Wave-induced Liquefaction and Sediment Transport in Coastal Environment

本研究项目旨在建立一个综合框架，以一致地描述波浪引起的液化、流化和沉积物输运过程，这些过程在沿海环境中具有深远的实际意义。主要研究结果如下：1)波浪加载历史对砂质沉积物抗液化能力的影响；一系列精心设计的波浪加载历史的离心波试验表明，由于在之前的波浪加载阶段通过“凝固”发生了明显的致密化，因此再液化阻力显著增加。2)泥沙重力流计算模型的建立；本研究开发了泥沙重力流三维分析程序3D-LIQSEDFLOW。将液化土建模为重粘性流体，用弹塑性固结理论描述土体固化过程。利用VOF技术对流动过程中的自由和凝固表面进行跟踪，便于分析一系列移动边界问题，如水下泥沙溃坝问题。3)泥沙重力流及其再沉积机制；采用PIV技术，对室内水槽试验中液化沉积物流出和静止的方式进行了研究。结果清楚地表明，高浓度的初始流体样沉积物在流动过程中如何凝固，最终突然停止或“冻结”。

This research project aims at developing an integrated framework by which to describe consistently the processes of wave-induced liquefaction, fluidization and sediment transport that have profound practical implications in coastal environment. The principal results obtained may be summarized as follows :1)Effect of wave-loading history upon liquefaction resistance of sandy sediments ; A series of centrifugal wave tests with carefully designed wave-loading histories showed that re-liquefaction resistance increased significantly due to marked densification that had occurred through "solidification" in the preceding wave-loading stage.2)Development of a computational model for sediment gravity flow ; A three-dimensional analysis procedure for sediment gravity flow (3D-LIQSEDFLOW) has been developed in the research project. The liquefied soil is modeled as a heavy viscous fluid and a soil domain undergoing solidification is described in terms of elastoplastic consolidation theory. The free and solidification surfaces during flowage are traced using a VOF technique, facilitating analyses of a range of moving-boundary problems such as underwater sediment-dam breaking problems.3)Mechanisms of sediment gravity flow and ensuing re-deposition ; The way in which liquefied sediment flows out and comes to a rest, was investigated in laboratory flume tests with a PIV technique introduced. The results clearly demonstrate how the initially fluid-like body of sediment with a high concentration underwent solidification in the course of flowage, eventually coming to an abrupt stop or "freezing".