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The excess pore water pressure generated under the combined vertical and horizontal earthquake excitations is generally greater than that under the unidirectional excitation, which may further affect the dynamic response of soil-pile-superstructure-quay wall (SPSQ) system. This study conducted a coupled effective-stress analysis for the response of SPSQ system to liquefaction-induced lateral displacement under horizontal and vertical earthquake excitations. To accurately describe the lateral displacement behind the quay wall, the liquefaction behavior of soils was described by a modified generalized plasticity model with parameters properly determined from laboratory tests. The numerical model of the SPSQ system was validated against the previously reported centrifuge model tests. The results show that the earthquake excitation with abundant low-frequency component causes greater residual lateral displacements of pile cap (ux,RC) and quay wall (ux,RQ) than that with abundant high-frequency component. The ux,RC and ux,RQ tend to increase as the peak vertical acceleration increases for both vertical and inclined piles. Increasing the fixity of the quay wall significantly reduces the influence of vertical ground motion on the ux,RC and ux,RQ. The polarity reversal of the vertical ground motion also has a significant effect on the ux,RC and ux,RQ and should be considered in the analyses. In addition, the lateral displacement of liquefied ground causes an amount of rotation of the cap of the inclined pile, probably leading to the potential shear failure at the head of piles. Special consideration should be given to the earthquake-induced shear force at deeper location because the shear force could be significantly greater than that at the head of both inclined and vertical piles in certain cases. [ABSTRACT FROM AUTHOR]

Marine sandy soils may liquefy under wave loading and/or seismic loading. Current research shows that the presence of fines can significantly affect the liquefaction potential of sandy soils. Thus, a quantitative evaluation of the effect of fines on the undrained behavior of sandy soils can provide useful information on soil liquefaction that can advance the design of foundations of coastal structures. However, little is known about how the grain size of nonplastic fines affects the mechanical behavior of sandy soils. In this study, a series of strain-controlled monotonic undrained triaxial compression tests and critical-state constitutive modeling are carried out on a medium dense saturated sandy soil for various fines contents (FCs), mean grain sizes ( d 50 f s) of nonplastic fines, and initial effective confining pressures. The results show that the peak deviatoric stress decreases significantly with decreasing d 50 f , especially for high FCs. The equivalent granular state parameter (ψ*) at the phase transformation can be used to characterize the effect of fines on the dilatancy of sandy soils in constitutive modeling. Additionally, the initial value of ψ*( ψ 0 * ) serves as physical index for characterizing the influence of fines on the undrained instability state of sandy soils. [ABSTRACT FROM AUTHOR]

The evaluation of seismic-induced responses in a porous seabed is a fundamental problem in geotechnical and coastal engineering. Although ground motions generally include both horizontal and vertical components, a majority of previous theoretical investigations assumed vertically propagating shear waves in a horizontally layered soil–rock system and simply ignored the effect of site response to vertical earthquake motion. In this paper, the dynamic response and instantaneous liquefaction of a porous seabed that is induced by vertical earthquake loading is studied using an analytical method. The seabed is treated as a two-layer poroelastic medium and characterized by the dynamic formulation of Biot theory. The analytical solutions for the response variables, such as induced displacement, pore pressure and vertical effective stress, are derived individually, and the mechanism of instantaneous liquefaction in liquefiable sediment is investigated based on the excess pore pressure criterion. A set of parametric analysis is performed to discuss the effects of seawater, the seabed and earthquake parameters on the seismic response and maximum liquefaction depth. It is worth noting that the properties of the surface seabed layer have a significant influence on the seismic response and, consequently, the potential stability of the seabed, which is important in the analysis of offshore structure foundations. [ABSTRACT FROM AUTHOR]

The seabed could be liquefied due to the wave-induced accumulation of residual excess pore water pressure (EPWP), resulting in the instability of offshore and marine structures. Thus, it is of importance to consider both the buildup of EPWP and the associated deformation behavior of the seabed. In this study, a dynamic poro-elasto-plastic seabed model, integrated with a state-dependent plasticity model, is developed in COMSOL Multiphysics. The numerical model of seabed is validated against the analytical solutions and model tests. The elliptical trajectories of soil particle at different depths of the poro-elastic seabed under the progressive wave are illustrated. The ratio of the amplitude of vertical displacement to that of horizontal displacement generally decreases as the depth increases for the poro-elastic seabed. In the poro-elasto-plastic seabed, however, the soil particles tend to move following the direction of the wave propagation. Moreover, the soil particles at the shallow part of the seabed go downwards before the initial liquefaction, while the soil particles at the lower position initially go upwards and then turn to go downwards when the initial liquefaction occurs. Particularly, the surface seabed with lower relative density is more prone to lose the stability, resulting in a dramatic upward vertical displacement. • A dynamic poro-elasto-plastic seabed model, integrated with a state-dependent plasticity model, is developed for wave-induced liquefaction analysis. • The elliptical trajectories of soil particle at different depths of the poro-elastic seabed under the progressive wave are illustrated. • The effects of soil plasticity and relative density on the soil particle trajectories are investigated. • The evolution of the soil particle trajectory before and after the liquefaction is discussed. [ABSTRACT FROM AUTHOR]