FOUR-DIMENSIONAL LOCAL BOUNDARY SURFACES OF AN ISOTROPICALLY CONSOLIDATED LOOSE SAND

Undrained anisotropy, together with the undrained response to monotonic as well as cyclic rotation of principal stress directions, of an isotropically consolidated loose Ham River sand has been investigated by performing three series of hollow cylinder tests. The initial anisotropy of the sand when subjected to a single consolidation pressure was successfully established in the first series of tests, each using different, but fixed in each test, values of a (i.e., the direction of major principal stress relative to the vertical deposition direction) at different b values (i.e., the relative magnitude of intermediate principal stress). The response against monotonic principal stress rotation was also examined in the second series of tests, in which the total stress path defined using the shear stress, t, and a was varied in various manner with b fixed at 0.5. In the third series of tests, the response to cyclic changes of both a and b was examined, and the results were interpreted with the comparative behaviour of the monotonic loading tests with different combinations of a and b. It was found that the sandʹs undrained anisotropy and cyclic response could be interpreted by invoking the concept of undrained local boundary surface (LBS). The fourdimensional LBS could be visualized in (t, pʹ, a) space as a family of superimposed three-dimensional shapes with different b values.