In recent years, the number of cases where tunnels are constructed in sedimentary rock layers has increased. It is essential to investigate the deformation characteristics of sedimentary rocks for predicting tunnel deformation. The mechanical properties of sedimentary rocks are widely varied due to moisture content. The rocks are dried by tunnel excavation and wetted by groundwater gushing or backfilling. It is necessary to grasp the changes of deformation characteristics of sedimentary rocks due to moisture changes. In this study, soaking tests were conducted on Neogene period Japanese tuff sampled at Utsunomiya, Japan. In the test, the cylindrical tuff specimens are air dried by over 240 hours at first. Then the tuff specimens are taken in pure water with measuring deformations in detail. There are no effective stress increases by soaking and only uniform matric suction are acted on the specimen without any restraints. The results demonstrated that strain tensor was reached to stable state for 2 - 3 days, and the value of the normal strain perpendicular to the bedding plane is greater than the other normal components and shear strains are also observed in both cases. Although the orientation of the maximum principal strain is in the near of the bedding orientation at the initial dry state, the orientation are suddenly rotated to the normal orientation of the bedding plane. It means that the principal orientation of anisotropy are rotated due to continuous moisture changes.

近年来，在沉积岩层中修建隧道的案例有所增加。研究沉积岩的变形特征对于预测隧道变形至关重要。沉积岩的力学性质因含水量而变化很大。岩石通过隧道开挖干燥，并通过地下水涌出或回填润湿。有必要把握水汽变化引起的沉积岩变形特征的变化。在这项研究中，对在日本宇都宫采样的新近纪日本凝灰岩进行了浸泡试验。试验中，首先将圆柱形凝灰岩试样风干240小时以上。然后将凝灰岩试样放入纯水中，详细测量变形。浸泡没有有效应力增加，只有均匀的基质吸力作用在试样上，没有任何约束。结果表明，应变张量在2～3天后达到稳定状态，垂直于层理面的法向应变值大于其他法向分量，两种情况下均观察到剪应变。虽然最大主应变的方位在初始干态时处于层理方位附近，但该方位突然旋转到层理面的法向方位。这意味着各向异性的主要方向由于连续的水分变化而旋转。并且垂直于层理平面的法向应变值大于其他法向分量，并且在两种情况下也观察到剪切应变。虽然最大主应变的方位在初始干态时处于层理方位附近，但该方位突然旋转到层理面的法向方位。这意味着各向异性的主要方向由于连续的水分变化而旋转。并且垂直于层理平面的法向应变值大于其他法向分量，并且在两种情况下也观察到剪切应变。虽然最大主应变的方位在初始干态时处于层理方位附近，但该方位突然旋转到层理面的法向方位。这意味着各向异性的主要方向由于连续的水分变化而旋转。