强震持时对河流堤防液化特性的影响

Effects of strong ground motion duration on the liquefaction behavior of a river levee

摘要:

日本中部地区极有可能经历两种不同持时特征的地震动，即①东南海—东海复合型海沟地震，持续时间大于100s，最大加速度约2.4 m/s2；②活断层内陆地震，持续时间小于20s，最大加速度约6.0m/s2。由于该地区的冲积平原下部广泛沉积了饱和松散砂层，因此具有很高的液化可能性。文中基于Biot两相饱和多孔介质动力耦合固结理论，采用一个经过广泛验证的砂土循环弹塑性本构模型，对这两种具有不同持时特征的强震所导致的河流堤防液化性状进行计算分析，比较了地震动持续时间对河堤液化特性的影响。计算结果显示，地震动持续时间对于堤防的超孔隙水压力、加速度、变形等液化特征有着显著的影响，持续时间较长的强震作用将导致较大的堤防液化变形。

Abstract:

In the Chubu region, central Japan, two kinds of earthquakes are likely to occur with different duration characteristics: ① the Tonankai-Tokai coupled earthquake, with duration longer than 100s at a maximum acceleration of about 2.4 m/s2; ② an inland earthquakes due to active faults, with duration shorter than 20s at a maximum acceleration of about 6.0 m/s2. Saturated loose sand deposits are widely distributed over the low alluvial plain in this region and therefore have a high liquefaction potential..Based on the Biot theory for simulating coupled hydro-dynamic behavior in saturated porous media, this study presents a numerical assessment of the seismic behavior of a river levee founded on liquefiable foundation soils under earthquake loading. Analysis is carried out using an effective stress-based, fully coupled, finite element method, in which the behavior of the liquefiable sand is described by means of a cyclic elastoplastic constitutive model. The liquefaction responses of the river levee are compared for two different earthquakes. From the numerical results, it is found that the strong motion duration has a significant effect on the liquefaction behavior of the levee including excess pore water pressures, accelerations, and deformations. The longer ground motion may lead to much larger settlement of the river levee.