Abstract: The excess pore water pressure (ue) in saturated coral sand with different relative densities (Dr) features complicated under complex cyclic loading conditions. In order to investigate its generation characteristics, a series of undrained cyclic shear tests subjected to 90º jump rotation of cyclic principal stresses with various orientations was conducted on such saturated coral sand. These laboratory cyclic tests by using the GDS hollow cylinder torsional apparatus showed that the patterns of ue generation in those test specimens are related to the paths of cyclic stress, levels of cyclic stress, and Dr. Then, the expression of excess pore water pressures ratio (ru) was established for different Dr values and cyclic loading modes. The unit cyclic stress ratio (USR) was introduced as a stress index for characterizing complex cyclic stress path, and the expressions of model parameters λ ₁ and θ based on USR and Dr were proposed. The established expression of ru can predict the generation of ru in saturated coral sand with various Dr under complex cyclic loading modes. Experimental data of different sand types in the literature independently verify the applicability of the proposed equation for ru.

Key words: saturated coral sand, undrained cyclic shear test, relative density, 90o jump rotation of principal stress, generation model of excess pore water pressure