Modeling Lateral Flow and Liquefaction-Induced Ground Movement

摘要：CMS-9613906，罗纳尔多·博尔哈，斯坦福大学这项研究计划的目标是建立一个数学模型，用于分析地震期间和地震后的侧向流动和液化引起的大地面移动问题。该模型以两相混合物理论为基础，开发了能够描述饱和土液化前和液化过程中行为的有限元程序。在液化之前，土被描述为一个已经被验证的基于非线性运动硬化的弹塑性本构模型的有效应力唯象本构模型。液化过程中，液化土采用全应力粘塑性模型，粘性由球体随机悬浮体的数值模拟确定。这两种本构模型都是在基于乘性塑性的有限变形理论框架内建立的。所建立的有限元模型被用于研究液化引起的地面大位移的机理，包括侧向流动和由此产生的自由地表的预测。为了验证模型的有效性，对两个案例进行了分析。第一种是浸入水中的Tooura沙的松散饱和样本，并倾斜到测试中，受到动态激励，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日地震期间在日本神户市中心附近的港口岛(靠近神户市市中心的填海土地)的井下阵列记录的非线性地面响应的重新分析，重点是这种改变的土壤特性在液化过程中的影响。假设地震波垂直传播，三个运动分量完全运动耦合，模拟了地面反应。

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.