Session: 10-01-01 Seabed Properties and Processes

Paper Number: 127019

127019 - Meshfree Coupled Model for Earthquake-Induced Pore Pressure Accumulations and Associated Seabed Liquefaction: U-P Approximation 

Over the past few decades, there has been a significant increase in the construction of marine structures due to the expansion of offshore explorations into deeper waters. The stability of these offshore structures is a critical consideration when subjected to complex natural environmental loads after being put into operation. While extensive research has been devoted to studying seabed instability under the influence of gravity waves and currents, as evidenced by numerous investigations, these studies have primarily concentrated on the response of the seabed soil to fluid-induced forces in oceanic environments, neglecting the impact of earthquake loading.

 

In addition to wave and current loading, earthquakes represent a major natural disaster that must be taken into account. Seismic activity can lead to liquefaction of saturated soil due to the shaking effect. For instance, the 1995 Greek Gulf earthquake resulted in damage within the upper seabed . However, the majority of earthquake loading studies have focused on onshore scenarios, with only a limited number addressing offshore situations, whether through analytical solutions, experiments, or numerical simulations. Notably, Noda et al. employed a combined approach involving sampling and modeling to assess the effects of earthquakes on shallow marine sediments. Ye simulated the seismic response of seabed and composite breakwaters using the elastic model of SWANDYNE II for loosely deposited seabed soil. Subsequently, seismic wave amplification traveling from offshore to shore areas was numerically estimated using the boundary element method. Recently, an analytical solution was derived to evaluate seabed response and instantaneous liquefaction under vertical seismic motion.

 

Up to this point, virtually all existing numerical models for earthquake-induced seabed responses have relied on traditional mesh-based methods, such as the Finite Element Method (FEM) and the Boundary Element Method (BEM). These methods have demonstrated excellent performance in seabed analysis. However, mesh-based approaches are ill-suited for addressing issues characterized by substantial element distortion, such as large deformations and moving boundary problems. Moreover, these methods involve complex mathematical procedures and are time-consuming, particularly when it comes to numerical integration over singularities present on the boundary elements. This complexity is exacerbated when dealing with earthquake loading, where the time step must align with earthquake records for accuracy considerations. Consequently, tedious calculations are required to accurately model the seismic wave, typically resulting in a time interval (Δt) for earthquake records of approximately 0.02 seconds. In such scenarios, meshfree methods emerge as a viable alternative for reducing computational time, as they rely on scattered nodes to approximate unknowns in Partial Differential Equations (PDEs). In this study, we establish a meshfree model based on Biot's "u − p" approximation for simulating the instantaneous seabed response under earthquake loading. The present model allows for an initial discussion of the effects of lateral boundary conditions, followed by a parametric study to explore the influence of soil parameters on earthquake-induced soil response.

Presenting Author: Shuang Han Hohai University

Presenting Author Biography: Dr Shuang Han graduated from Griffith University and continues doing a Postdoc at Hohai Univerisity right now. She mainly focuses on the topic of dynamic seabed response under natural dynamic loading. She adopted the newly-developed meshfree method instead of the traditional mesh-based approaches to simulate the seabed liquefaction.

Authors:

Shuang Han Hohai University
Jisheng Zhang Hohai University
Chia Cheng Tsai National Taiwan Ocean University
Dong Sheng Jeng Griffith University