This technique is, however, well known to be very expensive. On the other hand, the tube sampling technique is much cheaper then the ground freezing technique. The quality of the sample retrieved by the tube sampling technique has been, however, found to be lower than that by the ground freezing technique.In this study, to improve the quality of the sand sample by the tube sampling technique, the coring tube was redesigned and antifreeze liquid was used to solidify the sand particles and ground water before retrieving the coring tube. The proposed sampling technique was tried at the reclaimed ground in Kishiwada city, Osaka.Triaxial compression tests on undisturbed samples retrieved by the proposed technique were carried out using large diameter specimens. The experimental results were compared with those obtained from the reconstituted specimens. It is found that the undisturbed specimen has higher stiffness than the reconstituted specimen.Sand and clay samplings were also conducted at Port Island and Rokko Island to compare the liquefaction potential of both reclaimed islands. Laboratory tests on undisturbed clayey samples were carried out to investigate cyclic strength of clay and consolidation history. PS loggings were also conducted at both islands. Based on laboratory and in situ investigations, the difference in the liquefaction disaster appeared on both islands during the 1995 Hyogoken-Nambu Earthquake was explained.