Liquefaction and lateral spreading of breakwater foundation

Lateral spreading deformation induced by seismic liquefaction significantly affects the safety and stability of breakwaters. This study improves the Newmark sliding block method by determining residual strength through standard penetration test values of liquefied soil, calculating yield acceleration based on sand residual strength, and inputting seismic ground motions corresponding to site response spectra for lateral spreading analysis. Simultaneously, the finite difference program FLAC is employed with the PM4Sand constitutive model for sand plasticity, which incorporates critical state theory and stress control principles, to predict seismic-induced site liquefaction lateral spreading. Comparison of different lateral spreading calculation values shows that: the improved Newmark method for calculating liquefaction lateral spreading is influenced by yield acceleration and seismic time history curves but does not consider nonlinear behavior under dynamic loading. In contrast, the PM4Sand model, through improved sand constitutive theory, more accurately simulates strength degradation and excess pore pressure ratio development in liquefied soil during earthquakes, effectively predicting liquefaction-induced lateral spreading. Combined with FLAC software for nonlinear analysis, the PM4Sand model predicts larger lateral spreading values than the Newmark method, providing a greater safety margin and more intuitive results. Analysis of liquefaction lateral spreading factors indicates that improving soil relative density can significantly reduce lateral spreading and enhance seismic stability.