The accumulation of excess pore water pressure (EPWP) under cyclic loading may induce partial or complete liquefaction of saturated coral sands

posing significant threats to the safety of structures and foundations. In numerical simulations and analyses

accurate prediction of EPWP development is essential

with the determination of threshold strain serving as a critical step. A novel method has been developed to determine the threshold strains (pore pressure threshold strain

stiffness degradation threshold strain

and flow threshold strain ) for the EPWP generation and stiffness degradation in saturated coral sands under complex stress paths. This was achieved isotopically consolidated

undrained single-stage and multistage cyclic shear tests

including 90° jumps and continuous rotations of principal stress. The findings indicate that while

and are relatively insensitive to the cyclic stress

they are significantly influenced by the initial relative density (Dr). Additionally

the gap between and widens as D increases. Under varying cyclic loading conditions and initial physical states

corresponds to the EPWP ratio of approximately 0.9

with a corresponding stiffness index of around 0.10. The proposed method for determining

and can effectively reduce the number of required cyclic tests

making it suitable for use as input values in numerical calculations or analytical methods

and for characterizing soil behavior under stress and strain conditions.