1989 年 1989 巻 412 号 p. 143-151
Actual earthquakes generate complicated patterns of motions involving changes not only in amplitude but also in direction. In order to investigate the behavior under irregular pattern of shearing, several series of multi-directional drained simple shear tests on Toyoura sand were conducted by means of a simple shear test device incorporating two cyclic loading apparatus in two mutually perpendicular horizontal directions. Cumulative shear strain G and resultant shear strain Γ were introduced to find a unified law for dilatancy. And it was found that there exists a unique relationship between G and volumetric strains with a parameter of Γ independent of the shear strain history. Based on the arrangements of the test results, we find that the bowl-shaped slope, which compresses in accordance with G, exists in the strain space.