Effects of Fabric Evolution on Liquefaction Resistance of Sands

砂的结构（即物理结构）和老化的影响在决定地震荷载下触发液化所需的应力方面起着根本作用。最近的观察表明，在现场测量的砂土结构的变化可能会导致由于老化而导致的刚度的快速初始增加，但动态载荷，例如地震引起的载荷，会导致这种刚度的退化。这导致砂土液化阻力随时间的显著波动。这可能是物理和化学机制都可能有助于这些年龄相关的液化阻力变化。本研究项目的基本目的是在实验室中调查是否可以通过相对较低水平的循环应变来破坏对土壤结构的有益老化效应，从而模拟比给定地点的“设计地震”更小但更频繁的地震的影响。目的是调查地震引起的时间对砂结构影响的可逆性，从而得出结论，在评价某一地点的液化潜力时，这是否是一个实际关注的问题。如果事实证明是这样的话，它将对目前基于贯入计的设计方法的应用方式提出质疑，并将进一步表明，保守的设计方法可能是基于实验室中新沉积状态下砂的阻力来评估液化潜力。

The fabric (that is, the physical structure) of sand, and the effect of aging, play a fundamental role in determining the stresses necessary to trigger liquefaction under earthquake loading. Recent observations indicate that changes in sand fabric, as measured in the field, may result in a rapid initial gain in stiffness due to aging, but that dynamic loads, such as those induced by earthquakes, cause this stiffness to degrade. This results in significant fluctuations of the sand liquefaction resistance with time. It is possible that both physical and chemical mechanisms may contribute to these age-related changes in liquefaction resistance. The basic intent of this research project is to investigate in the laboratory whether beneficial ageing effects on soil fabric can be destroyed by relatively low levels of cyclic strain, thereby simulating the effects of earthquakes which are smaller, but more frequent, than the "design earthquake" for a given site. The goal is to investigate the earthquake- induced reversibility of the effects of time on sand fabric, thereby concluding whether it is a matter of practical concern in evaluating the liquefaction potential of a given site. If this turns out to be the case, it will bring into question the way in which penetrometer-based design methods are currently applied, and will further suggest that a conservative design approach may be to base the liquefaction potential evaluation on the resistance of the sand in a freshly-deposited state in the laboratory.