Analysis of Wave-Induced Liquefaction in Seabed Deposits of Sand

Abstract

To explore the nature of cyclic stress alteration in the seabed deposits of sand due to travelling waves, two-dimensional stress analysis was made for homogeneous elastic half-space subjected to a series of harmonic loads moving on its surface. The analysis indicated that changes in shear stress occur in such a way that, while its amplitude is maintained constant, the directions of the principal stresses rotate continuously. With a view to simulating such stress changes in the laboratory test, a series of cyclic triaxial torsion shear tests was conducted on loose specimens of sand. The test results indicated that the conventionally defined cyclic stress ratio is reduced by about 30% if the rotation of the principal stress directions is involved in the cyclic loading. The magnitude of wave-induced pressure at the seabed was determined on the basis of the linear theory of water wave propagation. This water pressure fluctuation was applied over the seabed, which is assumed to be an elastic half-space, to determine the cyclic stress ratio induced within the seabed deposit. The cyclic stress ratio thus determined is compared against the cyclic stress ratio causing liquefaction and cyclic mobility in which the continuous rotation of principal stress directions is taken into account. The procedures as above are integrated into a simple methodology to perform liquefaction analysis under wave loading conditions.