The generation of excess pore water pressure (EPWP) and liquefaction characteristic of soils under seismic loading have long been topics of interest and ongoing discussion. Based on the structural state exhibited in the liquefaction process, the mechanical property of saturated coral sand is divided into solid, pseudo-fluid, and liquid phases. New indices, zeta q (generalized deviator strain evolution) and zeta(y)q (generalized deviator strain evolution rate), are proposed to evaluate the evolution and evolution rate of complex deformation. In the solid phase, the saturated coral sand primarily exhibits the properties of a continuous solid medium, the peak EPWP ratio (rup) shows a power correlation with generalized deviator strain evolution amplitude (zeta qa). While in the pseudo-fluid phase, the saturated coral sand primarily exhibits mechanical behavior characteristic similar to that of a fluid, and the rup shows a significant arctangent function relationship with generalized deviator strain evolution rate amplitude (zeta(y)qa). The correlation of rup with zeta qa and zeta' qaduring liquefaction is significantly affected by loading conditions (cyclic stress ratio, CSR, loading direction angle, alpha sigma, and loading frequency, f). To quantify the impact of these loading conditions on the generation of rup in different phases, unified indicators delta S (for the solid phase) and delta L (for the pseudo-fluid phase) are defined. Eventually, An EPWP model based on mechanical property exhibited in different phases is developed, which has normalized the effects of loading conditions. It provides a comprehensive framework to predict the rup of saturated coral sand under complex geological activities, and this model facilitates the understanding and simulation of the mechanical properties and behavior of saturated coral sand during the liquefaction process.

Offshore wind turbines are usually founded on monopiles. During the operation period, the structure is subjected to complex lateral loading from wind, wave and current. The soils surrounding those monopiles may deform with increasing the number of loading cycles, leading to tilting of the whole structure; hence, it is vital to carry out physical model tests to examine the long-term performance of monopiles. This study proposes an innovative experimental setup for centrifuge modelling of the response of monopiles under complex lateral loading. Hydraulic actuators are adopted to apply lateral loads on model pile, and electrohydraulic servo-valves and associated controllers are used to achieve a closed loop position or load control. A carefully designed spherical hinge and load bars are used to connect the model pile and actuator shafts. This enables that the pile can rotate freely and can move vertically freely. A centrifuge test on a winged monopile subjected to perpendicular lateral loading was carried out at 100g. The experimental results shed light on pile responses in the cyclic loading and constant loading directions.