Effects of Fabric Evolution on Liquefaction Resistance of Sands

砂土的结构(即物理结构)和老化的影响在确定在地震荷载下触发液化所需的应力方面起着基本的作用。最近的观察表明，现场测量的砂岩组构的变化可能会导致老化导致硬度的快速初始增加，但动态载荷，如地震引起的载荷，会导致这种硬度降低。这导致了砂土的液化抗力随时间的显著波动。物理和化学机制可能都有助于这些与年龄相关的液化抗性的变化。这项研究项目的基本目的是在实验室中调查相对较低水平的循环应变是否可以破坏对土壤结构的有益老化效应，从而模拟地震的影响，这些地震比给定场地的“设计地震”更小，但更频繁。其目的是研究地震引起的时间对砂岩结构影响的可逆性，从而得出结论，在评估给定场地的液化潜力时，这是否是一个实际问题。如果事实证明是这样的话，这将使目前应用基于渗透仪的设计方法的方式受到质疑，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的砂土的抗力来评估液化潜力。

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.