Although it is essential for tunnel construction to evaluate the deformation behavior of sedimentary rock due to drying, the reasons for differences in the mechanical properties between dry and wet rock have not yet been clarified. A previous study on Neogene-period anisotropic tuff states that the magnitude correlation of the stiffness in the bedding orientation and its perpendicular one are reversed in the dry and wet states. Although this indicates the rotation of the principal orientation of the anisotropy, the mechanism is unclear. This phenomenon can clarify the stiffness differences between the dry and wet conditions if the deformation characteristics due to drying can be continuously obtained, in detail. In this study, drying tests on Japanese tuff are conducted, and the deformation behavior due to continuous moisture-content variation involving isotropic matric suction are investigated, in detail. The results of two specimens sampled in the bedding orientation and its perpendicular one show anisotropic deformations due to moisture variation. Normal strain in the orientation perpendicular to the bedding plane is dominant and shear strain occurs. Furthermore, principal strain rotation due to moisture variation is detected for the first time. The maximum and minimum principal strain orientations are rotated by approximately 90° from the wet state to dry state. It is determined that the hardest and softest orientations of tuff continuously alternate due to moisture variation.

尽管评估隧道因干燥引起的沉积岩变形特性对于隧道施工至关重要，但干岩石和湿岩石力学性能差异的原因尚未阐明。以前对新近纪各向异性凝灰岩的研究表明，在干湿状态下，层理方向上的刚度及其垂直方向的刚度大小相关性相反。尽管这表明各向异性的主要方向发生了旋转，但机制尚不清楚。如果能够连续地详细获得由于干燥引起的变形特性，则该现象可以弄清干湿条件之间的刚度差异。在这项研究中，对日本凝灰岩进行了干燥测试，详细研究了由于各向同性基质吸力引起的连续水分含量变化引起的变形行为。以层理方向取样的两个样本及其垂直样本的结果表明，由于水分变化，各向异性变形。垂直于顺层平面方向的法向应变占主导地位，并且发生剪切应变。此外，首次检测到由于水分变化引起的主应变旋转。从湿态到干态，最大和最小主应变方向旋转了大约90°。已确定由于水分变化，凝灰岩的最硬和最软的取向连续交替。以层理方向取样的两个样本及其垂直样本的结果表明，由于水分变化，各向异性变形。垂直于顺层平面方向的法向应变占主导地位，并且发生剪切应变。此外，首次检测到由于水分变化引起的主应变旋转。从湿态到干态，最大和最小主应变方向旋转了大约90°。已确定由于水分变化，凝灰岩的最硬和最软的取向连续交替。以层理方向取样的两个样本及其垂直样本的结果表明，由于水分变化，各向异性变形。垂直于顺层平面方向的法向应变占主导地位，并且发生剪切应变。此外，首次检测到由于水分变化引起的主应变旋转。从湿态到干态，最大和最小主应变方向旋转了大约90°。已确定由于水分变化，凝灰岩的最硬和最软的取向连续交替。从湿态到干态，最大和最小主应变方向旋转了大约90°。已确定由于水分变化，凝灰岩的最硬和最软的取向连续交替。从湿态到干态，最大和最小主应变方向旋转了大约90°。已确定由于水分变化，凝灰岩的最硬和最软的取向连续交替。