Collapse, Steady State Concept, and Liquefaction of Granular Soils

这个研究项目解决了理解颗粒材料（通常是沙子）在受到地震引起的强烈地面运动时（地下水位以下）饱和水的行为的基本概念。在这些条件下，这些土壤有可能“液化”，即失去抗剪强度并发生大变形，导致建筑地基、隧道和管道在液化土壤上建造或通过。这种现象与饱和松散砂的响应有关，饱和松散砂的应变足以导致流动滑动。毁灭性的山体滑坡就是这种泥石流的一个例子。稳定状态（流动滑动）与循环（地震）行为之间的关系正在通过基础实验研究得到解决。要研究的一个关键因素是砂土结构崩塌的概念。“崩塌”的概念与收缩砂的结构是亚稳的这一事实有关。在崩塌的骨架中，小的剪切应变可能足以产生颗粒的突然重排，并伴随着相邻颗粒之间接触点的损失，伴随着孔隙水压力的大幅增加。因此，砂的抗剪强度降低到一个小值，砂变得容易受到大的变形。这项调查的结果预计将有助于提高对液化现象和相关不稳定性的理解，并提高预测其发生的能力。

This research program addresses fundamental concepts for understanding the behavior of granular material (usually sand) saturated with water (below the ground water table) when subjected to the strong ground motions resulting from earthquake shaking. Under these conditions, such soils have the potential to "liquefy", that is to lose shear strength and undergo large deformations, resulting in damage to building foundations, tunnels and pipelines built on or passing through such liquefied soil. This phenomenon is related to the response of saturated loose sands strained sufficiently to result in flow slides. A devastating landslides is an example of such a flowslide. The relation between the steady state (flow slide) and the cyclic (earthquake) behavior is being addressed by fundamental experimental studies. A key element to be investigated is the concept of structural collapse of the sand fabric. The concept of "collapse" is associated with the fact that the structure of contractive sands is metastable. In a collapsive skeleton, small shear strains may be sufficient to produce a sudden rearrangement of grains with an associated loss of contact points between neighboring grains, accompanied by a large increase in pore water pressure. Consequently, the shear strength of the sand is reduced to a small value and the sand becomes susceptible to large deformations. The results of this investigation are expected to contribute to an improved understanding of liquefaction phenomena and associated instabilities, and to result in an improved ability to predict their occurrence.