Modeling Lateral Flow and Liquefaction-Induced Ground Movement

摘要：CMS-9613906， c罗·博尔加，斯坦福大学。本研究项目的目的是建立一个数学模型，用于分析地震期间和地震后的横向流动和液化引起的大地面运动问题。该模型基于两相混合理论，并涉及能够表示液化前和液化过程中饱和土壤行为的有限元代码的开发。在液化之前，土壤用基于非线性运动硬化弹塑性公式的有效应力现象学本构模型来表示。在液化过程中，液化土用全应力粘塑性模型来表示，该模型的黏度是通过大量随机悬浮球的数值模拟来确定的。这两个本构模型是在基于乘法塑性的有限变形理论框架内建立的。利用所建立的有限元模型研究液化相关大位移的机理，包括横向流动和由此产生的自由地表的预测。为了验证模型，考虑了两个案例研究。第一种方法是将松软饱和的Toyoura沙子样本浸泡在水中，并在动态激励下倾斜，使土壤液化并像粘性流体一样流动。第二项研究涉及对1995年1月17日地震期间港岛（日本神户市中心附近的填海土地）的井下阵列记录的非线性地面响应进行重新分析，重点关注液化过程中这种变化的土壤行为的影响。在地震波垂直传播的条件下，模拟了三分量运动的完全运动学耦合的地面响应。

ABSTRACT: CMS-9613906, Ronaldo Borja, Stanford U. The objective of this research program is to develop a mathematical model for analyzing the problem of lateral flow and liquefaction-induced large ground movement during and following an earthquake. The model is based on a two-phase mixture theory, and involves the development of a finite element code capable of representing the behavior of saturated soils prior to and during liquefaction. Prior to liquefaction, the soil is represented by an already- validated effective-stress phenomenological constitutive model based on an elastoplastic formulation with nonlinear kinematic hardening. During liquefaction, the liquefied soil is represented by a total-stress viscoplastic model whose viscosity is determined from extensive numerical simulations with random suspensions of spheres. The two constitutive models are developed within the framework of a finite deformation theory based on multiplicative plasticity. The resulting finite element model is used to study the mechanism of liquefaction-related large ground displacement, including the lateral flow and prediction of the free ground surface resulting from such flow. Two case studies are considered in order to validate the model. The first involves a loose saturated sample of Toyoura sand submerged in water and sloped inside a test subjected to dynamic excitation, causing the soil to liquefy and flow like a viscous fluid. The second study involves a re-analysis of the nonlinear ground response recorded by a downhole array in Port Island (reclaimed ground near downtown Kobe City, Japan) during the earthquake of January 17, 1995, focusing on the impact of this changed soil behavior during liquefaction. The ground response is simulated assuming a condition of vertically propagating seismic waves, with a full kinematical coupling of the three components of motion.