Understanding cyclic loading behavior of soil for offshore applications

Abstract

This paper discusses two categories of cyclic loading with special reference to offshore applications: one is the combination of static and cyclic shear stresses and the other is a continuous rotation of the principal stress axes. Particular attention is given to the fist type which is in close relation to the stability of gravity offshore structures. It is shown that the initial static shear stress, due to the installation of an offshore structure, is a key factor for the behavior of the sand beneath the structure. The impact of this factor strongly depends on the initial state of the sand in terms of its relative density and confining stress and on the magnitude of the static shear stress relative to the cyclic shear stress applied. The second type of loading is in relation to the seabed in the free field under ocean waves. It is shown for this loading condition that rotation of principal stress axes without changing the magnitude of deviatoric stress can generate pore water pressures and that the amount and rate of pore pressures is affected by the intermediate principal stress parameter. © 2011 Taylor & Francis Group, London.